/* Copyright (C) 2001 by First Peer, Inc. All rights reserved.
**
** Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions
** are met:
** 1. Redistributions of source code must retain the above copyright
**    notice, this list of conditions and the following disclaimer.
** 2. Redistributions in binary form must reproduce the above copyright
**    notice, this list of conditions and the following disclaimer in the
**    documentation and/or other materials provided with the distribution.
** 3. The name of the author may not be used to endorse or promote products
**    derived from this software without specific prior written permission. 
**  
** THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
** ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
** IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
** ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
** FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
** DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
** OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
** HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
** OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
** SUCH DAMAGE. */

#include "xmlrpc_config.h"

#include <stddef.h>

#include "bool.h"
#include "mallocvar.h"

#include "xmlrpc-c/base.h"
#include "xmlrpc-c/base_int.h"
#include "xmlrpc-c/string_int.h"
#include "xmlrpc-c/client.h"
#include "xmlrpc-c/client_int.h"

/* The libwww interface */

/* These headers mistakenly define the macro PACKAGE.  As
   xmlrpc_config.h already defines PACKAGE according to the package we're
   actually part of, this causes a conflict.  So we undef here and then
   to avoid possible problems with an incorrect PACKAGE, we undef it again
   after.
*/
#undef PACKAGE
#include "WWWLib.h"
#include "WWWHTTP.h"
#include "WWWInit.h"
#undef PACKAGE

/* Include our libwww SSL headers, if available. */
#if HAVE_LIBWWW_SSL
#include "WWWSSL.h"
#endif

#include "xmlrpc_libwww_transport.h"

/* This value was discovered by Rick Blair. His efforts shaved two seconds
** off of every request processed. Many thanks. */
#define SMALLEST_LEGAL_LIBWWW_TIMEOUT (21)

#define XMLRPC_CLIENT_USE_TIMEOUT   (2)


struct xmlrpc_client_transport {
    int saved_flags;
    HTList *xmlrpc_conversions;
    void * cookieJarP;
        /* This is a collection of all the cookies that servers have set
           via responses to prior requests.  It's not implemented today.
        */
    bool tracingOn;
};

static struct xmlrpc_client_transport clientTransport;


typedef struct {
/*----------------------------------------------------------------------------
   This object represents one RPC.
-----------------------------------------------------------------------------*/
    struct xmlrpc_client_transport * clientTransportP;

    /* These fields are used when performing synchronous calls. */
    bool is_done;
    int http_status;

    /* Low-level information used by libwww. */
    HTRequest *      request;
    HTChunk *        response_data;
    HTParentAnchor * source_anchor;
    HTAnchor *       dest_anchor;

    xmlrpc_transport_asynch_complete complete;
    struct xmlrpc_call_info * callInfoP; 
} rpc;



static void
createCookieJar(xmlrpc_env * const envP ATTR_UNUSED,
                void **      const cookieJarP ATTR_UNUSED) {

    /* Cookies not implemented yet */
}



static void
destroyCookieJar(void * cookieJarP ATTR_UNUSED) {

    /* Cookies not implemented yet */
}



static void
initLibwww(const char * const appname,
           const char * const appversion) {
    
    /* We initialize the library using a robot profile, because we don't
    ** care about redirects or HTTP authentication, and we want to
    ** reduce our application footprint as much as possible. */
    HTProfile_newRobot(appname, appversion);

    /* Ilya Goldberg <igg@mit.edu> provided the following code to access
    ** SSL-protected servers. */
#if HAVE_LIBWWW_SSL
    /* Set the SSL protocol method. By default, it is the highest
    ** available protocol. Setting it up to SSL_V23 allows the client
    ** to negotiate with the server and set up either TSLv1, SSLv3,
    ** or SSLv2 */
    HTSSL_protMethod_set(HTSSL_V23);
    
    /* Set the certificate verification depth to 2 in order to be able to
    ** validate self-signed certificates */
    HTSSL_verifyDepth_set(2);
    
    /* Register SSL stuff for handling ssl access. The parameter we pass
    ** is NO because we can't be pre-emptive with POST */
    HTSSLhttps_init(NO);
#endif /* HAVE_LIBWWW_SSL */
    
    /* For interoperability with Frontier, we need to tell libwww *not*
    ** to send 'Expect: 100-continue' headers. But if we're not sending
    ** these, we shouldn't wait for them. So set our built-in delays to
    ** the smallest legal values. */
    HTTP_setBodyWriteDelay (SMALLEST_LEGAL_LIBWWW_TIMEOUT,
                            SMALLEST_LEGAL_LIBWWW_TIMEOUT);
    
    /* We attempt to disable all of libwww's chatty, interactive
    ** prompts. Let's hope this works. */
    HTAlert_setInteractive(NO);
    
    /* Here are some alternate setup calls which will help greatly
    ** with debugging, should the need arise.
    **
    ** HTProfile_newNoCacheClient(appname, appversion);
    ** HTAlert_setInteractive(YES);
    ** HTPrint_setCallback(printer);
    ** HTTrace_setCallback(tracer); */
}



static void 
create(xmlrpc_env *                      const envP,
       int                               const flags,
       const char *                      const appname,
       const char *                      const appversion,
       const struct xmlrpc_xportparms *  const transportParmsP ATTR_UNUSED,
       size_t                            const parm_size ATTR_UNUSED,
       struct xmlrpc_client_transport ** const handlePP) {
/*----------------------------------------------------------------------------
   This does the 'create' operation for a Libwww client transport.
-----------------------------------------------------------------------------*/
    /* The Libwww transport is not re-entrant -- you can have only one
       per program instance.  Even if we changed the Xmlrpc-c code not
       to use global variables, that wouldn't help because Libwww
       itself is not re-entrant.  
       
       So we use a global variable ('clientTransport') for our transport state.
    */
    struct xmlrpc_client_transport * const clientTransportP = &clientTransport;
    *handlePP = clientTransportP;

    clientTransportP->saved_flags = flags;

    createCookieJar(envP, &clientTransportP->cookieJarP);
    if (!envP->fault_occurred) {
        if (!(clientTransportP->saved_flags & 
              XMLRPC_CLIENT_SKIP_LIBWWW_INIT))
            initLibwww(appname, appversion);

        /* Set up our list of conversions for XML-RPC requests. This is a
        ** massively stripped-down version of the list in libwww's HTInit.c.
        ** XXX - This is hackish; 10.0 is an arbitrary, large quality factor
        ** designed to override the built-in converter for XML. */
        clientTransportP->xmlrpc_conversions = HTList_new();
        HTConversion_add(clientTransportP->xmlrpc_conversions, 
                         "text/xml", "*/*",
                         HTThroughLine, 10.0, 0.0, 0.0);

        if (envP->fault_occurred)
            destroyCookieJar(clientTransportP->cookieJarP);
    }
    if (getenv("XMLRPC_LIBWWW_TRACE"))
        clientTransportP->tracingOn = TRUE;
    else
        clientTransportP->tracingOn = FALSE;
}



static void 
destroy(struct xmlrpc_client_transport * const clientTransportP) {
/*----------------------------------------------------------------------------
   This does the 'destroy' operation for a Libwww client transport.
-----------------------------------------------------------------------------*/
    XMLRPC_ASSERT(clientTransportP != NULL);

    if (!(clientTransportP->saved_flags & XMLRPC_CLIENT_SKIP_LIBWWW_INIT)) {
        HTProfile_delete();
    }
    destroyCookieJar(clientTransportP->cookieJarP);
}



/*=========================================================================
**  HTTP Error Reporting
**=======================================================================*/

static void
formatLibwwwError(HTRequest *   const requestP,
                  const char ** const msgP) {
/*----------------------------------------------------------------------------
   When something fails in a Libwww request, Libwww generates a stack
   of error information (precious little information, of course, in the
   Unix tradition) and attaches it to the request object.  We make a message
   out of that information.

   We rely on Libwww's HTDialog_errorMessage() to do the bulk of the
   formatting; we might be able to coax more information out of the request
   if we interpreted the error stack directly.
-----------------------------------------------------------------------------*/
    HTList * const errStack = HTRequest_error(requestP);
    
    if (errStack == NULL)
        xmlrpc_asprintf(msgP, "Libwww supplied no error details");
    else {
        /* Get an error message from libwww.  The middle three
           parameters to HTDialog_errorMessage appear to be ignored.
           XXX - The documentation for this API is terrible, so we may
           be using it incorrectly.  
        */
        const char * msg =
            HTDialog_errorMessage(requestP, HT_A_MESSAGE, HT_MSG_NULL,
                                  "An error occurred", errStack);
        
        if (msg == NULL)
            xmlrpc_asprintf(msgP, "Libwww supplied some error detail, "
                            "but its HTDialog_errorMessage() subroutine "
                            "mysteriously failed to interpret it for us.");
        else
            *msgP = msg;
    }
}



static void 
set_fault_from_http_request(xmlrpc_env * const envP,
                            int          const status,
                            HTRequest *  const requestP) {
/*----------------------------------------------------------------------------
   Assuming 'requestP' identifies a completed libwww HTTP request, set
   *envP according to its success/error status.
-----------------------------------------------------------------------------*/
    XMLRPC_ASSERT_PTR_OK(requestP);

    if (status == 200) {
        /* No error.  Don't set one in *envP */
    } else {
        const char * libwwwMsg;
        formatLibwwwError(requestP, &libwwwMsg);

        if (status == -1)
            xmlrpc_env_set_fault_formatted(
                envP, XMLRPC_NETWORK_ERROR,
                "Unable to complete the HTTP request.  %s", libwwwMsg);
        else {
            xmlrpc_env_set_fault_formatted(
                envP, XMLRPC_NETWORK_ERROR,
                "HTTP request completed with HTTp error %d.  %s",
                status, libwwwMsg);
        }
        xmlrpc_strfree(libwwwMsg);
    }
}



static BOOL 
setCookie(HTRequest * const request,
          HTCookie *  const cookieP ATTR_UNUSED,
          void *      const param ATTR_UNUSED) {
/*----------------------------------------------------------------------------
  This is the callback from libwww to tell us the server (according to
  its response) wants us to store a cookie (and include it in future
  requests).

  We assume that the cookies "domain" is the server's host name
  (there are options on the libwww connection to make libwww call this
  callback only when that's the case).
-----------------------------------------------------------------------------*/
    rpc * const rpcP = HTRequest_context(request);
    struct xmlrpc_client_transport * const clientTransportP = 
        rpcP->clientTransportP;

    BOOL retval;

    /* Avoid unused variable warning */
    if (clientTransportP->cookieJarP == clientTransportP->cookieJarP) {}
    /* Cookies are not implemented today */
    retval = NO;

    return retval;
}



static HTAssocList *
cookiesForHost(const char * const host ATTR_UNUSED,
               void *       const cookieJarP ATTR_UNUSED) {
/*----------------------------------------------------------------------------
  Find and return all the cookies in jar 'cookieJarP' that are for the
  host 'host'.
-----------------------------------------------------------------------------*/
    HTAssocList * hisCookiesP;

    hisCookiesP = HTAssocList_new();

    if (hisCookiesP) {
        /* Cookies are not implemented yet */
        /* Library/Examples/cookie.c in the w3c-libwww source tree contains
           an example of constructing the cookie list we are supposed to
           return.  But today, we return an empty list.
        */
    }
    return hisCookiesP;
}



static HTAssocList *
findCookie(HTRequest * const request,
           void *      const param ATTR_UNUSED) {
/*----------------------------------------------------------------------------
  This is the callback from libwww to get the cookies to include in a
  request (presumably values the server set via a prior response).
-----------------------------------------------------------------------------*/
    rpc * const rpcP = HTRequest_context(request);
    struct xmlrpc_client_transport * const clientTransportP = 
        rpcP->clientTransportP;
    const char * const addr = 
        HTAnchor_address((HTAnchor *) HTRequest_anchor(request));
    const char * const host = HTParse(addr, "", PARSE_HOST);

    return cookiesForHost(host, clientTransportP->cookieJarP);
}



static void 
deleteSourceAnchor(HTParentAnchor * const anchor) {

    /* We need to clear the document first, or else libwww won't
    ** really delete the anchor. */
    HTAnchor_setDocument(anchor, NULL);

    /* XXX - Deleting this anchor causes HTLibTerminate to dump core. */
    /* HTAnchor_delete(anchor); */
}



static void
createSourceAnchor(xmlrpc_env *       const envP,
                   HTParentAnchor **  const sourceAnchorPP,
                   xmlrpc_mem_block * const xmlP) {

    HTParentAnchor * const sourceAnchorP = HTTmpAnchor(NULL);

    if (sourceAnchorP == NULL)
        xmlrpc_env_set_fault_formatted(
            envP, XMLRPC_INTERNAL_ERROR, 
            "Unable to build source anchor.  HTTmpAnchor() failed.");
    else {
        HTAnchor_setDocument(sourceAnchorP,
                             XMLRPC_MEMBLOCK_CONTENTS(char, xmlP));
        HTAnchor_setFormat(sourceAnchorP, HTAtom_for("text/xml"));
        HTAnchor_setLength(sourceAnchorP, XMLRPC_MEMBLOCK_SIZE(char, xmlP));

        *sourceAnchorPP = sourceAnchorP;
    }
}



static void
createDestAnchor(xmlrpc_env *               const envP,
                 HTAnchor **                const destAnchorPP,
                 const xmlrpc_server_info * const serverP) {
                 
    *destAnchorPP = HTAnchor_findAddress(serverP->_server_url);

    if (*destAnchorPP == NULL)
        xmlrpc_env_set_fault_formatted(
            envP, XMLRPC_INTERNAL_ERROR,
            "Could not build destination anchor.  HTAnchor_findAddress() "
            "failed.");
}



static void
rpcCreate(xmlrpc_env *                       const envP,
          struct xmlrpc_client_transport *   const clientTransportP,
          const xmlrpc_server_info *         const serverP,
          xmlrpc_mem_block *                 const xmlP,
          xmlrpc_transport_asynch_complete         complete, 
          struct xmlrpc_call_info *          const callInfoP,
          rpc **                             const rpcPP) {

    rpc *rpcP;
    HTRqHd request_headers;
    HTStream *target_stream;

    /* Allocate our structure. */
    MALLOCVAR(rpcP);
    XMLRPC_FAIL_IF_NULL(rpcP, envP, XMLRPC_INTERNAL_ERROR,
                        "Out of memory in rpcCreate()");

    /* Set up our basic members. */
    rpcP->clientTransportP = clientTransportP;
    rpcP->is_done = FALSE;
    rpcP->http_status = 0;
    rpcP->complete = complete;
    rpcP->callInfoP = callInfoP;

    /* Start cookie handler. */
    HTCookie_init();
    HTCookie_setCallbacks(setCookie, NULL, findCookie, NULL);
    HTCookie_setCookieMode(HT_COOKIE_ACCEPT | 
                           HT_COOKIE_SEND | 
                           HT_COOKIE_SAME_HOST);

    /* Cookies aren't implemented today; reset. */
    HTCookie_setCookieMode(0);
    
    /* Create a HTRequest object. */
    rpcP->request = HTRequest_new();
    XMLRPC_FAIL_IF_NULL(rpcP, envP, XMLRPC_INTERNAL_ERROR,
                        "HTRequest_new failed");
    
    /* Install ourselves as the request context. */
    HTRequest_setContext(rpcP->request, rpcP);

    /* XXX - Disable the 'Expect:' header so we can talk to Frontier. */
    request_headers = HTRequest_rqHd(rpcP->request);
    request_headers = request_headers & ~HT_C_EXPECT;
    HTRequest_setRqHd(rpcP->request, request_headers);

    /* Send an authorization header if we need one. */
    if (serverP->_http_basic_auth)
        HTRequest_addCredentials(rpcP->request, "Authorization",
                                 serverP->_http_basic_auth);
    
    /* Make sure there is no XML conversion handler to steal our data.
    ** The 'override' parameter is currently ignored by libwww, so our
    ** list of conversions must be designed to co-exist with the built-in
    ** conversions. */
    HTRequest_setConversion(rpcP->request, 
                            clientTransportP->xmlrpc_conversions, NO);

    /* Set up our response buffer. */
    target_stream = HTStreamToChunk(rpcP->request, &rpcP->response_data, 0);
    XMLRPC_FAIL_IF_NULL(rpcP->response_data, envP, XMLRPC_INTERNAL_ERROR,
                        "HTStreamToChunk failed");
    XMLRPC_ASSERT(target_stream != NULL);
    HTRequest_setOutputStream(rpcP->request, target_stream);
    HTRequest_setOutputFormat(rpcP->request, WWW_SOURCE);

    createSourceAnchor(envP, &rpcP->source_anchor, xmlP);

    if (!envP->fault_occurred) {
        createDestAnchor(envP, &rpcP->dest_anchor, serverP);

        if (envP->fault_occurred)
            /* See below for comments about deleting the source and dest
            ** anchors. This is a bit of a black art. */
            deleteSourceAnchor(rpcP->source_anchor);
    }
    
 cleanup:
    if (envP->fault_occurred) {
        if (rpcP) {
            if (rpcP->request)
                HTRequest_delete(rpcP->request);
            if (rpcP->response_data)
                HTChunk_delete(rpcP->response_data);
            free(rpcP);
        }
    }
    *rpcPP = rpcP;
}



static void 
rpcDestroy(rpc * const rpcP) {

    XMLRPC_ASSERT_PTR_OK(rpcP);
    XMLRPC_ASSERT(rpcP->request != XMLRPC_BAD_POINTER);
    XMLRPC_ASSERT(rpcP->response_data != XMLRPC_BAD_POINTER);

    /* Junji Kanemaru reports on 05.04.11 that with asynch calls, he
       get a segfault, and reversing the order of deleting the request
       and the response chunk buffer cured it.  But we find no reason
       that should be so, so we're waiting for someone to arrive at an
       explanation before changing anything.  HTRequest_delete() does
       destroy the output stream, and the output stream refers to the
       response chunk, but HTRequest_delete() explicitly refrains from
       destroying the response chunk.  And the response chunk does not
       refer to the request.
    */

    HTRequest_delete(rpcP->request);
    rpcP->request = XMLRPC_BAD_POINTER;
    HTChunk_delete(rpcP->response_data);
    rpcP->response_data = XMLRPC_BAD_POINTER;

    /* This anchor points to private data, so we're allowed to delete it.  */
    deleteSourceAnchor(rpcP->source_anchor);

    /* WARNING: We can't delete the destination anchor, because this points
    ** to something in the outside world, and lives in a libwww hash table.
    ** Under certain circumstances, this anchor may have been reissued to
    ** somebody else. So over time, the anchor cache will grow. If this
    ** is a problem for your application, read the documentation for
    ** HTAnchor_deleteAll.
    **
    ** However, we CAN check to make sure that no documents have been
    ** attached to the anchor. This assertion may fail if you're using
    ** libwww for something else, so please feel free to comment it out. */
    /* XMLRPC_ASSERT(HTAnchor_document(rpcP->dest_anchor) == NULL);
     */

    HTCookie_deleteCallbacks();
    HTCookie_terminate();

    free(rpcP);
}



static void
extract_response_chunk(xmlrpc_env *        const envP,
                       rpc *               const rpcP,
                       xmlrpc_mem_block ** const responseXmlPP) {

    /* Check to make sure that w3c-libwww actually sent us some data.
    ** XXX - This may happen if libwww is shut down prematurely, believe it
    ** or not--we'll get a 200 OK and no data. Gag me with a bogus design
    ** decision. This may also fail if some naughty libwww converter
    ** ate our data unexpectedly. */
    if (!HTChunk_data(rpcP->response_data))
        xmlrpc_env_set_fault(envP, XMLRPC_NETWORK_ERROR,
                             "w3c-libwww returned no data");
    else {
        *responseXmlPP = XMLRPC_MEMBLOCK_NEW(char, envP, 0);
        if (!envP->fault_occurred) {
            if (rpcP->clientTransportP->tracingOn) {
                fprintf(stderr, "HTTP chunk received: %u bytes: '%.*s'",
                        HTChunk_size(rpcP->response_data),
                        HTChunk_size(rpcP->response_data),
                        HTChunk_data(rpcP->response_data));
            }

            XMLRPC_MEMBLOCK_APPEND(char, envP, *responseXmlPP,
                                   HTChunk_data(rpcP->response_data),
                                   HTChunk_size(rpcP->response_data));
            if (envP->fault_occurred)
                XMLRPC_MEMBLOCK_FREE(char, *responseXmlPP);
        }
    }
}



static int 
synch_terminate_handler(HTRequest *  const request,
                        HTResponse * const response ATTR_UNUSED,
                        void *       const param ATTR_UNUSED,
                        int          const status) {
/*----------------------------------------------------------------------------
   This is a libwww request completion handler.

   HTEventList_newLoop() calls this when it completes a request (with this
   registered as the completion handler).
-----------------------------------------------------------------------------*/
    rpc *rpcP;

    rpcP = HTRequest_context(request);

    rpcP->is_done = TRUE;
    rpcP->http_status = status;

    HTEventList_stopLoop();

    return HT_OK;
}



static void
call(xmlrpc_env *                     const envP,
     struct xmlrpc_client_transport * const clientTransportP,
     const xmlrpc_server_info *       const serverP,
     xmlrpc_mem_block *               const xmlP,
     xmlrpc_mem_block **              const responsePP) {
/*----------------------------------------------------------------------------
   This does the 'call' operation for a Libwww client transport.
-----------------------------------------------------------------------------*/
    rpc * rpcP;

    XMLRPC_ASSERT_ENV_OK(envP);
    XMLRPC_ASSERT_PTR_OK(serverP);
    XMLRPC_ASSERT_PTR_OK(xmlP);
    XMLRPC_ASSERT_PTR_OK(responsePP);

    rpcCreate(envP, clientTransportP, serverP, xmlP, NULL, NULL, &rpcP);
    if (!envP->fault_occurred) {
        int ok;
        
        /* Install our request handler. */
        HTRequest_addAfter(rpcP->request, &synch_terminate_handler, 
                           NULL, NULL, HT_ALL, HT_FILTER_LAST, NO);

        /* Start our request running. */
        ok = HTPostAnchor(rpcP->source_anchor, 
                          rpcP->dest_anchor, 
                          rpcP->request);
        if (!ok)
            xmlrpc_env_set_fault(
                envP, XMLRPC_NETWORK_ERROR,
                "Libwww HTPostAnchor() failed to start POST request");
        else {
            /* Run our event-processing loop.  HTEventList_newLoop()
               is what calls synch_terminate_handler(), by virtue of
               it being registered as a handler.  It may return for
               other reasons than the request being complete, though.
               so we call it in a loop until synch_terminate_handler()
               really has been called.
            */
            while (!rpcP->is_done)
                HTEventList_newLoop();
        
            /* Fail if we didn't get a "200 OK" response from the server */
            if (rpcP->http_status != 200)
                set_fault_from_http_request(
                    envP, rpcP->http_status, 
                    rpcP->request);
            else {
                /* XXX - Check to make sure response type is text/xml here. */
                
                extract_response_chunk(envP, rpcP, responsePP);
            }
        }
        rpcDestroy(rpcP);
    }
}



/*=========================================================================
**  Event Loop
**=========================================================================
**  We manage a fair bit of internal state about our event loop. This is
**  needed to determine when (and if) we should exit the loop.
*/

static int outstanding_asynch_calls = 0;
static int event_loop_flags = 0;
static int timer_called = 0;

static void 
register_asynch_call(void) {
    XMLRPC_ASSERT(outstanding_asynch_calls >= 0);
    outstanding_asynch_calls++;
}



static void 
unregister_asynch_call(void) {

    XMLRPC_ASSERT(outstanding_asynch_calls > 0);
    outstanding_asynch_calls--;
    if (outstanding_asynch_calls == 0)
        HTEventList_stopLoop();
}



static int 
timer_callback(HTTimer *   const timer     ATTR_UNUSED,
               void *      const user_data ATTR_UNUSED,
               HTEventType const event     ATTR_UNUSED) {
/*----------------------------------------------------------------------------
  A handy timer callback which cancels the running event loop. 
-----------------------------------------------------------------------------*/
    XMLRPC_ASSERT(event == HTEvent_TIMEOUT);
    timer_called = 1;
    HTEventList_stopLoop();
    
    /* XXX - The meaning of this return value is undocumented, but close
    ** inspection of libwww's source suggests that we want to return HT_OK. */
    return HT_OK;
}



static void 
eventLoopRun(int            const flags, 
             xmlrpc_timeout const milliseconds) {
/*----------------------------------------------------------------------------
   Process all responses from outstanding requests as they come in.
   Return when there are no more outstanding responses.

   Or, if 'flags' has the XMLRPC_CLIENT_USE_TIMEOUT flag set, return
   when 'milliseconds' milliseconds have elapsed, regardless of whether
   there are still outstanding responses.

   The processing we do consists of telling libwww to process the
   completion of the libwww request.  That normally includes calling
   the xmlrpc_libwww_transport request termination handler, because
   the submitter of the libwww request would have registered that as a
   callback.
-----------------------------------------------------------------------------*/
    if (outstanding_asynch_calls > 0) {
        HTTimer *timer;

        event_loop_flags = flags;
        
        /* Run an appropriate event loop.  The HTEeventList_newLoop()
           is what calls asynch_terminate_handler(), by virtue of it
           being registered as a handler.
        */
        if (event_loop_flags & XMLRPC_CLIENT_USE_TIMEOUT) {
            
            /* Run our event loop with a timer. Note that we need to be very
            ** careful about race conditions--timers can be fired in either
            ** HTimer_new or HTEventList_newLoop. And if our callback were to
            ** get called before we entered the loop, we would never exit.
            ** So we use a private flag of our own--we can't even rely on
            ** HTTimer_hasTimerExpired, because that only checks the time,
            ** not whether our callback has been run. Yuck. */
            timer_called = 0;
            timer = HTTimer_new(NULL, &timer_callback, NULL,
                                milliseconds, YES, NO);
            XMLRPC_ASSERT(timer != NULL);
            if (!timer_called)
                HTEventList_newLoop();
            HTTimer_delete(timer);
            
        } else {
            /* Run our event loop without a timer. */
            HTEventList_newLoop();
        }
        
        /* Reset our flags, so we don't interfere with direct calls to the
        ** libwww event loop functions. */
        event_loop_flags = 0;
    } else {
        /* There are *no* calls to process.  This may mean that none
           of the asynch calls were ever set up, and the client's
           callbacks have already been called with an error, or that
           all outstanding calls were completed during a previous
           synchronous call.  
        */
    }
}



static void 
finishAsynch(
    struct xmlrpc_client_transport * const clientTransportP ATTR_UNUSED,
    xmlrpc_timeoutType               const timeoutType,
    xmlrpc_timeout                   const timeout) {
/*----------------------------------------------------------------------------
   This does the 'finish_asynch' operation for a Libwww client transport.
-----------------------------------------------------------------------------*/
    eventLoopRun(timeoutType == timeout_yes ? XMLRPC_CLIENT_USE_TIMEOUT : 0,
                 timeout);
}



static int 
asynch_terminate_handler(HTRequest *  const request,
                         HTResponse * const response ATTR_UNUSED,
                         void *       const param ATTR_UNUSED,
                         int          const status) {
/*----------------------------------------------------------------------------
   Handle the completion of a libwww request.

   This is the bottom half of the xmlrpc_libwww_transport asynchronous
   call dispatcher.  It's what the dispatcher registers with libwww as
   a "local after filter" so that libwww calls it when a request that
   xmlrpc_libwww_transport submitted to it is complete.

   We destroy the RPC, including the request which is our argument.
   Strange as that may seem, it is apparently legal for an after filter
   to destroy the request that was passed to it -- or not.
-----------------------------------------------------------------------------*/
    xmlrpc_env env;
    rpc * rpcP;
    xmlrpc_mem_block * responseXmlP;

    XMLRPC_ASSERT_PTR_OK(request);

    xmlrpc_env_init(&env);

    rpcP = HTRequest_context(request);

    /* Unregister this call from the event loop. Among other things, this
    ** may decide to stop the event loop.
    **/
    unregister_asynch_call();

    /* Give up if an error occurred. */
    if (status != 200)
        set_fault_from_http_request(&env, status, request);
    else {
        /* XXX - Check to make sure response type is text/xml here. */
        extract_response_chunk(&env, rpcP, &responseXmlP);
    }
    rpcP->complete(rpcP->callInfoP, responseXmlP, env);

    if (!env.fault_occurred)
        XMLRPC_MEMBLOCK_FREE(char, responseXmlP);

    rpcDestroy(rpcP);
    
    xmlrpc_env_clean(&env);
    return HT_OK;
}



static void 
sendRequest(xmlrpc_env *                     const envP, 
            struct xmlrpc_client_transport * const clientTransportP,
            const xmlrpc_server_info *       const serverP,
            xmlrpc_mem_block *               const xmlP,
            xmlrpc_transport_asynch_complete       complete,
            struct xmlrpc_call_info *        const callInfoP) {
/*----------------------------------------------------------------------------
   Initiate an XML-RPC rpc asynchronously.  Don't wait for it to go to
   the server.

   Unless we return failure, we arrange to have complete() called when
   the rpc completes.

   This does the 'send_request' operation for a Libwww client transport.
-----------------------------------------------------------------------------*/
    rpc * rpcP;

    XMLRPC_ASSERT_PTR_OK(envP);
    XMLRPC_ASSERT_PTR_OK(serverP);
    XMLRPC_ASSERT_PTR_OK(xmlP);
    XMLRPC_ASSERT_PTR_OK(callInfoP);

    rpcCreate(envP, clientTransportP, serverP, xmlP, complete, callInfoP, 
              &rpcP);
    if (!envP->fault_occurred) {
        int ok;

        /* Install our request handler. */
        HTRequest_addAfter(rpcP->request, &asynch_terminate_handler, 
                           NULL, NULL, HT_ALL, HT_FILTER_LAST, NO);

        /* Register our asynchronous call with the event loop.  This means
           the user's callback is guaranteed to be called eventually.
        */
        register_asynch_call();

        /* This makes the TCP connection and sends the XML to the server
           as an HTTP POST request.

           There was a comment here that said this might return failure
           (!ok) and still invoke our completion handler
           (asynch_terminate_handler().  The code attempted to deal with
           that.  Well, it's impossible to deal with that, so if it really
           happens, we must fix Libwww.  -Bryan 04.11.23.
        */

        ok = HTPostAnchor(rpcP->source_anchor, 
                          rpcP->dest_anchor, 
                          rpcP->request);
        if (!ok) {
            unregister_asynch_call();
            xmlrpc_env_set_fault(envP, XMLRPC_NETWORK_ERROR,
                                 "Libwww (HTPostAnchor()) failed to start the "
                                 "POST request.");
        }
        if (envP->fault_occurred)
            rpcDestroy(rpcP);
    }
}



struct xmlrpc_client_transport_ops xmlrpc_libwww_transport_ops = {
    NULL,
    NULL,
    &create,
    &destroy,
    &sendRequest,
    &call,
    &finishAsynch,
};
