curl/lib/multi.c

/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 1998 - 2005, 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 http://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.
 *
 * $Id$
 ***************************************************************************/

#include "setup.h"
#include <stdlib.h>
#include <string.h>

#ifdef HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif
#ifdef HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include <curl/curl.h>

#include "urldata.h"
#include "transfer.h"
#include "url.h"
#include "connect.h"
#include "progress.h"
#include "memory.h"
#include "easyif.h"
#include "multiif.h"
#include "sendf.h"

/* The last #include file should be: */
#include "memdebug.h"

struct Curl_message {
  /* the 'CURLMsg' is the part that is visible to the external user */
  struct CURLMsg extmsg;
  struct Curl_message *next;
};

typedef enum {
  CURLM_STATE_INIT,        /* start in this state */
  CURLM_STATE_CONNECT,     /* resolve/connect has been sent off */
  CURLM_STATE_WAITRESOLVE, /* awaiting the resolve to finalize */
  CURLM_STATE_WAITCONNECT, /* awaiting the connect to finalize */
  CURLM_STATE_PROTOCONNECT, /* completing the protocol-specific connect
                               phase */
  CURLM_STATE_DO,          /* start send off the request (part 1) */
  CURLM_STATE_DOING,       /* sending off the request (part 1) */
  CURLM_STATE_DO_MORE,     /* send off the request (part 2) */
  CURLM_STATE_PERFORM,     /* transfer data */
  CURLM_STATE_DONE,        /* post data transfer operation */
  CURLM_STATE_COMPLETED,   /* operation complete */

  CURLM_STATE_LAST /* not a true state, never use this */
} CURLMstate;

struct Curl_one_easy {
  /* first, two fields for the linked list of these */
  struct Curl_one_easy *next;
  struct Curl_one_easy *prev;

  struct SessionHandle *easy_handle; /* the easy handle for this unit */
  struct connectdata *easy_conn;     /* the "unit's" connection */

  CURLMstate state;  /* the handle's state */
  CURLcode result;   /* previous result */

  struct Curl_message *msg; /* A pointer to one single posted message.
                               Cleanup should be done on this pointer NOT on
                               the linked list in Curl_multi.  This message
                               will be deleted when this handle is removed
                               from the multi-handle */
  int msg_num; /* number of messages left in 'msg' to return */
};


#define CURL_MULTI_HANDLE 0x000bab1e

#define GOOD_MULTI_HANDLE(x) ((x)&&(((struct Curl_multi *)x)->type == CURL_MULTI_HANDLE))
#define GOOD_EASY_HANDLE(x) (x)

/* This is the struct known as CURLM on the outside */
struct Curl_multi {
  /* First a simple identifier to easier detect if a user mix up
     this multi handle with an easy handle. Set this to CURL_MULTI_HANDLE. */
  long type;

  /* We have a linked list with easy handles */
  struct Curl_one_easy easy;
  /* This is the amount of entries in the linked list above. */
  int num_easy;

  int num_msgs; /* total amount of messages in the easy handles */

  /* Hostname cache */
  struct curl_hash *hostcache;
};

/* always use this function to change state, to make debugging easier */
static void multistate(struct Curl_one_easy *easy, CURLMstate state)
{
#ifdef CURLDEBUG
  const char *statename[]={
    "INIT",
    "CONNECT",
    "WAITRESOLVE",
    "WAITCONNECT",
    "PROTOCONNECT",
    "DO",
    "DOING",
    "DO_MORE",
    "PERFORM",
    "DONE",
    "COMPLETED",
  };
  CURLMstate oldstate = easy->state;
#endif
  easy->state = state;

#ifdef CURLDEBUG
  infof(easy->easy_handle,
        "STATE: %s => %s handle %p: \n",
        statename[oldstate], statename[easy->state], (char *)easy);
#endif
}

CURLM *curl_multi_init(void)
{
  struct Curl_multi *multi;

  multi = (void *)malloc(sizeof(struct Curl_multi));

  if(multi) {
    memset(multi, 0, sizeof(struct Curl_multi));
    multi->type = CURL_MULTI_HANDLE;
  }
  else
    return NULL;

  multi->hostcache = Curl_mk_dnscache();
  if(!multi->hostcache) {
    /* failure, free mem and bail out */
    free(multi);
    multi = NULL;
  }
  return (CURLM *) multi;
}

CURLMcode curl_multi_add_handle(CURLM *multi_handle,
                                CURL *easy_handle)
{
  struct Curl_multi *multi=(struct Curl_multi *)multi_handle;
  struct Curl_one_easy *easy;

  /* First, make some basic checks that the CURLM handle is a good handle */
  if(!GOOD_MULTI_HANDLE(multi))
    return CURLM_BAD_HANDLE;

  /* Verify that we got a somewhat good easy handle too */
  if(!GOOD_EASY_HANDLE(easy_handle))
    return CURLM_BAD_EASY_HANDLE;

  /* Now, time to add an easy handle to the multi stack */
  easy = (struct Curl_one_easy *)malloc(sizeof(struct Curl_one_easy));
  if(!easy)
    return CURLM_OUT_OF_MEMORY;

  /* clean it all first (just to be sure) */
  memset(easy, 0, sizeof(struct Curl_one_easy));

  /* set the easy handle */
  easy->easy_handle = easy_handle;
  multistate(easy, CURLM_STATE_INIT);

  /* for multi interface connections, we share DNS cache automaticly */
  easy->easy_handle->hostcache = multi->hostcache;

  /* We add this new entry first in the list. We make our 'next' point to the
     previous next and our 'prev' point back to the 'first' struct */
  easy->next = multi->easy.next;
  easy->prev = &multi->easy;

  /* make 'easy' the first node in the chain */
  multi->easy.next = easy;

  /* if there was a next node, make sure its 'prev' pointer links back to
     the new node */
  if(easy->next)
    easy->next->prev = easy;

  Curl_easy_addmulti(easy_handle, multi_handle);

  /* increase the node-counter */
  multi->num_easy++;

  return CURLM_OK;
}

CURLMcode curl_multi_remove_handle(CURLM *multi_handle,
                                   CURL *curl_handle)
{
  struct Curl_multi *multi=(struct Curl_multi *)multi_handle;
  struct Curl_one_easy *easy;

  /* First, make some basic checks that the CURLM handle is a good handle */
  if(!GOOD_MULTI_HANDLE(multi))
    return CURLM_BAD_HANDLE;

  /* Verify that we got a somewhat good easy handle too */
  if(!GOOD_EASY_HANDLE(curl_handle))
    return CURLM_BAD_EASY_HANDLE;

  /* scan through the list and remove the 'curl_handle' */
  easy = multi->easy.next;
  while(easy) {
    if(easy->easy_handle == (struct SessionHandle *)curl_handle)
      break;
    easy=easy->next;
  }
  if(easy) {
    /* If the 'state' is not INIT or COMPLETED, we might need to do something
       nice to put the easy_handle in a good known state when this returns. */

    /* clear out the usage of the shared DNS cache */
    easy->easy_handle->hostcache = NULL;
    Curl_easy_addmulti(easy->easy_handle, NULL); /* clear the association
                                                    to this multi handle */

    /* make the previous node point to our next */
    if(easy->prev)
      easy->prev->next = easy->next;
    /* make our next point to our previous node */
    if(easy->next)
      easy->next->prev = easy->prev;

    /* NOTE NOTE NOTE
       We do not touch the easy handle here! */
    if (easy->msg)
      free(easy->msg);
    free(easy);

    multi->num_easy--; /* one less to care about now */

    return CURLM_OK;
  }
  else
    return CURLM_BAD_EASY_HANDLE; /* twasn't found */
}

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)
{
  /* Scan through all the easy handles to get the file descriptors set.
     Some easy handles may not have connected to the remote host yet,
     and then we must make sure that is done. */
  struct Curl_multi *multi=(struct Curl_multi *)multi_handle;
  struct Curl_one_easy *easy;
  int this_max_fd=-1;

  if(!GOOD_MULTI_HANDLE(multi))
    return CURLM_BAD_HANDLE;

  *max_fd = -1; /* so far none! */

  easy=multi->easy.next;
  while(easy) {
    switch(easy->state) {
    default:
      break;
    case CURLM_STATE_WAITRESOLVE:
      /* waiting for a resolve to complete */
      Curl_resolv_fdset(easy->easy_conn, read_fd_set, write_fd_set,
                        &this_max_fd);
      if(this_max_fd > *max_fd)
        *max_fd = this_max_fd;
      break;

    case CURLM_STATE_PROTOCONNECT:
      Curl_protocol_fdset(easy->easy_conn, read_fd_set, write_fd_set,
                          &this_max_fd);
      if(this_max_fd > *max_fd)
        *max_fd = this_max_fd;
      break;

    case CURLM_STATE_DOING:
      Curl_doing_fdset(easy->easy_conn, read_fd_set, write_fd_set,
                       &this_max_fd);
      if(this_max_fd > *max_fd)
        *max_fd = this_max_fd;
      break;

    case CURLM_STATE_WAITCONNECT:
    case CURLM_STATE_DO_MORE:
      {
        /* when we're waiting for a connect, we wait for the socket to
           become writable */
        struct connectdata *conn = easy->easy_conn;
        curl_socket_t sockfd;

        if(CURLM_STATE_WAITCONNECT == easy->state) {
          sockfd = conn->sock[FIRSTSOCKET];
          FD_SET(sockfd, write_fd_set);
        }
        else {
          /* When in DO_MORE state, we could be either waiting for us
             to connect to a remote site, or we could wait for that site
             to connect to us. It makes a difference in the way: if we
             connect to the site we wait for the socket to become writable, if
             the site connects to us we wait for it to become readable */
          sockfd = conn->sock[SECONDARYSOCKET];
          FD_SET(sockfd, write_fd_set);
        }

        if((int)sockfd > *max_fd)
          *max_fd = (int)sockfd;
      }
      break;
    case CURLM_STATE_PERFORM:
      /* This should have a set of file descriptors for us to set.  */
      /* after the transfer is done, go DONE */

      Curl_single_fdset(easy->easy_conn,
                        read_fd_set, write_fd_set,
                        exc_fd_set, &this_max_fd);

      /* remember the maximum file descriptor */
      if(this_max_fd > *max_fd)
        *max_fd = this_max_fd;

      break;
    }
    easy = easy->next; /* check next handle */
  }

  return CURLM_OK;
}

CURLMcode curl_multi_perform(CURLM *multi_handle, int *running_handles)
{
  struct Curl_multi *multi=(struct Curl_multi *)multi_handle;
  struct Curl_one_easy *easy;
  bool done;
  CURLMcode result=CURLM_OK;
  struct Curl_message *msg = NULL;
  bool connected;
  bool async;
  bool protocol_connect;
  bool dophase_done;

  *running_handles = 0; /* bump this once for every living handle */

  if(!GOOD_MULTI_HANDLE(multi))
    return CURLM_BAD_HANDLE;

  easy=multi->easy.next;
  while(easy) {
    do {
      if (CURLM_STATE_WAITCONNECT <= easy->state &&
          easy->state <= CURLM_STATE_DO &&
          easy->easy_handle->change.url_changed) {
        char *gotourl;
        Curl_posttransfer(easy->easy_handle);

        easy->result = Curl_done(&easy->easy_conn, CURLE_OK);
        if(CURLE_OK == easy->result) {
          gotourl = strdup(easy->easy_handle->change.url);
          if(gotourl) {
            easy->easy_handle->change.url_changed = FALSE;
            easy->result = Curl_follow(easy->easy_handle, gotourl, FALSE);
            if(CURLE_OK == easy->result)
              multistate(easy, CURLM_STATE_CONNECT);
            else
              free(gotourl);
          }
          else {
            easy->result = CURLE_OUT_OF_MEMORY;
            multistate(easy, CURLM_STATE_COMPLETED);
            break;
          }
        }
      }

      easy->easy_handle->change.url_changed = FALSE;

      switch(easy->state) {
      case CURLM_STATE_INIT:
        /* init this transfer. */
        easy->result=Curl_pretransfer(easy->easy_handle);

        if(CURLE_OK == easy->result) {
          /* after init, go CONNECT */
          multistate(easy, CURLM_STATE_CONNECT);
          result = CURLM_CALL_MULTI_PERFORM;

          easy->easy_handle->state.used_interface = Curl_if_multi;
        }
        break;

      case CURLM_STATE_CONNECT:
        /* Connect. We get a connection identifier filled in. */
        Curl_pgrsTime(easy->easy_handle, TIMER_STARTSINGLE);
        easy->result = Curl_connect(easy->easy_handle, &easy->easy_conn,
                                    &async, &protocol_connect);

        if(CURLE_OK == easy->result) {
          if(async)
            /* We're now waiting for an asynchronous name lookup */
            multistate(easy, CURLM_STATE_WAITRESOLVE);
          else {
            /* after the connect has been sent off, go WAITCONNECT unless the
               protocol connect is already done and we can go directly to
               DO! */
            result = CURLM_CALL_MULTI_PERFORM;

            if(protocol_connect)
              multistate(easy, CURLM_STATE_DO);
            else
              multistate(easy, CURLM_STATE_WAITCONNECT);
          }
        }
        break;

      case CURLM_STATE_WAITRESOLVE:
        /* awaiting an asynch name resolve to complete */
      {
        struct Curl_dns_entry *dns = NULL;

        /* check if we have the name resolved by now */
        easy->result = Curl_is_resolved(easy->easy_conn, &dns);

        if(dns) {
          /* Perform the next step in the connection phase, and then move on
             to the WAITCONNECT state */
          easy->result = Curl_async_resolved(easy->easy_conn,
                                             &protocol_connect);

          if(CURLE_OK != easy->result)
            /* if Curl_async_resolved() returns failure, the connection struct
               is already freed and gone */
            easy->easy_conn = NULL;           /* no more connection */
          else {
            /* FIX: what if protocol_connect is TRUE here?! */
            multistate(easy, CURLM_STATE_WAITCONNECT);
          }
        }

        if(CURLE_OK != easy->result) {
          /* failure detected */
          Curl_disconnect(easy->easy_conn); /* disconnect properly */
          easy->easy_conn = NULL;           /* no more connection */
          break;
        }
      }
      break;

      case CURLM_STATE_WAITCONNECT:
        /* awaiting a completion of an asynch connect */
        easy->result = Curl_is_connected(easy->easy_conn, FIRSTSOCKET,
                                         &connected);
        if(connected)
          easy->result = Curl_protocol_connect(easy->easy_conn,
                                               &protocol_connect);

        if(CURLE_OK != easy->result) {
          /* failure detected */
          Curl_disconnect(easy->easy_conn); /* close the connection */
          easy->easy_conn = NULL;           /* no more connection */
          break;
        }

        if(connected) {
          if(!protocol_connect) {
            /* We have a TCP connection, but 'protocol_connect' may be false
               and then we continue to 'STATE_PROTOCONNECT'. If protocol
               connect is TRUE, we move on to STATE_DO. */
            multistate(easy, CURLM_STATE_PROTOCONNECT);
          }
          else {
            /* after the connect has completed, go DO */
            multistate(easy, CURLM_STATE_DO);
            result = CURLM_CALL_MULTI_PERFORM;
          }
        }
        break;

      case CURLM_STATE_PROTOCONNECT:
        /* protocol-specific connect phase */
        easy->result = Curl_protocol_connecting(easy->easy_conn,
                                                &protocol_connect);
        if(protocol_connect) {
          /* after the connect has completed, go DO */
          multistate(easy, CURLM_STATE_DO);
          result = CURLM_CALL_MULTI_PERFORM;
        }
        else if(easy->result) {
          /* failure detected */
          Curl_posttransfer(easy->easy_handle);
          Curl_done(&easy->easy_conn, easy->result);
          Curl_disconnect(easy->easy_conn); /* close the connection */
          easy->easy_conn = NULL;           /* no more connection */
        }
        break;

      case CURLM_STATE_DO:
        /* Perform the protocol's DO action */
        easy->result = Curl_do(&easy->easy_conn, &dophase_done);

        if(CURLE_OK == easy->result) {

          if(!dophase_done) {
            /* DO was not completed in one function call, we must continue
               DOING... */
            multistate(easy, CURLM_STATE_DOING);
            result = CURLM_OK;
          }

          /* after DO, go PERFORM... or DO_MORE */
          else if(easy->easy_conn->bits.do_more) {
            /* we're supposed to do more, but we need to sit down, relax
               and wait a little while first */
            multistate(easy, CURLM_STATE_DO_MORE);
            result = CURLM_OK;
          }
          else {
            /* we're done with the DO, now PERFORM */
            easy->result = Curl_readwrite_init(easy->easy_conn);
            if(CURLE_OK == easy->result) {
              multistate(easy, CURLM_STATE_PERFORM);
              result = CURLM_CALL_MULTI_PERFORM;
            }
          }
        }
        else {
          /* failure detected */
          Curl_posttransfer(easy->easy_handle);
          Curl_done(&easy->easy_conn, easy->result);
          Curl_disconnect(easy->easy_conn); /* close the connection */
          easy->easy_conn = NULL;           /* no more connection */
        }
        break;

      case CURLM_STATE_DOING:
        /* we continue DOING until the DO phase is complete */
        easy->result = Curl_protocol_doing(easy->easy_conn, &dophase_done);
        if(CURLE_OK == easy->result) {
          if(dophase_done) {
            /* after DO, go PERFORM... or DO_MORE */
            if(easy->easy_conn->bits.do_more) {
              /* we're supposed to do more, but we need to sit down, relax
                 and wait a little while first */
              multistate(easy, CURLM_STATE_DO_MORE);
              result = CURLM_OK;
            }
            else {
              /* we're done with the DO, now PERFORM */
              easy->result = Curl_readwrite_init(easy->easy_conn);
              if(CURLE_OK == easy->result) {
                multistate(easy, CURLM_STATE_PERFORM);
                result = CURLM_CALL_MULTI_PERFORM;
              }
            }
          } /* dophase_done */
        }
        else {
          /* failure detected */
          Curl_posttransfer(easy->easy_handle);
          Curl_done(&easy->easy_conn, easy->result);
          Curl_disconnect(easy->easy_conn); /* close the connection */
          easy->easy_conn = NULL;           /* no more connection */
        }
        break;

      case CURLM_STATE_DO_MORE:
        /* Ready to do more? */
        easy->result = Curl_is_connected(easy->easy_conn, SECONDARYSOCKET,
                                         &connected);
        if(connected) {
          /*
           * When we are connected, DO MORE and then go PERFORM
           */
          easy->result = Curl_do_more(easy->easy_conn);

          if(CURLE_OK == easy->result)
            easy->result = Curl_readwrite_init(easy->easy_conn);

          if(CURLE_OK == easy->result) {
            multistate(easy, CURLM_STATE_PERFORM);
            result = CURLM_CALL_MULTI_PERFORM;
          }
        }
        break;

      case CURLM_STATE_PERFORM:
        /* read/write data if it is ready to do so */
        easy->result = Curl_readwrite(easy->easy_conn, &done);

        if(easy->result)  {
          /* The transfer phase returned error, we mark the connection to get
           * closed to prevent being re-used. This is becasue we can't
           * possibly know if the connection is in a good shape or not now. */
          easy->easy_conn->bits.close = TRUE;

          if(CURL_SOCKET_BAD != easy->easy_conn->sock[SECONDARYSOCKET]) {
            /* if we failed anywhere, we must clean up the secondary socket if
               it was used */
            sclose(easy->easy_conn->sock[SECONDARYSOCKET]);
            easy->easy_conn->sock[SECONDARYSOCKET]=-1;
          }
          Curl_posttransfer(easy->easy_handle);
          Curl_done(&easy->easy_conn, easy->result);
        }

        else if(TRUE == done) {
          char *newurl;
          bool retry = Curl_retry_request(easy->easy_conn, &newurl);

          /* call this even if the readwrite function returned error */
          Curl_posttransfer(easy->easy_handle);

          /* When we follow redirects, must to go back to the CONNECT state */
          if(easy->easy_conn->newurl || retry) {
            if(!retry) {
              /* if the URL is a follow-location and not just a retried request
                 then figure out the URL here */
              newurl = easy->easy_conn->newurl;
              easy->easy_conn->newurl = NULL;
            }
            easy->result = Curl_done(&easy->easy_conn, CURLE_OK);
            if(easy->result == CURLE_OK)
              easy->result = Curl_follow(easy->easy_handle, newurl, retry);
            if(CURLE_OK == easy->result) {
              multistate(easy, CURLM_STATE_CONNECT);
              result = CURLM_CALL_MULTI_PERFORM;
            }
            else
              /* Since we "took it", we are in charge of freeing this on
                 failure */
              free(newurl);
          }
          else {
            /* after the transfer is done, go DONE */
            multistate(easy, CURLM_STATE_DONE);
            result = CURLM_CALL_MULTI_PERFORM;
          }
        }
        break;
      case CURLM_STATE_DONE:
        /* post-transfer command */
        easy->result = Curl_done(&easy->easy_conn, CURLE_OK);

        /* after we have DONE what we're supposed to do, go COMPLETED, and
           it doesn't matter what the Curl_done() returned! */
        multistate(easy, CURLM_STATE_COMPLETED);
        break;

      case CURLM_STATE_COMPLETED:
        /* this is a completed transfer, it is likely to still be connected */

        /* This node should be delinked from the list now and we should post
           an information message that we are complete. */
        break;
      default:
        return CURLM_INTERNAL_ERROR;
      }

      if(CURLM_STATE_COMPLETED != easy->state) {
        if(CURLE_OK != easy->result) {
          /*
           * If an error was returned, and we aren't in completed state now,
           * then we go to completed and consider this transfer aborted.  */
          multistate(easy, CURLM_STATE_COMPLETED);
        }
        else
          /* this one still lives! */
          (*running_handles)++;
      }

    } while (easy->easy_handle->change.url_changed);

    if ((CURLM_STATE_COMPLETED == easy->state) && !easy->msg) {
      /* clear out the usage of the shared DNS cache */
      easy->easy_handle->hostcache = NULL;

      /* now add a node to the Curl_message linked list with this info */
      msg = (struct Curl_message *)malloc(sizeof(struct Curl_message));

      if(!msg)
        return CURLM_OUT_OF_MEMORY;

      msg->extmsg.msg = CURLMSG_DONE;
      msg->extmsg.easy_handle = easy->easy_handle;
      msg->extmsg.data.result = easy->result;
      msg->next=NULL;

      easy->msg = msg;
      easy->msg_num = 1; /* there is one unread message here */

      multi->num_msgs++; /* increase message counter */
    }
    easy = easy->next; /* operate on next handle */
  }

  return result;
}

/* This is called when an easy handle is cleanup'ed that is part of a multi
   handle */
void Curl_multi_rmeasy(void *multi_handle, CURL *easy_handle)
{
  curl_multi_remove_handle(multi_handle, easy_handle);
}

CURLMcode curl_multi_cleanup(CURLM *multi_handle)
{
  struct Curl_multi *multi=(struct Curl_multi *)multi_handle;
  struct Curl_one_easy *easy;
  struct Curl_one_easy *nexteasy;

  if(GOOD_MULTI_HANDLE(multi)) {
    multi->type = 0; /* not good anymore */
    Curl_hash_destroy(multi->hostcache);

    /* remove all easy handles */
    easy = multi->easy.next;
    while(easy) {
      nexteasy=easy->next;
      /* clear out the usage of the shared DNS cache */
      easy->easy_handle->hostcache = NULL;
      Curl_easy_addmulti(easy->easy_handle, NULL); /* clear the association */

      if (easy->msg)
        free(easy->msg);
      free(easy);
      easy = nexteasy;
    }

    free(multi);

    return CURLM_OK;
  }
  else
    return CURLM_BAD_HANDLE;
}

CURLMsg *curl_multi_info_read(CURLM *multi_handle, int *msgs_in_queue)
{
  struct Curl_multi *multi=(struct Curl_multi *)multi_handle;

  *msgs_in_queue = 0; /* default to none */

  if(GOOD_MULTI_HANDLE(multi)) {
    struct Curl_one_easy *easy;

    if(!multi->num_msgs)
      return NULL; /* no messages left to return */

    easy=multi->easy.next;
    while(easy) {
      if(easy->msg_num) {
        easy->msg_num--;
        break;
      }
      easy = easy->next;
    }
    if(!easy)
      return NULL; /* this means internal count confusion really */

    multi->num_msgs--;
    *msgs_in_queue = multi->num_msgs;

    return &easy->msg->extmsg;
  }
  else
    return NULL;
}