transfer.c

            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 */
            for(start=k->p+17;
                *start && ISSPACE(*start);
                start++)
              ;  /* empty loop */

            /* 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 advices us to use instead */
            char *ptr;
            char *start=k->p;
            char backup;

            start += 9; /* pass "Location:" */

            /* Skip spaces and tabs. We do this to support multiple
               white spaces after the "Location:" keyword. */
            while(*start && ISSPACE(*start ))
              start++;

            /* Scan through the string from the end to find the last
               non-space. k->end_ptr points to the actual terminating zero
               letter, move pointer one letter back and start from
               there. This logic strips off trailing whitespace, but keeps
               any embedded whitespace. */
            ptr = k->end_ptr-1;
            while((ptr>=start) && ISSPACE(*ptr))
              ptr--;
            ptr++;

            backup = *ptr; /* store the ending letter */
            if(ptr != start) {
              *ptr = '\0';   /* zero terminate */
              data->req.location = strdup(start); /* clone string */
              *ptr = backup; /* restore ending letter */
              if(!data->req.location)
                return CURLE_OUT_OF_MEMORY;
              if(data->set.http_follow_location) {
                data->req.newurl = strdup(data->req.location); /* clone */
                if(!data->req.newurl)
                  return CURLE_OUT_OF_MEMORY;
              }
            }
          }
#endif   /* CURL_DISABLE_HTTP */

          /*
           * 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 */

        if(stop_reading)
          /* We've stopped dealing with input, get out of the do-while loop */
          break;

        /* 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. */

      }                       /* end if header mode */

      /* This is not an 'else if' since it may be a rest from the header
         parsing, where the beginning of the buffer is headers and the end
         is non-headers. */
      if(k->str && !k->header && (nread > 0 || is_empty_data)) {

        if(0 == k->bodywrites && !is_empty_data) {
          /* These checks are only made the first time we are about to
             write a piece of the body */
          if(conn->protocol&PROT_HTTP) {
            /* HTTP-only checks */

            if(data->req.newurl) {
              if(conn->bits.close) {
                /* Abort after the headers if "follow Location" is set
                   and we're set to close anyway. */
                k->keepon &= ~KEEP_READ;
                *done = TRUE;
                return CURLE_OK;
              }
              /* We have a new url to load, but since we want to be able
                 to re-use this connection properly, we read the full
                 response in "ignore more" */
              k->ignorebody = TRUE;
              infof(data, "Ignoring the response-body\n");
            }
            if(data->state.resume_from && !k->content_range &&
               (data->set.httpreq==HTTPREQ_GET) &&
               !k->ignorebody) {
              /* we wanted to resume a download, although the server doesn't
               * seem to support this and we did this with a GET (if it
               * wasn't a GET we did a POST or PUT resume) */
              failf(data, "HTTP server doesn't seem to support "
                    "byte ranges. Cannot resume.");
              return CURLE_RANGE_ERROR;
            }

            if(data->set.timecondition && !data->state.range) {
              /* A time condition has been set AND no ranges have been
                 requested. This seems to be what chapter 13.3.4 of
                 RFC 2616 defines to be the correct action for a
                 HTTP/1.1 client */
              if((k->timeofdoc > 0) && (data->set.timevalue > 0)) {
                switch(data->set.timecondition) {
                case CURL_TIMECOND_IFMODSINCE:
                default:
                  if(k->timeofdoc < data->set.timevalue) {
                    infof(data,
                          "The requested document is not new enough\n");
                    *done = TRUE;
                    return CURLE_OK;
                  }
                  break;
                case CURL_TIMECOND_IFUNMODSINCE:
                  if(k->timeofdoc > data->set.timevalue) {
                    infof(data,
                          "The requested document is not old enough\n");
                    *done = TRUE;
                    return CURLE_OK;
                  }
                  break;
                } /* switch */
              } /* two valid time strings */
            } /* we have a time condition */

          } /* this is HTTP */
        } /* this is the first time we write a body part */
        k->bodywrites++;

        /* pass data to the debug function before it gets "dechunked" */
        if(data->set.verbose) {
          if(k->badheader) {
            Curl_debug(data, CURLINFO_DATA_IN, data->state.headerbuff,
                       (size_t)k->hbuflen, conn);
            if(k->badheader == HEADER_PARTHEADER)
              Curl_debug(data, CURLINFO_DATA_IN,
                         k->str, (size_t)nread, conn);
          }
          else
            Curl_debug(data, CURLINFO_DATA_IN,
                       k->str, (size_t)nread, conn);
        }

#ifndef CURL_DISABLE_HTTP
        if(k->chunk) {
          /*
           * Here comes a chunked transfer flying and we need to decode this
           * properly.  While the name says read, this function both reads
           * and writes away the data. The returned 'nread' holds the number
           * of actual data it wrote to the client.
           */

          CHUNKcode res =
            Curl_httpchunk_read(conn, k->str, nread, &nread);

          if(CHUNKE_OK < res) {
            if(CHUNKE_WRITE_ERROR == res) {
              failf(data, "Failed writing data");
              return CURLE_WRITE_ERROR;
            }
            failf(data, "Received problem %d in the chunky parser", res);
            return CURLE_RECV_ERROR;
          }
          else if(CHUNKE_STOP == res) {
            size_t dataleft;
            /* we're done reading chunks! */
            k->keepon &= ~KEEP_READ; /* read no more */

            /* There are now possibly N number of bytes at the end of the
               str buffer that weren't written to the client.

               We DO care about this data if we are pipelining.
               Push it back to be read on the next pass. */

            dataleft = conn->chunk.dataleft;
            if(dataleft != 0) {
              infof(conn->data, "Leftovers after chunking. "
                    " Rewinding %d bytes\n",dataleft);
              read_rewind(conn, dataleft);
            }
          }
          /* If it returned OK, we just keep going */
        }
#endif   /* CURL_DISABLE_HTTP */

        if((-1 != k->maxdownload) &&
           (k->bytecount + nread >= k->maxdownload)) {
          /* The 'excess' amount below can't be more than BUFSIZE which
             always will fit in a size_t */
          size_t excess = (size_t)(k->bytecount + nread - k->maxdownload);
          if(excess > 0 && !k->ignorebody) {
            infof(data,
                  "Rewinding stream by : %d"
                  " bytes on url %s (size = %" FORMAT_OFF_T
                  ", maxdownload = %" FORMAT_OFF_T
                  ", bytecount = %" FORMAT_OFF_T ", nread = %d)\n",
                  excess, data->state.path,
                  k->size, k->maxdownload, k->bytecount, nread);
            read_rewind(conn, excess);
          }

          nread = (ssize_t) (k->maxdownload - k->bytecount);
          if(nread < 0 ) /* this should be unusual */
            nread = 0;

          k->keepon &= ~KEEP_READ; /* we're done reading */
        }

        k->bytecount += nread;

        Curl_pgrsSetDownloadCounter(data, k->bytecount);

        if(!k->chunk && (nread || k->badheader || is_empty_data)) {
          /* If this is chunky transfer, it was already written */

          if(k->badheader && !k->ignorebody) {
            /* we parsed a piece of data wrongly assuming it was a header
               and now we output it as body instead */
            result = Curl_client_write(conn, CLIENTWRITE_BODY,
                                       data->state.headerbuff,
                                       k->hbuflen);
            if(result)
              return result;
          }
          if(k->badheader < HEADER_ALLBAD) {
            /* This switch handles various content encodings. If there's an
               error here, be sure to check over the almost identical code
               in http_chunks.c.
               Make sure that ALL_CONTENT_ENCODINGS contains all the
               encodings handled here. */
#ifdef HAVE_LIBZ
            switch (conn->data->set.http_ce_skip ?
                    IDENTITY : k->content_encoding) {
            case IDENTITY:
#endif
              /* This is the default when the server sends no
                 Content-Encoding header. See Curl_readwrite_init; the
                 memset() call initializes k->content_encoding to zero. */
              if(!k->ignorebody)
                result = Curl_client_write(conn, CLIENTWRITE_BODY, k->str,
                                           nread);
#ifdef HAVE_LIBZ
              break;

            case DEFLATE:
              /* Assume CLIENTWRITE_BODY; headers are not encoded. */
              if(!k->ignorebody)
                result = Curl_unencode_deflate_write(conn, k, nread);
              break;

            case GZIP:
              /* Assume CLIENTWRITE_BODY; headers are not encoded. */
              if(!k->ignorebody)
                result = Curl_unencode_gzip_write(conn, k, nread);
              break;

            case COMPRESS:
            default:
              failf (data, "Unrecognized content encoding type. "
                     "libcurl understands `identity', `deflate' and `gzip' "
                     "content encodings.");
              result = CURLE_BAD_CONTENT_ENCODING;
              break;
            }
#endif
          }
          k->badheader = HEADER_NORMAL; /* taken care of now */

          if(result)
            return result;
        }

      } /* if(! header and data to read ) */

      if(is_empty_data) {
        /* if we received nothing, the server closed the connection and we
           are done */
        k->keepon &= ~KEEP_READ;
      }

    } while(data_pending(conn));

  } /* if( read from socket ) */

  /* 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 */

    ssize_t i, si;
    ssize_t bytes_written;

    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! */

  } /* if(something to write) */

  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;
      }
    }
  }

  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(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;

  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. */

    switch (Curl_socket_ready(fd_read, fd_write, 1000)) {
    case -1: /* select() error, stop reading */
#ifdef EINTR
      /* The EINTR is not serious, and it seems you might get this more
         ofen when using the lib in a multi-threaded environment! */
      if(SOCKERRNO == EINTR)
        ;
      else
#endif
        done = TRUE; /* no more read or write */
      continue;
    case 0:  /* timeout */
    default: /* readable descriptors */

      result = Curl_readwrite(conn, &done);
      break;
    }
    if(result)
      return result;

    /* "done" signals to us if the transfer(s) are ready */
  }

  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 wihout 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.authproblem = FALSE;
  data->state.authhost.want = data->set.httpauth;
  data->state.authproxy.want = data->set.proxyauth;

  /* 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;
}

/*
 * 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;
    }
  }
  return newlen;
}

/* strcpy_url() copies a url to a output buffer and URL-encodes the spaces in
 * the source URL accordingly.
 */
static void strcpy_url(char *output, const char *url)
{
  /* we must add this with whitespace-replacing */
  bool left=TRUE;
  const char *iptr;
  char *optr = output;
  for(iptr = url;    /* read from here */
      *iptr;         /* until zero byte */
      iptr++) {
    switch(*iptr) {
    case '?':
      left=FALSE;
      /* fall through */
    default:
      *optr++=*iptr;
      break;
    case ' ':
      if(left) {
        *optr++='%'; /* add a '%' */
        *optr++='2'; /* add a '2' */
        *optr++='0'; /* add a '0' */
      }
      else
        *optr++='+'; /* add a '+' here */
      break;
    }
  }
  *optr=0; /* zero terminate output buffer */

}

/*
 * Curl_follow() handles the URL redirect magic. Pass in the 'newurl' string
 * as given by the remote server and set up the new URL to request.
 */
CURLcode Curl_follow(struct SessionHandle *data,
                     char *newurl, /* this 'newurl' is the Location: string,
                                      and it must be malloc()ed before passed
                                      here */
                     followtype type) /* see transfer.h */
{
  /* Location: redirect */
  char prot[16]; /* URL protocol string storage */
  char letter;   /* used for a silly sscanf */
  size_t newlen;
  char *newest;
  bool disallowport = FALSE;

  if(type == FOLLOW_REDIR) {
    if((data->set.maxredirs != -1) &&
        (data->set.followlocation >= data->set.maxredirs)) {
      failf(data,"Maximum (%d) redirects followed", data->set.maxredirs);
      return CURLE_TOO_MANY_REDIRECTS;
    }

    /* mark the next request as a followed location: */
    data->state.this_is_a_follow = TRUE;

    data->set.followlocation++; /* count location-followers */

    if(data->set.http_auto_referer) {