curl_setup: Disable by default recv-before-send in Windows

Prior to this change a workaround for Windows to recv before every send
was enabled by default. The way it works is a recv is called before
every send and saves the received data, in case send fails because in
Windows apparently that can wipe out the socket's internal received
data buffer.

This feature has led to several bugs because the way libcurl operates
it waits on a socket to read or to write, and may not at all times
check for buffered receive data.

Two recent significant bugs this workaround caused:
- Broken Schannel TLS 1.3 connections (curl#9431)
- HTTP/2 arbitrary hangs (curl#10253)

The actual code remains though it is disabled by default. Though future
changes to connection filter buffering could improve the situation IMO
it's just not tenable to manage this workaround.

Ref: curl#657
Ref: curl#668
Ref: curl#720

Ref: curl#9431
Ref: curl#10253

Closes curl#10409

lib/curl_setup.h

@@ -777,14 +777,16 @@ endings either CRLF or LF so 't' is appropriate.
 #define FOPEN_APPENDTEXT "a"
 #endif
 
-/* WinSock destroys recv() buffer when send() failed.
- * Enabled automatically for Windows and for Cygwin as Cygwin sockets are
- * wrappers for WinSock sockets. https://github.com/curl/curl/issues/657
- * Define DONT_USE_RECV_BEFORE_SEND_WORKAROUND to force disable workaround.
+/* Windows workaround to recv before every send, because apparently Winsock
+ * destroys destroys recv() buffer when send() failed.
+ * This workaround is now disabled by default since it caused hard to fix bugs.
+ * Define USE_RECV_BEFORE_SEND_WORKAROUND to enable it.
+ * https://github.com/curl/curl/issues/657
+ * https://github.com/curl/curl/pull/10409
  */
 #if !defined(DONT_USE_RECV_BEFORE_SEND_WORKAROUND)
 #  if defined(WIN32) || defined(__CYGWIN__)
-#    define USE_RECV_BEFORE_SEND_WORKAROUND
+/* #    define USE_RECV_BEFORE_SEND_WORKAROUND */
 #  endif
 #else  /* DONT_USE_RECV_BEFORE_SEND_WORKAROUND */
 #  ifdef USE_RECV_BEFORE_SEND_WORKAROUND

tests/data/test1517

@@ -9,7 +9,11 @@ early response
 </keywords>
 </info>
 #
-# This reproduces issue #657, fixed with PR #668 - on Windows
+# This test checks to make sure curl can call recv() without failing after a
+# send() fails on the same socket (#657). Most OSes should support this
+# natively but on Windows curl must be built with a workaround (#668) for the
+# test to succeed. The precheck will skip this test on Windows if curl was
+# built without the workaround (USE_RECV_BEFORE_SEND_WORKAROUND isn't defined).
 #
 # Server-side
 <reply>
@@ -39,6 +43,11 @@ http
 <tool>
 lib%TESTNUMBER
 </tool>
+# precheck is a command line to run before the test, to see if we can execute
+# the test or not
+<precheck>
+./libtest/lib%TESTNUMBER check
+</precheck>
 
  <name>
 HTTP POST, server responds before completed send

tests/libtest/lib1517.c

@@ -60,6 +60,16 @@ int test(char *URL)
 
   struct WriteThis pooh;
 
+  if(!strcmp(URL, "check")) {
+#if (defined(WIN32) || defined(__CYGWIN__)) && \
+    !defined(USE_RECV_BEFORE_SEND_WORKAROUND)
+    printf("test requires recv-before-send workaround on Windows\n");
+    return 1; /* skip since test will fail on Windows without workaround */
+#else
+    return 0; /* sure, run this! */
+#endif
+  }
+
   pooh.readptr = data;
   pooh.sizeleft = strlen(data);