protobuf-gwt

A version of the protobuf-java that is modified to be GWT/J2CL compatible. Presently only supports binary encoding, with a focus on CodedInputStream and CodedOutputStream, and a handful of tools that protoc output requires. Not all generated protoc output will be supported automatically.

Makes use of standard OpenRewrite rules, some rules specifically written to simplify projects for GWT, and some custom rules just for protobuf-gwt.

There appears to be a bug in JDT that we don't have a rewrite rule for yet, so there is a workaround in a manual patch made to this project.

Presently only binary format is supported.

Contrast with https://github.com/google/j2cl-protobuf, which is archived and unmaintained, was J2CL only, and only supported the text format.

Usage

Add com.vertispan.protobuf:protobuf-gwt to your project dependencies. The version will be based on the protobuf-java build being used, with an integer suffix to allow for packaging changes. For example, current released versions:

protobuf-java	protobuf-gwt	Description
3.25.4	3.25.4-1	Initial release, with an internal copy of StaticImpls rather than shared
3.25.4	3.25.4-2	Corrected License to correctly follow protobuf-java's instead of relicensing

Building

The modified protobuf-java sources are checked in to the project both to allow us to more easily see differences over the stock classes, and to allow for manual modifications as needed.

A fresh build will try to download the original sources, so will be missing the manual modifications - revert changes or apply them manually as needed.

CI builds set -Dmdep.skip=true instead of otherwise keeping the old target/ dir or reverting changes.

Manual changes

diff --git a/protobuf-gwt/src/main/java/com/google/protobuf/GeneratedMessageLite.java b/protobuf-gwt/src/main/java/com/google/protobuf/GeneratedMessageLite.java
index df2842a..a7a4fcb 100644
--- a/protobuf-gwt/src/main/java/com/google/protobuf/GeneratedMessageLite.java
+++ b/protobuf-gwt/src/main/java/com/google/protobuf/GeneratedMessageLite.java
@@ -964,7 +964,7 @@ public abstract class GeneratedMessageLite<
 
     protected void copyOnWriteInternal() {
       super.copyOnWriteInternal();
-      if (instance.extensions != FieldSet.emptySet()) {
+      if (instance.extensions != FieldSet.<ExtensionDescriptor>emptySet()) {
         instance.extensions = instance.extensions.clone();
       }
     }
diff --git a/protobuf-gwt/src/main/java/com/google/protobuf/GeneratedMessageV3.java b/protobuf-gwt/src/main/java/com/google/protobuf/GeneratedMessageV3.java
index 019a1ac..b23f833 100644
--- a/protobuf-gwt/src/main/java/com/google/protobuf/GeneratedMessageV3.java
+++ b/protobuf-gwt/src/main/java/com/google/protobuf/GeneratedMessageV3.java
@@ -1328,7 +1328,7 @@ public abstract class GeneratedMessageV3 extends AbstractMessage implements Seri
      */
     private FieldSet<FieldDescriptor> buildExtensions() {
       return extensions == null
-          ? (FieldSet<FieldDescriptor>) FieldSet.emptySet()
+          ? (FieldSet<FieldDescriptor>) FieldSet.<FieldDescriptor>emptySet()
           : extensions.buildPartial();
     }
 

License

The protobuf-gwt project is BSD-3 licensed, in keeping with the protobuf-java license. See the protobuf-java/LICENSE file for details.

The rest of the project is Apache 2.0 licensed at this time, though not yet distributed through Maven Central.