Harden message handling in the debugger agent

src/debug-agent.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 236 matching lines @@
         value = header_buffer + i + 1;
         while (*value == ' ') {
           value++;
         }
         break;
       }
     }
 
     // Check that key is Content-Length.
     if (strcmp(key, kContentLength) == 0) {
-      // Get the content length value if within a sensible range.
-      if (strlen(value) > 7) {
+      // Get the content length value if present and within a sensible range.
+      if (value == NULL || strlen(value) > 7) {
         return SmartPointer<char>();
       }
       for (int i = 0; value[i] != '\0'; i++) {
         // Bail out if illegal data.
         if (value[i] < '0' || value[i] > '9') {
           return SmartPointer<char>();
         }
         content_length = 10 * content_length + (value[i] - '0');
       }
     } else {
@@ skipping 140 matching lines @@
       return total_received;
     }
     total_received += received;
   }
   return total_received;
 }
 
 } }  // namespace v8::internal
 
 #endif  // ENABLE_DEBUGGER_SUPPORT