curl_easy_pause: on unpause, trigger mulit-socket handling

When the multi-socket API is used, we need the handle to be checked
again when it gets unpaused.

Bug: http://curl.haxx.se/mail/lib-2013-07/0239.html
Reported-by: Justin Karneges

docs/libcurl/curl_easy_pause.3

@@ -5,7 +5,7 @@
 .\" *                            | (__| |_| |  _ <| |___
 .\" *                             \___|\___/|_| \_\_____|
 .\" *
-.\" * Copyright (C) 1998 - 2011, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" * Copyright (C) 1998 - 2013, Daniel Stenberg, <daniel@haxx.se>, et al.
 .\" *
 .\" * This software is licensed as described in the file COPYING, which
 .\" * you should have received as part of this distribution. The terms
@@ -68,6 +68,18 @@ code means something wrong occurred after the new state was set.  See the
 .SH AVAILABILITY
 This function was added in libcurl 7.18.0. Before this version, there was no
 explicit support for pausing transfers.
+.SH "USAGE WITH THE MULTI-SOCKET INTERFACE"
+Before libcurl 7.32.0, when a specific handle was unpaused with this function,
+there was no particular forced rechecking or similar of the socket's state,
+which made the continuation of the transfer get delayed until next
+multi-socket call invoke or even longer. Alternatively, the user could
+forcibly call for example curl_multi_socket_all(3) - with a rather hefty
+performance penalty.
+
+Starting in libcurl 7.32.0, unpausing a transfer will schedule a timeout
+trigger for that handle 1 millisecond into the future, so that a
+curl_multi_socket_action( ... CURL_SOCKET_TIMEOUT) can be used immediately
+afterwards to get the transfer going again as desired.
 .SH "MEMORY USE"
 When pausing a read by returning the magic return code from a write callback,
 the read data is already in libcurl's internal buffers so it'll have to keep

lib/easy.c

@@ -854,6 +854,13 @@ CURLcode curl_easy_pause(CURL *curl, int action)
     free(freewrite); /* this is unconditionally no longer used */
   }
 
+  /* if there's no error and we're not pausing both directions, we want
+     to have this handle checked soon */
+  if(!result &&
+     ((newstate&(KEEP_RECV_PAUSE|KEEP_SEND_PAUSE)) !=
+      (KEEP_RECV_PAUSE|KEEP_SEND_PAUSE)) )
+    Curl_expire(data, 1); /* get this handle going again */
+
   return result;
 }