The current WinSock API documentation for select() states:
"Any two of the parameters, readfds, writefds, or exceptfds, can be
given as null. At least one must be non-null, and any non-null
descriptor set must contain at least one handle to a socket."
http://msdn.microsoft.com/en-ca/library/windows/desktop/ms740141(v=vs.85).aspx
When using select(), cURL doesn't adhere to this (WinSock-specific)
rule, and can ask to monitor empty fd_sets, which leads to select()
returning WSAEINVAL (i.e. EINVAL) and connections failing in mysterious
ways as a result (at least when using the curl_multi_socket_action()
interface).
The attached patch (against 7.37.0) changes how select() is called when
USE_WINSOCK is defined to conform to the above rule.
--
Brad Spencer
--- curl-7.37.0/lib/select.c~ 2013-09-08 19:11:15 -0300
+++ curl-7.37.0/lib/select.c 2014-05-16 14:52:55 -0300
@@ -288,7 +288,37 @@
pending_tv.tv_sec = 0;
pending_tv.tv_usec = 0;
}
- r = select((int)maxfd + 1, &fds_read, &fds_write, &fds_err, ptimeout);
+
+ /* WinSock select() must not be called with an fd_set that contains zero
+ fd flags, or it will return WSAEINVAL. But, it also can't be called
+ with no fd_sets at all! From the documentation:
+
+ Any two of the parameters, readfds, writefds, or exceptfds, can be
+ given as null. At least one must be non-null, and any non-null
+ descriptor set must contain at least one handle to a socket.
+
+ We know that we have at least one bit set in at least two fd_sets in
+ this case, but we may have no bits set in either fds_read or fd_write,
+ so check for that and handle it. Luckily, with WinSock, we can _also_
+ ask how many bits are set on an fd_set.
+
+ It is unclear why WinSock doesn't just handle this for us instead of
+ calling this an error.
+
+ Note also that WinSock ignores the first argument, so we don't worry
+ about the fact that maxfd is computed incorrectly with WinSock (since
+ curl_socket_t is unsigned in such cases and thus -1 is the largest
+ value).
+ */
+ r = select((int)maxfd + 1,
+#ifndef USE_WINSOCK
+ &fds_read,
+ &fds_write,
+#else
+ fds_read.fd_count ? &fds_read : NULL,
+ fds_write.fd_count ? &fds_write : NULL,
+#endif
+ &fds_err, ptimeout);
if(r != -1)
break;
error = SOCKERRNO;
@@ -446,6 +471,16 @@
}
}
+#ifdef USE_WINSOCK
+ /* WinSock select() can't handle zero events. See the comment about this in
+ Curl_check_socket(). */
+ if(fds_read.fd_count == 0 && fds_write.fd_count == 0
+ && fds_err.fd_count == 0) {
+ r = Curl_wait_ms(timeout_ms);
+ return r;
+ }
+#endif
+
ptimeout = (timeout_ms < 0) ? NULL : &pending_tv;
do {
@@ -457,7 +492,19 @@
pending_tv.tv_sec = 0;
pending_tv.tv_usec = 0;
}
- r = select((int)maxfd + 1, &fds_read, &fds_write, &fds_err, ptimeout);
+ r = select((int)maxfd + 1,
+#ifndef USE_WINSOCK
+ &fds_read, &fds_write, &fds_err,
+#else
+ /* WinSock select() can't handle fd_sets with zero bits set, so
+ don't give it such arguments. See the comment about this in
+ Curl_check_socket().
+ */
+ fds_read.fd_count ? &fds_read : NULL,
+ fds_write.fd_count ? &fds_write : NULL,
+ fds_err.fd_count ? &fds_err : NULL,
+#endif
+ ptimeout);
if(r != -1)
break;
error = SOCKERRNO;
-------------------------------------------------------------------
List admin: http://cool.haxx.se/list/listinfo/curl-library
Etiquette: http://curl.haxx.se/mail/etiquette.html
