Fix closed enum parsing

packages/bundle-size/README.md

@@ -16,11 +16,11 @@ usually do. We repeat this for an increasing number of files.
 
 | code generator      | files | bundle size |  minified | compressed |
 | ------------------- | ----: | ----------: | --------: | ---------: |
-| Protobuf-ES         |     1 |   131,530 b |  68,233 b |   15,681 b |
-| Protobuf-ES         |     4 |   133,719 b |  69,743 b |   16,342 b |
-| Protobuf-ES         |     8 |   136,481 b |  71,514 b |   16,880 b |
-| Protobuf-ES         |    16 |   146,931 b |  79,495 b |   19,248 b |
-| Protobuf-ES         |    32 |   174,722 b | 101,511 b |   24,714 b |
+| Protobuf-ES         |     1 |   132,069 b |  68,479 b |   15,746 b |
+| Protobuf-ES         |     4 |   134,258 b |  69,989 b |   16,445 b |
+| Protobuf-ES         |     8 |   137,020 b |  71,760 b |   16,938 b |
+| Protobuf-ES         |    16 |   147,470 b |  79,741 b |   19,274 b |
+| Protobuf-ES         |    32 |   175,261 b | 101,759 b |   24,722 b |
 | protobuf-javascript |     1 |   104,048 b |  70,320 b |   15,540 b |
 | protobuf-javascript |     4 |   130,537 b |  85,672 b |   16,956 b |
 | protobuf-javascript |     8 |   152,429 b |  98,044 b |   18,138 b |

packages/protobuf-test/src/enum-open-closed.test.ts

@@ -0,0 +1,73 @@
+// Copyright 2021-2025 Buf Technologies, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import { describe, expect, test } from "@jest/globals";
+import { BinaryWriter, WireType } from "@bufbuild/protobuf/wire";
+import { fromBinary, isFieldSet } from "@bufbuild/protobuf";
+import * as proto3_ts from "./gen/ts/extra/proto3_pb.js";
+import * as proto2_ts from "./gen/ts/extra/proto2_pb.js";
+
+describe("open enum", () => {
+  test("from binary sets foreign value", () => {
+    expect(proto3_ts.Proto3EnumSchema.open).toBe(true);
+    const foreignValue = 4;
+    expect(proto3_ts.Proto3Enum[foreignValue]).toBeUndefined();
+    const bytes = new BinaryWriter()
+      .tag(
+        proto3_ts.Proto3MessageSchema.field.singularEnumField.number,
+        WireType.Varint,
+      )
+      .int32(foreignValue)
+      .finish();
+    const msg = fromBinary(proto3_ts.Proto3MessageSchema, bytes);
+    const set = isFieldSet(
+      msg,
+      proto3_ts.Proto3MessageSchema.field.singularEnumField,
+    );
+    expect(set).toBe(true);
+    expect(msg.singularEnumField).toBe(foreignValue);
+    expect(msg.$unknown).toBeUndefined();
+  });
+});
+
+describe("closed enum", () => {
+  test("from binary sets foreign value as unknown field", () => {
+    expect(proto2_ts.Proto2EnumSchema.open).toBe(false);
+    const foreignValue = 4;
+    expect(proto2_ts.Proto2Enum[foreignValue]).toBeUndefined();
+    const bytes = new BinaryWriter()
+      .tag(
+        proto2_ts.Proto2MessageSchema.field.optionalEnumField.number,
+        WireType.Varint,
+      )
+      .int32(foreignValue)
+      .finish();
+    const msg = fromBinary(proto2_ts.Proto2MessageSchema, bytes);
+    const set = isFieldSet(
+      msg,
+      proto2_ts.Proto2MessageSchema.field.optionalEnumField,
+    );
+    expect(set).toBe(false);
+    expect(msg.optionalEnumField).toBe(proto2_ts.Proto2Enum.YES);
+    expect(msg.$unknown).toBeDefined();
+    expect(msg.$unknown?.length).toBe(1);
+    expect(msg.$unknown?.[0].no).toBe(
+      proto2_ts.Proto2MessageSchema.field.optionalEnumField.number,
+    );
+    expect(msg.$unknown?.[0].wireType).toBe(WireType.Varint);
+    expect(msg.$unknown?.[0].data).toStrictEqual(
+      new BinaryWriter().int32(foreignValue).finish(),
+    );
+  });
+});

packages/protobuf/src/from-binary.ts

@@ -22,7 +22,11 @@ import type {
 import { scalarZeroValue } from "./reflect/scalar.js";
 import type { ScalarValue } from "./reflect/scalar.js";
 import { reflect } from "./reflect/reflect.js";
-import { BinaryReader, WireType } from "./wire/binary-encoding.js";
+import {
+  BinaryReader,
+  BinaryWriter,
+  WireType,
+} from "./wire/binary-encoding.js";
 
 /**
  * Options for parsing binary data.
@@ -151,7 +155,20 @@ export function readField(
       message.set(field, readScalar(reader, field.scalar));
       break;
     case "enum":
-      message.set(field, readScalar(reader, ScalarType.INT32) as number);
+      const val = readScalar(reader, ScalarType.INT32);
+      if (field.enum.open) {
+        message.set(field, val);
+      } else {
+        const ok = field.enum.values.some((v) => v.number === val);
+        if (ok) {
+          message.set(field, val);
+        } else if (options.readUnknownFields) {
+          const data = new BinaryWriter().int32(val as number).finish();
+          const unknownFields = message.getUnknown() ?? [];
+          unknownFields.push({ no: field.number, wireType, data });
+          message.setUnknown(unknownFields);
+        }
+      }
       break;
     case "message":
       message.set(