text: /**
   * @file
   * LWIP HTTP server implementation
   */
  
  /*
   * Copyright (c) 2001-2003 Swedish Institute of Computer Science.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without modification,
   * are permitted provided that the following conditions are met:
   *
   * 1. Redistributions of source code must retain the above copyright notice,
   *    this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright notice,
   *    this list of conditions and the following disclaimer in the documentation
   *    and/or other materials provided with the distribution.
   * 3. The name of the author may not be used to endorse or promote products
   *    derived from this software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
   * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
   * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
   * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
   * OF SUCH DAMAGE.
   *
   * This file is part of the lwIP TCP/IP stack.
   *
   * Author: Adam Dunkels <adam@sics.se>
   *         Simon Goldschmidt
   *
   */
  
  /**
   * @defgroup httpd HTTP server
   * @ingroup apps
   *
   * This httpd supports for a
   * rudimentary server-side-include facility which will replace tags of the form
   * <!--#tag--> in any file whose extension is .shtml, .shtm or .ssi with
   * strings provided by an include handler whose pointer is provided to the
   * module via function http_set_ssi_handler().
   * Additionally, a simple common
   * gateway interface (CGI) handling mechanism has been added to allow clients
   * to hook functions to particular request URIs.
   *
   * To enable SSI support, define label LWIP_HTTPD_SSI in lwipopts.h.
   * To enable CGI support, define label LWIP_HTTPD_CGI in lwipopts.h.
   *
   * By default, the server assumes that HTTP headers are already present in
   * each file stored in the file system.  By defining LWIP_HTTPD_DYNAMIC_HEADERS in
   * lwipopts.h, this behavior can be changed such that the server inserts the
   * headers automatically based on the extension of the file being served.  If
   * this mode is used, be careful to ensure that the file system image used
   * does not already contain the header information.
   *
   * File system images without headers can be created using the makefsfile
   * tool with the -h command line option.
   *
   *
   * Notes about valid SSI tags
   * --------------------------
   *
   * The following assumptions are made about tags used in SSI markers:
   *
   * 1. No tag may contain '-' or whitespace characters within the tag name.
   * 2. Whitespace is allowed between the tag leadin "<!--#" and the start of
   *    the tag name and between the tag name and the leadout string "-->".
   * 3. The maximum tag name length is LWIP_HTTPD_MAX_TAG_NAME_LEN, currently 8 characters.
   *
   * Notes on CGI usage
   * ------------------
   *
   * The simple CGI support offered here works with GET method requests only
   * and can handle up to 16 parameters encoded into the URI. The handler
   * function may not write directly to the HTTP output but must return a
   * filename that the HTTP server will send to the browser as a response to
   * the incoming CGI request.
   *
   *
   *
   * The list of supported file types is quite short, so if makefsdata complains
   * about an unknown extension, make sure to add it (and its doctype) to
   * the 'g_psHTTPHeaders' list.
   */
  #include "lwip/init.h"
  #include "lwip/apps/httpd.h"
  #include "lwip/debug.h"
  #include "lwip/stats.h"
  #include "lwip/apps/fs.h"
  #include "httpd_structs.h"
  #include "lwip/def.h"
  
  #include "lwip/altcp.h"
  #include "lwip/altcp_tcp.h"
  #if HTTPD_ENABLE_HTTPS
  #include "lwip/altcp_tls.h"
  #endif
  #ifdef LWIP_HOOK_FILENAME
  #include LWIP_HOOK_FILENAME
  #endif
  #if LWIP_HTTPD_TIMING
  #include "lwip/sys.h"
  #endif /* LWIP_HTTPD_TIMING */
  
  #include <string.h> /* memset */
  #include <stdlib.h> /* atoi */
  #include <stdio.h>
  
  #if LWIP_TCP && LWIP_CALLBACK_API
  
  /** Minimum length for a valid HTTP/0.9 request: "GET /\r\n" -> 7 bytes */
  #define MIN_REQ_LEN   7
  
  #define CRLF "\r\n"
  #if LWIP_HTTPD_SUPPORT_11_KEEPALIVE
  #define HTTP11_CONNECTIONKEEPALIVE  "Connection: keep-alive"
  #define HTTP11_CONNECTIONKEEPALIVE2 "Connection: Keep-Alive"
  #endif
  
  #if LWIP_HTTPD_DYNAMIC_FILE_READ
  #define HTTP_IS_DYNAMIC_FILE(hs) ((hs)->buf != NULL)
  #else
  #define HTTP_IS_DYNAMIC_FILE(hs) 0
  #endif
  
  /* This defines checks whether tcp_write has to copy data or not */
  
  #ifndef HTTP_IS_DATA_VOLATILE
  /** tcp_write does not have to copy data when sent from rom-file-system directly */
  #define HTTP_IS_DATA_VOLATILE(hs)       (HTTP_IS_DYNAMIC_FILE(hs) ? TCP_WRITE_FLAG_COPY : 0)
  #endif
  /** Default: dynamic headers are sent from ROM (non-dynamic headers are handled like file data) */
  #ifndef HTTP_IS_HDR_VOLATILE
  #define HTTP_IS_HDR_VOLATILE(hs, ptr)   0
  #endif
  
  /* Return values for http_send_*() */
  #define HTTP_DATA_TO_SEND_FREED    3
  #define HTTP_DATA_TO_SEND_BREAK    2
  #define HTTP_DATA_TO_SEND_CONTINUE 1
  #define HTTP_NO_DATA_TO_SEND       0
  
  typedef struct {
    const char *name;
    u8_t shtml;
  } default_filename;
  
  static const default_filename httpd_default_filenames[] = {
    {"/index.shtml", 1 },
    {"/index.ssi",   1 },
    {"/index.shtm",  1 },
    {"/index.html",  0 },
    {"/index.htm",   0 }
  };
  
  #define NUM_DEFAULT_FILENAMES LWIP_ARRAYSIZE(httpd_default_filenames)
  
  #if LWIP_HTTPD_SUPPORT_REQUESTLIST
  /** HTTP request is copied here from pbufs for simple parsing */
  static char httpd_req_buf[LWIP_HTTPD_MAX_REQ_LENGTH + 1];
  #endif /* LWIP_HTTPD_SUPPORT_REQUESTLIST */
  
  #if LWIP_HTTPD_SUPPORT_POST
  #if LWIP_HTTPD_POST_MAX_RESPONSE_URI_LEN > LWIP_HTTPD_MAX_REQUEST_URI_LEN
  #define LWIP_HTTPD_URI_BUF_LEN LWIP_HTTPD_POST_MAX_RESPONSE_URI_LEN
  #endif
  #endif
  #ifndef LWIP_HTTPD_URI_BUF_LEN
  #define LWIP_HTTPD_URI_BUF_LEN LWIP_HTTPD_MAX_REQUEST_URI_LEN
  #endif
  #if LWIP_HTTPD_URI_BUF_LEN
  /* Filename for response file to send when POST is finished or
   * search for default files when a directory is requested. */
  static char http_uri_buf[LWIP_HTTPD_URI_BUF_LEN + 1];
  #endif
  
  #if LWIP_HTTPD_DYNAMIC_HEADERS
  /* The number of individual strings that comprise the headers sent before each
   * requested file.
   */
  #define NUM_FILE_HDR_STRINGS 5
  #define HDR_STRINGS_IDX_HTTP_STATUS           0 /* e.g. "HTTP/1.0 200 OK\r\n" */
  #define HDR_STRINGS_IDX_SERVER_NAME           1 /* e.g. "Server: "HTTPD_SERVER_AGENT"\r\n" */
  #define HDR_STRINGS_IDX_CONTENT_LEN_KEEPALIVE 2 /* e.g. "Content-Length: xy\r\n" and/or "Connection: keep-alive\r\n" */
  #define HDR_STRINGS_IDX_CONTENT_LEN_NR        3 /* the byte count, when content-length is used */
  #define HDR_STRINGS_IDX_CONTENT_TYPE          4 /* the content type (or default answer content type including default document) */
  
  /* The dynamically generated Content-Length buffer needs space for CRLF + NULL */
  #define LWIP_HTTPD_MAX_CONTENT_LEN_OFFSET 3
  #ifndef LWIP_HTTPD_MAX_CONTENT_LEN_SIZE
  /* The dynamically generated Content-Length buffer shall be able to work with
     ~953 MB (9 digits) */
  #define LWIP_HTTPD_MAX_CONTENT_LEN_SIZE   (9 + LWIP_HTTPD_MAX_CONTENT_LEN_OFFSET)
  #endif
  #endif /* LWIP_HTTPD_DYNAMIC_HEADERS */
  
  #if LWIP_HTTPD_SSI
  
  #define HTTPD_LAST_TAG_PART 0xFFFF
  
  enum tag_check_state {
    TAG_NONE,       /* Not processing an SSI tag */
    TAG_LEADIN,     /* Tag lead in "<!--#" being processed */
    TAG_FOUND,      /* Tag name being read, looking for lead-out start */
    TAG_LEADOUT,    /* Tag lead out "-->" being processed */
    TAG_SENDING     /* Sending tag replacement string */
  };
  
  struct http_ssi_state {
    const char *parsed;     /* Pointer to the first unparsed byte in buf. */
  #if !LWIP_HTTPD_SSI_INCLUDE_TAG
    const char *tag_started;/* Pointer to the first opening '<' of the tag. */
  #endif /* !LWIP_HTTPD_SSI_INCLUDE_TAG */
    const char *tag_end;    /* Pointer to char after the closing '>' of the tag. */
    u32_t parse_left; /* Number of unparsed bytes in buf. */
    u16_t tag_index;   /* Counter used by tag parsing state machine */
    u16_t tag_insert_len; /* Length of insert in string tag_insert */
  #if LWIP_HTTPD_SSI_MULTIPART
    u16_t tag_part; /* Counter passed to and changed by tag insertion function to insert multiple times */
  #endif /* LWIP_HTTPD_SSI_MULTIPART */
    u8_t tag_type; /* index into http_ssi_tag_desc array */
    u8_t tag_name_len; /* Length of the tag name in string tag_name */
    char tag_name[LWIP_HTTPD_MAX_TAG_NAME_LEN + 1]; /* Last tag name extracted */
    char tag_insert[LWIP_HTTPD_MAX_TAG_INSERT_LEN + 1]; /* Insert string for tag_name */
    enum tag_check_state tag_state; /* State of the tag processor */
  };
  
  struct http_ssi_tag_description {
    const char *lead_in;
    const char *lead_out;
  };
  
  #endif /* LWIP_HTTPD_SSI */
  
  struct http_state {
  #if LWIP_HTTPD_KILL_OLD_ON_CONNECTIONS_EXCEEDED
    struct http_state *next;
  #endif /* LWIP_HTTPD_KILL_OLD_ON_CONNECTIONS_EXCEEDED */
    struct fs_file file_handle;
    struct fs_file *handle;
    const char *file;       /* Pointer to first unsent byte in buf. */
  
    struct altcp_pcb *pcb;
  #if LWIP_HTTPD_SUPPORT_REQUESTLIST
    struct pbuf *req;
  #endif /* LWIP_HTTPD_SUPPORT_REQUESTLIST */
  
  #if LWIP_HTTPD_DYNAMIC_FILE_READ
    char *buf;        /* File read buffer. */
    int buf_len;      /* Size of file read buffer, buf. */
  #endif /* LWIP_HTTPD_DYNAMIC_FILE_READ */
    u32_t left;       /* Number of unsent bytes in buf. */
    u8_t retries;
  #if LWIP_HTTPD_SUPPORT_11_KEEPALIVE
    u8_t keepalive;
  #endif /* LWIP_HTTPD_SUPPORT_11_KEEPALIVE */
  #if LWIP_HTTPD_SSI
    struct http_ssi_state *ssi;
  #endif /* LWIP_HTTPD_SSI */
  #if LWIP_HTTPD_CGI
    char *params[LWIP_HTTPD_MAX_CGI_PARAMETERS]; /* Params extracted from the request URI */
    char *param_vals[LWIP_HTTPD_MAX_CGI_PARAMETERS]; /* Values for each extracted param */
  #endif /* LWIP_HTTPD_CGI */
  #if LWIP_HTTPD_DYNAMIC_HEADERS
    const char *hdrs[NUM_FILE_HDR_STRINGS]; /* HTTP headers to be sent. */
    char hdr_content_len[LWIP_HTTPD_MAX_CONTENT_LEN_SIZE];
    u16_t hdr_pos;     /* The position of the first unsent header byte in the
                          current string */
    u16_t hdr_index;   /* The index of the hdr string currently being sent. */
  #endif /* LWIP_HTTPD_DYNAMIC_HEADERS */
  #if LWIP_HTTPD_TIMING
    u32_t time_started;
  #endif /* LWIP_HTTPD_TIMING */
  #if LWIP_HTTPD_SUPPORT_POST
    u32_t post_content_len_left;
  #if LWIP_HTTPD_POST_MANUAL_WND
    u32_t unrecved_bytes;
    u8_t no_auto_wnd;
    u8_t post_finished;
  #endif /* LWIP_HTTPD_POST_MANUAL_WND */
  #endif /* LWIP_HTTPD_SUPPORT_POST*/
  };
  
  #if HTTPD_USE_MEM_POOL
  LWIP_MEMPOOL_DECLARE(HTTPD_STATE,     MEMP_NUM_PARALLEL_HTTPD_CONNS,     sizeof(struct http_state),     "HTTPD_STATE")
  #if LWIP_HTTPD_SSI
  LWIP_MEMPOOL_DECLARE(HTTPD_SSI_STATE, MEMP_NUM_PARALLEL_HTTPD_SSI_CONNS, sizeof(struct http_ssi_state), "HTTPD_SSI_STATE")
  #define HTTP_FREE_SSI_STATE(x)  LWIP_MEMPOOL_FREE(HTTPD_SSI_STATE, (x))
  #define HTTP_ALLOC_SSI_STATE()  (struct http_ssi_state *)LWIP_MEMPOOL_ALLOC(HTTPD_SSI_STATE)
  #endif /* LWIP_HTTPD_SSI */
  #define HTTP_ALLOC_HTTP_STATE() (struct http_state *)LWIP_MEMPOOL_ALLOC(HTTPD_STATE)
  #define HTTP_FREE_HTTP_STATE(x) LWIP_MEMPOOL_FREE(HTTPD_STATE, (x))
  #else /* HTTPD_USE_MEM_POOL */
  #define HTTP_ALLOC_HTTP_STATE() (struct http_state *)mem_malloc(sizeof(struct http_state))
  #define HTTP_FREE_HTTP_STATE(x) mem_free(x)
  #if LWIP_HTTPD_SSI
  #define HTTP_ALLOC_SSI_STATE()  (struct http_ssi_state *)mem_malloc(sizeof(struct http_ssi_state))
  #define HTTP_FREE_SSI_STATE(x)  mem_free(x)
  #endif /* LWIP_HTTPD_SSI */
  #endif /* HTTPD_USE_MEM_POOL */
  
  static err_t http_close_conn(struct altcp_pcb *pcb, struct http_state *hs);
  static err_t http_close_or_abort_conn(struct altcp_pcb *pcb, struct http_state *hs, u8_t abort_conn);
  static err_t http_find_file(struct http_state *hs, const char *uri, int is_09);
  static err_t http_init_file(struct http_state *hs, struct fs_file *file, int is_09, const char *uri, u8_t tag_check, char *params);
  static err_t http_poll(void *arg, struct altcp_pcb *pcb);
  static u8_t http_check_eof(struct altcp_pcb *pcb, struct http_state *hs);
  #if LWIP_HTTPD_FS_ASYNC_READ
  static void http_continue(void *connection);
  #endif /* LWIP_HTTPD_FS_ASYNC_READ */
  
  #if LWIP_HTTPD_SSI
  /* SSI insert handler function pointer. */
  static tSSIHandler httpd_ssi_handler;
  #if !LWIP_HTTPD_SSI_RAW
  static int httpd_num_tags;
  static const char **httpd_tags;
  #endif /* !LWIP_HTTPD_SSI_RAW */
  
  /* Define the available tag lead-ins and corresponding lead-outs.
   * ATTENTION: for the algorithm below using this array, it is essential
   * that the lead in differs in the first character! */
  const struct http_ssi_tag_description http_ssi_tag_desc[] = {
    {"<!--#", "-->"},
    {"/*#", "*/"}
  };
  
  #endif /* LWIP_HTTPD_SSI */
  
  #if LWIP_HTTPD_CGI
  /* CGI handler information */
  static const tCGI *httpd_cgis;
  static int httpd_num_cgis;
  static int http_cgi_paramcount;
  #define http_cgi_params     hs->params
  #define http_cgi_param_vals hs->param_vals
  #elif LWIP_HTTPD_CGI_SSI
  static char *http_cgi_params[LWIP_HTTPD_MAX_CGI_PARAMETERS]; /* Params extracted from the request URI */
  static char *http_cgi_param_vals[LWIP_HTTPD_MAX_CGI_PARAMETERS]; /* Values for each extracted param */
  #endif /* LWIP_HTTPD_CGI */
  
  #if LWIP_HTTPD_KILL_OLD_ON_CONNECTIONS_EXCEEDED
  /** global list of active HTTP connections, use to kill the oldest when
      running out of memory */
  static struct http_state *http_connections;
  
  static void
  http_add_connection(struct http_state *hs)
  {
    /* add the connection to the list */
    hs->next = http_connections;
    http_connections = hs;
  }
  
  static void
  http_remove_connection(struct http_state *hs)
  {
    /* take the connection off the list */
    if (http_connections) {
      if (http_connections == hs) {
        http_connections = hs->next;
      } else {
        struct http_state *last;
        for (last = http_connections; last->next != NULL; last = last->next) {
          if (last->next == hs) {
            last->next = hs->next;
            break;
          }
        }
      }
    }
  }
  
  static void
  http_kill_oldest_connection(u8_t ssi_required)
  {
    struct http_state *hs = http_connections;
    struct http_state *hs_free_next = NULL;
    while (hs && hs->next) {
  #if LWIP_HTTPD_SSI
      if (ssi_required) {
        if (hs->next->ssi != NULL) {
          hs_free_next = hs;
        }
      } else
  #else /* LWIP_HTTPD_SSI */
      LWIP_UNUSED_ARG(ssi_required);
  #endif /* LWIP_HTTPD_SSI */
      {
        hs_free_next = hs;
      }
      LWIP_ASSERT("broken list", hs != hs->next);
      hs = hs->next;
    }
    if (hs_free_next != NULL) {
      LWIP_ASSERT("hs_free_next->next != NULL", hs_free_next->next != NULL);
      LWIP_ASSERT("hs_free_next->next->pcb != NULL", hs_free_next->next->pcb != NULL);
      /* send RST when killing a connection because of memory shortage */
      http_close_or_abort_conn(hs_free_next->next->pcb, hs_free_next->next, 1); /* this also unlinks the http_state from the list */
    }
  }
  #else /* LWIP_HTTPD_KILL_OLD_ON_CONNECTIONS_EXCEEDED */
  
  #define http_add_connection(hs)
  #define http_remove_connection(hs)
  
  #endif /* LWIP_HTTPD_KILL_OLD_ON_CONNECTIONS_EXCEEDED */
  
  #if LWIP_HTTPD_SSI
  /** Allocate as struct http_ssi_state. */
  static struct http_ssi_state *
  http_ssi_state_alloc(void)
  {
    struct http_ssi_state *ret = HTTP_ALLOC_SSI_STATE();
  #if LWIP_HTTPD_KILL_OLD_ON_CONNECTIONS_EXCEEDED
    if (ret == NULL) {
      http_kill_oldest_connection(1);
      ret = HTTP_ALLOC_SSI_STATE();
    }
  #endif /* LWIP_HTTPD_KILL_OLD_ON_CONNECTIONS_EXCEEDED */
    if (ret != NULL) {
      memset(ret, 0, sizeof(struct http_ssi_state));
    }
    return ret;
  }
  
  /** Free a struct http_ssi_state. */
  static void
  http_ssi_state_free(struct http_ssi_state *ssi)
  {
    if (ssi != NULL) {
      HTTP_FREE_SSI_STATE(ssi);
    }
  }
  #endif /* LWIP_HTTPD_SSI */
  
  /** Initialize a struct http_state.
   */
  static void
  http_state_init(struct http_state *hs)
  {
    /* Initialize the structure. */
    memset(hs, 0, sizeof(struct http_state));
  #if LWIP_HTTPD_DYNAMIC_HEADERS
    /* Indicate that the headers are not yet valid */
    hs->hdr_index = NUM_FILE_HDR_STRINGS;
  #endif /* LWIP_HTTPD_DYNAMIC_HEADERS */
  }
  
  /** Allocate a struct http_state. */
  static struct http_state *
  http_state_alloc(void)
  {
    struct http_state *ret = HTTP_ALLOC_HTTP_STATE();
  #if LWIP_HTTPD_KILL_OLD_ON_CONNECTIONS_EXCEEDED
    if (ret == NULL) {
      http_kill_oldest_connection(0);
      ret = HTTP_ALLOC_HTTP_STATE();
    }
  #endif /* LWIP_HTTPD_KILL_OLD_ON_CONNECTIONS_EXCEEDED */
    if (ret != NULL) {
      http_state_init(ret);
      http_add_connection(ret);
    }
    return ret;
  }
  
  /** Free a struct http_state.
   * Also frees the file data if dynamic.
   */
  static void
  http_state_eof(struct http_state *hs)
  {
    if (hs->handle) {
  #if LWIP_HTTPD_TIMING
      u32_t ms_needed = sys_now() - hs->time_started;
      u32_t needed = LWIP_MAX(1, (ms_needed / 100));
      LWIP_DEBUGF(HTTPD_DEBUG_TIMING, ("httpd: needed %"U32_F" ms to send file of %d bytes -> %"U32_F" bytes/sec\n",
                                       ms_needed, hs->handle->len, ((((u32_t)hs->handle->len) * 10) / needed)));
  #endif /* LWIP_HTTPD_TIMING */
      fs_close(hs->handle);
      hs->handle = NULL;
    }
  #if LWIP_HTTPD_DYNAMIC_FILE_READ
    if (hs->buf != NULL) {
      mem_free(hs->buf);
      hs->buf = NULL;
    }
  #endif /* LWIP_HTTPD_DYNAMIC_FILE_READ */
  #if LWIP_HTTPD_SSI
    if (hs->ssi) {
      http_ssi_state_free(hs->ssi);
      hs->ssi = NULL;
    }
  #endif /* LWIP_HTTPD_SSI */
  #if LWIP_HTTPD_SUPPORT_REQUESTLIST
    if (hs->req) {
      pbuf_free(hs->req);
      hs->req = NULL;
    }
  #endif /* LWIP_HTTPD_SUPPORT_REQUESTLIST */
  }
  
  /** Free a struct http_state.
   * Also frees the file data if dynamic.
   */
  static void
  http_state_free(struct http_state *hs)
  {
    if (hs != NULL) {
      http_state_eof(hs);
      http_remove_connection(hs);
      HTTP_FREE_HTTP_STATE(hs);
    }
  }
  
  /** Call tcp_write() in a loop trying smaller and smaller length
   *
   * @param pcb altcp_pcb to send
   * @param ptr Data to send
   * @param length Length of data to send (in/out: on return, contains the
   *        amount of data sent)
   * @param apiflags directly passed to tcp_write
   * @return the return value of tcp_write
   */
  static err_t
  http_write(struct altcp_pcb *pcb, const void *ptr, u16_t *length, u8_t apiflags)
  {
    u16_t len, max_len;
    err_t err;
    LWIP_ASSERT("length != NULL", length != NULL);
    len = *length;
    if (len == 0) {
      return ERR_OK;
    }
    /* We cannot send more data than space available in the send buffer. */
    max_len = altcp_sndbuf(pcb);
    if (max_len < len) {
      len = max_len;
    }
  #ifdef HTTPD_MAX_WRITE_LEN
    /* Additional limitation: e.g. don't enqueue more than 2*mss at once */
    max_len = HTTPD_MAX_WRITE_LEN(pcb);
    if (len > max_len) {
      len = max_len;
    }
  #endif /* HTTPD_MAX_WRITE_LEN */
    do {
      LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("Trying to send %d bytes\n", len));
      err = altcp_write(pcb, ptr, len, apiflags);
      if (err == ERR_MEM) {
        if ((altcp_sndbuf(pcb) == 0) ||
            (altcp_sndqueuelen(pcb) >= TCP_SND_QUEUELEN)) {
          /* no need to try smaller sizes */
          len = 1;
        } else {
          len /= 2;
        }
        LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE,
                    ("Send failed, trying less (%d bytes)\n", len));
      }
    } while ((err == ERR_MEM) && (len > 1));
  
    if (err == ERR_OK) {
      LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("Sent %d bytes\n", len));
      *length = len;
    } else {
      LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("Send failed with err %d (\"%s\")\n", err, lwip_strerr(err)));
      *length = 0;
    }
  
  #if LWIP_HTTPD_SUPPORT_11_KEEPALIVE
    /* ensure nagle is normally enabled (only disabled for persistent connections
       when all data has been enqueued but the connection stays open for the next
       request */
    altcp_nagle_enable(pcb);
  #endif
  
    return err;
  }
  
  /**
   * The connection shall be actively closed (using RST to close from fault states).
   * Reset the sent- and recv-callbacks.
   *
   * @param pcb the tcp pcb to reset callbacks
   * @param hs connection state to free
   */
  static err_t
  http_close_or_abort_conn(struct altcp_pcb *pcb, struct http_state *hs, u8_t abort_conn)
  {
    err_t err;
    LWIP_DEBUGF(HTTPD_DEBUG, ("Closing connection %p\n", (void *)pcb));
  
  #if LWIP_HTTPD_SUPPORT_POST
    if (hs != NULL) {
      if ((hs->post_content_len_left != 0)
  #if LWIP_HTTPD_POST_MANUAL_WND
          || ((hs->no_auto_wnd != 0) && (hs->unrecved_bytes != 0))
  #endif /* LWIP_HTTPD_POST_MANUAL_WND */
         ) {
        /* make sure the post code knows that the connection is closed */
        http_uri_buf[0] = 0;
        httpd_post_finished(hs, http_uri_buf, LWIP_HTTPD_URI_BUF_LEN);
      }
    }
  #endif /* LWIP_HTTPD_SUPPORT_POST*/
  
  
    altcp_arg(pcb, NULL);
    altcp_recv(pcb, NULL);
    altcp_err(pcb, NULL);
    altcp_poll(pcb, NULL, 0);
    altcp_sent(pcb, NULL);
    if (hs != NULL) {
      http_state_free(hs);
    }
  
    if (abort_conn) {
      altcp_abort(pcb);
      return ERR_OK;
    }
    err = altcp_close(pcb);
    if (err != ERR_OK) {
      LWIP_DEBUGF(HTTPD_DEBUG, ("Error %d closing %p\n", err, (void *)pcb));
      /* error closing, try again later in poll */
      altcp_poll(pcb, http_poll, HTTPD_POLL_INTERVAL);
    }
    return err;
  }
  
  /**
   * The connection shall be actively closed.
   * Reset the sent- and recv-callbacks.
   *
   * @param pcb the tcp pcb to reset callbacks
   * @param hs connection state to free
   */
  static err_t
  http_close_conn(struct altcp_pcb *pcb, struct http_state *hs)
  {
    return http_close_or_abort_conn(pcb, hs, 0);
  }
  
  /** End of file: either close the connection (Connection: close) or
   * close the file (Connection: keep-alive)
   */
  static void
  http_eof(struct altcp_pcb *pcb, struct http_state *hs)
  {
    /* HTTP/1.1 persistent connection? (Not supported for SSI) */
  #if LWIP_HTTPD_SUPPORT_11_KEEPALIVE
    if (hs->keepalive) {
      http_remove_connection(hs);
  
      http_state_eof(hs);
      http_state_init(hs);
      /* restore state: */
      hs->pcb = pcb;
      hs->keepalive = 1;
      http_add_connection(hs);
      /* ensure nagle doesn't interfere with sending all data as fast as possible: */
      altcp_nagle_disable(pcb);
    } else
  #endif /* LWIP_HTTPD_SUPPORT_11_KEEPALIVE */
    {
      http_close_conn(pcb, hs);
    }
  }
  
  #if LWIP_HTTPD_CGI || LWIP_HTTPD_CGI_SSI
  /**
   * Extract URI parameters from the parameter-part of an URI in the form
   * "test.cgi?x=y" @todo: better explanation!
   * Pointers to the parameters are stored in hs->param_vals.
   *
   * @param hs http connection state
   * @param params pointer to the NULL-terminated parameter string from the URI
   * @return number of parameters extracted
   */
  static int
  extract_uri_parameters(struct http_state *hs, char *params)
  {
    char *pair;
    char *equals;
    int loop;
  
    LWIP_UNUSED_ARG(hs);
  
    /* If we have no parameters at all, return immediately. */
    if (!params || (params[0] == '\0')) {
      return (0);
    }
  
    /* Get a pointer to our first parameter */
    pair = params;
  
    /* Parse up to LWIP_HTTPD_MAX_CGI_PARAMETERS from the passed string and ignore the
     * remainder (if any) */
    for (loop = 0; (loop < LWIP_HTTPD_MAX_CGI_PARAMETERS) && pair; loop++) {
  
      /* Save the name of the parameter */
      http_cgi_params[loop] = pair;
  
      /* Remember the start of this name=value pair */
      equals = pair;
  
      /* Find the start of the next name=value pair and replace the delimiter
       * with a 0 to terminate the previous pair string. */
      pair = strchr(pair, '&');
      if (pair) {
        *pair = '\0';
        pair++;
      } else {
        /* We didn't find a new parameter so find the end of the URI and
         * replace the space with a '\0' */
        pair = strchr(equals, ' ');
        if (pair) {
          *pair = '\0';
        }
  
        /* Revert to NULL so that we exit the loop as expected. */
        pair = NULL;
      }
  
      /* Now find the '=' in the previous pair, replace it with '\0' and save
       * the parameter value string. */
      equals = strchr(equals, '=');
      if (equals) {
        *equals = '\0';
        http_cgi_param_vals[loop] = equals + 1;
      } else {
        http_cgi_param_vals[loop] = NULL;
      }
    }
  
    return loop;
  }
  #endif /* LWIP_HTTPD_CGI || LWIP_HTTPD_CGI_SSI */
  
  #if LWIP_HTTPD_SSI
  /**
   * Insert a tag (found in an shtml in the form of "<!--#tagname-->" into the file.
   * The tag's name is stored in ssi->tag_name (NULL-terminated), the replacement
   * should be written to hs->tag_insert (up to a length of LWIP_HTTPD_MAX_TAG_INSERT_LEN).
   * The amount of data written is stored to ssi->tag_insert_len.
   *
   * @todo: return tag_insert_len - maybe it can be removed from struct http_state?
   *
   * @param hs http connection state
   */
  static void
  get_tag_insert(struct http_state *hs)
  {
  #if LWIP_HTTPD_SSI_RAW
    const char *tag;
  #else /* LWIP_HTTPD_SSI_RAW */
    int tag;
  #endif /* LWIP_HTTPD_SSI_RAW */
    size_t len;
    struct http_ssi_state *ssi;
  #if LWIP_HTTPD_SSI_MULTIPART
    u16_t current_tag_part;
  #endif /* LWIP_HTTPD_SSI_MULTIPART */
  
    LWIP_ASSERT("hs != NULL", hs != NULL);
    ssi = hs->ssi;
    LWIP_ASSERT("ssi != NULL", ssi != NULL);
  #if LWIP_HTTPD_SSI_MULTIPART
    current_tag_part = ssi->tag_part;
    ssi->tag_part = HTTPD_LAST_TAG_PART;
  #endif /* LWIP_HTTPD_SSI_MULTIPART */
  #if LWIP_HTTPD_SSI_RAW
    tag = ssi->tag_name;
  #endif
  
    if (httpd_ssi_handler
  #if !LWIP_HTTPD_SSI_RAW
        && httpd_tags && httpd_num_tags
  #endif /* !LWIP_HTTPD_SSI_RAW */
       ) {
  
      /* Find this tag in the list we have been provided. */
  #if LWIP_HTTPD_SSI_RAW
      {
  #else /* LWIP_HTTPD_SSI_RAW */
      for (tag = 0; tag < httpd_num_tags; tag++) {
        if (strcmp(ssi->tag_name, httpd_tags[tag]) == 0)
  #endif /* LWIP_HTTPD_SSI_RAW */
        {
          ssi->tag_insert_len = httpd_ssi_handler(tag, ssi->tag_insert,
                                                LWIP_HTTPD_MAX_TAG_INSERT_LEN
  #if LWIP_HTTPD_SSI_MULTIPART
                                                , current_tag_part, &ssi->tag_part
  #endif /* LWIP_HTTPD_SSI_MULTIPART */
  #if LWIP_HTTPD_FILE_STATE
                                                , (hs->handle ? hs->handle->state : NULL)
  #endif /* LWIP_HTTPD_FILE_STATE */
                                               );
  #if LWIP_HTTPD_SSI_RAW
          if (ssi->tag_insert_len != HTTPD_SSI_TAG_UNKNOWN)
  #endif /* LWIP_HTTPD_SSI_RAW */
          {
            return;
          }
        }
      }
    }
  
    /* If we drop out, we were asked to serve a page which contains tags that
     * we don't have a handler for. Merely echo back the tags with an error
     * marker. */
  #define UNKNOWN_TAG1_TEXT "<b>***UNKNOWN TAG "
  #define UNKNOWN_TAG1_LEN  18
  #define UNKNOWN_TAG2_TEXT "***</b>"
  #define UNKNOWN_TAG2_LEN  7
    len = LWIP_MIN(sizeof(ssi->tag_name), LWIP_MIN(strlen(ssi->tag_name),
                   LWIP_HTTPD_MAX_TAG_INSERT_LEN - (UNKNOWN_TAG1_LEN + UNKNOWN_TAG2_LEN)));
    MEMCPY(ssi->tag_insert, UNKNOWN_TAG1_TEXT, UNKNOWN_TAG1_LEN);
    MEMCPY(&ssi->tag_insert[UNKNOWN_TAG1_LEN], ssi->tag_name, len);
    MEMCPY(&ssi->tag_insert[UNKNOWN_TAG1_LEN + len], UNKNOWN_TAG2_TEXT, UNKNOWN_TAG2_LEN);
    ssi->tag_insert[UNKNOWN_TAG1_LEN + len + UNKNOWN_TAG2_LEN] = 0;
  
    len = strlen(ssi->tag_insert);
    LWIP_ASSERT("len <= 0xffff", len <= 0xffff);
    ssi->tag_insert_len = (u16_t)len;
  }
  #endif /* LWIP_HTTPD_SSI */
  
  #if LWIP_HTTPD_DYNAMIC_HEADERS
  /**
   * Generate the relevant HTTP headers for the given filename and write
   * them into the supplied buffer.
   */
  static void
  get_http_headers(struct http_state *hs, const char *uri)
  {
    size_t content_type;
    char *tmp;
    char *ext;
    char *vars;
  
    /* In all cases, the second header we send is the server identification
       so set it here. */
    hs->hdrs[HDR_STRINGS_IDX_SERVER_NAME] = g_psHTTPHeaderStrings[HTTP_HDR_SERVER];
    hs->hdrs[HDR_STRINGS_IDX_CONTENT_LEN_KEEPALIVE] = NULL;
    hs->hdrs[HDR_STRINGS_IDX_CONTENT_LEN_NR] = NULL;
  
    /* Is this a normal file or the special case we use to send back the
       default "404: Page not found" response? */
    if (uri == NULL) {
      hs->hdrs[HDR_STRINGS_IDX_HTTP_STATUS] = g_psHTTPHeaderStrings[HTTP_HDR_NOT_FOUND];
  #if LWIP_HTTPD_SUPPORT_11_KEEPALIVE
      if (hs->keepalive) {
        hs->hdrs[HDR_STRINGS_IDX_CONTENT_TYPE] = g_psHTTPHeaderStrings[DEFAULT_404_HTML_PERSISTENT];
      } else
  #endif
      {
        hs->hdrs[HDR_STRINGS_IDX_CONTENT_TYPE] = g_psHTTPHeaderStrings[DEFAULT_404_HTML];
      }
  
      /* Set up to send the first header string. */
      hs->hdr_index = 0;
      hs->hdr_pos = 0;
      return;
    }
    /* We are dealing with a particular filename. Look for one other
       special case.  We assume that any filename with "404" in it must be
       indicative of a 404 server error whereas all other files require
       the 200 OK header. */
    if (memcmp(uri, "/404.", 5) == 0) {
      hs->hdrs[HDR_STRINGS_IDX_HTTP_STATUS] = g_psHTTPHeaderStrings[HTTP_HDR_NOT_FOUND];
    } else if (memcmp(uri, "/400.", 5) == 0) {
      hs->hdrs[HDR_STRINGS_IDX_HTTP_STATUS] = g_psHTTPHeaderStrings[HTTP_HDR_BAD_REQUEST];
    } else if (memcmp(uri, "/501.", 5) == 0) {
      hs->hdrs[HDR_STRINGS_IDX_HTTP_STATUS] = g_psHTTPHeaderStrings[HTTP_HDR_NOT_IMPL];
    } else {
      hs->hdrs[HDR_STRINGS_IDX_HTTP_STATUS] = g_psHTTPHeaderStrings[HTTP_HDR_OK];
    }
  
    /* Determine if the URI has any variables and, if so, temporarily remove
        them. */
    vars = strchr(uri, '?');
    if (vars) {
      *vars = '\0';
    }
  
    /* Get a pointer to the file extension.  We find this by looking for the
        last occurrence of "." in the filename passed. */
    ext = NULL;
    tmp = strchr(uri, '.');
    while (tmp) {
      ext = tmp + 1;
      tmp = strchr(ext, '.');
    }
    if (ext != NULL) {
      /* Now determine the content type and add the relevant header for that. */
      for (content_type = 0; content_type < NUM_HTTP_HEADERS; content_type++) {
        /* Have we found a matching extension? */
        if (!lwip_stricmp(g_psHTTPHeaders[content_type].extension, ext)) {
          break;
        }
      }
    } else {
      content_type = NUM_HTTP_HEADERS;
    }
  
    /* Reinstate the parameter marker if there was one in the original URI. */
    if (vars) {
      *vars = '?';
    }
  
  #if LWIP_HTTPD_OMIT_HEADER_FOR_EXTENSIONLESS_URI
    /* Does the URL passed have any file extension?  If not, we assume it
       is a special-case URL used for control state notification and we do
       not send any HTTP headers with the response. */
    if (!ext) {
      /* Force the header index to a value indicating that all headers
         have already been sent. */
      hs->hdr_index = NUM_FILE_HDR_STRINGS;
      return;
    }
  #endif /* LWIP_HTTPD_OMIT_HEADER_FOR_EXTENSIONLESS_URI */
    /* Did we find a matching extension? */
    if (content_type < NUM_HTTP_HEADERS) {
      /* yes, store it */
      hs->hdrs[HDR_STRINGS_IDX_CONTENT_TYPE] = g_psHTTPHeaders[content_type].content_type;
    } else if (!ext) {
      /* no, no extension found -> use binary transfer to prevent the browser adding '.txt' on save */
      hs->hdrs[HDR_STRINGS_IDX_CONTENT_TYPE] = HTTP_HDR_APP;
    } else {
      /* No - use the default, plain text file type. */
      hs->hdrs[HDR_STRINGS_IDX_CONTENT_TYPE] = HTTP_HDR_DEFAULT_TYPE;
    }
    /* Set up to send the first header string. */
    hs->hdr_index = 0;
    hs->hdr_pos = 0;
  }
  
  /* Add content-length header? */
  static void
  get_http_content_length(struct http_state *hs)
  {
    u8_t add_content_len = 0;
  
    LWIP_ASSERT("already been here?", hs->hdrs[HDR_STRINGS_IDX_CONTENT_LEN_KEEPALIVE] == NULL);
  
    add_content_len = 0;
  #if LWIP_HTTPD_SSI
    if (hs->ssi == NULL) /* @todo: get maximum file length from SSI */
  #endif /* LWIP_HTTPD_SSI */
    {
      if ((hs->handle != NULL) && (hs->handle->flags & FS_FILE_FLAGS_HEADER_PERSISTENT)) {
        add_content_len = 1;
      }
    }
    if (add_content_len) {
      size_t len;
      lwip_itoa(hs->hdr_content_len, (size_t)LWIP_HTTPD_MAX_CONTENT_LEN_SIZE,
                hs->handle->len);
      len = strlen(hs->hdr_content_len);
      if (len <= LWIP_HTTPD_MAX_CONTENT_LEN_SIZE - LWIP_HTTPD_MAX_CONTENT_LEN_OFFSET) {
        SMEMCPY(&hs->hdr_content_len[len], CRLF, 3);
        hs->hdrs[HDR_STRINGS_IDX_CONTENT_LEN_NR] = hs->hdr_content_len;
      } else {
        add_content_len = 0;
      }
    }
  #if LWIP_HTTPD_SUPPORT_11_KEEPALIVE
    if (add_content_len) {
      hs->hdrs[HDR_STRINGS_IDX_CONTENT_LEN_KEEPALIVE] = g_psHTTPHeaderStrings[HTTP_HDR_KEEPALIVE_LEN];
    } else {
      hs->hdrs[HDR_STRINGS_IDX_CONTENT_LEN_KEEPALIVE] = g_psHTTPHeaderStrings[HTTP_HDR_CONN_CLOSE];
      hs->keepalive = 0;
    }
  #else /* LWIP_HTTPD_SUPPORT_11_KEEPALIVE */
    if (add_content_len) {
      hs->hdrs[HDR_STRINGS_IDX_CONTENT_LEN_KEEPALIVE] = g_psHTTPHeaderStrings[HTTP_HDR_CONTENT_LENGTH];
    }
  #endif /* LWIP_HTTPD_SUPPORT_11_KEEPALIVE */
  }
  
  /** Sub-function of http_send(): send dynamic headers
   *
   * @returns: - HTTP_NO_DATA_TO_SEND: no new data has been enqueued
   *           - HTTP_DATA_TO_SEND_CONTINUE: continue with sending HTTP body
   *           - HTTP_DATA_TO_SEND_BREAK: data has been enqueued, headers pending,
   *                                      so don't send HTTP body yet
   *           - HTTP_DATA_TO_SEND_FREED: http_state and pcb are already freed
   */
  static u8_t
  http_send_headers(struct altcp_pcb *pcb, struct http_state *hs)
  {
    err_t err;
    u16_t len;
    u8_t data_to_send = HTTP_NO_DATA_TO_SEND;
    u16_t hdrlen, sendlen;
  
    if (hs->hdrs[HDR_STRINGS_IDX_CONTENT_LEN_KEEPALIVE] == NULL) {
      /* set up "content-length" and "connection:" headers */
      get_http_content_length(hs);
    }
  
    /* How much data can we send? */
    len = altcp_sndbuf(pcb);
    sendlen = len;
  
    while (len && (hs->hdr_index < NUM_FILE_HDR_STRINGS) && sendlen) {
      const void *ptr;
      u16_t old_sendlen;
      u8_t apiflags;
      /* How much do we have to send from the current header? */
      hdrlen = (u16_t)strlen(hs->hdrs[hs->hdr_index]);
  
      /* How much of this can we send? */
      sendlen = (len < (hdrlen - hs->hdr_pos)) ? len : (hdrlen - hs->hdr_pos);
  
      /* Send this amount of data or as much as we can given memory
       * constraints. */
      ptr = (const void *)(hs->hdrs[hs->hdr_index] + hs->hdr_pos);
      old_sendlen = sendlen;
      apiflags = HTTP_IS_HDR_VOLATILE(hs, ptr);
      if (hs->hdr_index == HDR_STRINGS_IDX_CONTENT_LEN_NR) {
        /* content-length is always volatile */
        apiflags |= TCP_WRITE_FLAG_COPY;
      }
      if (hs->hdr_index < NUM_FILE_HDR_STRINGS - 1) {
        apiflags |= TCP_WRITE_FLAG_MORE;
      }
      err = http_write(pcb, ptr, &sendlen, apiflags);
      if ((err == ERR_OK) && (old_sendlen != sendlen)) {
        /* Remember that we added some more data to be transmitted. */
        data_to_send = HTTP_DATA_TO_SEND_CONTINUE;
      } else if (err != ERR_OK) {
        /* special case: http_write does not try to send 1 byte */
        sendlen = 0;
      }
  
      /* Fix up the header position for the next time round. */
      hs->hdr_pos += sendlen;
      len -= sendlen;
  
      /* Have we finished sending this string? */
      if (hs->hdr_pos == hdrlen) {
        /* Yes - move on to the next one */
        hs->hdr_index++;
        /* skip headers that are NULL (not all headers are required) */
        while ((hs->hdr_index < NUM_FILE_HDR_STRINGS) &&
               (hs->hdrs[hs->hdr_index] == NULL)) {
          hs->hdr_index++;
        }
        hs->hdr_pos = 0;
      }
    }
  
    if ((hs->hdr_index >= NUM_FILE_HDR_STRINGS) && (hs->file == NULL)) {
      /* When we are at the end of the headers, check for data to send
       * instead of waiting for ACK from remote side to continue
       * (which would happen when sending files from async read). */
      if (http_check_eof(pcb, hs)) {
        data_to_send = HTTP_DATA_TO_SEND_BREAK;
      } else {
        /* At this point, for non-keepalive connections, hs is deallocated an
           pcb is closed. */
        return HTTP_DATA_TO_SEND_FREED;
      }
    }
    /* If we get here and there are still header bytes to send, we send
     * the header information we just wrote immediately. If there are no
     * more headers to send, but we do have file data to send, drop through
     * to try to send some file data too. */
    if ((hs->hdr_index < NUM_FILE_HDR_STRINGS) || !hs->file) {
      LWIP_DEBUGF(HTTPD_DEBUG, ("tcp_output\n"));
      return HTTP_DATA_TO_SEND_BREAK;
    }
    return data_to_send;
  }
  #endif /* LWIP_HTTPD_DYNAMIC_HEADERS */
  
  /** Sub-function of http_send(): end-of-file (or block) is reached,
   * either close the file or read the next block (if supported).
   *
   * @returns: 0 if the file is finished or no data has been read
   *           1 if the file is not finished and data has been read
   */
  static u8_t
  http_check_eof(struct altcp_pcb *pcb, struct http_state *hs)
  {
    int bytes_left;
  #if LWIP_HTTPD_DYNAMIC_FILE_READ
    int count;
  #ifdef HTTPD_MAX_WRITE_LEN
    int max_write_len;
  #endif /* HTTPD_MAX_WRITE_LEN */
  #endif /* LWIP_HTTPD_DYNAMIC_FILE_READ */
  
    /* Do we have a valid file handle? */
    if (hs->handle == NULL) {
      /* No - close the connection. */
      http_eof(pcb, hs);
      return 0;
    }
    bytes_left = fs_bytes_left(hs->handle);
    if (bytes_left <= 0) {
      /* We reached the end of the file so this request is done. */
      LWIP_DEBUGF(HTTPD_DEBUG, ("End of file.\n"));
      http_eof(pcb, hs);
      return 0;
    }
  #if LWIP_HTTPD_DYNAMIC_FILE_READ
    /* Do we already have a send buffer allocated? */
    if (hs->buf) {
      /* Yes - get the length of the buffer */
      count = LWIP_MIN(hs->buf_len, bytes_left);
    } else {
      /* We don't have a send buffer so allocate one now */
      count = altcp_sndbuf(pcb);
      if (bytes_left < count) {
        count = bytes_left;
      }
  #ifdef HTTPD_MAX_WRITE_LEN
      /* Additional limitation: e.g. don't enqueue more than 2*mss at once */
      max_write_len = HTTPD_MAX_WRITE_LEN(pcb);
      if (count > max_write_len) {
        count = max_write_len;
      }
  #endif /* HTTPD_MAX_WRITE_LEN */
      do {
        hs->buf = (char *)mem_malloc((mem_size_t)count);
        if (hs->buf != NULL) {
          hs->buf_len = count;
          break;
        }
        count = count / 2;
      } while (count > 100);
  
      /* Did we get a send buffer? If not, return immediately. */
      if (hs->buf == NULL) {
        LWIP_DEBUGF(HTTPD_DEBUG, ("No buff\n"));
        return 0;
      }
    }
  
    /* Read a block of data from the file. */
    LWIP_DEBUGF(HTTPD_DEBUG, ("Trying to read %d bytes.\n", count));
  
  #if LWIP_HTTPD_FS_ASYNC_READ
    count = fs_read_async(hs->handle, hs->buf, count, http_continue, hs);
  #else /* LWIP_HTTPD_FS_ASYNC_READ */
    count = fs_read(hs->handle, hs->buf, count);
  #endif /* LWIP_HTTPD_FS_ASYNC_READ */
    if (count < 0) {
      if (count == FS_READ_DELAYED) {
        /* Delayed read, wait for FS to unblock us */
        return 0;
      }
      /* We reached the end of the file so this request is done.
       * @todo: close here for HTTP/1.1 when reading file fails */
      LWIP_DEBUGF(HTTPD_DEBUG, ("End of file.\n"));
      http_eof(pcb, hs);
      return 0;
    }
  
    /* Set up to send the block of data we just read */
    LWIP_DEBUGF(HTTPD_DEBUG, ("Read %d bytes.\n", count));
    hs->left = count;
    hs->file = hs->buf;
  #if LWIP_HTTPD_SSI
    if (hs->ssi) {
      hs->ssi->parse_left = count;
      hs->ssi->parsed = hs->buf;
    }
  #endif /* LWIP_HTTPD_SSI */
  #else /* LWIP_HTTPD_DYNAMIC_FILE_READ */
    LWIP_ASSERT("SSI and DYNAMIC_HEADERS turned off but eof not reached", 0);
  #endif /* LWIP_HTTPD_SSI || LWIP_HTTPD_DYNAMIC_HEADERS */
    return 1;
  }
  
  /** Sub-function of http_send(): This is the normal send-routine for non-ssi files
   *
   * @returns: - 1: data has been written (so call tcp_ouput)
   *           - 0: no data has been written (no need to call tcp_output)
   */
  static u8_t
  http_send_data_nonssi(struct altcp_pcb *pcb, struct http_state *hs)
  {
    err_t err;
    u16_t len;
    u8_t data_to_send = 0;
  
    /* We are not processing an SHTML file so no tag checking is necessary.
     * Just send the data as we received it from the file. */
    len = (u16_t)LWIP_MIN(hs->left, 0xffff);
  
    err = http_write(pcb, hs->file, &len, HTTP_IS_DATA_VOLATILE(hs));
    if (err == ERR_OK) {
      data_to_send = 1;
      hs->file += len;
      hs->left -= len;
    }
  
    return data_to_send;
  }
  
  #if LWIP_HTTPD_SSI
  /** Sub-function of http_send(): This is the send-routine for ssi files
   *
   * @returns: - 1: data has been written (so call tcp_ouput)
   *           - 0: no data has been written (no need to call tcp_output)
   */
  static u8_t
  http_send_data_ssi(struct altcp_pcb *pcb, struct http_state *hs)
  {
    err_t err = ERR_OK;
    u16_t len;
    u8_t data_to_send = 0;
    u8_t tag_type;
  
    struct http_ssi_state *ssi = hs->ssi;
    LWIP_ASSERT("ssi != NULL", ssi != NULL);
    /* We are processing an SHTML file so need to scan for tags and replace
     * them with insert strings. We need to be careful here since a tag may
     * straddle the boundary of two blocks read from the file and we may also
     * have to split the insert string between two tcp_write operations. */
  
    /* How much data could we send? */
    len = altcp_sndbuf(pcb);
  
    /* Do we have remaining data to send before parsing more? */
    if (ssi->parsed > hs->file) {
      len = (u16_t)LWIP_MIN(ssi->parsed - hs->file, 0xffff);
  
      err = http_write(pcb, hs->file, &len, HTTP_IS_DATA_VOLATILE(hs));
      if (err == ERR_OK) {
        data_to_send = 1;
        hs->file += len;
        hs->left -= len;
      }
  
      /* If the send buffer is full, return now. */
      if (altcp_sndbuf(pcb) == 0) {
        return data_to_send;
      }
    }
  
    LWIP_DEBUGF(HTTPD_DEBUG, ("State %d, %d left\n", ssi->tag_state, (int)ssi->parse_left));
  
    /* We have sent all the data that was already parsed so continue parsing
     * the buffer contents looking for SSI tags. */
    while (((ssi->tag_state == TAG_SENDING) || ssi->parse_left) && (err == ERR_OK)) {
      if (len == 0) {
        return data_to_send;
      }
      switch (ssi->tag_state) {
        case TAG_NONE:
          /* We are not currently processing an SSI tag so scan for the
           * start of the lead-in marker. */
          for (tag_type = 0; tag_type < LWIP_ARRAYSIZE(http_ssi_tag_desc); tag_type++) {
            if (*ssi->parsed == http_ssi_tag_desc[tag_type].lead_in[0]) {
              /* We found what could be the lead-in for a new tag so change
               * state appropriately. */
              ssi->tag_type = tag_type;
              ssi->tag_state = TAG_LEADIN;
              ssi->tag_index = 1;
    #if !LWIP_HTTPD_SSI_INCLUDE_TAG
              ssi->tag_started = ssi->parsed;
    #endif /* !LWIP_HTTPD_SSI_INCLUDE_TAG */
              break;
            }
          }
  
          /* Move on to the next character in the buffer */
          ssi->parse_left--;
          ssi->parsed++;
          break;
  
        case TAG_LEADIN:
          /* We are processing the lead-in marker, looking for the start of
           * the tag name. */
  
          /* Have we reached the end of the leadin? */
          if (http_ssi_tag_desc[ssi->tag_type].lead_in[ssi->tag_index] == 0) {
            ssi->tag_index = 0;
            ssi->tag_state = TAG_FOUND;
          } else {
            /* Have we found the next character we expect for the tag leadin? */
            if (*ssi->parsed == http_ssi_tag_desc[ssi->tag_type].lead_in[ssi->tag_index]) {
              /* Yes - move to the next one unless we have found the complete
               * leadin, in which case we start looking for the tag itself */
              ssi->tag_index++;
            } else {
              /* We found an unexpected character so this is not a tag. Move
               * back to idle state. */
              ssi->tag_state = TAG_NONE;
            }
  
  #if LWIP_HTTPD_DYNAMIC_FILE_READ && !LWIP_HTTPD_SSI_INCLUDE_TAG
            if ((ssi->tag_state == TAG_NONE) &&
                (ssi->parsed - hs->file < ssi->tag_index)) {
              for(u16_t i = 0;i < ssi->tag_index;i++) {
                ssi->tag_insert[i] = http_ssi_tag_desc[ssi->tag_type].lead_in[i];
              }
              ssi->tag_insert_len = ssi->tag_index;
              hs->file += ssi->parsed - hs->file;
              hs->left -= ssi->parsed - hs->file;
              ssi->tag_end = hs->file;
              ssi->tag_index = 0;
              ssi->tag_state = TAG_SENDING;
              break;
            }
  #endif
  
            /* Move on to the next character in the buffer */
            ssi->parse_left--;
            ssi->parsed++;
          }
          break;
  
        case TAG_FOUND:
          /* We are reading the tag name, looking for the start of the
           * lead-out marker and removing any whitespace found. */
  
          /* Remove leading whitespace between the tag leading and the first
           * tag name character. */
          if ((ssi->tag_index == 0) && ((*ssi->parsed == ' ') ||
                                        (*ssi->parsed == '\t') || (*ssi->parsed == '\n') ||
                                        (*ssi->parsed == '\r'))) {
            /* Move on to the next character in the buffer */
            ssi->parse_left--;
            ssi->parsed++;
            break;
          }
  
          /* Have we found the end of the tag name? This is signalled by
           * us finding the first leadout character or whitespace */
          if ((*ssi->parsed == http_ssi_tag_desc[ssi->tag_type].lead_out[0]) ||
              (*ssi->parsed == ' ')  || (*ssi->parsed == '\t') ||
              (*ssi->parsed == '\n') || (*ssi->parsed == '\r')) {
  
            if (ssi->tag_index == 0) {
              /* We read a zero length tag so ignore it. */
              ssi->tag_state = TAG_NONE;
            } else {
              /* We read a non-empty tag so go ahead and look for the
               * leadout string. */
              ssi->tag_state = TAG_LEADOUT;
              LWIP_ASSERT("ssi->tag_index <= 0xff", ssi->tag_index <= 0xff);
              ssi->tag_name_len = (u8_t)ssi->tag_index;
              ssi->tag_name[ssi->tag_index] = '\0';
              if (*ssi->parsed == http_ssi_tag_desc[ssi->tag_type].lead_out[0]) {
                ssi->tag_index = 1;
              } else {
                ssi->tag_index = 0;
              }
            }
          } else {
            /* This character is part of the tag name so save it */
            if (ssi->tag_index < LWIP_HTTPD_MAX_TAG_NAME_LEN) {
              ssi->tag_name[ssi->tag_index++] = *ssi->parsed;
            } else {
              /* The tag was too long so ignore it. */
              ssi->tag_state = TAG_NONE;
            }
          }
  
          /* Move on to the next character in the buffer */
          ssi->parse_left--;
          ssi->parsed++;
  
          break;
  
        /* We are looking for the end of the lead-out marker. */
        case TAG_LEADOUT:
          /* Remove leading whitespace between the tag leading and the first
           * tag leadout character. */
          if ((ssi->tag_index == 0) && ((*ssi->parsed == ' ') ||
                                        (*ssi->parsed == '\t') || (*ssi->parsed == '\n') ||
                                        (*ssi->parsed == '\r'))) {
            /* Move on to the next character in the buffer */
            ssi->parse_left--;
            ssi->parsed++;
            break;
          }
  
          /* Have we found the next character we expect for the tag leadout? */
          if (*ssi->parsed == http_ssi_tag_desc[ssi->tag_type].lead_out[ssi->tag_index]) {
            /* Yes - move to the next one unless we have found the complete
             * leadout, in which case we need to call the client to process
             * the tag. */
  
            /* Move on to the next character in the buffer */
            ssi->parse_left--;
            ssi->parsed++;
            ssi->tag_index++;
  
            if (http_ssi_tag_desc[ssi->tag_type].lead_out[ssi->tag_index] == 0) {
              /* Call the client to ask for the insert string for the
               * tag we just found. */
  #if LWIP_HTTPD_SSI_MULTIPART
              ssi->tag_part = 0; /* start with tag part 0 */
  #endif /* LWIP_HTTPD_SSI_MULTIPART */
              get_tag_insert(hs);
  
              /* Next time through, we are going to be sending data
               * immediately, either the end of the block we start
               * sending here or the insert string. */
              ssi->tag_index = 0;
              ssi->tag_state = TAG_SENDING;
              ssi->tag_end = ssi->parsed;
  #if !LWIP_HTTPD_SSI_INCLUDE_TAG
              ssi->parsed = ssi->tag_started;
  #endif /* !LWIP_HTTPD_SSI_INCLUDE_TAG*/
  
              /* If there is any unsent data in the buffer prior to the
               * tag, we need to send it now. */
              if (ssi->tag_end > hs->file) {
                /* How much of the data can we send? */
  #if LWIP_HTTPD_SSI_INCLUDE_TAG
                len = (u16_t)LWIP_MIN(ssi->tag_end - hs->file, 0xffff);
  #else /* LWIP_HTTPD_SSI_INCLUDE_TAG*/
                /* we would include the tag in sending */
                len = (u16_t)LWIP_MIN(ssi->tag_started - hs->file, 0xffff);
  #endif /* LWIP_HTTPD_SSI_INCLUDE_TAG*/
  
                err = http_write(pcb, hs->file, &len, HTTP_IS_DATA_VOLATILE(hs));
                if (err == ERR_OK) {
                  data_to_send = 1;
  #if !LWIP_HTTPD_SSI_INCLUDE_TAG
                  if (ssi->tag_started <= hs->file) {
                    /* pretend to have sent the tag, too */
                    len += (u16_t)(ssi->tag_end - ssi->tag_started);
                  }
  #endif /* !LWIP_HTTPD_SSI_INCLUDE_TAG*/
                  hs->file += len;
                  hs->left -= len;
                }
              }
            }
          } else {
            /* We found an unexpected character so this is not a tag. Move
             * back to idle state. */
            ssi->parse_left--;
            ssi->parsed++;
            ssi->tag_state = TAG_NONE;
          }
          break;
  
        /*
         * We have found a valid tag and are in the process of sending
         * data as a result of that discovery. We send either remaining data
         * from the file prior to the insert point or the insert string itself.
         */
        case TAG_SENDING:
          /* Do we have any remaining file data to send from the buffer prior
           * to the tag? */
          if (ssi->tag_end > hs->file) {
            /* How much of the data can we send? */
  #if LWIP_HTTPD_SSI_INCLUDE_TAG
            len = (u16_t)LWIP_MIN(ssi->tag_end - hs->file, 0xffff);
  #else /* LWIP_HTTPD_SSI_INCLUDE_TAG*/
            LWIP_ASSERT("hs->started >= hs->file", ssi->tag_started >= hs->file);
            /* we would include the tag in sending */
            len = (u16_t)LWIP_MIN(ssi->tag_started - hs->file, 0xffff);
  #endif /* LWIP_HTTPD_SSI_INCLUDE_TAG*/
            if (len != 0) {
              err = http_write(pcb, hs->file, &len, HTTP_IS_DATA_VOLATILE(hs));
            } else {
              err = ERR_OK;
            }
            if (err == ERR_OK) {
              data_to_send = 1;
  #if !LWIP_HTTPD_SSI_INCLUDE_TAG
              if (ssi->tag_started <= hs->file) {
                /* pretend to have sent the tag, too */
                len += (u16_t)(ssi->tag_end - ssi->tag_started);
              }
  #endif /* !LWIP_HTTPD_SSI_INCLUDE_TAG*/
              hs->file += len;
              hs->left -= len;
            }
          } else {
  #if LWIP_HTTPD_SSI_MULTIPART
            if (ssi->tag_index >= ssi->tag_insert_len) {
              /* Did the last SSIHandler have more to send? */
              if (ssi->tag_part != HTTPD_LAST_TAG_PART) {
                /* If so, call it again */
                ssi->tag_index = 0;
                get_tag_insert(hs);
              }
            }
  #endif /* LWIP_HTTPD_SSI_MULTIPART */
  
            /* Do we still have insert data left to send? */
            if (ssi->tag_index < ssi->tag_insert_len) {
              /* We are sending the insert string itself. How much of the
               * insert can we send? */
              len = (ssi->tag_insert_len - ssi->tag_index);
  
              /* Note that we set the copy flag here since we only have a
               * single tag insert buffer per connection. If we don't do
               * this, insert corruption can occur if more than one insert
               * is processed before we call tcp_output. */
              err = http_write(pcb, &(ssi->tag_insert[ssi->tag_index]), &len,
                               HTTP_IS_TAG_VOLATILE(hs));
              if (err == ERR_OK) {
                data_to_send = 1;
                ssi->tag_index += len;
                /* Don't return here: keep on sending data */
              }
            } else {
  #if LWIP_HTTPD_SSI_MULTIPART
              if (ssi->tag_part == HTTPD_LAST_TAG_PART)
  #endif /* LWIP_HTTPD_SSI_MULTIPART */
              {
                /* We have sent all the insert data so go back to looking for
                 * a new tag. */
                LWIP_DEBUGF(HTTPD_DEBUG, ("Everything sent.\n"));
                ssi->tag_index = 0;
                ssi->tag_state = TAG_NONE;
  #if !LWIP_HTTPD_SSI_INCLUDE_TAG
                ssi->parsed = ssi->tag_end;
  #endif /* !LWIP_HTTPD_SSI_INCLUDE_TAG*/
              }
            }
            break;
          default:
            break;
          }
      }
    }
  
    /* If we drop out of the end of the for loop, this implies we must have
     * file data to send so send it now. In TAG_SENDING state, we've already
     * handled this so skip the send if that's the case. */
    if ((ssi->tag_state != TAG_SENDING) && (ssi->parsed > hs->file)) {
  #if LWIP_HTTPD_DYNAMIC_FILE_READ && !LWIP_HTTPD_SSI_INCLUDE_TAG
      if ((ssi->tag_state != TAG_NONE) && (ssi->tag_started > ssi->tag_end)) {
        /* If we found tag on the edge of the read buffer: just throw away the first part
           (we have copied/saved everything required for parsing on later). */
        len = (u16_t)(ssi->tag_started - hs->file);
        hs->left -= (ssi->parsed - ssi->tag_started);
        ssi->parsed = ssi->tag_started;
        ssi->tag_started = hs->buf;
      } else
  #endif /* LWIP_HTTPD_DYNAMIC_FILE_READ && !LWIP_HTTPD_SSI_INCLUDE_TAG */
      {
        len = (u16_t)LWIP_MIN(ssi->parsed - hs->file, 0xffff);
      }
  
      err = http_write(pcb, hs->file, &len, HTTP_IS_DATA_VOLATILE(hs));
      if (err == ERR_OK) {
        data_to_send = 1;
        hs->file += len;
        hs->left -= len;
      }
    }
    return data_to_send;
  }
  #endif /* LWIP_HTTPD_SSI */
  
  /**
   * Try to send more data on this pcb.
   *
   * @param pcb the pcb to send data
   * @param hs connection state
   */
  static u8_t
  http_send(struct altcp_pcb *pcb, struct http_state *hs)
  {
    u8_t data_to_send = HTTP_NO_DATA_TO_SEND;
  
    LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("http_send: pcb=%p hs=%p left=%d\n", (void *)pcb,
                (void *)hs, hs != NULL ? (int)hs->left : 0));
  
  #if LWIP_HTTPD_SUPPORT_POST && LWIP_HTTPD_POST_MANUAL_WND
    if (hs->unrecved_bytes != 0) {
      return 0;
    }
  #endif /* LWIP_HTTPD_SUPPORT_POST && LWIP_HTTPD_POST_MANUAL_WND */
  
    /* If we were passed a NULL state structure pointer, ignore the call. */
    if (hs == NULL) {
      return 0;
    }
  
  #if LWIP_HTTPD_FS_ASYNC_READ
    /* Check if we are allowed to read from this file.
       (e.g. SSI might want to delay sending until data is available) */
    if (!fs_is_file_ready(hs->handle, http_continue, hs)) {
      return 0;
    }
  #endif /* LWIP_HTTPD_FS_ASYNC_READ */
  
  #if LWIP_HTTPD_DYNAMIC_HEADERS
    /* Do we have any more header data to send for this file? */
    if (hs->hdr_index < NUM_FILE_HDR_STRINGS) {
      data_to_send = http_send_headers(pcb, hs);
      if ((data_to_send == HTTP_DATA_TO_SEND_FREED) ||
          ((data_to_send != HTTP_DATA_TO_SEND_CONTINUE) &&
           (hs->hdr_index < NUM_FILE_HDR_STRINGS))) {
        return data_to_send;
      }
    }
  #endif /* LWIP_HTTPD_DYNAMIC_HEADERS */
  
  #if LWIP_HTTPD_SSI
    if (hs->ssi && (hs->ssi->tag_state == TAG_SENDING)) {
      /* do not check the condition below */
    } else
  #endif
    /* Have we run out of file data to send? If so, we need to read the next
     * block from the file. */
    if (hs->left == 0) {
      if (!http_check_eof(pcb, hs)) {
        return 0;
      }
    }
  
  #if LWIP_HTTPD_SSI
    if (hs->ssi) {
      data_to_send = http_send_data_ssi(pcb, hs);
      if (hs->ssi->tag_state == TAG_SENDING) {
        return data_to_send;
      }
    } else
  #endif /* LWIP_HTTPD_SSI */
    {
      data_to_send = http_send_data_nonssi(pcb, hs);
    }
  
    if ((hs->left == 0) && (fs_bytes_left(hs->handle) <= 0)) {
      /* We reached the end of the file so this request is done.
       * This adds the FIN flag right into the last data segment. */
      LWIP_DEBUGF(HTTPD_DEBUG, ("End of file.\n"));
      http_eof(pcb, hs);
      return 0;
    }
    LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("send_data end.\n"));
    return data_to_send;
  }
  
  #if LWIP_HTTPD_SUPPORT_EXTSTATUS
  /** Initialize a http connection with a file to send for an error message
   *
   * @param hs http connection state
   * @param error_nr HTTP error number
   * @return ERR_OK if file was found and hs has been initialized correctly
   *         another err_t otherwise
   */
  static err_t
  http_find_error_file(struct http_state *hs, u16_t error_nr)
  {
    const char *uri, *uri1, *uri2, *uri3;
  
    if (error_nr == 501) {
      uri1 = "/501.html";
      uri2 = "/501.htm";
      uri3 = "/501.shtml";
    } else {
      /* 400 (bad request is the default) */
      uri1 = "/400.html";
      uri2 = "/400.htm";
      uri3 = "/400.shtml";
    }
    if (fs_open(&hs->file_handle, uri1) == ERR_OK) {
      uri = uri1;
    } else if (fs_open(&hs->file_handle, uri2) == ERR_OK) {
      uri = uri2;
    } else if (fs_open(&hs->file_handle, uri3) == ERR_OK) {
      uri = uri3;
    } else {
      LWIP_DEBUGF(HTTPD_DEBUG, ("Error page for error %"U16_F" not found\n",
                                error_nr));
      return ERR_ARG;
    }
    return http_init_file(hs, &hs->file_handle, 0, uri, 0, NULL);
  }
  #else /* LWIP_HTTPD_SUPPORT_EXTSTATUS */
  #define http_find_error_file(hs, error_nr) ERR_ARG
  #endif /* LWIP_HTTPD_SUPPORT_EXTSTATUS */
  
  /**
   * Get the file struct for a 404 error page.
   * Tries some file names and returns NULL if none found.
   *
   * @param uri pointer that receives the actual file name URI
   * @return file struct for the error page or NULL no matching file was found
   */
  static struct fs_file *
  http_get_404_file(struct http_state *hs, const char **uri)
  {
    err_t err;
  
    *uri = "/404.html";
    err = fs_open(&hs->file_handle, *uri);
    if (err != ERR_OK) {
      /* 404.html doesn't exist. Try 404.htm instead. */
      *uri = "/404.htm";
      err = fs_open(&hs->file_handle, *uri);
      if (err != ERR_OK) {
        /* 404.htm doesn't exist either. Try 404.shtml instead. */
        *uri = "/404.shtml";
        err = fs_open(&hs->file_handle, *uri);
        if (err != ERR_OK) {
          /* 404.htm doesn't exist either. Indicate to the caller that it should
           * send back a default 404 page.
           */
          *uri = NULL;
          return NULL;
        }
      }
    }
  
    return &hs->file_handle;
  }
  
  #if LWIP_HTTPD_SUPPORT_POST
  static err_t
  http_handle_post_finished(struct http_state *hs)
  {
  #if LWIP_HTTPD_POST_MANUAL_WND
    /* Prevent multiple calls to httpd_post_finished, since it might have already
       been called before from httpd_post_data_recved(). */
    if (hs->post_finished) {
      return ERR_OK;
    }
    hs->post_finished = 1;
  #endif /* LWIP_HTTPD_POST_MANUAL_WND */
    /* application error or POST finished */
    /* NULL-terminate the buffer */
    http_uri_buf[0] = 0;
    httpd_post_finished(hs, http_uri_buf, LWIP_HTTPD_URI_BUF_LEN);
    return http_find_file(hs, http_uri_buf, 0);
  }
  
  /** Pass received POST body data to the application and correctly handle
   * returning a response document or closing the connection.
   * ATTENTION: The application is responsible for the pbuf now, so don't free it!
   *
   * @param hs http connection state
   * @param p pbuf to pass to the application
   * @return ERR_OK if passed successfully, another err_t if the response file
   *         hasn't been found (after POST finished)
   */
  static err_t
  http_post_rxpbuf(struct http_state *hs, struct pbuf *p)
  {
    err_t err;
  
    if (p != NULL) {
      /* adjust remaining Content-Length */
      if (hs->post_content_len_left < p->tot_len) {
        hs->post_content_len_left = 0;
      } else {
        hs->post_content_len_left -= p->tot_len;
      }
    }
  #if LWIP_HTTPD_SUPPORT_POST && LWIP_HTTPD_POST_MANUAL_WND
    /* prevent connection being closed if httpd_post_data_recved() is called nested */
    hs->unrecved_bytes++;
  #endif
    if (p != NULL) {
      err = httpd_post_receive_data(hs, p);
    } else {
      err = ERR_OK;
    }
  #if LWIP_HTTPD_SUPPORT_POST && LWIP_HTTPD_POST_MANUAL_WND
    hs->unrecved_bytes--;
  #endif
    if (err != ERR_OK) {
      /* Ignore remaining content in case of application error */
      hs->post_content_len_left = 0;
    }
    if (hs->post_content_len_left == 0) {
  #if LWIP_HTTPD_SUPPORT_POST && LWIP_HTTPD_POST_MANUAL_WND
      if (hs->unrecved_bytes != 0) {
        return ERR_OK;
      }
  #endif /* LWIP_HTTPD_SUPPORT_POST && LWIP_HTTPD_POST_MANUAL_WND */
      /* application error or POST finished */
      return http_handle_post_finished(hs);
    }
  
    return ERR_OK;
  }
  
  /** Handle a post request. Called from http_parse_request when method 'POST'
   * is found.
   *
   * @param p The input pbuf (containing the POST header and body).
   * @param hs The http connection state.
   * @param data HTTP request (header and part of body) from input pbuf(s).
   * @param data_len Size of 'data'.
   * @param uri The HTTP URI parsed from input pbuf(s).
   * @param uri_end Pointer to the end of 'uri' (here, the rest of the HTTP
   *                header starts).
   * @return ERR_OK: POST correctly parsed and accepted by the application.
   *         ERR_INPROGRESS: POST not completely parsed (no error yet)
   *         another err_t: Error parsing POST or denied by the application
   */
  static err_t
  http_post_request(struct pbuf *inp, struct http_state *hs,
                    char *data, u16_t data_len, char *uri, char *uri_end)
  {
    err_t err;
    /* search for end-of-header (first double-CRLF) */
    char *crlfcrlf = lwip_strnstr(uri_end + 1, CRLF CRLF, data_len - (uri_end + 1 - data));
  
    if (crlfcrlf != NULL) {
      /* search for "Content-Length: " */
  #define HTTP_HDR_CONTENT_LEN                "Content-Length: "
  #define HTTP_HDR_CONTENT_LEN_LEN            16
  #define HTTP_HDR_CONTENT_LEN_DIGIT_MAX_LEN  10
      char *scontent_len = lwip_strnstr(uri_end + 1, HTTP_HDR_CONTENT_LEN, crlfcrlf - (uri_end + 1));
      if (scontent_len != NULL) {
        char *scontent_len_end = lwip_strnstr(scontent_len + HTTP_HDR_CONTENT_LEN_LEN, CRLF, HTTP_HDR_CONTENT_LEN_DIGIT_MAX_LEN);
        if (scontent_len_end != NULL) {
          int content_len;
          char *content_len_num = scontent_len + HTTP_HDR_CONTENT_LEN_LEN;
          content_len = atoi(content_len_num);
          if (content_len == 0) {
            /* if atoi returns 0 on error, fix this */
            if ((content_len_num[0] != '0') || (content_len_num[1] != '\r')) {
              content_len = -1;
            }
          }
          if (content_len >= 0) {
            /* adjust length of HTTP header passed to application */
            const char *hdr_start_after_uri = uri_end + 1;
            u16_t hdr_len = (u16_t)LWIP_MIN(data_len, crlfcrlf + 4 - data);
            u16_t hdr_data_len = (u16_t)LWIP_MIN(data_len, crlfcrlf + 4 - hdr_start_after_uri);
            u8_t post_auto_wnd = 1;
            http_uri_buf[0] = 0;
            /* trim http header */
            *crlfcrlf = 0;
            err = httpd_post_begin(hs, uri, hdr_start_after_uri, hdr_data_len, content_len,
                                   http_uri_buf, LWIP_HTTPD_URI_BUF_LEN, &post_auto_wnd);
            if (err == ERR_OK) {
              /* try to pass in data of the first pbuf(s) */
              struct pbuf *q = inp;
              u16_t start_offset = hdr_len;
  #if LWIP_HTTPD_POST_MANUAL_WND
              hs->no_auto_wnd = !post_auto_wnd;
  #endif /* LWIP_HTTPD_POST_MANUAL_WND */
              /* set the Content-Length to be received for this POST */
              hs->post_content_len_left = (u32_t)content_len;
  
              /* get to the pbuf where the body starts */
              while ((q != NULL) && (q->len <= start_offset)) {
                start_offset -= q->len;
                q = q->next;
              }
              if (q != NULL) {
                /* hide the remaining HTTP header */
                pbuf_remove_header(q, start_offset);
  #if LWIP_HTTPD_POST_MANUAL_WND
                if (!post_auto_wnd) {
                  /* already tcp_recved() this data... */
                  hs->unrecved_bytes = q->tot_len;
                }
  #endif /* LWIP_HTTPD_POST_MANUAL_WND */
                pbuf_ref(q);
                return http_post_rxpbuf(hs, q);
              } else if (hs->post_content_len_left == 0) {
                q = pbuf_alloc(PBUF_RAW, 0, PBUF_REF);
                return http_post_rxpbuf(hs, q);
              } else {
                return ERR_OK;
              }
            } else {
              /* return file passed from application */
              return http_find_file(hs, http_uri_buf, 0);
            }
          } else {
            LWIP_DEBUGF(HTTPD_DEBUG, ("POST received invalid Content-Length: %s\n",
                                      content_len_num));
            return ERR_ARG;
          }
        }
      }
      /* If we come here, headers are fully received (double-crlf), but Content-Length
         was not included. Since this is currently the only supported method, we have
         to fail in this case! */
      LWIP_DEBUGF(HTTPD_DEBUG, ("Error when parsing Content-Length\n"));
      return ERR_ARG;
    }
    /* if we come here, the POST is incomplete */
  #if LWIP_HTTPD_SUPPORT_REQUESTLIST
    return ERR_INPROGRESS;
  #else /* LWIP_HTTPD_SUPPORT_REQUESTLIST */
    return ERR_ARG;
  #endif /* LWIP_HTTPD_SUPPORT_REQUESTLIST */
  }
  
  #if LWIP_HTTPD_POST_MANUAL_WND
  /**
   * @ingroup httpd
   * A POST implementation can call this function to update the TCP window.
   * This can be used to throttle data reception (e.g. when received data is
   * programmed to flash and data is received faster than programmed).
   *
   * @param connection A connection handle passed to httpd_post_begin for which
   *        httpd_post_finished has *NOT* been called yet!
   * @param recved_len Length of data received (for window update)
   */
  void httpd_post_data_recved(void *connection, u16_t recved_len)
  {
    struct http_state *hs = (struct http_state *)connection;
    if (hs != NULL) {
      if (hs->no_auto_wnd) {
        u16_t len = recved_len;
        if (hs->unrecved_bytes >= recved_len) {
          hs->unrecved_bytes -= recved_len;
        } else {
          LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_LEVEL_WARNING, ("httpd_post_data_recved: recved_len too big\n"));
          len = (u16_t)hs->unrecved_bytes;
          hs->unrecved_bytes = 0;
        }
        if (hs->pcb != NULL) {
          if (len != 0) {
            altcp_recved(hs->pcb, len);
          }
          if ((hs->post_content_len_left == 0) && (hs->unrecved_bytes == 0)) {
            /* finished handling POST */
            http_handle_post_finished(hs);
            http_send(hs->pcb, hs);
          }
        }
      }
    }
  }
  #endif /* LWIP_HTTPD_POST_MANUAL_WND */
  
  #endif /* LWIP_HTTPD_SUPPORT_POST */
  
  #if LWIP_HTTPD_FS_ASYNC_READ
  /** Try to send more data if file has been blocked before
   * This is a callback function passed to fs_read_async().
   */
  static void
  http_continue(void *connection)
  {
    struct http_state *hs = (struct http_state *)connection;
    LWIP_ASSERT_CORE_LOCKED();
    if (hs && (hs->pcb) && (hs->handle)) {
      LWIP_ASSERT("hs->pcb != NULL", hs->pcb != NULL);
      LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("httpd_continue: try to send more data\n"));
      if (http_send(hs->pcb, hs)) {
        /* If we wrote anything to be sent, go ahead and send it now. */
        LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("tcp_output\n"));
        altcp_output(hs->pcb);
      }
    }
  }
  #endif /* LWIP_HTTPD_FS_ASYNC_READ */
  
  /**
   * When data has been received in the correct state, try to parse it
   * as a HTTP request.
   *
   * @param inp the received pbuf
   * @param hs the connection state
   * @param pcb the altcp_pcb which received this packet
   * @return ERR_OK if request was OK and hs has been initialized correctly
   *         ERR_INPROGRESS if request was OK so far but not fully received
   *         another err_t otherwise
   */
  static err_t
  http_parse_request(struct pbuf *inp, struct http_state *hs, struct altcp_pcb *pcb)
  {
    char *data;
    char *crlf;
    u16_t data_len;
    struct pbuf *p = inp;
  #if LWIP_HTTPD_SUPPORT_REQUESTLIST
    u16_t clen;
  #endif /* LWIP_HTTPD_SUPPORT_REQUESTLIST */
  #if LWIP_HTTPD_SUPPORT_POST
    err_t err;
  #endif /* LWIP_HTTPD_SUPPORT_POST */
  
    LWIP_UNUSED_ARG(pcb); /* only used for post */
    LWIP_ASSERT("p != NULL", p != NULL);
    LWIP_ASSERT("hs != NULL", hs != NULL);
  
    if ((hs->handle != NULL) || (hs->file != NULL)) {
      LWIP_DEBUGF(HTTPD_DEBUG, ("Received data while sending a file\n"));
      /* already sending a file */
      /* @todo: abort? */
      return ERR_USE;
    }
  
  #if LWIP_HTTPD_SUPPORT_REQUESTLIST
  
    LWIP_DEBUGF(HTTPD_DEBUG, ("Received %"U16_F" bytes\n", p->tot_len));
  
    /* first check allowed characters in this pbuf? */
  
    /* enqueue the pbuf */
    if (hs->req == NULL) {
      LWIP_DEBUGF(HTTPD_DEBUG, ("First pbuf\n"));
      hs->req = p;
    } else {
      LWIP_DEBUGF(HTTPD_DEBUG, ("pbuf enqueued\n"));
      pbuf_cat(hs->req, p);
    }
    /* increase pbuf ref counter as it is freed when we return but we want to
       keep it on the req list */
    pbuf_ref(p);
  
    if (hs->req->next != NULL) {
      data_len = LWIP_MIN(hs->req->tot_len, LWIP_HTTPD_MAX_REQ_LENGTH);
      pbuf_copy_partial(hs->req, httpd_req_buf, data_len, 0);
      data = httpd_req_buf;
    } else
  #endif /* LWIP_HTTPD_SUPPORT_REQUESTLIST */
    {
      data = (char *)p->payload;
      data_len = p->len;
      if (p->len != p->tot_len) {
        LWIP_DEBUGF(HTTPD_DEBUG, ("Warning: incomplete header due to chained pbufs\n"));
      }
    }
  
    /* received enough data for minimal request? */
    if (data_len >= MIN_REQ_LEN) {
      /* wait for CRLF before parsing anything */
      crlf = lwip_strnstr(data, CRLF, data_len);
      if (crlf != NULL) {
  #if LWIP_HTTPD_SUPPORT_POST
        int is_post = 0;
  #endif /* LWIP_HTTPD_SUPPORT_POST */
        int is_09 = 0;
        char *sp1, *sp2;
        u16_t left_len, uri_len;
        LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("CRLF received, parsing request\n"));
        /* parse method */
        if (!strncmp(data, "GET ", 4)) {
          sp1 = data + 3;
          /* received GET request */
          LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("Received GET request\"\n"));
  #if LWIP_HTTPD_SUPPORT_POST
        } else if (!strncmp(data, "POST ", 5)) {
          /* store request type */
          is_post = 1;
          sp1 = data + 4;
          /* received GET request */
          LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("Received POST request\n"));
  #endif /* LWIP_HTTPD_SUPPORT_POST */
        } else {
          /* null-terminate the METHOD (pbuf is freed anyway wen returning) */
          data[4] = 0;
          /* unsupported method! */
          LWIP_DEBUGF(HTTPD_DEBUG, ("Unsupported request method (not implemented): \"%s\"\n",
                                    data));
          return http_find_error_file(hs, 501);
        }
        /* if we come here, method is OK, parse URI */
        left_len = (u16_t)(data_len - ((sp1 + 1) - data));
        sp2 = lwip_strnstr(sp1 + 1, " ", left_len);
  #if LWIP_HTTPD_SUPPORT_V09
        if (sp2 == NULL) {
          /* HTTP 0.9: respond with correct protocol version */
          sp2 = lwip_strnstr(sp1 + 1, CRLF, left_len);
          is_09 = 1;
  #if LWIP_HTTPD_SUPPORT_POST
          if (is_post) {
            /* HTTP/0.9 does not support POST */
            goto badrequest;
          }
  #endif /* LWIP_HTTPD_SUPPORT_POST */
        }
  #endif /* LWIP_HTTPD_SUPPORT_V09 */
        uri_len = (u16_t)(sp2 - (sp1 + 1));
        if ((sp2 != 0) && (sp2 > sp1)) {
          /* wait for CRLFCRLF (indicating end of HTTP headers) before parsing anything */
          if (lwip_strnstr(data, CRLF CRLF, data_len) != NULL) {
            char *uri = sp1 + 1;
  #if LWIP_HTTPD_SUPPORT_11_KEEPALIVE
            /* This is HTTP/1.0 compatible: for strict 1.1, a connection
               would always be persistent unless "close" was specified. */
            if (!is_09 && (lwip_strnstr(data, HTTP11_CONNECTIONKEEPALIVE, data_len) ||
                           lwip_strnstr(data, HTTP11_CONNECTIONKEEPALIVE2, data_len))) {
              hs->keepalive = 1;
            } else {
              hs->keepalive = 0;
            }
  #endif /* LWIP_HTTPD_SUPPORT_11_KEEPALIVE */
            /* null-terminate the METHOD (pbuf is freed anyway wen returning) */
            *sp1 = 0;
            uri[uri_len] = 0;
            LWIP_DEBUGF(HTTPD_DEBUG, ("Received \"%s\" request for URI: \"%s\"\n",
                                      data, uri));
  #if LWIP_HTTPD_SUPPORT_POST
            if (is_post) {
  #if LWIP_HTTPD_SUPPORT_REQUESTLIST
              struct pbuf *q = hs->req;
  #else /* LWIP_HTTPD_SUPPORT_REQUESTLIST */
              struct pbuf *q = inp;
  #endif /* LWIP_HTTPD_SUPPORT_REQUESTLIST */
              err = http_post_request(q, hs, data, data_len, uri, sp2);
              if (err != ERR_OK) {
                /* restore header for next try */
                *sp1 = ' ';
                *sp2 = ' ';
                uri[uri_len] = ' ';
              }
              if (err == ERR_ARG) {
                goto badrequest;
              }
              return err;
            } else
  #endif /* LWIP_HTTPD_SUPPORT_POST */
            {
              return http_find_file(hs, uri, is_09);
            }
          }
        } else {
          LWIP_DEBUGF(HTTPD_DEBUG, ("invalid URI\n"));
        }
      }
    }
  
  #if LWIP_HTTPD_SUPPORT_REQUESTLIST
    clen = pbuf_clen(hs->req);
    if ((hs->req->tot_len <= LWIP_HTTPD_REQ_BUFSIZE) &&
        (clen <= LWIP_HTTPD_REQ_QUEUELEN)) {
      /* request not fully received (too short or CRLF is missing) */
      return ERR_INPROGRESS;
    } else
  #endif /* LWIP_HTTPD_SUPPORT_REQUESTLIST */
    {
  #if LWIP_HTTPD_SUPPORT_POST
  badrequest:
  #endif /* LWIP_HTTPD_SUPPORT_POST */
      LWIP_DEBUGF(HTTPD_DEBUG, ("bad request\n"));
      /* could not parse request */
      return http_find_error_file(hs, 400);
    }
  }
  
  #if LWIP_HTTPD_SSI && (LWIP_HTTPD_SSI_BY_FILE_EXTENSION == 1)
  /* Check if SSI should be parsed for this file/URL
   * (With LWIP_HTTPD_SSI_BY_FILE_EXTENSION == 2, this function can be
   * overridden by an external implementation.)
   *
   * @return 1 for SSI, 0 for standard files
   */
  static u8_t
  http_uri_is_ssi(struct fs_file *file, const char *uri)
  {
    size_t loop;
    u8_t tag_check = 0;
    if (file != NULL) {
      /* See if we have been asked for an shtml file and, if so,
          enable tag checking. */
      const char *ext = NULL, *sub;
      char *param = (char *)strstr(uri, "?");
      if (param != NULL) {
        /* separate uri from parameters for now, set back later */
        *param = 0;
      }
      sub = uri;
      ext = uri;
      for (sub = strstr(sub, "."); sub != NULL; sub = strstr(sub, ".")) {
        ext = sub;
        sub++;
      }
      for (loop = 0; loop < NUM_SHTML_EXTENSIONS; loop++) {
        if (!lwip_stricmp(ext, g_pcSSIExtensions[loop])) {
          tag_check = 1;
          break;
        }
      }
      if (param != NULL) {
        *param = '?';
      }
    }
    return tag_check;
  }
  #endif /* LWIP_HTTPD_SSI */
  
  /** Try to find the file specified by uri and, if found, initialize hs
   * accordingly.
   *
   * @param hs the connection state
   * @param uri the HTTP header URI
   * @param is_09 1 if the request is HTTP/0.9 (no HTTP headers in response)
   * @return ERR_OK if file was found and hs has been initialized correctly
   *         another err_t otherwise
   */
  static err_t
  http_find_file(struct http_state *hs, const char *uri, int is_09)
  {
    size_t loop;
    struct fs_file *file = NULL;
    char *params = NULL;
    err_t err;
  #if LWIP_HTTPD_CGI
    int i;
  #endif /* LWIP_HTTPD_CGI */
  #if !LWIP_HTTPD_SSI
    const
  #endif /* !LWIP_HTTPD_SSI */
    /* By default, assume we will not be processing server-side-includes tags */
    u8_t tag_check = 0;
  
    /* Have we been asked for the default file (in root or a directory) ? */
  #if LWIP_HTTPD_MAX_REQUEST_URI_LEN
    size_t uri_len = strlen(uri);
    if ((uri_len > 0) && (uri[uri_len - 1] == '/') &&
        ((uri != http_uri_buf) || (uri_len == 1))) {
      size_t copy_len = LWIP_MIN(sizeof(http_uri_buf) - 1, uri_len - 1);
      if (copy_len > 0) {
        MEMCPY(http_uri_buf, uri, copy_len);
        http_uri_buf[copy_len] = 0;
      }
  #else /* LWIP_HTTPD_MAX_REQUEST_URI_LEN */
    if ((uri[0] == '/') &&  (uri[1] == 0)) {
  #endif /* LWIP_HTTPD_MAX_REQUEST_URI_LEN */
      /* Try each of the configured default filenames until we find one
         that exists. */
      for (loop = 0; loop < NUM_DEFAULT_FILENAMES; loop++) {
        const char *file_name;
  #if LWIP_HTTPD_MAX_REQUEST_URI_LEN
        if (copy_len > 0) {
          size_t len_left = sizeof(http_uri_buf) - copy_len - 1;
          if (len_left > 0) {
            size_t name_len = strlen(httpd_default_filenames[loop].name);
            size_t name_copy_len = LWIP_MIN(len_left, name_len);
            MEMCPY(&http_uri_buf[copy_len], httpd_default_filenames[loop].name, name_copy_len);
            http_uri_buf[copy_len + name_copy_len] = 0;
          }
          file_name = http_uri_buf;
        } else
  #endif /* LWIP_HTTPD_MAX_REQUEST_URI_LEN */
        {
          file_name = httpd_default_filenames[loop].name;
        }
        LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("Looking for %s...\n", file_name));
        err = fs_open(&hs->file_handle, file_name);
        if (err == ERR_OK) {
          uri = file_name;
          file = &hs->file_handle;
          LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("Opened.\n"));
  #if LWIP_HTTPD_SSI
          tag_check = httpd_default_filenames[loop].shtml;
  #endif /* LWIP_HTTPD_SSI */
          break;
        }
      }
    }
    if (file == NULL) {
      /* No - we've been asked for a specific file. */
      /* First, isolate the base URI (without any parameters) */
      params = (char *)strchr(uri, '?');
      if (params != NULL) {
        /* URI contains parameters. NULL-terminate the base URI */
        *params = '\0';
        params++;
      }
  
  #if LWIP_HTTPD_CGI
      http_cgi_paramcount = -1;
      /* Does the base URI we have isolated correspond to a CGI handler? */
      if (httpd_num_cgis && httpd_cgis) {
        for (i = 0; i < httpd_num_cgis; i++) {
          if (strcmp(uri, httpd_cgis[i].pcCGIName) == 0) {
            /*
             * We found a CGI that handles this URI so extract the
             * parameters and call the handler.
             */
            http_cgi_paramcount = extract_uri_parameters(hs, params);
            uri = httpd_cgis[i].pfnCGIHandler(i, http_cgi_paramcount, hs->params,
                                           hs->param_vals);
            break;
          }
        }
      }
  #endif /* LWIP_HTTPD_CGI */
  
      LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("Opening %s\n", uri));
  
      err = fs_open(&hs->file_handle, uri);
      if (err == ERR_OK) {
        file = &hs->file_handle;
      } else {
        file = http_get_404_file(hs, &uri);
      }
  #if LWIP_HTTPD_SSI
      if (file != NULL) {
        if (file->flags & FS_FILE_FLAGS_SSI) {
          tag_check = 1;
        } else {
  #if LWIP_HTTPD_SSI_BY_FILE_EXTENSION
          tag_check = http_uri_is_ssi(file, uri);
  #endif /* LWIP_HTTPD_SSI_BY_FILE_EXTENSION */
        }
      }
  #endif /* LWIP_HTTPD_SSI */
    }
    if (file == NULL) {
      /* None of the default filenames exist so send back a 404 page */
      file = http_get_404_file(hs, &uri);
    }
    return http_init_file(hs, file, is_09, uri, tag_check, params);
  }
  
  /** Initialize a http connection with a file to send (if found).
   * Called by http_find_file and http_find_error_file.
   *
   * @param hs http connection state
   * @param file file structure to send (or NULL if not found)
   * @param is_09 1 if the request is HTTP/0.9 (no HTTP headers in response)
   * @param uri the HTTP header URI
   * @param tag_check enable SSI tag checking
   * @param params != NULL if URI has parameters (separated by '?')
   * @return ERR_OK if file was found and hs has been initialized correctly
   *         another err_t otherwise
   */
  static err_t
  http_init_file(struct http_state *hs, struct fs_file *file, int is_09, const char *uri,
                 u8_t tag_check, char *params)
  {
  #if !LWIP_HTTPD_SUPPORT_V09
    LWIP_UNUSED_ARG(is_09);
  #endif
    if (file != NULL) {
      /* file opened, initialise struct http_state */
  #if !LWIP_HTTPD_DYNAMIC_FILE_READ
      /* If dynamic read is disabled, file data must be in one piece and available now */
      LWIP_ASSERT("file->data != NULL", file->data != NULL);
  #endif
  
  #if LWIP_HTTPD_SSI
      if (tag_check) {
        struct http_ssi_state *ssi = http_ssi_state_alloc();
        if (ssi != NULL) {
          ssi->tag_index = 0;
          ssi->tag_state = TAG_NONE;
          ssi->parsed = file->data;
          ssi->parse_left = file->len;
          ssi->tag_end = file->data;
          hs->ssi = ssi;
        }
      }
  #else /* LWIP_HTTPD_SSI */
      LWIP_UNUSED_ARG(tag_check);
  #endif /* LWIP_HTTPD_SSI */
      hs->handle = file;
  #if LWIP_HTTPD_CGI_SSI
      if (params != NULL) {
        /* URI contains parameters, call generic CGI handler */
        int count;
  #if LWIP_HTTPD_CGI
        if (http_cgi_paramcount >= 0) {
          count = http_cgi_paramcount;
        } else
  #endif
        {
          count = extract_uri_parameters(hs, params);
        }
        httpd_cgi_handler(file, uri, count, http_cgi_params, http_cgi_param_vals
  #if defined(LWIP_HTTPD_FILE_STATE) && LWIP_HTTPD_FILE_STATE
                          , file->state
  #endif /* LWIP_HTTPD_FILE_STATE */
                         );
      }
  #else /* LWIP_HTTPD_CGI_SSI */
      LWIP_UNUSED_ARG(params);
  #endif /* LWIP_HTTPD_CGI_SSI */
      hs->file = file->data;
      LWIP_ASSERT("File length must be positive!", (file->len >= 0));
  #if LWIP_HTTPD_CUSTOM_FILES
      if (((file->flags & FS_FILE_FLAGS_CUSTOM) != 0) && (file->data == NULL)) {
        /* custom file, need to read data first (via fs_read_custom) */
        hs->left = 0;
      } else
  #endif /* LWIP_HTTPD_CUSTOM_FILES */
      {
        hs->left = (u32_t)file->len;
      }
      hs->retries = 0;
  #if LWIP_HTTPD_TIMING
      hs->time_started = sys_now();
  #endif /* LWIP_HTTPD_TIMING */
  #if !LWIP_HTTPD_DYNAMIC_HEADERS
      LWIP_ASSERT("HTTP headers not included in file system",
                  (hs->handle->flags & FS_FILE_FLAGS_HEADER_INCLUDED) != 0);
  #endif /* !LWIP_HTTPD_DYNAMIC_HEADERS */
  #if LWIP_HTTPD_SUPPORT_V09
      if (is_09 && ((hs->handle->flags & FS_FILE_FLAGS_HEADER_INCLUDED) != 0)) {
        /* HTTP/0.9 responses are sent without HTTP header,
           search for the end of the header. */
        char *file_start = lwip_strnstr(hs->file, CRLF CRLF, hs->left);
        if (file_start != NULL) {
          int diff = file_start + 4 - hs->file;
          hs->file += diff;
          hs->left -= (u32_t)diff;
        }
      }
  #endif /* LWIP_HTTPD_SUPPORT_V09*/
    } else {
      hs->handle = NULL;
      hs->file = NULL;
      hs->left = 0;
      hs->retries = 0;
    }
  #if LWIP_HTTPD_DYNAMIC_HEADERS
    /* Determine the HTTP headers to send based on the file extension of
     * the requested URI. */
    if ((hs->handle == NULL) || ((hs->handle->flags & FS_FILE_FLAGS_HEADER_INCLUDED) == 0)) {
      get_http_headers(hs, uri);
    }
  #else /* LWIP_HTTPD_DYNAMIC_HEADERS */
    LWIP_UNUSED_ARG(uri);
  #endif /* LWIP_HTTPD_DYNAMIC_HEADERS */
  #if LWIP_HTTPD_SUPPORT_11_KEEPALIVE
    if (hs->keepalive) {
  #if LWIP_HTTPD_SSI
      if (hs->ssi != NULL) {
        hs->keepalive = 0;
      } else
  #endif /* LWIP_HTTPD_SSI */
      {
        if ((hs->handle != NULL) &&
            ((hs->handle->flags & (FS_FILE_FLAGS_HEADER_INCLUDED | FS_FILE_FLAGS_HEADER_PERSISTENT)) == FS_FILE_FLAGS_HEADER_INCLUDED)) {
          hs->keepalive = 0;
        }
      }
    }
  #endif /* LWIP_HTTPD_SUPPORT_11_KEEPALIVE */
    return ERR_OK;
  }
  
  /**
   * The pcb had an error and is already deallocated.
   * The argument might still be valid (if != NULL).
   */
  static void
  http_err(void *arg, err_t err)
  {
    struct http_state *hs = (struct http_state *)arg;
    LWIP_UNUSED_ARG(err);
  
    LWIP_DEBUGF(HTTPD_DEBUG, ("http_err: %s", lwip_strerr(err)));
  
    if (hs != NULL) {
      http_state_free(hs);
    }
  }
  
  /**
   * Data has been sent and acknowledged by the remote host.
   * This means that more data can be sent.
   */
  static err_t
  http_sent(void *arg, struct altcp_pcb *pcb, u16_t len)
  {
    struct http_state *hs = (struct http_state *)arg;
  
    LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("http_sent %p\n", (void *)pcb));
  
    LWIP_UNUSED_ARG(len);
  
    if (hs == NULL) {
      return ERR_OK;
    }
  
    hs->retries = 0;
  
    http_send(pcb, hs);
  
    return ERR_OK;
  }
  
  /**
   * The poll function is called every 2nd second.
   * If there has been no data sent (which resets the retries) in 8 seconds, close.
   * If the last portion of a file has not been sent in 2 seconds, close.
   *
   * This could be increased, but we don't want to waste resources for bad connections.
   */
  static err_t
  http_poll(void *arg, struct altcp_pcb *pcb)
  {
    struct http_state *hs = (struct http_state *)arg;
    LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("http_poll: pcb=%p hs=%p pcb_state=%s\n",
                (void *)pcb, (void *)hs, tcp_debug_state_str(altcp_dbg_get_tcp_state(pcb))));
  
    if (hs == NULL) {
      err_t closed;
      /* arg is null, close. */
      LWIP_DEBUGF(HTTPD_DEBUG, ("http_poll: arg is NULL, close\n"));
      closed = http_close_conn(pcb, NULL);
      LWIP_UNUSED_ARG(closed);
  #if LWIP_HTTPD_ABORT_ON_CLOSE_MEM_ERROR
      if (closed == ERR_MEM) {
        altcp_abort(pcb);
        return ERR_ABRT;
      }
  #endif /* LWIP_HTTPD_ABORT_ON_CLOSE_MEM_ERROR */
      return ERR_OK;
    } else {
      hs->retries++;
      if (hs->retries == HTTPD_MAX_RETRIES) {
        LWIP_DEBUGF(HTTPD_DEBUG, ("http_poll: too many retries, close\n"));
        http_close_conn(pcb, hs);
        return ERR_OK;
      }
  
      /* If this connection has a file open, try to send some more data. If
       * it has not yet received a GET request, don't do this since it will
       * cause the connection to close immediately. */
      if (hs->handle) {
        LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("http_poll: try to send more data\n"));
        if (http_send(pcb, hs)) {
          /* If we wrote anything to be sent, go ahead and send it now. */
          LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("tcp_output\n"));
          altcp_output(pcb);
        }
      }
    }
  
    return ERR_OK;
  }
  
  /**
   * Data has been received on this pcb.
   * For HTTP 1.0, this should normally only happen once (if the request fits in one packet).
   */
  static err_t
  http_recv(void *arg, struct altcp_pcb *pcb, struct pbuf *p, err_t err)
  {
    struct http_state *hs = (struct http_state *)arg;
    LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("http_recv: pcb=%p pbuf=%p err=%s\n", (void *)pcb,
                (void *)p, lwip_strerr(err)));
  
    if ((err != ERR_OK) || (p == NULL) || (hs == NULL)) {
      /* error or closed by other side? */
      if (p != NULL) {
        /* Inform TCP that we have taken the data. */
        altcp_recved(pcb, p->tot_len);
        pbuf_free(p);
      }
      if (hs == NULL) {
        /* this should not happen, only to be robust */
        LWIP_DEBUGF(HTTPD_DEBUG, ("Error, http_recv: hs is NULL, close\n"));
      }
      http_close_conn(pcb, hs);
      return ERR_OK;
    }
  
  #if LWIP_HTTPD_SUPPORT_POST && LWIP_HTTPD_POST_MANUAL_WND
    if (hs->no_auto_wnd) {
      hs->unrecved_bytes += p->tot_len;
    } else
  #endif /* LWIP_HTTPD_SUPPORT_POST && LWIP_HTTPD_POST_MANUAL_WND */
    {
      /* Inform TCP that we have taken the data. */
      altcp_recved(pcb, p->tot_len);
    }
  
  #if LWIP_HTTPD_SUPPORT_POST
    if (hs->post_content_len_left > 0) {
      /* reset idle counter when POST data is received */
      hs->retries = 0;
      /* this is data for a POST, pass the complete pbuf to the application */
      http_post_rxpbuf(hs, p);
      /* pbuf is passed to the application, don't free it! */
      if (hs->post_content_len_left == 0) {
        /* all data received, send response or close connection */
        http_send(pcb, hs);
      }
      return ERR_OK;
    } else
  #endif /* LWIP_HTTPD_SUPPORT_POST */
    {
      if (hs->handle == NULL) {
        err_t parsed = http_parse_request(p, hs, pcb);
        LWIP_ASSERT("http_parse_request: unexpected return value", parsed == ERR_OK
                    || parsed == ERR_INPROGRESS || parsed == ERR_ARG || parsed == ERR_USE);
  #if LWIP_HTTPD_SUPPORT_REQUESTLIST
        if (parsed != ERR_INPROGRESS) {
          /* request fully parsed or error */
          if (hs->req != NULL) {
            pbuf_free(hs->req);
            hs->req = NULL;
          }
        }
  #endif /* LWIP_HTTPD_SUPPORT_REQUESTLIST */
        pbuf_free(p);
        if (parsed == ERR_OK) {
  #if LWIP_HTTPD_SUPPORT_POST
          if (hs->post_content_len_left == 0)
  #endif /* LWIP_HTTPD_SUPPORT_POST */
          {
            LWIP_DEBUGF(HTTPD_DEBUG | LWIP_DBG_TRACE, ("http_recv: data %p len %"S32_F"\n", (const void *)hs->file, hs->left));
            http_send(pcb, hs);
          }
        } else if (parsed == ERR_ARG) {
          /* @todo: close on ERR_USE? */
          http_close_conn(pcb, hs);
        }
      } else {
        LWIP_DEBUGF(HTTPD_DEBUG, ("http_recv: already sending data\n"));
        /* already sending but still receiving data, we might want to RST here? */
        pbuf_free(p);
      }
    }
    return ERR_OK;
  }
  
  /**
   * A new incoming connection has been accepted.
   */
  static err_t
  http_accept(void *arg, struct altcp_pcb *pcb, err_t err)
  {
    struct http_state *hs;
    LWIP_UNUSED_ARG(err);
    LWIP_UNUSED_ARG(arg);
    LWIP_DEBUGF(HTTPD_DEBUG, ("http_accept %p / %p\n", (void *)pcb, arg));
  
    if ((err != ERR_OK) || (pcb == NULL)) {
      return ERR_VAL;
    }
  
    /* Set priority */
    altcp_setprio(pcb, HTTPD_TCP_PRIO);
  
    /* Allocate memory for the structure that holds the state of the
       connection - initialized by that function. */
    hs = http_state_alloc();
    if (hs == NULL) {
      LWIP_DEBUGF(HTTPD_DEBUG, ("http_accept: Out of memory, RST\n"));
      return ERR_MEM;
    }
    hs->pcb = pcb;
  
    /* Tell TCP that this is the structure we wish to be passed for our
       callbacks. */
    altcp_arg(pcb, hs);
  
    /* Set up the various callback functions */
    altcp_recv(pcb, http_recv);
    altcp_err(pcb, http_err);
    altcp_poll(pcb, http_poll, HTTPD_POLL_INTERVAL);
    altcp_sent(pcb, http_sent);
  
    return ERR_OK;
  }
  
  static void
  httpd_init_pcb(struct altcp_pcb *pcb, u16_t port)
  {
    err_t err;
  
    if (pcb) {
      altcp_setprio(pcb, HTTPD_TCP_PRIO);
      /* set SOF_REUSEADDR here to explicitly bind httpd to multiple interfaces */
      err = altcp_bind(pcb, IP_ANY_TYPE, port);
      LWIP_UNUSED_ARG(err); /* in case of LWIP_NOASSERT */
      LWIP_ASSERT("httpd_init: tcp_bind failed", err == ERR_OK);
      pcb = altcp_listen(pcb);
      LWIP_ASSERT("httpd_init: tcp_listen failed", pcb != NULL);
      altcp_accept(pcb, http_accept);
    }
  }
  
  /**
   * @ingroup httpd
   * Initialize the httpd: set up a listening PCB and bind it to the defined port
   */
  void
  httpd_init(void)
  {
    struct altcp_pcb *pcb;
  
  #if HTTPD_USE_MEM_POOL
    LWIP_MEMPOOL_INIT(HTTPD_STATE);
  #if LWIP_HTTPD_SSI
    LWIP_MEMPOOL_INIT(HTTPD_SSI_STATE);
  #endif
  #endif
    LWIP_DEBUGF(HTTPD_DEBUG, ("httpd_init\n"));
  
    /* LWIP_ASSERT_CORE_LOCKED(); is checked by tcp_new() */
  
    pcb = altcp_tcp_new_ip_type(IPADDR_TYPE_ANY);
    LWIP_ASSERT("httpd_init: tcp_new failed", pcb != NULL);
    httpd_init_pcb(pcb, HTTPD_SERVER_PORT);
  }
  
  #if HTTPD_ENABLE_HTTPS
  /**
   * @ingroup httpd
   * Initialize the httpd: set up a listening PCB and bind it to the defined port.
   * Also set up TLS connection handling (HTTPS).
   */
  void
  httpd_inits(struct altcp_tls_config *conf)
  {
  #if LWIP_ALTCP_TLS
    struct altcp_pcb *pcb_tls = altcp_tls_new(conf, IPADDR_TYPE_ANY);
    LWIP_ASSERT("httpd_init: altcp_tls_new failed", pcb_tls != NULL);
    httpd_init_pcb(pcb_tls, HTTPD_SERVER_PORT_HTTPS);
  #else /* LWIP_ALTCP_TLS */
    LWIP_UNUSED_ARG(conf);
  #endif /* LWIP_ALTCP_TLS */
  }
  #endif /* HTTPD_ENABLE_HTTPS */
  
  #if LWIP_HTTPD_SSI
  /**
   * @ingroup httpd
   * Set the SSI handler function.
   *
   * @param ssi_handler the SSI handler function
   * @param tags an array of SSI tag strings to search for in SSI-enabled files
   * @param num_tags number of tags in the 'tags' array
   */
  void
  http_set_ssi_handler(tSSIHandler ssi_handler, const char **tags, int num_tags)
  {
    LWIP_DEBUGF(HTTPD_DEBUG, ("http_set_ssi_handler\n"));
  
    LWIP_ASSERT("no ssi_handler given", ssi_handler != NULL);
    httpd_ssi_handler = ssi_handler;
  
  #if LWIP_HTTPD_SSI_RAW
    LWIP_UNUSED_ARG(tags);
    LWIP_UNUSED_ARG(num_tags);
  #else /* LWIP_HTTPD_SSI_RAW */
    LWIP_ASSERT("no tags given", tags != NULL);
    LWIP_ASSERT("invalid number of tags", num_tags > 0);
  
    httpd_tags = tags;
    httpd_num_tags = num_tags;
  #endif /* !LWIP_HTTPD_SSI_RAW */
  }
  #endif /* LWIP_HTTPD_SSI */
  
  #if LWIP_HTTPD_CGI
  /**
   * @ingroup httpd
   * Set an array of CGI filenames/handler functions
   *
   * @param cgis an array of CGI filenames/handler functions
   * @param num_handlers number of elements in the 'cgis' array
   */
  void
  http_set_cgi_handlers(const tCGI *cgis, int num_handlers)
  {
    LWIP_ASSERT("no cgis given", cgis != NULL);
    LWIP_ASSERT("invalid number of handlers", num_handlers > 0);
  
    httpd_cgis = cgis;
    httpd_num_cgis = num_handlers;
  }
  #endif /* LWIP_HTTPD_CGI */
  
  #endif /* LWIP_TCP && LWIP_CALLBACK_API */
  