text: /* Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  #include "mod_proxy.h"
  #include "mod_watchdog.h"
  #include "ap_slotmem.h"
  #include "ap_expr.h"
  #if APR_HAS_THREADS
  #include "apr_thread_pool.h"
  #endif
  
  module AP_MODULE_DECLARE_DATA proxy_hcheck_module;
  
  #define HCHECK_WATHCHDOG_NAME ("_proxy_hcheck_")
  #define HC_THREADPOOL_SIZE (16)
  
  /* Why? So we can easily set/clear HC_USE_THREADS during dev testing */
  #if APR_HAS_THREADS
  #ifndef HC_USE_THREADS
  #define HC_USE_THREADS 1
  #endif
  #else
  #define HC_USE_THREADS 0
  #endif
  
  typedef struct {
      char *name;
      hcmethod_t method;
      int passes;
      int fails;
      apr_interval_time_t interval;
      char *hurl;
      char *hcexpr;
  } hc_template_t;
  
  typedef struct {
      char *expr;
      ap_expr_info_t *pexpr;       /* parsed expression */
  } hc_condition_t;
  
  typedef struct {
      apr_pool_t *p;
      apr_array_header_t *templates;
      apr_table_t *conditions;
      apr_hash_t *hcworkers;
      server_rec *s;
  } sctx_t;
  
  /* Used in the HC worker via the context field */
  typedef struct {
      const char *path;   /* The path of the original worker URL */
      const char *method; /* Method string for the HTTP/AJP request */
      const char *req;    /* pre-formatted HTTP/AJP request */
      proxy_worker *w;    /* Pointer to the actual worker */
  } wctx_t;
  
  typedef struct {
      apr_pool_t *ptemp;
      sctx_t *ctx;
      proxy_balancer *balancer;
      proxy_worker *worker;
      proxy_worker *hc;
      apr_time_t *now;
  } baton_t;
  
  static APR_OPTIONAL_FN_TYPE(ajp_handle_cping_cpong) *ajp_handle_cping_cpong = NULL;
  
  static void *hc_create_config(apr_pool_t *p, server_rec *s)
  {
      sctx_t *ctx = apr_pcalloc(p, sizeof(sctx_t));
      ctx->s = s;
      apr_pool_create(&ctx->p, p);
      apr_pool_tag(ctx->p, "proxy_hcheck");
      ctx->templates = apr_array_make(p, 10, sizeof(hc_template_t));
      ctx->conditions = apr_table_make(p, 10);
      ctx->hcworkers = apr_hash_make(p);
      return ctx;
  }
  
  static ap_watchdog_t *watchdog;
  #if HC_USE_THREADS
  static apr_thread_pool_t *hctp;
  static int tpsize;
  #endif
  
  /*
   * This serves double duty by not only validating (and creating)
   * the health-check template, but also ties into set_worker_param()
   * which does the actual setting of worker params in shm.
   */
  static const char *set_worker_hc_param(apr_pool_t *p,
                                      server_rec *s,
                                      proxy_worker *worker,
                                      const char *key,
                                      const char *val,
                                      void *v)
  {
      int ival;
      hc_template_t *temp;
      sctx_t *ctx = (sctx_t *) ap_get_module_config(s->module_config,
                                                    &proxy_hcheck_module);
      if (!worker && !v) {
          return "Bad call to set_worker_hc_param()";
      }
      if (!ctx) {
          ctx = hc_create_config(p, s);
          ap_set_module_config(s->module_config, &proxy_hcheck_module, ctx);
      }
      temp = (hc_template_t *)v;
      if (!strcasecmp(key, "hctemplate")) {
          hc_template_t *template;
          template = (hc_template_t *)ctx->templates->elts;
          for (ival = 0; ival < ctx->templates->nelts; ival++, template++) {
              if (!ap_cstr_casecmp(template->name, val)) {
                  if (worker) {
                      worker->s->method = template->method;
                      worker->s->interval = template->interval;
                      worker->s->passes = template->passes;
                      worker->s->fails = template->fails;
                      PROXY_STRNCPY(worker->s->hcuri, template->hurl);
                      PROXY_STRNCPY(worker->s->hcexpr, template->hcexpr);
                  } else {
                      temp->method = template->method;
                      temp->interval = template->interval;
                      temp->passes = template->passes;
                      temp->fails = template->fails;
                      temp->hurl = apr_pstrdup(p, template->hurl);
                      temp->hcexpr = apr_pstrdup(p, template->hcexpr);
                  }
                  return NULL;
              }
          }
          return apr_psprintf(p, "Unknown ProxyHCTemplate name: %s", val);
      }
      else if (!strcasecmp(key, "hcmethod")) {
          proxy_hcmethods_t *method = proxy_hcmethods;
          for (; method->name; method++) {
              if (!ap_cstr_casecmp(val, method->name)) {
                  if (!method->implemented) {
                      return apr_psprintf(p, "Health check method %s not (yet) implemented",
                                          val);
                  }
                  if (worker) {
                      worker->s->method = method->method;
                  } else {
                      temp->method = method->method;
                  }
                  return NULL;
              }
          }
          return "Unknown method";
      }
      else if (!strcasecmp(key, "hcinterval")) {
          apr_interval_time_t hci;
          apr_status_t rv;
          rv = ap_timeout_parameter_parse(val, &hci, "s");
          if (rv != APR_SUCCESS)
              return "Unparse-able hcinterval setting";
          if (hci < AP_WD_TM_SLICE)
              return apr_psprintf(p, "Interval must be a positive value greater than %"
                                  APR_TIME_T_FMT "ms", apr_time_as_msec(AP_WD_TM_SLICE));
          if (worker) {
              worker->s->interval = hci;
          } else {
              temp->interval = hci;
          }
      }
      else if (!strcasecmp(key, "hcpasses")) {
          ival = atoi(val);
          if (ival < 0)
              return "Passes must be a positive value";
          if (worker) {
              worker->s->passes = ival;
          } else {
              temp->passes = ival;
          }
      }
      else if (!strcasecmp(key, "hcfails")) {
          ival = atoi(val);
          if (ival < 0)
              return "Fails must be a positive value";
          if (worker) {
              worker->s->fails = ival;
          } else {
              temp->fails = ival;
          }
      }
      else if (!strcasecmp(key, "hcuri")) {
          if (strlen(val) >= sizeof(worker->s->hcuri))
              return apr_psprintf(p, "Health check uri length must be < %d characters",
                      (int)sizeof(worker->s->hcuri));
          if (worker) {
              PROXY_STRNCPY(worker->s->hcuri, val);
          } else {
              temp->hurl = apr_pstrdup(p, val);
          }
      }
      else if (!strcasecmp(key, "hcexpr")) {
          hc_condition_t *cond;
          cond = (hc_condition_t *)apr_table_get(ctx->conditions, val);
          if (!cond) {
              return apr_psprintf(p, "Unknown health check condition expr: %s", val);
          }
          /* This check is wonky... a known expr can't be this big. Check anyway */
          if (strlen(val) >= sizeof(worker->s->hcexpr))
              return apr_psprintf(p, "Health check uri length must be < %d characters",
                      (int)sizeof(worker->s->hcexpr));
          if (worker) {
              PROXY_STRNCPY(worker->s->hcexpr, val);
          } else {
              temp->hcexpr = apr_pstrdup(p, val);
          }
      }
    else {
          return "unknown Worker hcheck parameter";
      }
      return NULL;
  }
  
  static const char *set_hc_condition(cmd_parms *cmd, void *dummy, const char *arg)
  {
      char *name = NULL;
      char *expr;
      sctx_t *ctx;
      hc_condition_t *cond;
  
      const char *err = ap_check_cmd_context(cmd, NOT_IN_HTACCESS);
      if (err)
          return err;
      ctx = (sctx_t *) ap_get_module_config(cmd->server->module_config,
                                            &proxy_hcheck_module);
  
      name = ap_getword_conf(cmd->pool, &arg);
      if (!*name) {
          return apr_pstrcat(cmd->temp_pool, "Missing expression name for ",
                             cmd->cmd->name, NULL);
      }
      if (strlen(name) > (PROXY_WORKER_MAX_SCHEME_SIZE - 1)) {
          return apr_psprintf(cmd->temp_pool, "Expression name limited to %d characters",
                             (PROXY_WORKER_MAX_SCHEME_SIZE - 1));
      }
      /* get expr. Allow fancy new {...} quoting style */
      expr = ap_getword_conf2(cmd->temp_pool, &arg);
      if (!*expr) {
          return apr_pstrcat(cmd->temp_pool, "Missing expression for ",
                             cmd->cmd->name, NULL);
      }
      cond = apr_palloc(cmd->pool, sizeof(hc_condition_t));
      cond->pexpr = ap_expr_parse_cmd(cmd, expr, 0, &err, NULL);
      if (err) {
          return apr_psprintf(cmd->temp_pool, "Could not parse expression \"%s\": %s",
                              expr, err);
      }
      cond->expr = apr_pstrdup(cmd->pool, expr);
      apr_table_setn(ctx->conditions, name, (void *)cond);
      expr = ap_getword_conf(cmd->temp_pool, &arg);
      if (*expr) {
          return "error: extra parameter(s)";
      }
      return NULL;
  }
  
  static const char *set_hc_template(cmd_parms *cmd, void *dummy, const char *arg)
  {
      char *name = NULL;
      char *word, *val;
      hc_template_t *template;
      sctx_t *ctx;
  
      const char *err = ap_check_cmd_context(cmd, NOT_IN_HTACCESS);
      if (err)
          return err;
      ctx = (sctx_t *) ap_get_module_config(cmd->server->module_config,
                                            &proxy_hcheck_module);
  
      name = ap_getword_conf(cmd->temp_pool, &arg);
      if (!*name) {
          return apr_pstrcat(cmd->temp_pool, "Missing template name for ",
                             cmd->cmd->name, NULL);
      }
  
      template = (hc_template_t *)apr_array_push(ctx->templates);
  
      template->name = apr_pstrdup(cmd->pool, name);
      template->method = template->passes = template->fails = 1;
      template->interval = apr_time_from_sec(HCHECK_WATHCHDOG_DEFAULT_INTERVAL);
      template->hurl = NULL;
      template->hcexpr = NULL;
      while (*arg) {
          word = ap_getword_conf(cmd->pool, &arg);
          val = strchr(word, '=');
          if (!val) {
              return "Invalid ProxyHCTemplate parameter. Parameter must be "
                     "in the form 'key=value'";
          }
          else
              *val++ = '\0';
          err = set_worker_hc_param(cmd->pool, ctx->s, NULL, word, val, template);
  
          if (err) {
              /* get rid of recently pushed (bad) template */
              apr_array_pop(ctx->templates);
              return apr_pstrcat(cmd->temp_pool, "ProxyHCTemplate: ", err, " ", word, "=", val, "; ", name, NULL);
          }
          /* No error means we have a valid template */
      }
      return NULL;
  }
  
  #if HC_USE_THREADS
  static const char *set_hc_tpsize (cmd_parms *cmd, void *dummy, const char *arg)
  {
      const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
      if (err)
          return err;
  
      tpsize = atoi(arg);
      if (tpsize < 0)
          return "Invalid ProxyHCTPsize parameter. Parameter must be "
                 ">= 0";
      return NULL;
  }
  #endif
  
  /*
   * Create a dummy request rec, simply so we can use ap_expr.
   * Use our short-lived pool for bucket_alloc so that we can simply move
   * buckets and use them after the backend connection is released.
   */
  static request_rec *create_request_rec(apr_pool_t *p, server_rec *s,
                                         proxy_balancer *balancer,
                                         const char *method)
  {
      request_rec *r;
  
      r = apr_pcalloc(p, sizeof(request_rec));
      r->pool            = p;
      r->server          = s;
  
      r->per_dir_config = r->server->lookup_defaults;
      if (balancer->section_config) {
          r->per_dir_config = ap_merge_per_dir_configs(r->pool,
                                                       r->per_dir_config,
                                                       balancer->section_config);
      }
  
      r->proxyreq        = PROXYREQ_RESPONSE;
  
      r->user            = NULL;
      r->ap_auth_type    = NULL;
  
      r->allowed_methods = ap_make_method_list(p, 2);
  
      r->headers_in      = apr_table_make(r->pool, 1);
      r->trailers_in     = apr_table_make(r->pool, 1);
      r->subprocess_env  = apr_table_make(r->pool, 25);
      r->headers_out     = apr_table_make(r->pool, 12);
      r->err_headers_out = apr_table_make(r->pool, 5);
      r->trailers_out    = apr_table_make(r->pool, 1);
      r->notes           = apr_table_make(r->pool, 5);
  
      r->request_config  = ap_create_request_config(r->pool);
      /* Must be set before we run create request hook */
  
      r->sent_bodyct     = 0;                      /* bytect isn't for body */
  
      r->read_length     = 0;
      r->read_body       = REQUEST_NO_BODY;
  
      r->status          = HTTP_OK;  /* Until further notice */
      r->the_request     = NULL;
  
      /* Begin by presuming any module can make its own path_info assumptions,
       * until some module interjects and changes the value.
       */
      r->used_path_info = AP_REQ_DEFAULT_PATH_INFO;
  
  
      /* Time to populate r with the data we have. */
      r->method = method;
      /* Provide quick information about the request method as soon as known */
      r->method_number = ap_method_number_of(r->method);
      if (r->method_number == M_OPTIONS
              || (r->method_number == M_GET && r->method[0] == 'H')) {
          r->header_only = 1;
      }
      else {
          r->header_only = 0;
      }
  
      r->protocol = "HTTP/1.0";
      r->proto_num = HTTP_VERSION(1, 0);
  
      r->hostname = NULL;
  
      return r;
  }
  
  static void set_request_connection(request_rec *r, conn_rec *conn)
  {
      conn->bucket_alloc = apr_bucket_alloc_create(r->pool);
      r->connection = conn;
  
      r->kept_body = apr_brigade_create(r->pool, conn->bucket_alloc);
      r->output_filters = r->proto_output_filters = conn->output_filters;
      r->input_filters = r->proto_input_filters = conn->input_filters;
  
      r->useragent_addr = conn->client_addr;
      r->useragent_ip = conn->client_ip;
  }
  
  static void create_hcheck_req(wctx_t *wctx, proxy_worker *hc,
                                apr_pool_t *p)
  {
      char *req = NULL;
      const char *method = NULL;
      switch (hc->s->method) {
          case OPTIONS:
              method = "OPTIONS";
              req = apr_psprintf(p,
                                 "OPTIONS * HTTP/1.0\r\n"
                                 "Host: %s:%d\r\n"
                                 "\r\n",
                                 hc->s->hostname_ex, (int)hc->s->port);
              break;
  
          case HEAD:
              method = "HEAD";
              /* fallthru */
          case GET:
              if (!method) { /* did we fall thru? If not, we are GET */
                  method = "GET";
              }
              req = apr_psprintf(p,
                                 "%s %s%s%s HTTP/1.0\r\n"
                                 "Host: %s:%d\r\n"
                                 "\r\n",
                                 method,
                                 (wctx->path ? wctx->path : ""),
                                 (wctx->path && *hc->s->hcuri ? "/" : "" ),
                                 (*hc->s->hcuri ? hc->s->hcuri : ""),
                                 hc->s->hostname_ex, (int)hc->s->port);
              break;
  
          default:
              break;
      }
      wctx->req = req;
      wctx->method = method;
  }
  
  static proxy_worker *hc_get_hcworker(sctx_t *ctx, proxy_worker *worker,
                                       apr_pool_t *p)
  {
      proxy_worker *hc = NULL;
      apr_port_t port;
  
      hc = (proxy_worker *)apr_hash_get(ctx->hcworkers, &worker, sizeof worker);
      if (!hc) {
          apr_uri_t uri;
          apr_status_t rv;
          const char *url = worker->s->name;
          wctx_t *wctx = apr_pcalloc(ctx->p, sizeof(wctx_t));
  
          port = (worker->s->port ? worker->s->port
                                  : ap_proxy_port_of_scheme(worker->s->scheme));
          ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, ctx->s, APLOGNO(03248)
                       "Creating hc worker %pp for %s://%s:%d",
                       worker, worker->s->scheme, worker->s->hostname_ex,
                       (int)port);
  
          ap_proxy_define_worker(ctx->p, &hc, NULL, NULL, worker->s->name, 0);
          apr_snprintf(hc->s->name, sizeof hc->s->name, "%pp", worker);
          PROXY_STRNCPY(hc->s->hostname, worker->s->hostname); /* for compatibility */
          PROXY_STRNCPY(hc->s->hostname_ex, worker->s->hostname_ex);
          PROXY_STRNCPY(hc->s->scheme,   worker->s->scheme);
          PROXY_STRNCPY(hc->s->hcuri,    worker->s->hcuri);
          PROXY_STRNCPY(hc->s->hcexpr,   worker->s->hcexpr);
          hc->hash.def = hc->s->hash.def = ap_proxy_hashfunc(hc->s->name, PROXY_HASHFUNC_DEFAULT);
          hc->hash.fnv = hc->s->hash.fnv = ap_proxy_hashfunc(hc->s->name, PROXY_HASHFUNC_FNV);
          hc->s->port = port;
          if (worker->s->conn_timeout_set) {
              hc->s->conn_timeout_set = worker->s->conn_timeout_set;
              hc->s->conn_timeout = worker->s->conn_timeout;
          }
          /* Do not disable worker in case of errors */
          hc->s->status |= PROXY_WORKER_IGNORE_ERRORS;
          /* Mark as the "generic" worker */
          hc->s->status |= PROXY_WORKER_GENERIC;
          ap_proxy_initialize_worker(hc, ctx->s, ctx->p);
          hc->s->is_address_reusable = worker->s->is_address_reusable;
          hc->s->disablereuse = worker->s->disablereuse;
          hc->s->method = worker->s->method;
          rv = apr_uri_parse(p, url, &uri);
          if (rv == APR_SUCCESS) {
              wctx->path = apr_pstrdup(ctx->p, uri.path);
          }
          wctx->w = worker;
          create_hcheck_req(wctx, hc, ctx->p);
          hc->context = wctx;
          apr_hash_set(ctx->hcworkers, &worker, sizeof worker, hc);
      }
      /* This *could* have changed via the Balancer Manager */
      /* TODO */
      if (hc->s->method != worker->s->method) {
          wctx_t *wctx = hc->context;
          port = (worker->s->port ? worker->s->port
                                  : ap_proxy_port_of_scheme(worker->s->scheme));
          ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, ctx->s, APLOGNO(03311)
                       "Updating hc worker %pp for %s://%s:%d",
                       worker, worker->s->scheme, worker->s->hostname_ex,
                       (int)port);
          hc->s->method = worker->s->method;
          create_hcheck_req(wctx, hc, ctx->p);
      }
      return hc;
  }
  
  static int hc_determine_connection(sctx_t *ctx, proxy_worker *worker,
                                     apr_sockaddr_t **addr, apr_pool_t *p)
  {
      apr_status_t rv = APR_SUCCESS;
      /*
       * normally, this is done in ap_proxy_determine_connection().
       * TODO: Look at using ap_proxy_determine_connection() with a
       * fake request_rec
       */
      if (worker->cp->addr) {
          *addr = worker->cp->addr;
      }
      else {
          rv = apr_sockaddr_info_get(addr, worker->s->hostname_ex,
                                     APR_UNSPEC, worker->s->port, 0, p);
          if (rv != APR_SUCCESS) {
              ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, ctx->s, APLOGNO(03249)
                           "DNS lookup failure for: %s:%d",
                           worker->s->hostname_ex, (int)worker->s->port);
          }
      }
      return (rv == APR_SUCCESS ? OK : !OK);
  }
  
  static apr_status_t hc_init_worker(sctx_t *ctx, proxy_worker *worker)
  {
      apr_status_t rv = APR_SUCCESS;
      /*
       * Since this is the watchdog, workers never actually handle a
       * request here, and so the local data isn't initialized (of
       * course, the shared memory is). So we need to bootstrap
       * worker->cp. Note, we only need do this once.
       */
      if (!worker->cp) {
          rv = ap_proxy_initialize_worker(worker, ctx->s, ctx->p);
          if (rv != APR_SUCCESS) {
              ap_log_error(APLOG_MARK, APLOG_EMERG, rv, ctx->s, APLOGNO(03250) "Cannot init worker");
              return rv;
          }
          if (worker->s->is_address_reusable && !worker->s->disablereuse &&
                  hc_determine_connection(ctx, worker, &worker->cp->addr,
                                          worker->cp->pool) != OK) {
              rv = APR_EGENERAL;
          }
      }
      return rv;
  }
  
  static apr_status_t backend_cleanup(const char *proxy_function, proxy_conn_rec *backend,
                                      server_rec *s, int status)
  {
      if (backend) {
          backend->close = 1;
          ap_proxy_release_connection(proxy_function, backend, s);
          ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s, APLOGNO(03251)
                           "Health check %s Status (%d) for %s.",
                           ap_proxy_show_hcmethod(backend->worker->s->method),
                           status,
                           backend->worker->s->name);
      }
      if (status != OK) {
          return APR_EGENERAL;
      }
      return APR_SUCCESS;
  }
  
  static int hc_get_backend(const char *proxy_function, proxy_conn_rec **backend,
                            proxy_worker *hc, sctx_t *ctx, apr_pool_t *ptemp)
  {
      int status;
      status = ap_proxy_acquire_connection(proxy_function, backend, hc, ctx->s);
      if (status == OK) {
          (*backend)->addr = hc->cp->addr;
          (*backend)->hostname = hc->s->hostname_ex;
          if (strcmp(hc->s->scheme, "https") == 0 || strcmp(hc->s->scheme, "wss") == 0 ) {
              if (!ap_proxy_ssl_enable(NULL)) {
                  ap_log_error(APLOG_MARK, APLOG_WARNING, 0, ctx->s, APLOGNO(03252)
                                "mod_ssl not configured?");
                  return !OK;
              }
              (*backend)->is_ssl = 1;
          }
  
      }
      return hc_determine_connection(ctx, hc, &(*backend)->addr, ptemp);
  }
  
  static apr_status_t hc_check_cping(baton_t *baton, apr_thread_t *thread)
  {
      int status;
      sctx_t *ctx = baton->ctx;
      proxy_worker *hc = baton->hc;
      proxy_conn_rec *backend = NULL;
      apr_pool_t *ptemp = baton->ptemp;
      request_rec *r;
      apr_interval_time_t timeout;
  
      if (!ajp_handle_cping_cpong) {
          return APR_ENOTIMPL;
      }
  
      ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, baton->ctx->s, "HCCPING starting");
      if ((status = hc_get_backend("HCCPING", &backend, hc, ctx, baton->ptemp)) != OK) {
          return backend_cleanup("HCCPING", backend, ctx->s, status);
      }
      if ((status = ap_proxy_connect_backend("HCCPING", backend, hc, ctx->s)) != OK) {
          return backend_cleanup("HCCPING", backend, ctx->s, status);
      }
      r = create_request_rec(ptemp, ctx->s, baton->balancer, "CPING");
      if ((status = ap_proxy_connection_create_ex("HCCPING", backend, r)) != OK) {
          return backend_cleanup("HCCPING", backend, ctx->s, status);
      }
      set_request_connection(r, backend->connection);
      backend->connection->current_thread = thread;
  
      if (hc->s->ping_timeout_set) {
          timeout = hc->s->ping_timeout;
      } else if ( hc->s->conn_timeout_set) {
          timeout = hc->s->conn_timeout;
      } else if ( hc->s->timeout_set) {
          timeout = hc->s->timeout;
      } else {
          /* default to socket timeout */
          apr_socket_timeout_get(backend->sock, &timeout); 
      }
      status = ajp_handle_cping_cpong(backend->sock, r, timeout);
      ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, baton->ctx->s, "HCCPING done %d", status);
      return backend_cleanup("HCCPING", backend, ctx->s, status);
  }
  
  static apr_status_t hc_check_tcp(baton_t *baton)
  {
      int status;
      sctx_t *ctx = baton->ctx;
      proxy_worker *hc = baton->hc;
      proxy_conn_rec *backend = NULL;
  
      status = hc_get_backend("HCTCP", &backend, hc, ctx, baton->ptemp);
      if (status == OK) {
          status = ap_proxy_connect_backend("HCTCP", backend, hc, ctx->s);
          /* does an unconditional ap_proxy_is_socket_connected() */
      }
      return backend_cleanup("HCTCP", backend, ctx->s, status);
  }
  
  static int hc_send(request_rec *r, const char *out, apr_bucket_brigade *bb)
  {
      apr_status_t rv;
      conn_rec *c = r->connection;
      apr_bucket_alloc_t *ba = c->bucket_alloc;
      ap_log_error(APLOG_MARK, APLOG_TRACE7, 0, r->server, "%s", out);
      APR_BRIGADE_INSERT_TAIL(bb, apr_bucket_pool_create(out, strlen(out),
                                                         r->pool, ba));
      APR_BRIGADE_INSERT_TAIL(bb, apr_bucket_flush_create(ba));
      rv = ap_pass_brigade(c->output_filters, bb);
      apr_brigade_cleanup(bb);
      return (rv) ? !OK : OK;
  }
  
  static int hc_read_headers(request_rec *r)
  {
      char buffer[HUGE_STRING_LEN];
      int len;
      const char *ct;
  
      len = ap_getline(buffer, sizeof(buffer), r, 1);
      if (len <= 0) {
          return !OK;
      }
      ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server, APLOGNO(03254)
                   "%.*s", len, buffer);
      /* for the below, see ap_proxy_http_process_response() */
      if (apr_date_checkmask(buffer, "HTTP/#.# ###*")) {
          int major;
          char keepchar;
          int proxy_status = OK;
          const char *proxy_status_line = NULL;
  
          major = buffer[5] - '0';
          if ((major != 1) || (len >= sizeof(buffer)-1)) {
              return !OK;
          }
  
          keepchar = buffer[12];
          buffer[12] = '\0';
          proxy_status = atoi(&buffer[9]);
          if (keepchar != '\0') {
              buffer[12] = keepchar;
          } else {
              buffer[12] = ' ';
              buffer[13] = '\0';
          }
          proxy_status_line = apr_pstrdup(r->pool, &buffer[9]);
          r->status = proxy_status;
          r->status_line = proxy_status_line;
      } else {
          return !OK;
      }
  
      /* OK, 1st line is OK... scarf in the headers */
      while ((len = ap_getline(buffer, sizeof(buffer), r, 1)) > 0) {
          char *value, *end;
          ap_log_error(APLOG_MARK, APLOG_TRACE7, 0, r->server, "%.*s",
                       len, buffer);
          if (!(value = strchr(buffer, ':'))) {
              return !OK;
          }
          *value = '\0';
          ++value;
          while (apr_isspace(*value))
              ++value;            /* Skip to start of value   */
          for (end = &value[strlen(value)-1]; end > value && apr_isspace(*end); --end)
              *end = '\0';
          apr_table_add(r->headers_out, buffer, value);
      }
  
      /* Set the Content-Type for the request if set */
      if ((ct = apr_table_get(r->headers_out, "Content-Type")) != NULL)
          ap_set_content_type(r, ct);
  
      return OK;
  }
  
  static int hc_read_body(request_rec *r, apr_bucket_brigade *bb)
  {
      apr_status_t rv = APR_SUCCESS;
      int seen_eos = 0;
  
      do {
          apr_size_t len = HUGE_STRING_LEN;
  
          apr_brigade_cleanup(bb);
          rv = ap_get_brigade(r->proto_input_filters, bb, AP_MODE_READBYTES,
                              APR_BLOCK_READ, len);
  
          if (rv != APR_SUCCESS) {
              if (APR_STATUS_IS_EOF(rv)) {
                  rv = APR_SUCCESS;
                  break;
              }
              ap_log_error(APLOG_MARK, APLOG_DEBUG, rv, r->server, APLOGNO(03300)
                            "Error reading response body");
              break;
          }
  
          while (!APR_BRIGADE_EMPTY(bb)) {
              apr_bucket *bucket = APR_BRIGADE_FIRST(bb);
              if (APR_BUCKET_IS_EOS(bucket)) {
                  seen_eos = 1;
                  break;
              }
              if (APR_BUCKET_IS_FLUSH(bucket)) {
                  apr_bucket_delete(bucket);
                  continue;
              }
              APR_BUCKET_REMOVE(bucket);
              APR_BRIGADE_INSERT_TAIL(r->kept_body, bucket);
          }
      }
      while (!seen_eos);
      apr_brigade_cleanup(bb);
      return (rv == APR_SUCCESS ? OK : !OK);
  }
  
  /*
   * Send the HTTP OPTIONS, HEAD or GET request to the backend
   * server associated w/ worker. If we have Conditions,
   * then apply those to the resulting response, otherwise
   * any status code 2xx or 3xx is considered "passing"
   */
  static apr_status_t hc_check_http(baton_t *baton, apr_thread_t *thread)
  {
      int status;
      proxy_conn_rec *backend = NULL;
      sctx_t *ctx = baton->ctx;
      proxy_worker *hc = baton->hc;
      proxy_worker *worker = baton->worker;
      apr_pool_t *ptemp = baton->ptemp;
      request_rec *r;
      wctx_t *wctx;
      hc_condition_t *cond;
      apr_bucket_brigade *bb;
  
      wctx = (wctx_t *)hc->context;
      if (!wctx->req || !wctx->method) {
          return APR_ENOTIMPL;
      }
  
      if ((status = hc_get_backend("HCOH", &backend, hc, ctx, ptemp)) != OK) {
          return backend_cleanup("HCOH", backend, ctx->s, status);
      }
      if ((status = ap_proxy_connect_backend("HCOH", backend, hc, ctx->s)) != OK) {
          return backend_cleanup("HCOH", backend, ctx->s, status);
      }
  
      r = create_request_rec(ptemp, ctx->s, baton->balancer, wctx->method);
      if ((status = ap_proxy_connection_create_ex("HCOH", backend, r)) != OK) {
          return backend_cleanup("HCOH", backend, ctx->s, status);
      }
      set_request_connection(r, backend->connection);
      backend->connection->current_thread = thread;
  
      bb = apr_brigade_create(r->pool, r->connection->bucket_alloc);
  
      if ((status = hc_send(r, wctx->req, bb)) != OK) {
          return backend_cleanup("HCOH", backend, ctx->s, status);
      }
      if ((status = hc_read_headers(r)) != OK) {
          return backend_cleanup("HCOH", backend, ctx->s, status);
      }
      if (!r->header_only) {
          apr_table_t *saved_headers_in = r->headers_in;
          r->headers_in = apr_table_copy(r->pool, r->headers_out);
          ap_proxy_pre_http_request(backend->connection, r);
          status = hc_read_body(r, bb);
          r->headers_in = saved_headers_in;
          if (status != OK) {
              return backend_cleanup("HCOH", backend, ctx->s, status);
          }
          r->trailers_out = apr_table_copy(r->pool, r->trailers_in);
      }
  
      if (*worker->s->hcexpr &&
              (cond = (hc_condition_t *)apr_table_get(ctx->conditions, worker->s->hcexpr)) != NULL) {
          const char *err;
          int ok = ap_expr_exec(r, cond->pexpr, &err);
          if (ok > 0) {
              ap_log_error(APLOG_MARK, APLOG_TRACE2, 0, ctx->s,
                           "Condition %s for %s (%s): passed", worker->s->hcexpr,
                           hc->s->name, worker->s->name);
          } else if (ok < 0 || err) {
              ap_log_error(APLOG_MARK, APLOG_INFO, 0, ctx->s, APLOGNO(03301)
                           "Error on checking condition %s for %s (%s): %s", worker->s->hcexpr,
                           hc->s->name, worker->s->name, err);
              status = !OK;
          } else {
              ap_log_error(APLOG_MARK, APLOG_TRACE2, 0, ctx->s,
                           "Condition %s for %s (%s) : failed", worker->s->hcexpr,
                           hc->s->name, worker->s->name);
              status = !OK;
          }
      } else if (r->status < 200 || r->status > 399) {
          ap_log_error(APLOG_MARK, APLOG_TRACE2, 0, ctx->s,
                       "Response status %i for %s (%s): failed", r->status,
                       hc->s->name, worker->s->name);
          status = !OK;
      }
      return backend_cleanup("HCOH", backend, ctx->s, status);
  }
  
  static void * APR_THREAD_FUNC hc_check(apr_thread_t *thread, void *b)
  {
      baton_t *baton = (baton_t *)b;
      server_rec *s = baton->ctx->s;
      proxy_worker *worker = baton->worker;
      proxy_worker *hc = baton->hc;
      apr_time_t now;
      apr_status_t rv;
  
      ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s, APLOGNO(03256)
                   "%sHealth checking %s", (thread ? "Threaded " : ""),
                   worker->s->name);
  
      if (hc->s->method == TCP) {
          rv = hc_check_tcp(baton);
      }
      else if (hc->s->method == CPING) {
          rv = hc_check_cping(baton, thread);
      }
      else {
          rv = hc_check_http(baton, thread);
      }
  
      now = apr_time_now();
      if (rv == APR_ENOTIMPL) {
          ap_log_error(APLOG_MARK, APLOG_ERR, 0, s, APLOGNO(03257)
                           "Somehow tried to use unimplemented hcheck method: %d",
                           (int)hc->s->method);
      }
      /* what state are we in ? */
      else if (PROXY_WORKER_IS_HCFAILED(worker)) {
          if (rv == APR_SUCCESS) {
              worker->s->pcount += 1;
              if (worker->s->pcount >= worker->s->passes) {
                  ap_proxy_set_wstatus(PROXY_WORKER_HC_FAIL_FLAG, 0, worker);
                  ap_proxy_set_wstatus(PROXY_WORKER_IN_ERROR_FLAG, 0, worker);
                  worker->s->pcount = 0;
                  ap_log_error(APLOG_MARK, APLOG_INFO, 0, s, APLOGNO(03302)
                               "%sHealth check ENABLING %s", (thread ? "Threaded " : ""),
                               worker->s->name);
  
              }
          }
      }
      else {
          if (rv != APR_SUCCESS) {
              worker->s->error_time = now;
              worker->s->fcount += 1;
              if (worker->s->fcount >= worker->s->fails) {
                  ap_proxy_set_wstatus(PROXY_WORKER_HC_FAIL_FLAG, 1, worker);
                  worker->s->fcount = 0;
                  ap_log_error(APLOG_MARK, APLOG_INFO, 0, s, APLOGNO(03303)
                               "%sHealth check DISABLING %s", (thread ? "Threaded " : ""),
                               worker->s->name);
              }
          }
      }
      if (baton->now) {
          *baton->now = now;
      }
      apr_pool_destroy(baton->ptemp);
      worker->s->updated = now;
  
      return NULL;
  }
  
  static apr_status_t hc_watchdog_callback(int state, void *data,
                                           apr_pool_t *pool)
  {
      apr_status_t rv = APR_SUCCESS;
      proxy_balancer *balancer;
      sctx_t *ctx = (sctx_t *)data;
      server_rec *s = ctx->s;
      proxy_server_conf *conf;
  
      switch (state) {
          case AP_WATCHDOG_STATE_STARTING:
              ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s, APLOGNO(03258)
                           "%s watchdog started.",
                           HCHECK_WATHCHDOG_NAME);
  #if HC_USE_THREADS
              if (tpsize && hctp == NULL) {
                  rv =  apr_thread_pool_create(&hctp, tpsize,
                                               tpsize, ctx->p);
                  if (rv != APR_SUCCESS) {
                      ap_log_error(APLOG_MARK, APLOG_INFO, rv, s, APLOGNO(03312)
                                   "apr_thread_pool_create() with %d threads failed",
                                   tpsize);
                      /* we can continue on without the threadpools */
                      hctp = NULL;
                  } else {
                      ap_log_error(APLOG_MARK, APLOG_DEBUG, rv, s, APLOGNO(03313)
                                   "apr_thread_pool_create() with %d threads succeeded",
                                   tpsize);
                  }
              } else {
                  ap_log_error(APLOG_MARK, APLOG_DEBUG, rv, s, APLOGNO(03314)
                               "Skipping apr_thread_pool_create()");
                  hctp = NULL;
              }
  #endif
              break;
  
          case AP_WATCHDOG_STATE_RUNNING:
              /* loop thru all workers */
              if (s) {
                  int i;
                  conf = (proxy_server_conf *) ap_get_module_config(s->module_config, &proxy_module);
                  balancer = (proxy_balancer *)conf->balancers->elts;
                  ctx->s = s;
                  for (i = 0; i < conf->balancers->nelts; i++, balancer++) {
                      int n;
                      apr_time_t now;
                      proxy_worker **workers;
                      proxy_worker *worker;
                      /* Have any new balancers or workers been added dynamically? */
                      ap_proxy_sync_balancer(balancer, s, conf);
                      workers = (proxy_worker **)balancer->workers->elts;
                      now = apr_time_now();
                      for (n = 0; n < balancer->workers->nelts; n++) {
                          worker = *workers;
                          if (!PROXY_WORKER_IS(worker, PROXY_WORKER_STOPPED) &&
                              (worker->s->method != NONE) &&
                              (worker->s->updated != 0) &&
                              (now > worker->s->updated + worker->s->interval)) {
                              baton_t *baton;
                              apr_pool_t *ptemp;
  
                              ap_log_error(APLOG_MARK, APLOG_TRACE3, 0, s,
                                           "Checking %s worker: %s  [%d] (%pp)", balancer->s->name,
                                           worker->s->name, worker->s->method, worker);
  
                              if ((rv = hc_init_worker(ctx, worker)) != APR_SUCCESS) {
                                  worker->s->updated = now;
                                  return rv;
                              }
                              worker->s->updated = 0;
  
                              /* This pool has the lifetime of the check */
                              apr_pool_create(&ptemp, ctx->p);
                              apr_pool_tag(ptemp, "hc_request");
                              baton = apr_pcalloc(ptemp, sizeof(baton_t));
                              baton->ctx = ctx;
                              baton->balancer = balancer;
                              baton->worker = worker;
                              baton->ptemp = ptemp;
                              baton->hc = hc_get_hcworker(ctx, worker, ptemp);
  #if HC_USE_THREADS
                              if (hctp) {
                                  apr_thread_pool_push(hctp, hc_check, (void *)baton,
                                                       APR_THREAD_TASK_PRIORITY_NORMAL,
                                                       NULL);
                              }
                              else
  #endif
                              {
                                  baton->now = &now;
                                  hc_check(NULL, baton);
                              }
                          }
                          workers++;
                      }
                  }
              }
              break;
  
          case AP_WATCHDOG_STATE_STOPPING:
              ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s, APLOGNO(03261)
                           "stopping %s watchdog.",
                           HCHECK_WATHCHDOG_NAME);
  #if HC_USE_THREADS
              if (hctp) {
                  rv =  apr_thread_pool_destroy(hctp);
                  if (rv != APR_SUCCESS) {
                      ap_log_error(APLOG_MARK, APLOG_INFO, rv, s, APLOGNO(03315)
                                   "apr_thread_pool_destroy() failed");
                  }
                  hctp = NULL;
              }
  #endif
              break;
      }
      return rv;
  }
  static int hc_pre_config(apr_pool_t *pconf, apr_pool_t *plog,
                           apr_pool_t *ptemp)
  {
  #if HC_USE_THREADS
      hctp = NULL;
      tpsize = HC_THREADPOOL_SIZE;
  #endif
      return OK;
  }
  static int hc_post_config(apr_pool_t *p, apr_pool_t *plog,
                         apr_pool_t *ptemp, server_rec *main_s)
  {
      apr_status_t rv;
      server_rec *s = main_s;
  
      APR_OPTIONAL_FN_TYPE(ap_watchdog_get_instance) *hc_watchdog_get_instance;
      APR_OPTIONAL_FN_TYPE(ap_watchdog_register_callback) *hc_watchdog_register_callback;
  
      if (ap_state_query(AP_SQ_MAIN_STATE) == AP_SQ_MS_CREATE_PRE_CONFIG) {
          return OK;
      }
      hc_watchdog_get_instance = APR_RETRIEVE_OPTIONAL_FN(ap_watchdog_get_instance);
      hc_watchdog_register_callback = APR_RETRIEVE_OPTIONAL_FN(ap_watchdog_register_callback);
      if (!hc_watchdog_get_instance || !hc_watchdog_register_callback) {
          ap_log_error(APLOG_MARK, APLOG_CRIT, 0, s, APLOGNO(03262)
                       "mod_watchdog is required");
          return !OK;
      }
      rv = hc_watchdog_get_instance(&watchdog,
                                    HCHECK_WATHCHDOG_NAME,
                                    0, 1, p);
      if (rv) {
          ap_log_error(APLOG_MARK, APLOG_CRIT, rv, s, APLOGNO(03263)
                       "Failed to create watchdog instance (%s)",
                       HCHECK_WATHCHDOG_NAME);
          return !OK;
      }
      while (s) {
          sctx_t *ctx = ap_get_module_config(s->module_config,
                                             &proxy_hcheck_module);
  
          if (s != ctx->s) {
              ap_log_error(APLOG_MARK, APLOG_TRACE4, 0, s, APLOGNO(10019)
                           "Missing unique per-server context: %s (%pp:%pp) (no hchecks)",
                           s->server_hostname, s, ctx->s);
              s = s->next;
              continue;
          }
          rv = hc_watchdog_register_callback(watchdog,
                  AP_WD_TM_SLICE,
                  ctx,
                  hc_watchdog_callback);
          if (rv) {
              ap_log_error(APLOG_MARK, APLOG_CRIT, rv, s, APLOGNO(03264)
                           "Failed to register watchdog callback (%s)",
                           HCHECK_WATHCHDOG_NAME);
              return !OK;
          }
          ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s, APLOGNO(03265)
                       "watchdog callback registered (%s for %s)", HCHECK_WATHCHDOG_NAME, s->server_hostname);
          s = s->next;
      }
  
      ajp_handle_cping_cpong = APR_RETRIEVE_OPTIONAL_FN(ajp_handle_cping_cpong);
      if (ajp_handle_cping_cpong) {
         proxy_hcmethods_t *method = proxy_hcmethods;
         for (; method->name; method++) {
             if (method->method == CPING) {
                 method->implemented = 1;
                 break;
             }
         }
      }
  
      return OK;
  }
  
  static void hc_show_exprs(request_rec *r)
  {
      const apr_table_entry_t *elts;
      const apr_array_header_t *hdr;
      int i;
      sctx_t *ctx = (sctx_t *) ap_get_module_config(r->server->module_config,
                                                    &proxy_hcheck_module);
      if (!ctx)
          return;
      if (apr_is_empty_table(ctx->conditions))
          return;
  
      ap_rputs("\n\n<table>"
               "<tr><th colspan='2'>Health check cond. expressions:</th></tr>\n"
               "<tr><th>Expr name</th><th>Expression</th></tr>\n", r);
  
      hdr = apr_table_elts(ctx->conditions);
      elts = (const apr_table_entry_t *) hdr->elts;
      for (i = 0; i < hdr->nelts; ++i) {
          hc_condition_t *cond;
          if (!elts[i].key) {
              continue;
          }
          cond = (hc_condition_t *)elts[i].val;
          ap_rprintf(r, "<tr><td>%s</td><td>%s</td></tr>\n",
                     ap_escape_html(r->pool, elts[i].key),
                     ap_escape_html(r->pool, cond->expr));
      }
      ap_rputs("</table><hr/>\n", r);
  }
  
  static void hc_select_exprs(request_rec *r, const char *expr)
  {
      const apr_table_entry_t *elts;
      const apr_array_header_t *hdr;
      int i;
      sctx_t *ctx = (sctx_t *) ap_get_module_config(r->server->module_config,
                                                    &proxy_hcheck_module);
      if (!ctx)
          return;
      if (apr_is_empty_table(ctx->conditions))
          return;
  
      hdr = apr_table_elts(ctx->conditions);
      elts = (const apr_table_entry_t *) hdr->elts;
      for (i = 0; i < hdr->nelts; ++i) {
          if (!elts[i].key) {
              continue;
          }
          ap_rprintf(r, "<option value='%s' %s >%s</option>\n",
                     ap_escape_html(r->pool, elts[i].key),
                     (!strcmp(elts[i].key, expr)) ? "selected" : "",
                             ap_escape_html(r->pool, elts[i].key));
      }
  }
  
  static int hc_valid_expr(request_rec *r, const char *expr)
  {
      const apr_table_entry_t *elts;
      const apr_array_header_t *hdr;
      int i;
      sctx_t *ctx = (sctx_t *) ap_get_module_config(r->server->module_config,
                                                    &proxy_hcheck_module);
      if (!ctx)
          return 0;
      if (apr_is_empty_table(ctx->conditions))
          return 0;
  
      hdr = apr_table_elts(ctx->conditions);
      elts = (const apr_table_entry_t *) hdr->elts;
      for (i = 0; i < hdr->nelts; ++i) {
          if (!elts[i].key) {
              continue;
          }
          if (!strcmp(elts[i].key, expr))
              return 1;
      }
      return 0;
  }
  
  static const char *hc_get_body(request_rec *r)
  {
      apr_off_t length;
      apr_size_t len;
      apr_status_t rv;
      char *buf;
  
      if (!r || !r->kept_body)
          return "";
  
      rv = apr_brigade_length(r->kept_body, 1, &length);
      len = (apr_size_t)length;
      if (rv != APR_SUCCESS || len == 0)
          return "";
  
      buf = apr_palloc(r->pool, len + 1);
      rv = apr_brigade_flatten(r->kept_body, buf, &len);
      if (rv != APR_SUCCESS)
          return "";
      buf[len] = '\0'; /* ensure */
      return (const char*)buf;
  }
  
  static const char *hc_expr_var_fn(ap_expr_eval_ctx_t *ctx, const void *data)
  {
      char *var = (char *)data;
  
      if (var && *var && ctx->r && ap_cstr_casecmp(var, "BODY") == 0) {
          return hc_get_body(ctx->r);
      }
      return NULL;
  }
  
  static const char *hc_expr_func_fn(ap_expr_eval_ctx_t *ctx, const void *data,
                                  const char *arg)
  {
      char *var = (char *)arg;
  
      if (var && *var && ctx->r && ap_cstr_casecmp(var, "BODY") == 0) {
          return hc_get_body(ctx->r);
      }
      return NULL;
  }
  
  static int hc_expr_lookup(ap_expr_lookup_parms *parms)
  {
      switch (parms->type) {
      case AP_EXPR_FUNC_VAR:
          /* for now, we just handle everything that starts with HC_.
           */
          if (strncasecmp(parms->name, "HC_", 3) == 0) {
              *parms->func = hc_expr_var_fn;
              *parms->data = parms->name + 3;
              return OK;
          }
          break;
      case AP_EXPR_FUNC_STRING:
          /* Function HC() is implemented by us.
           */
          if (strcasecmp(parms->name, "HC") == 0) {
              *parms->func = hc_expr_func_fn;
              *parms->data = parms->arg;
              return OK;
          }
          break;
      }
      return DECLINED;
  }
  
  static const command_rec command_table[] = {
      AP_INIT_RAW_ARGS("ProxyHCTemplate", set_hc_template, NULL, OR_FILEINFO,
                       "Health check template"),
      AP_INIT_RAW_ARGS("ProxyHCExpr", set_hc_condition, NULL, OR_FILEINFO,
                       "Define a health check condition ruleset expression"),
  #if HC_USE_THREADS
      AP_INIT_TAKE1("ProxyHCTPsize", set_hc_tpsize, NULL, RSRC_CONF,
                       "Set size of health check thread pool"),
  #endif
      { NULL }
  };
  
  static void hc_register_hooks(apr_pool_t *p)
  {
      static const char *const aszPre[] = { "mod_proxy_balancer.c", "mod_proxy.c", NULL};
      static const char *const aszSucc[] = { "mod_watchdog.c", NULL};
      APR_REGISTER_OPTIONAL_FN(set_worker_hc_param);
      APR_REGISTER_OPTIONAL_FN(hc_show_exprs);
      APR_REGISTER_OPTIONAL_FN(hc_select_exprs);
      APR_REGISTER_OPTIONAL_FN(hc_valid_expr);
      ap_hook_pre_config(hc_pre_config, NULL, NULL, APR_HOOK_MIDDLE);
      ap_hook_post_config(hc_post_config, aszPre, aszSucc, APR_HOOK_LAST);
      ap_hook_expr_lookup(hc_expr_lookup, NULL, NULL, APR_HOOK_MIDDLE);
  }
  
  /* the main config structure */
  
  AP_DECLARE_MODULE(proxy_hcheck) =
  {
      STANDARD20_MODULE_STUFF,
      NULL,              /* create per-dir config structures */
      NULL,              /* merge  per-dir config structures */
      hc_create_config,  /* create per-server config structures */
      NULL,              /* merge  per-server config structures */
      command_table,     /* table of config file commands */
      hc_register_hooks  /* register hooks */
  };
  