Bug 669938: nsIJSON::decodeFromStream fails for streams containing fewer than 4 bytes, r=jwalden

dom/src/json/nsJSON.cpp

@@ -545,9 +545,10 @@ nsJSONListener::OnStopRequest(nsIRequest *aRequest, nsISupports *aContext,
 {
   nsresult rv;
 
-  // This can happen with short UTF-8 messages
+  // This can happen with short UTF-8 messages (<4 bytes)
   if (!mSniffBuffer.IsEmpty()) {
-    rv = ProcessBytes(mSniffBuffer.get(), mSniffBuffer.Length());
+    // Just consume mSniffBuffer
+    rv = ProcessBytes(nsnull, 0);
     NS_ENSURE_SUCCESS(rv, rv);
   }
 
@@ -617,6 +618,9 @@ nsJSONListener::ProcessBytes(const char* aBuffer, PRUint32 aByteLength)
                    buffer[2] != 0x00 && buffer[3] != 0x00) {
           charset = "UTF-8";
         }
+      } else {
+        // Not enough bytes to sniff, assume UTF-8
+        charset = "UTF-8";
       }
     }
 
@@ -635,6 +639,9 @@ nsJSONListener::ProcessBytes(const char* aBuffer, PRUint32 aByteLength)
     mSniffBuffer.Truncate();
   }
 
+  if (!aBuffer)
+    return NS_OK;
+
   if (mNeedsConverter) {
     rv = ConsumeConverted(aBuffer, aByteLength);
   } else {

dom/src/json/test/unit/decodeFromStream-small.json

@@ -0,0 +1 @@
+{}

dom/src/json/test/unit/test_decodeFromStream.js

@@ -23,4 +23,7 @@ function run_test()
   var x = read_file("decodeFromStream-01.json");
   do_check_eq(x["JSON Test Pattern pass3"]["The outermost value"], "must be an object or array.");
   do_check_eq(x["JSON Test Pattern pass3"]["In this test"], "It is an object.");
+
+  x = read_file("decodeFromStream-small.json");
+  do_check_eq(x.toSource(), "({})", "empty object parsed");
 }