SSL_ForceHandshake should send the saved write data in the SSL socket.

net/third_party/nss/ssl/sslsecur.c

 /*
  * Various SSL functions.
  *
  * ***** BEGIN LICENSE BLOCK *****
  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
  *
  * The contents of this file are subject to the Mozilla Public License Version
  * 1.1 (the "License"); you may not use this file except in compliance with
  * the License. You may obtain a copy of the License at
  * http://www.mozilla.org/MPL/
@@ skipping 370 matching lines @@
     if (!ss) {
         SSL_DBG(("%d: SSL[%d]: bad socket in ForceHandshake",
                  SSL_GETPID(), fd));
         return rv;
     }
 
     /* Don't waste my time */
     if (!ss->opt.useSecurity) 
         return SECSuccess;
 
+    if (!ssl_SocketIsBlocking(ss)) {
+        ssl_GetXmitBufLock(ss);
+        if (ss->pendingBuf.len != 0) {
+            rv = ssl_SendSavedWriteData(ss);
+            if ((rv < 0) && (PORT_GetError() != PR_WOULD_BLOCK_ERROR)) {
+                ssl_ReleaseXmitBufLock(ss);
+                return SECFailure;
+            }
+        }
+        ssl_ReleaseXmitBufLock(ss);
+    }
+
     ssl_Get1stHandshakeLock(ss);
 
     if (ss->version >= SSL_LIBRARY_VERSION_3_0) {
         int gatherResult;
 
         ssl_GetRecvBufLock(ss);
         gatherResult = ssl3_GatherCompleteHandshake(ss, 0);
         ssl_ReleaseRecvBufLock(ss);
         if (gatherResult > 0) {
             rv = SECSuccess;
@@ skipping 720 matching lines @@
     }
 
     if (!ssl_SocketIsBlocking(ss) && !ss->opt.fdx) {
         ssl_GetXmitBufLock(ss);
         if (ss->pendingBuf.len != 0) {
             rv = ssl_SendSavedWriteData(ss);
             if ((rv < 0) && (PORT_GetError() != PR_WOULD_BLOCK_ERROR)) {
                 ssl_ReleaseXmitBufLock(ss);
                 return SECFailure;
             }
-            /* XXX short write? */
         }
         ssl_ReleaseXmitBufLock(ss);
     }
     
     rv = 0;
     /* If any of these is non-zero, the initial handshake is not done. */
     if (!ss->firstHsDone) {
         ssl_Get1stHandshakeLock(ss);
         if (ss->handshake || ss->nextHandshake || ss->securityHandshake) {
             rv = ssl_Do1stHandshake(ss);
@@ skipping 381 matching lines @@
     if (!ss) {
         SSL_DBG(("%d: SSL[%d]: bad socket in SNISocketConfigHook",
                  SSL_GETPID(), fd));
         return SECFailure;
     }
 
     ss->sniSocketConfig = func;
     ss->sniSocketConfigArg = arg;
     return SECSuccess;
 }