Make string_util::WriteInto() DCHECK() that the supplied |length_with_null| > 1, meaning that the...

net/http/http_mac_signature.cc

Index: net/http/http_mac_signature.cc
===================================================================
--- net/http/http_mac_signature.cc	(revision 107404)
+++ net/http/http_mac_signature.cc	(working copy)
@@ -158,9 +158,12 @@
 
   std::string signature;
   size_t length = hmac.DigestLength();
-  char* buffer = WriteInto(&signature, length);
-  if (!hmac.Sign(request, reinterpret_cast<unsigned char*>(buffer),
-                 length)) {
+  DCHECK_GT(length, 0u);
+  if (!hmac.Sign(request,
+          // We need the + 1 here not because the call will write a trailing \0,
+          // but so that signature.length() is correctly set to |length|.
+          reinterpret_cast<unsigned char*>(WriteInto(&signature, length + 1)),
+          length)) {
     NOTREACHED();
     return false;
   }