text: #ifndef __CURL_MULTI_H
  #define __CURL_MULTI_H
  /***************************************************************************
   *                                  _   _ ____  _
   *  Project                     ___| | | |  _ \| |
   *                             / __| | | | |_) | |
   *                            | (__| |_| |  _ <| |___
   *                             \___|\___/|_| \_\_____|
   *
   * Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.
   *
   * This software is licensed as described in the file COPYING, which
   * you should have received as part of this distribution. The terms
   * are also available at https://curl.haxx.se/docs/copyright.html.
   *
   * You may opt to use, copy, modify, merge, publish, distribute and/or sell
   * copies of the Software, and permit persons to whom the Software is
   * furnished to do so, under the terms of the COPYING file.
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
   * KIND, either express or implied.
   *
   ***************************************************************************/
  /*
    This is an "external" header file. Don't give away any internals here!
  
    GOALS
  
    o Enable a "pull" interface. The application that uses libcurl decides where
      and when to ask libcurl to get/send data.
  
    o Enable multiple simultaneous transfers in the same thread without making it
      complicated for the application.
  
    o Enable the application to select() on its own file descriptors and curl's
      file descriptors simultaneous easily.
  
  */
  
  /*
   * This header file should not really need to include "curl.h" since curl.h
   * itself includes this file and we expect user applications to do #include
   * <curl/curl.h> without the need for especially including multi.h.
   *
   * For some reason we added this include here at one point, and rather than to
   * break existing (wrongly written) libcurl applications, we leave it as-is
   * but with this warning attached.
   */
  #include "curl.h"
  
  #ifdef  __cplusplus
  extern "C" {
  #endif
  
  #if defined(BUILDING_LIBCURL) || defined(CURL_STRICTER)
  typedef struct Curl_multi CURLM;
  #else
  typedef void CURLM;
  #endif
  
  typedef enum {
    CURLM_CALL_MULTI_PERFORM = -1, /* please call curl_multi_perform() or
                                      curl_multi_socket*() soon */
    CURLM_OK,
    CURLM_BAD_HANDLE,      /* the passed-in handle is not a valid CURLM handle */
    CURLM_BAD_EASY_HANDLE, /* an easy handle was not good/valid */
    CURLM_OUT_OF_MEMORY,   /* if you ever get this, you're in deep sh*t */
    CURLM_INTERNAL_ERROR,  /* this is a libcurl bug */
    CURLM_BAD_SOCKET,      /* the passed in socket argument did not match */
    CURLM_UNKNOWN_OPTION,  /* curl_multi_setopt() with unsupported option */
    CURLM_ADDED_ALREADY,   /* an easy handle already added to a multi handle was
                              attempted to get added - again */
    CURLM_LAST
  } CURLMcode;
  
  /* just to make code nicer when using curl_multi_socket() you can now check
     for CURLM_CALL_MULTI_SOCKET too in the same style it works for
     curl_multi_perform() and CURLM_CALL_MULTI_PERFORM */
  #define CURLM_CALL_MULTI_SOCKET CURLM_CALL_MULTI_PERFORM
  
  /* bitmask bits for CURLMOPT_PIPELINING */
  #define CURLPIPE_NOTHING   0L
  #define CURLPIPE_HTTP1     1L
  #define CURLPIPE_MULTIPLEX 2L
  
  typedef enum {
    CURLMSG_NONE, /* first, not used */
    CURLMSG_DONE, /* This easy handle has completed. 'result' contains
                     the CURLcode of the transfer */
    CURLMSG_LAST /* last, not used */
  } CURLMSG;
  
  struct CURLMsg {
    CURLMSG msg;       /* what this message means */
    CURL *easy_handle; /* the handle it concerns */
    union {
      void *whatever;    /* message-specific data */
      CURLcode result;   /* return code for transfer */
    } data;
  };
  typedef struct CURLMsg CURLMsg;
  
  /* Based on poll(2) structure and values.
   * We don't use pollfd and POLL* constants explicitly
   * to cover platforms without poll(). */
  #define CURL_WAIT_POLLIN    0x0001
  #define CURL_WAIT_POLLPRI   0x0002
  #define CURL_WAIT_POLLOUT   0x0004
  
  struct curl_waitfd {
    curl_socket_t fd;
    short events;
    short revents; /* not supported yet */
  };
  
  /*
   * Name:    curl_multi_init()
   *
   * Desc:    inititalize multi-style curl usage
   *
   * Returns: a new CURLM handle to use in all 'curl_multi' functions.
   */
  CURL_EXTERN CURLM *curl_multi_init(void);
  
  /*
   * Name:    curl_multi_add_handle()
   *
   * Desc:    add a standard curl handle to the multi stack
   *
   * Returns: CURLMcode type, general multi error code.
   */
  CURL_EXTERN CURLMcode curl_multi_add_handle(CURLM *multi_handle,
                                              CURL *curl_handle);
  
   /*
    * Name:    curl_multi_remove_handle()
    *
    * Desc:    removes a curl handle from the multi stack again
    *
    * Returns: CURLMcode type, general multi error code.
    */
  CURL_EXTERN CURLMcode curl_multi_remove_handle(CURLM *multi_handle,
                                                 CURL *curl_handle);
  
   /*
    * Name:    curl_multi_fdset()
    *
    * Desc:    Ask curl for its fd_set sets. The app can use these to select() or
    *          poll() on. We want curl_multi_perform() called as soon as one of
    *          them are ready.
    *
    * Returns: CURLMcode type, general multi error code.
    */
  CURL_EXTERN CURLMcode curl_multi_fdset(CURLM *multi_handle,
                                         fd_set *read_fd_set,
                                         fd_set *write_fd_set,
                                         fd_set *exc_fd_set,
                                         int *max_fd);
  
  /*
   * Name:     curl_multi_wait()
   *
   * Desc:     Poll on all fds within a CURLM set as well as any
   *           additional fds passed to the function.
   *
   * Returns:  CURLMcode type, general multi error code.
   */
  CURL_EXTERN CURLMcode curl_multi_wait(CURLM *multi_handle,
                                        struct curl_waitfd extra_fds[],
                                        unsigned int extra_nfds,
                                        int timeout_ms,
                                        int *ret);
  
   /*
    * Name:    curl_multi_perform()
    *
    * Desc:    When the app thinks there's data available for curl it calls this
    *          function to read/write whatever there is right now. This returns
    *          as soon as the reads and writes are done. This function does not
    *          require that there actually is data available for reading or that
    *          data can be written, it can be called just in case. It returns
    *          the number of handles that still transfer data in the second
    *          argument's integer-pointer.
    *
    * Returns: CURLMcode type, general multi error code. *NOTE* that this only
    *          returns errors etc regarding the whole multi stack. There might
    *          still have occurred problems on invidual transfers even when this
    *          returns OK.
    */
  CURL_EXTERN CURLMcode curl_multi_perform(CURLM *multi_handle,
                                           int *running_handles);
  
   /*
    * Name:    curl_multi_cleanup()
    *
    * Desc:    Cleans up and removes a whole multi stack. It does not free or
    *          touch any individual easy handles in any way. We need to define
    *          in what state those handles will be if this function is called
    *          in the middle of a transfer.
    *
    * Returns: CURLMcode type, general multi error code.
    */
  CURL_EXTERN CURLMcode curl_multi_cleanup(CURLM *multi_handle);
  
  /*
   * Name:    curl_multi_info_read()
   *
   * Desc:    Ask the multi handle if there's any messages/informationals from
   *          the individual transfers. Messages include informationals such as
   *          error code from the transfer or just the fact that a transfer is
   *          completed. More details on these should be written down as well.
   *
   *          Repeated calls to this function will return a new struct each
   *          time, until a special "end of msgs" struct is returned as a signal
   *          that there is no more to get at this point.
   *
   *          The data the returned pointer points to will not survive calling
   *          curl_multi_cleanup().
   *
   *          The 'CURLMsg' struct is meant to be very simple and only contain
   *          very basic informations. If more involved information is wanted,
   *          we will provide the particular "transfer handle" in that struct
   *          and that should/could/would be used in subsequent
   *          curl_easy_getinfo() calls (or similar). The point being that we
   *          must never expose complex structs to applications, as then we'll
   *          undoubtably get backwards compatibility problems in the future.
   *
   * Returns: A pointer to a filled-in struct, or NULL if it failed or ran out
   *          of structs. It also writes the number of messages left in the
   *          queue (after this read) in the integer the second argument points
   *          to.
   */
  CURL_EXTERN CURLMsg *curl_multi_info_read(CURLM *multi_handle,
                                            int *msgs_in_queue);
  
  /*
   * Name:    curl_multi_strerror()
   *
   * Desc:    The curl_multi_strerror function may be used to turn a CURLMcode
   *          value into the equivalent human readable error string.  This is
   *          useful for printing meaningful error messages.
   *
   * Returns: A pointer to a zero-terminated error message.
   */
  CURL_EXTERN const char *curl_multi_strerror(CURLMcode);
  
  /*
   * Name:    curl_multi_socket() and
   *          curl_multi_socket_all()
   *
   * Desc:    An alternative version of curl_multi_perform() that allows the
   *          application to pass in one of the file descriptors that have been
   *          detected to have "action" on them and let libcurl perform.
   *          See man page for details.
   */
  #define CURL_POLL_NONE   0
  #define CURL_POLL_IN     1
  #define CURL_POLL_OUT    2
  #define CURL_POLL_INOUT  3
  #define CURL_POLL_REMOVE 4
  
  #define CURL_SOCKET_TIMEOUT CURL_SOCKET_BAD
  
  #define CURL_CSELECT_IN   0x01
  #define CURL_CSELECT_OUT  0x02
  #define CURL_CSELECT_ERR  0x04
  
  typedef int (*curl_socket_callback)(CURL *easy,      /* easy handle */
                                      curl_socket_t s, /* socket */
                                      int what,        /* see above */
                                      void *userp,     /* private callback
                                                          pointer */
                                      void *socketp);  /* private socket
                                                          pointer */
  /*
   * Name:    curl_multi_timer_callback
   *
   * Desc:    Called by libcurl whenever the library detects a change in the
   *          maximum number of milliseconds the app is allowed to wait before
   *          curl_multi_socket() or curl_multi_perform() must be called
   *          (to allow libcurl's timed events to take place).
   *
   * Returns: The callback should return zero.
   */
  typedef int (*curl_multi_timer_callback)(CURLM *multi,    /* multi handle */
                                           long timeout_ms, /* see above */
                                           void *userp);    /* private callback
                                                               pointer */
  
  CURL_EXTERN CURLMcode curl_multi_socket(CURLM *multi_handle, curl_socket_t s,
                                          int *running_handles);
  
  CURL_EXTERN CURLMcode curl_multi_socket_action(CURLM *multi_handle,
                                                 curl_socket_t s,
                                                 int ev_bitmask,
                                                 int *running_handles);
  
  CURL_EXTERN CURLMcode curl_multi_socket_all(CURLM *multi_handle,
                                              int *running_handles);
  
  #ifndef CURL_ALLOW_OLD_MULTI_SOCKET
  /* This macro below was added in 7.16.3 to push users who recompile to use
     the new curl_multi_socket_action() instead of the old curl_multi_socket()
  */
  #define curl_multi_socket(x,y,z) curl_multi_socket_action(x,y,0,z)
  #endif
  
  /*
   * Name:    curl_multi_timeout()
   *
   * Desc:    Returns the maximum number of milliseconds the app is allowed to
   *          wait before curl_multi_socket() or curl_multi_perform() must be
   *          called (to allow libcurl's timed events to take place).
   *
   * Returns: CURLM error code.
   */
  CURL_EXTERN CURLMcode curl_multi_timeout(CURLM *multi_handle,
                                           long *milliseconds);
  
  #undef CINIT /* re-using the same name as in curl.h */
  
  #ifdef CURL_ISOCPP
  #define CINIT(name,type,num) CURLMOPT_ ## name = CURLOPTTYPE_ ## type + num
  #else
  /* The macro "##" is ISO C, we assume pre-ISO C doesn't support it. */
  #define LONG          CURLOPTTYPE_LONG
  #define OBJECTPOINT   CURLOPTTYPE_OBJECTPOINT
  #define FUNCTIONPOINT CURLOPTTYPE_FUNCTIONPOINT
  #define OFF_T         CURLOPTTYPE_OFF_T
  #define CINIT(name,type,number) CURLMOPT_/**/name = type + number
  #endif
  
  typedef enum {
    /* This is the socket callback function pointer */
    CINIT(SOCKETFUNCTION, FUNCTIONPOINT, 1),
  
    /* This is the argument passed to the socket callback */
    CINIT(SOCKETDATA, OBJECTPOINT, 2),
  
      /* set to 1 to enable pipelining for this multi handle */
    CINIT(PIPELINING, LONG, 3),
  
     /* This is the timer callback function pointer */
    CINIT(TIMERFUNCTION, FUNCTIONPOINT, 4),
  
    /* This is the argument passed to the timer callback */
    CINIT(TIMERDATA, OBJECTPOINT, 5),
  
    /* maximum number of entries in the connection cache */
    CINIT(MAXCONNECTS, LONG, 6),
  
    /* maximum number of (pipelining) connections to one host */
    CINIT(MAX_HOST_CONNECTIONS, LONG, 7),
  
    /* maximum number of requests in a pipeline */
    CINIT(MAX_PIPELINE_LENGTH, LONG, 8),
  
    /* a connection with a content-length longer than this
       will not be considered for pipelining */
    CINIT(CONTENT_LENGTH_PENALTY_SIZE, OFF_T, 9),
  
    /* a connection with a chunk length longer than this
       will not be considered for pipelining */
    CINIT(CHUNK_LENGTH_PENALTY_SIZE, OFF_T, 10),
  
    /* a list of site names(+port) that are blacklisted from
       pipelining */
    CINIT(PIPELINING_SITE_BL, OBJECTPOINT, 11),
  
    /* a list of server types that are blacklisted from
       pipelining */
    CINIT(PIPELINING_SERVER_BL, OBJECTPOINT, 12),
  
    /* maximum number of open connections in total */
    CINIT(MAX_TOTAL_CONNECTIONS, LONG, 13),
  
     /* This is the server push callback function pointer */
    CINIT(PUSHFUNCTION, FUNCTIONPOINT, 14),
  
    /* This is the argument passed to the server push callback */
    CINIT(PUSHDATA, OBJECTPOINT, 15),
  
    CURLMOPT_LASTENTRY /* the last unused */
  } CURLMoption;
  
  
  /*
   * Name:    curl_multi_setopt()
   *
   * Desc:    Sets options for the multi handle.
   *
   * Returns: CURLM error code.
   */
  CURL_EXTERN CURLMcode curl_multi_setopt(CURLM *multi_handle,
                                          CURLMoption option, ...);
  
  
  /*
   * Name:    curl_multi_assign()
   *
   * Desc:    This function sets an association in the multi handle between the
   *          given socket and a private pointer of the application. This is
   *          (only) useful for curl_multi_socket uses.
   *
   * Returns: CURLM error code.
   */
  CURL_EXTERN CURLMcode curl_multi_assign(CURLM *multi_handle,
                                          curl_socket_t sockfd, void *sockp);
  
  
  /*
   * Name: curl_push_callback
   *
   * Desc: This callback gets called when a new stream is being pushed by the
   *       server. It approves or denies the new stream.
   *
   * Returns: CURL_PUSH_OK or CURL_PUSH_DENY.
   */
  #define CURL_PUSH_OK   0
  #define CURL_PUSH_DENY 1
  
  struct curl_pushheaders;  /* forward declaration only */
  
  CURL_EXTERN char *curl_pushheader_bynum(struct curl_pushheaders *h,
                                          size_t num);
  CURL_EXTERN char *curl_pushheader_byname(struct curl_pushheaders *h,
                                           const char *name);
  
  typedef int (*curl_push_callback)(CURL *parent,
                                    CURL *easy,
                                    size_t num_headers,
                                    struct curl_pushheaders *headers,
                                    void *userp);
  
  #ifdef __cplusplus
  } /* end of extern "C" */
  #endif
  
  #endif
  