transfer.c

	 don't know if it's the 1st header line or the body.
	 So we do a partial conversion into a scratch area,
	 leaving the data at k->p as-is.
      */
      strncpy(&scratch[0], k->p, SCRATCHSIZE);
      scratch[SCRATCHSIZE] = 0; /* null terminate */
      res = Curl_convert_from_network(data,
				      &scratch[0],
				      SCRATCHSIZE);
      if(CURLE_OK != res) {
	/* Curl_convert_from_network calls failf if unsuccessful */
	return res;
      }
#else
#define HEADER1 k->p /* no conversion needed, just use k->p */
#endif /* CURL_DOES_CONVERSIONS */

      nc = sscanf(HEADER1,
		  " HTTP/%d.%d %3d",
		  &httpversion_major,
		  &conn->httpversion,
		  &k->httpcode);
      if(nc==3) {
	conn->httpversion += 10 * httpversion_major;
      }
      else {
	/* this is the real world, not a Nirvana
	   NCSA 1.5.x returns this crap when asked for HTTP/1.1
	*/
	nc=sscanf(HEADER1, " HTTP %3d", &k->httpcode);
	conn->httpversion = 10;

	/* If user has set option HTTP200ALIASES,
	   compare header line against list of aliases
	*/
	if(!nc) {
	  if(checkhttpprefix(data, k->p)) {
	    nc = 1;
	    k->httpcode = 200;
	    conn->httpversion = 10;
	  }
	}
      }

      if(nc) {
	data->info.httpcode = k->httpcode;
	data->info.httpversion = conn->httpversion;
        if (!data->state.httpversion ||
            data->state.httpversion > conn->httpversion)
          /* store the lowest server version we encounter */
          data->state.httpversion = conn->httpversion;

	/*
	 * This code executes as part of processing the header.  As a
	 * result, it's not totally clear how to interpret the
	 * response code yet as that depends on what other headers may
	 * be present.  401 and 407 may be errors, but may be OK
	 * depending on how authentication is working.  Other codes
	 * are definitely errors, so give up here.
	 */
	if(data->set.http_fail_on_error && (k->httpcode >= 400) &&
	   ((k->httpcode != 401) || !conn->bits.user_passwd) &&
	   ((k->httpcode != 407) || !conn->bits.proxy_user_passwd) ) {

	  if(data->state.resume_from &&
	     (data->set.httpreq==HTTPREQ_GET) &&
	     (k->httpcode == 416)) {
	    /* "Requested Range Not Satisfiable", just proceed and
	       pretend this is no error */
	  }
	  else {
	    /* serious error, go home! */
	    failf (data, "The requested URL returned error: %d",
		   k->httpcode);
	    return CURLE_HTTP_RETURNED_ERROR;
	  }
	}

	if(conn->httpversion == 10) {
	  /* Default action for HTTP/1.0 must be to close, unless
	     we get one of those fancy headers that tell us the
	     server keeps it open for us! */
	  infof(data, "HTTP 1.0, assume close after body\n");
	  conn->bits.close = TRUE;
	}
	else if(conn->httpversion >= 11 &&
		!conn->bits.close) {
	  /* If HTTP version is >= 1.1 and connection is persistent
	     server supports pipelining. */
	  DEBUGF(infof(data,
		       "HTTP 1.1 or later with persistent connection, "
		       "pipelining supported\n"));
	  conn->server_supports_pipelining = TRUE;
	}

	switch(k->httpcode) {
	case 204:
	  /* (quote from RFC2616, section 10.2.5): The server has
	   * fulfilled the request but does not need to return an
	   * entity-body ... The 204 response MUST NOT include a
	   * message-body, and thus is always terminated by the first
	   * empty line after the header fields. */
	  /* FALLTHROUGH */
	case 416: /* Requested Range Not Satisfiable, it has the
		     Content-Length: set as the "real" document but no
		     actual response is sent. */
	case 304:
	  /* (quote from RFC2616, section 10.3.5): The 304 response
	   * MUST NOT contain a message-body, and thus is always
	   * terminated by the first empty line after the header
	   * fields.  */
          if(data->set.timecondition)
            data->info.timecond = TRUE;
	  k->size=0;
	  k->maxdownload=0;
	  k->ignorecl = TRUE; /* ignore Content-Length headers */
	  break;
	default:
	  /* nothing */
	  break;
	}
      }
      else {
	k->header = FALSE;   /* this is not a header line */
	break;
      }
    }

#ifdef CURL_DOES_CONVERSIONS
    /* convert from the network encoding */
    result = Curl_convert_from_network(data, k->p, strlen(k->p));
    if(CURLE_OK != result) {
      return(result);
    }
    /* Curl_convert_from_network calls failf if unsuccessful */
#endif /* CURL_DOES_CONVERSIONS */

    /* Check for Content-Length: header lines to get size. Ignore
       the header completely if we get a 416 response as then we're
       resuming a document that we don't get, and this header contains
       info about the true size of the document we didn't get now. */
    if(!k->ignorecl && !data->set.ignorecl &&
       checkprefix("Content-Length:", k->p)) {
      curl_off_t contentlength = curlx_strtoofft(k->p+15, NULL, 10);
      if(data->set.max_filesize &&
	 contentlength > data->set.max_filesize) {
	failf(data, "Maximum file size exceeded");
	return CURLE_FILESIZE_EXCEEDED;
      }
      if(contentlength >= 0) {
	k->size = contentlength;
	k->maxdownload = k->size;
	/* we set the progress download size already at this point
	   just to make it easier for apps/callbacks to extract this
	   info as soon as possible */
	Curl_pgrsSetDownloadSize(data, k->size);
      }
      else {
	/* Negative Content-Length is really odd, and we know it
	   happens for example when older Apache servers send large
	   files */
	conn->bits.close = TRUE;
	infof(data, "Negative content-length: %" FORMAT_OFF_T
	      ", closing after transfer\n", contentlength);
      }
    }
    /* check for Content-Type: header lines to get the MIME-type */
    else if(checkprefix("Content-Type:", k->p)) {
      char *contenttype = Curl_copy_header_value(k->p);
      if (!contenttype)
	return CURLE_OUT_OF_MEMORY;
      if (!*contenttype)
	/* ignore empty data */
	free(contenttype);
      else {
	Curl_safefree(data->info.contenttype);
	data->info.contenttype = contenttype;
      }
    }
    else if((conn->httpversion == 10) &&
	    conn->bits.httpproxy &&
	    Curl_compareheader(k->p,
			       "Proxy-Connection:", "keep-alive")) {
      /*
       * When a HTTP/1.0 reply comes when using a proxy, the
       * 'Proxy-Connection: keep-alive' line tells us the
       * connection will be kept alive for our pleasure.
       * Default action for 1.0 is to close.
       */
      conn->bits.close = FALSE; /* don't close when done */
      infof(data, "HTTP/1.0 proxy connection set to keep alive!\n");
    }
    else if((conn->httpversion == 11) &&
	    conn->bits.httpproxy &&
	    Curl_compareheader(k->p,
			       "Proxy-Connection:", "close")) {
      /*
       * We get a HTTP/1.1 response from a proxy and it says it'll
       * close down after this transfer.
       */
      conn->bits.close = TRUE; /* close when done */
      infof(data, "HTTP/1.1 proxy connection set close!\n");
    }
    else if((conn->httpversion == 10) &&
	    Curl_compareheader(k->p, "Connection:", "keep-alive")) {
      /*
       * A HTTP/1.0 reply with the 'Connection: keep-alive' line
       * tells us the connection will be kept alive for our
       * pleasure.  Default action for 1.0 is to close.
       *
       * [RFC2068, section 19.7.1] */
      conn->bits.close = FALSE; /* don't close when done */
      infof(data, "HTTP/1.0 connection set to keep alive!\n");
    }
    else if(Curl_compareheader(k->p, "Connection:", "close")) {
      /*
       * [RFC 2616, section 8.1.2.1]
       * "Connection: close" is HTTP/1.1 language and means that
       * the connection will close when this request has been
       * served.
       */
      conn->bits.close = TRUE; /* close when done */
    }
    else if(Curl_compareheader(k->p,
			       "Transfer-Encoding:", "chunked")) {
      /*
       * [RFC 2616, section 3.6.1] A 'chunked' transfer encoding
       * means that the server will send a series of "chunks". Each
       * chunk starts with line with info (including size of the
       * coming block) (terminated with CRLF), then a block of data
       * with the previously mentioned size. There can be any amount
       * of chunks, and a chunk-data set to zero signals the
       * end-of-chunks. */
      k->chunk = TRUE; /* chunks coming our way */

      /* init our chunky engine */
      Curl_httpchunk_init(conn);
    }

    else if(checkprefix("Trailer:", k->p) ||
	    checkprefix("Trailers:", k->p)) {
      /*
       * This test helps Curl_httpchunk_read() to determine to look
       * for well formed trailers after the zero chunksize record. In
       * this case a CRLF is required after the zero chunksize record
       * when no trailers are sent, or after the last trailer record.
       *
       * It seems both Trailer: and Trailers: occur in the wild.
       */
      k->trailerhdrpresent = TRUE;
    }

    else if(checkprefix("Content-Encoding:", k->p) &&
	    data->set.str[STRING_ENCODING]) {
      /*
       * Process Content-Encoding. Look for the values: identity,
       * gzip, deflate, compress, x-gzip and x-compress. x-gzip and
       * x-compress are the same as gzip and compress. (Sec 3.5 RFC
       * 2616). zlib cannot handle compress.  However, errors are
       * handled further down when the response body is processed
       */
      char *start;

      /* Find the first non-space letter */
      start = k->p + 17;
      while(*start && ISSPACE(*start))
        start++;

      /* Record the content-encoding for later use */
      if(checkprefix("identity", start))
	k->content_encoding = IDENTITY;
      else if(checkprefix("deflate", start))
	k->content_encoding = DEFLATE;
      else if(checkprefix("gzip", start)
	      || checkprefix("x-gzip", start))
	k->content_encoding = GZIP;
      else if(checkprefix("compress", start)
	      || checkprefix("x-compress", start))
	k->content_encoding = COMPRESS;
    }
    else if(checkprefix("Content-Range:", k->p)) {
      /* Content-Range: bytes [num]-
	 Content-Range: bytes: [num]-
	 Content-Range: [num]-

	 The second format was added since Sun's webserver
	 JavaWebServer/1.1.1 obviously sends the header this way!
	 The third added since some servers use that!
      */

      char *ptr = k->p + 14;

      /* Move forward until first digit */
      while(*ptr && !ISDIGIT(*ptr))
	ptr++;

      k->offset = curlx_strtoofft(ptr, NULL, 10);

      if(data->state.resume_from == k->offset)
	/* we asked for a resume and we got it */
	k->content_range = TRUE;
    }
#if !defined(CURL_DISABLE_COOKIES)
    else if(data->cookies &&
	    checkprefix("Set-Cookie:", k->p)) {
      Curl_share_lock(data, CURL_LOCK_DATA_COOKIE,
		      CURL_LOCK_ACCESS_SINGLE);
      Curl_cookie_add(data,
		      data->cookies, TRUE, k->p+11,
		      /* If there is a custom-set Host: name, use it
			 here, or else use real peer host name. */
		      conn->allocptr.cookiehost?
		      conn->allocptr.cookiehost:conn->host.name,
		      data->state.path);
      Curl_share_unlock(data, CURL_LOCK_DATA_COOKIE);
    }
#endif
    else if(checkprefix("Last-Modified:", k->p) &&
	    (data->set.timecondition || data->set.get_filetime) ) {
      time_t secs=time(NULL);
      k->timeofdoc = curl_getdate(k->p+strlen("Last-Modified:"),
				  &secs);
      if(data->set.get_filetime)
	data->info.filetime = (long)k->timeofdoc;
    }
    else if((checkprefix("WWW-Authenticate:", k->p) &&
	     (401 == k->httpcode)) ||
	    (checkprefix("Proxy-authenticate:", k->p) &&
	     (407 == k->httpcode))) {
      result = Curl_http_input_auth(conn, k->httpcode, k->p);
      if(result)
	return result;
    }
    else if((k->httpcode >= 300 && k->httpcode < 400) &&
	    checkprefix("Location:", k->p)) {
      /* this is the URL that the server advises us to use instead */
      char *location = Curl_copy_header_value(k->p);
      if (!location)
	return CURLE_OUT_OF_MEMORY;
      if (!*location)
	/* ignore empty data */
	free(location);
      else {
	DEBUGASSERT(!data->req.location);
	data->req.location = location;

	if(data->set.http_follow_location) {
	  DEBUGASSERT(!data->req.newurl);
	  data->req.newurl = strdup(data->req.location); /* clone */
	  if(!data->req.newurl)
	    return CURLE_OUT_OF_MEMORY;

	  /* some cases of POST and PUT etc needs to rewind the data
	     stream at this point */
	  result = Curl_http_perhapsrewind(conn);
	  if(result)
	    return result;
	}
      }
    }

    /*
     * End of header-checks. Write them to the client.
     */

    writetype = CLIENTWRITE_HEADER;
    if(data->set.include_header)
      writetype |= CLIENTWRITE_BODY;

    if(data->set.verbose)
      Curl_debug(data, CURLINFO_HEADER_IN,
		 k->p, (size_t)k->hbuflen, conn);

    result = Curl_client_write(conn, writetype, k->p, k->hbuflen);
    if(result)
      return result;

    data->info.header_size += (long)k->hbuflen;
    data->req.headerbytecount += (long)k->hbuflen;

    /* reset hbufp pointer && hbuflen */
    k->hbufp = data->state.headerbuff;
    k->hbuflen = 0;
  }
  while(!*stop_reading && *k->str); /* header line within buffer */

  /* We might have reached the end of the header part here, but
     there might be a non-header part left in the end of the read
     buffer. */

  return CURLE_OK;
}
#endif   /* CURL_DISABLE_HTTP */

/*
 * Send data to upload to the server, when the socket is writable.
 */
static CURLcode readwrite_upload(struct SessionHandle *data,
                                 struct connectdata *conn,
                                 struct SingleRequest *k,
                                 int *didwhat)
{
  ssize_t i, si;
  ssize_t bytes_written;
  CURLcode result;
  ssize_t nread; /* number of bytes read */

  if((k->bytecount == 0) && (k->writebytecount == 0))
    Curl_pgrsTime(data, TIMER_STARTTRANSFER);

  *didwhat |= KEEP_WRITE;

  /*
   * We loop here to do the READ and SEND loop until we run out of
   * data to send or until we get EWOULDBLOCK back
   */
  do {

    /* only read more data if there's no upload data already
       present in the upload buffer */
    if(0 == data->req.upload_present) {
      /* init the "upload from here" pointer */
      data->req.upload_fromhere = k->uploadbuf;

      if(!k->upload_done) {
	/* HTTP pollution, this should be written nicer to become more
	   protocol agnostic. */
	int fillcount;

	if((k->exp100 == EXP100_SENDING_REQUEST) &&
	   (data->state.proto.http->sending == HTTPSEND_BODY)) {
	  /* If this call is to send body data, we must take some action:
	     We have sent off the full HTTP 1.1 request, and we shall now
	     go into the Expect: 100 state and await such a header */
	  k->exp100 = EXP100_AWAITING_CONTINUE; /* wait for the header */
	  k->keepon &= ~KEEP_WRITE;         /* disable writing */
	  k->start100 = Curl_tvnow();       /* timeout count starts now */
	  *didwhat &= ~KEEP_WRITE;  /* we didn't write anything actually */
	  break;
	}

	result = Curl_fillreadbuffer(conn, BUFSIZE, &fillcount);
	if(result)
	  return result;

	nread = (ssize_t)fillcount;
      }
      else
	nread = 0; /* we're done uploading/reading */

      if(!nread && (k->keepon & KEEP_WRITE_PAUSE)) {
	/* this is a paused transfer */
	break;
      }
      else if(nread<=0) {
	/* done */
	k->keepon &= ~KEEP_WRITE; /* we're done writing */

	if(conn->bits.rewindaftersend) {
	  result = Curl_readrewind(conn);
	  if(result)
	    return result;
	}
	break;
      }

      /* store number of bytes available for upload */
      data->req.upload_present = nread;

      /* convert LF to CRLF if so asked */
#ifdef CURL_DO_LINEEND_CONV
      /* always convert if we're FTPing in ASCII mode */
      if((data->set.crlf) || (data->set.prefer_ascii))
#else
	if(data->set.crlf)
#endif /* CURL_DO_LINEEND_CONV */
	{
	  if(data->state.scratch == NULL)
	    data->state.scratch = malloc(2*BUFSIZE);
	  if(data->state.scratch == NULL) {
	    failf (data, "Failed to alloc scratch buffer!");
	    return CURLE_OUT_OF_MEMORY;
	  }
	  /*
	   * ASCII/EBCDIC Note: This is presumably a text (not binary)
	   * transfer so the data should already be in ASCII.
	   * That means the hex values for ASCII CR (0x0d) & LF (0x0a)
	   * must be used instead of the escape sequences \r & \n.
	   */
	  for(i = 0, si = 0; i < nread; i++, si++) {
	    if(data->req.upload_fromhere[i] == 0x0a) {
	      data->state.scratch[si++] = 0x0d;
	      data->state.scratch[si] = 0x0a;
	      if(!data->set.crlf) {
		/* we're here only because FTP is in ASCII mode...
		   bump infilesize for the LF we just added */
		data->set.infilesize++;
	      }
	    }
	    else
	      data->state.scratch[si] = data->req.upload_fromhere[i];
	  }
	  if(si != nread) {
	    /* only perform the special operation if we really did replace
	       anything */
	    nread = si;

	    /* upload from the new (replaced) buffer instead */
	    data->req.upload_fromhere = data->state.scratch;

	    /* set the new amount too */
	    data->req.upload_present = nread;
	  }
	}
    } /* if 0 == data->req.upload_present */
    else {
      /* We have a partial buffer left from a previous "round". Use
	 that instead of reading more data */
    }

    /* write to socket (send away data) */
    result = Curl_write(conn,
			conn->writesockfd,     /* socket to send to */
			data->req.upload_fromhere, /* buffer pointer */
			data->req.upload_present,  /* buffer size */
			&bytes_written);       /* actually send away */

    if(result)
      return result;

    if(data->set.verbose)
      /* show the data before we change the pointer upload_fromhere */
      Curl_debug(data, CURLINFO_DATA_OUT, data->req.upload_fromhere,
		 (size_t)bytes_written, conn);

    if(data->req.upload_present != bytes_written) {
      /* we only wrote a part of the buffer (if anything), deal with it! */

      /* store the amount of bytes left in the buffer to write */
      data->req.upload_present -= bytes_written;

      /* advance the pointer where to find the buffer when the next send
	 is to happen */
      data->req.upload_fromhere += bytes_written;
    }
    else {
      /* we've uploaded that buffer now */
      data->req.upload_fromhere = k->uploadbuf;
      data->req.upload_present = 0; /* no more bytes left */

      if(k->upload_done) {
	/* switch off writing, we're done! */
	k->keepon &= ~KEEP_WRITE; /* we're done writing */
      }
    }

    k->writebytecount += bytes_written;
    Curl_pgrsSetUploadCounter(data, k->writebytecount);

  } while(0); /* just to break out from! */

  return CURLE_OK;
}

/*
 * Curl_readwrite() is the low-level function to be called when data is to
 * be read and written to/from the connection.
 */
CURLcode Curl_readwrite(struct connectdata *conn,
                        bool *done)
{
  struct SessionHandle *data = conn->data;
  struct SingleRequest *k = &data->req;
  CURLcode result;
  int didwhat=0;

  curl_socket_t fd_read;
  curl_socket_t fd_write;
  int select_res = conn->cselect_bits;

  conn->cselect_bits = 0;

  /* only use the proper socket if the *_HOLD bit is not set simultaneously as
     then we are in rate limiting state in that transfer direction */

  if((k->keepon & KEEP_READBITS) == KEEP_READ) {
    fd_read = conn->sockfd;
#if defined(USE_LIBSSH2)
    if(conn->protocol & (PROT_SCP|PROT_SFTP))
      select_res |= CURL_CSELECT_IN;
#endif /* USE_LIBSSH2 */
  } else
    fd_read = CURL_SOCKET_BAD;

  if((k->keepon & KEEP_WRITEBITS) == KEEP_WRITE)
    fd_write = conn->writesockfd;
  else
    fd_write = CURL_SOCKET_BAD;

   if(!select_res) { /* Call for select()/poll() only, if read/write/error
                         status is not known. */
       select_res = Curl_socket_ready(fd_read, fd_write, 0);
   }

  if(select_res == CURL_CSELECT_ERR) {
    failf(data, "select/poll returned error");
    return CURLE_SEND_ERROR;
  }

  /* We go ahead and do a read if we have a readable socket or if
     the stream was rewound (in which case we have data in a
     buffer) */
  if((k->keepon & KEEP_READ) &&
     ((select_res & CURL_CSELECT_IN) || conn->bits.stream_was_rewound)) {

    result = readwrite_data(data, conn, k, &didwhat, done);
    if(result || *done)
      return result;
  }

  /* If we still have writing to do, we check if we have a writable socket. */
  if((k->keepon & KEEP_WRITE) && (select_res & CURL_CSELECT_OUT)) {
    /* write */

    result = readwrite_upload(data, conn, k, &didwhat);
    if(result)
      return result;
  }

  k->now = Curl_tvnow();
  if(didwhat) {
    /* Update read/write counters */
    if(k->bytecountp)
      *k->bytecountp = k->bytecount; /* read count */
    if(k->writebytecountp)
      *k->writebytecountp = k->writebytecount; /* write count */
  }
  else {
    /* no read no write, this is a timeout? */
    if(k->exp100 == EXP100_AWAITING_CONTINUE) {
      /* This should allow some time for the header to arrive, but only a
         very short time as otherwise it'll be too much wasted time too
         often. */

      /* Quoting RFC2616, section "8.2.3 Use of the 100 (Continue) Status":

         Therefore, when a client sends this header field to an origin server
         (possibly via a proxy) from which it has never seen a 100 (Continue)
         status, the client SHOULD NOT wait for an indefinite period before
         sending the request body.

      */

      long ms = Curl_tvdiff(k->now, k->start100);
      if(ms > CURL_TIMEOUT_EXPECT_100) {
        /* we've waited long enough, continue anyway */
        k->exp100 = EXP100_SEND_DATA;
        k->keepon |= KEEP_WRITE;
        infof(data, "Done waiting for 100-continue\n");
      }
    }
  }

  if(Curl_pgrsUpdate(conn))
    result = CURLE_ABORTED_BY_CALLBACK;
  else
    result = Curl_speedcheck(data, k->now);
  if(result)
    return result;

  if(data->set.timeout &&
     (Curl_tvdiff(k->now, k->start) >= data->set.timeout)) {
    if(k->size != -1) {
      failf(data, "Operation timed out after %ld milliseconds with %"
            FORMAT_OFF_T " out of %" FORMAT_OFF_T " bytes received",
            data->set.timeout, k->bytecount, k->size);
    } else {
      failf(data, "Operation timed out after %ld milliseconds with %"
            FORMAT_OFF_T " bytes received",
            data->set.timeout, k->bytecount);
    }
    return CURLE_OPERATION_TIMEDOUT;
  }

  if(!k->keepon) {
    /*
     * The transfer has been performed. Just make some general checks before
     * returning.
     */

    if(!(data->set.opt_no_body) && (k->size != -1) &&
       (k->bytecount != k->size) &&
#ifdef CURL_DO_LINEEND_CONV
       /* Most FTP servers don't adjust their file SIZE response for CRLFs,
          so we'll check to see if the discrepancy can be explained
          by the number of CRLFs we've changed to LFs.
       */
       (k->bytecount != (k->size + data->state.crlf_conversions)) &&
#endif /* CURL_DO_LINEEND_CONV */
       !data->req.newurl) {
      failf(data, "transfer closed with %" FORMAT_OFF_T
            " bytes remaining to read",
            k->size - k->bytecount);
      return CURLE_PARTIAL_FILE;
    }
    else if(!(data->set.opt_no_body) &&
            k->chunk &&
            (conn->chunk.state != CHUNK_STOP)) {
      /*
       * In chunked mode, return an error if the connection is closed prior to
       * the empty (terminiating) chunk is read.
       *
       * The condition above used to check for
       * conn->proto.http->chunk.datasize != 0 which is true after reading
       * *any* chunk, not just the empty chunk.
       *
       */
      failf(data, "transfer closed with outstanding read data remaining");
      return CURLE_PARTIAL_FILE;
    }
    if(Curl_pgrsUpdate(conn))
      return CURLE_ABORTED_BY_CALLBACK;
  }

  /* Now update the "done" boolean we return */
  *done = (bool)(0 == (k->keepon&(KEEP_READ|KEEP_WRITE|
                                  KEEP_READ_PAUSE|KEEP_WRITE_PAUSE)));

  return CURLE_OK;
}

/*
 * Curl_single_getsock() gets called by the multi interface code when the app
 * has requested to get the sockets for the current connection. This function
 * will then be called once for every connection that the multi interface
 * keeps track of. This function will only be called for connections that are
 * in the proper state to have this information available.
 */
int Curl_single_getsock(const struct connectdata *conn,
                        curl_socket_t *sock, /* points to numsocks number
                                                of sockets */
                        int numsocks)
{
  const struct SessionHandle *data = conn->data;
  int bitmap = GETSOCK_BLANK;
  unsigned sockindex = 0;

  if(conn->handler->perform_getsock)
    return conn->handler->perform_getsock(conn, sock, numsocks);

  if(numsocks < 2)
    /* simple check but we might need two slots */
    return GETSOCK_BLANK;

  /* don't include HOLD and PAUSE connections */
  if((data->req.keepon & KEEP_READBITS) == KEEP_READ) {

    DEBUGASSERT(conn->sockfd != CURL_SOCKET_BAD);

    bitmap |= GETSOCK_READSOCK(sockindex);
    sock[sockindex] = conn->sockfd;
  }

  /* don't include HOLD and PAUSE connections */
  if((data->req.keepon & KEEP_WRITEBITS) == KEEP_WRITE) {

    if((conn->sockfd != conn->writesockfd) ||
       !(data->req.keepon & KEEP_READ)) {
      /* only if they are not the same socket or we didn't have a readable
         one, we increase index */
      if(data->req.keepon & KEEP_READ)
        sockindex++; /* increase index if we need two entries */

      DEBUGASSERT(conn->writesockfd != CURL_SOCKET_BAD);

      sock[sockindex] = conn->writesockfd;
    }

    bitmap |= GETSOCK_WRITESOCK(sockindex);
  }

  return bitmap;
}


/*
 * Transfer()
 *
 * This function is what performs the actual transfer. It is capable of
 * doing both ways simultaneously.
 * The transfer must already have been setup by a call to Curl_setup_transfer().
 *
 * Note that headers are created in a preallocated buffer of a default size.
 * That buffer can be enlarged on demand, but it is never shrunken again.
 *
 * Parts of this function was once written by the friendly Mark Butler
 * <butlerm@xmission.com>.
 */

static CURLcode
Transfer(struct connectdata *conn)
{
  CURLcode result;
  struct SessionHandle *data = conn->data;
  struct SingleRequest *k = &data->req;
  bool done=FALSE;
  bool first=TRUE;
  int timeout_ms;

  if((conn->sockfd == CURL_SOCKET_BAD) &&
     (conn->writesockfd == CURL_SOCKET_BAD))
    /* nothing to read, nothing to write, we're already OK! */
    return CURLE_OK;

  /* we want header and/or body, if neither then don't do this! */
  if(!k->getheader && data->set.opt_no_body)
    return CURLE_OK;

  while(!done) {
    curl_socket_t fd_read;
    curl_socket_t fd_write;

    /* limit-rate logic: if speed exceeds threshold, then do not include fd in
       select set. The current speed is recalculated in each Curl_readwrite()
       call */
    if((k->keepon & KEEP_WRITE) &&
        (!data->set.max_send_speed ||
         (data->progress.ulspeed < data->set.max_send_speed) )) {
      fd_write = conn->writesockfd;
      k->keepon &= ~KEEP_WRITE_HOLD;
    }
    else {
      fd_write = CURL_SOCKET_BAD;
      if(k->keepon & KEEP_WRITE)
        k->keepon |= KEEP_WRITE_HOLD; /* hold it */
    }

    if((k->keepon & KEEP_READ) &&
        (!data->set.max_recv_speed ||
         (data->progress.dlspeed < data->set.max_recv_speed)) ) {
      fd_read = conn->sockfd;
      k->keepon &= ~KEEP_READ_HOLD;
    }
    else {
      fd_read = CURL_SOCKET_BAD;
      if(k->keepon & KEEP_READ)
        k->keepon |= KEEP_READ_HOLD; /* hold it */
    }

    /* pause logic. Don't check descriptors for paused connections */
    if(k->keepon & KEEP_READ_PAUSE)
      fd_read = CURL_SOCKET_BAD;
    if(k->keepon & KEEP_WRITE_PAUSE)
      fd_write = CURL_SOCKET_BAD;

    /* The *_HOLD and *_PAUSE logic is necessary since even though there might
       be no traffic during the select interval, we still call
       Curl_readwrite() for the timeout case and if we limit transfer speed we
       must make sure that this function doesn't transfer anything while in
       HOLD status.

       The no timeout for the first round is for the protocols for which data
       has already been slurped off the socket and thus waiting for action
       won't work since it'll wait even though there is already data present
       to work with. */
    if(first &&
       ((fd_read != CURL_SOCKET_BAD) || (fd_write != CURL_SOCKET_BAD)))
      /* if this is the first lap and one of the file descriptors is fine
         to work with, skip the timeout */
      timeout_ms = 0;
    else
      timeout_ms = 1000;

    switch (Curl_socket_ready(fd_read, fd_write, timeout_ms)) {
    case -1: /* select() error, stop reading */
#ifdef EINTR
      /* The EINTR is not serious, and it seems you might get this more
         often when using the lib in a multi-threaded environment! */
      if(SOCKERRNO == EINTR)
        continue;
#endif
      return CURLE_RECV_ERROR;  /* indicate a network problem */
    case 0:  /* timeout */
    default: /* readable descriptors */

      result = Curl_readwrite(conn, &done);
      /* "done" signals to us if the transfer(s) are ready */
      break;
    }
    if(result)
      return result;

    first = FALSE; /* not the first lap anymore */
  }

  return CURLE_OK;
}

/*
 * Curl_pretransfer() is called immediately before a transfer starts.
 */
CURLcode Curl_pretransfer(struct SessionHandle *data)
{
  CURLcode res;
  if(!data->change.url) {
    /* we can't do anything without URL */
    failf(data, "No URL set!");
    return CURLE_URL_MALFORMAT;
  }

  /* Init the SSL session ID cache here. We do it here since we want to do it
     after the *_setopt() calls (that could change the size of the cache) but
     before any transfer takes place. */
  res = Curl_ssl_initsessions(data, data->set.ssl.numsessions);
  if(res)
    return res;

  data->set.followlocation=0; /* reset the location-follow counter */
  data->state.this_is_a_follow = FALSE; /* reset this */
  data->state.errorbuf = FALSE; /* no error has occurred */
  data->state.httpversion = 0; /* don't assume any particular server version */

  data->state.authproblem = FALSE;
  data->state.authhost.want = data->set.httpauth;
  data->state.authproxy.want = data->set.proxyauth;
  Curl_safefree(data->info.wouldredirect);
  data->info.wouldredirect = NULL;

  /* If there is a list of cookie files to read, do it now! */
  if(data->change.cookielist) {
    Curl_cookie_loadfiles(data);
  }

 /* Allow data->set.use_port to set which port to use. This needs to be
  * disabled for example when we follow Location: headers to URLs using
  * different ports! */
  data->state.allow_port = TRUE;

#if defined(HAVE_SIGNAL) && defined(SIGPIPE) && !defined(HAVE_MSG_NOSIGNAL)
  /*************************************************************
   * Tell signal handler to ignore SIGPIPE
   *************************************************************/
  if(!data->set.no_signal)
    data->state.prev_signal = signal(SIGPIPE, SIG_IGN);
#endif

  Curl_initinfo(data); /* reset session-specific information "variables" */
  Curl_pgrsStartNow(data);

  return CURLE_OK;
}

/*
 * Curl_posttransfer() is called immediately after a transfer ends
 */
CURLcode Curl_posttransfer(struct SessionHandle *data)
{
#if defined(HAVE_SIGNAL) && defined(SIGPIPE) && !defined(HAVE_MSG_NOSIGNAL)
  /* restore the signal handler for SIGPIPE before we get back */
  if(!data->set.no_signal)
    signal(SIGPIPE, data->state.prev_signal);
#else
  (void)data; /* unused parameter */
#endif

  if(!(data->progress.flags & PGRS_HIDE) &&
     !data->progress.callback)
    /* only output if we don't use a progress callback and we're not hidden */
    fprintf(data->set.err, "\n");

  return CURLE_OK;
}

#ifndef CURL_DISABLE_HTTP
/*
 * strlen_url() returns the length of the given URL if the spaces within the
 * URL were properly URL encoded.
 */
static size_t strlen_url(const char *url)
{
  const char *ptr;
  size_t newlen=0;
  bool left=TRUE; /* left side of the ? */

  for(ptr=url; *ptr; ptr++) {
    switch(*ptr) {
    case '?':
      left=FALSE;
      /* fall through */
    default:
      newlen++;
      break;
    case ' ':
      if(left)
        newlen+=3;
      else
        newlen++;
      break;
    }
  }