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fix(cursor): bound protobuf map entries #739

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fix(cursor): bound protobuf map entries #739

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13 changes: 6 additions & 7 deletions extensions/ai-providers/cursor/protobuf.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -447,13 +447,12 @@ function compileMapField(desc: MapFieldDesc): CompiledField {
decode(message, reader, wireType, _fieldNumber) {
assertWireType(wireType, 2);
const target = mapField(message, name);
const limit = reader.uint32();
const end = reader.pos + limit;
const entryReader = new Reader(reader.bytes());
let entryKey = "";
let entryValue: unknown = valCodec.defaultValue;

while (reader.pos < end) {
const tag = reader.uint32();
while (entryReader.pos < entryReader.len) {
const tag = entryReader.uint32();
const entryNumber = tag >>> 3;
const entryWireType = tag & 7;
if (!isWireType(entryWireType)) {
Expand All @@ -463,12 +462,12 @@ function compileMapField(desc: MapFieldDesc): CompiledField {
}
if (entryNumber === 1) {
assertWireType(entryWireType, key.wireType);
entryKey = requireString(key.decode(reader));
entryKey = requireString(key.decode(entryReader));
} else if (entryNumber === 2) {
assertWireType(entryWireType, valCodec.wireType);
entryValue = valCodec.decode(reader);
entryValue = valCodec.decode(entryReader);
} else {
reader.skip(entryWireType);
entryReader.skip(entryWireType);
}
}

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28 changes: 28 additions & 0 deletions tests/extensions/ai-providers/cursor-protobuf.test.ts
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Original file line number Diff line number Diff line change
@@ -0,0 +1,28 @@
import assert from "node:assert/strict";
import test from "node:test";
import {
pb,
type ProtoMessage,
} from "../../../extensions/ai-providers/cursor/protobuf.ts";

interface StringMapMessage extends ProtoMessage {
values: Record<string, string>;
}

const StringMap = pb<StringMapMessage>("test.StringMap", [
{ kind: "map", no: 1, name: "values", K: "string", V: "string" },
]);

test("protobuf maps do not decode beyond a declared entry boundary", () => {
const valid = Uint8Array.from([
0x0a, 0x0a, 0x0a, 0x03, 0x75, 0x72, 0x6c, 0x12, 0x03, 0x66, 0x6f, 0x6f,
]);
const malformed = Uint8Array.from(valid);
malformed[1] = 9;

assert.equal(StringMap.decode(valid).values.url, "foo");
assert.throws(
() => StringMap.decode(malformed),
/Unexpected EOF reading bytes/,
);
});
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