On Mon, Aug 19, 2013 at 1:32 PM, Ivan Bazhenov <ivan.bazhe...@fastdev.se>wrote:
>         // register extensions
>         ExtensionRegistry registry = ExtensionRegistry.newInstance();
>         Foobar.registerAllExtensions(registry);
>         final DescriptorProtos.FileDescriptorSet fds =
>                 DescriptorProtos.FileDescriptorSet.parseFrom(new
> FileInputStream("foobar.desc"));
>         Descriptors.Descriptor descriptor =
>                 Descriptors.FileDescriptor.buildFrom(fds.getFile(0), new
> Descriptors.FileDescriptor[]{})
>                         .findMessageTypeByName("Msg");
        // build Msg from data using dynamically created descriptor
>         DynamicMessage dynamicMessage =
> DynamicMessage.parseFrom(descriptor, msgData, registry);
>         System.out.println("dynamically created descriptor: " +
> JsonFormat.printToString(dynamicMessage));
>         // build Msg from data using manually created descriptor
>         DynamicMessage dynamicMessage1 =
> DynamicMessage.parseFrom(Foobar.Msg.getDescriptor(), msgData, registry);
>         System.out.println("manually created descriptor: " +
> JsonFormat.printToString(dynamicMessage1));
> Result:
> dynamically created descriptor: {"foo": {"i": 123, "10001": [456],
> "10002": ["simpleName"]}}
> manually created descriptor: {"foo": {"i": 123,"Bar.j": 456,"Bar.name":
> "simpleName"}}
> So, dynamicMessage1 parsed correctly - it has fields "Bar.j" and
> "Bar.name" which were parsed as extensions.
> But dynamicMessage parsed incorrectly - those fields parsed as unknown
> fields and their names are equal to thier numbers - "10001" and "10002".

I ran into something similar and, IIRC, the problem here is that the parser
calls ExtensionRegistry.findExtensionByNumber(Descriptor containingType,
int fieldNumber) to locate possible extensions; this fails to find the
extension because containingType is the descriptor instance that was
recreated from the serialized form, but the extension registry contains the
precompiled descriptor instance which is a different instance.
ExtensionRegistry does the lookup by object identity, not by descriptor
equality or message name equality, so the extension is not found.

The workaround I ended up with was to have a map of message types that are
compiled into the receiver, and prefer to use that precompiled code rather
than DynamicMessage when a message is encountered that contains a
serialized descriptor that appears to match the local message definition.
It was sufficient for my purposes to just compare the message names, but
you might want a deeper comparison.


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