[boost] [system] patch for access violation on FormatMessage failure

From: David Deakins (ddeakins_at_[hidden])
Date: 2007-11-02 14:31:21

I ran across a case this morning where the FormatMessage Win32 call in 
boost::system_error_category::message() fails (the error message table 
did not have an entry for the error code that was passed). 
Unfortunately, when this happens lpMsgBuf is not initialized to anything 
and trying to use it can result in an access violation.  The attached 
patch adds checks to catch situations where FormatMessage fails.

Thanks,
-Dave

Index: error_code.cpp
===================================================================
--- error_code.cpp	(revision 40686)
+++ error_code.cpp	(working copy)
@@ -347,7 +347,7 @@
   {
 # ifndef BOOST_NO_ANSI_APIS  
     LPVOID lpMsgBuf;
-    ::FormatMessageA( 
+    DWORD retval = ::FormatMessageA( 
         FORMAT_MESSAGE_ALLOCATE_BUFFER | 
         FORMAT_MESSAGE_FROM_SYSTEM | 
         FORMAT_MESSAGE_IGNORE_INSERTS,
@@ -358,11 +358,14 @@
         0,
         NULL 
     );
+    if (retval == 0)
+        return std::string();
+        
     std::string str( static_cast<LPCSTR>(lpMsgBuf) );
     ::LocalFree( lpMsgBuf ); // free the buffer
 # else  // WinCE workaround
     LPVOID lpMsgBuf;
-    ::FormatMessageW( 
+    DWORD retval = ::FormatMessageW( 
         FORMAT_MESSAGE_ALLOCATE_BUFFER | 
         FORMAT_MESSAGE_FROM_SYSTEM | 
         FORMAT_MESSAGE_IGNORE_INSERTS,
@@ -373,10 +376,13 @@
         0,
         NULL 
     );
+    if (retval == 0)
+        return std::string();
     
     int num_chars = (wcslen( static_cast<LPCWSTR>(lpMsgBuf) ) + 1) * 2;
     LPSTR narrow_buffer = (LPSTR)_alloca( num_chars );
-    ::WideCharToMultiByte(CP_ACP, 0, static_cast<LPCWSTR>(lpMsgBuf), -1, narrow_buffer, num_chars, NULL, NULL);
+    if (::WideCharToMultiByte(CP_ACP, 0, static_cast<LPCWSTR>(lpMsgBuf), -1, narrow_buffer, num_chars, NULL, NULL) == 0)
+        return std::string();
 
     std::string str( narrow_buffer );
     ::LocalFree( lpMsgBuf ); // free the buffer