fix(engine.io-parser): respect binary view boundaries in browsers

packages/engine.io-parser/lib/decodePacket.browser.ts

@@ -66,7 +66,13 @@ const mapBinary = (data: any, binaryType?: BinaryType) => {
         return data;
       } else {
         // from WebTransport (Uint8Array)
-        return data.buffer;
+        return data.byteOffset === 0 &&
+          data.byteLength === data.buffer.byteLength
+          ? data.buffer
+          : data.buffer.slice(
+              data.byteOffset,
+              data.byteOffset + data.byteLength,
+            );
       }
   }
 };

packages/engine.io-parser/test/index.ts

@@ -14,6 +14,24 @@ import "./node"; // replaced by "./browser" for the tests in the browser (see "b
 
 describe("engine.io-parser", () => {
   describe("single packet", () => {
+    for (const [start, end] of [
+      [1, 3],
+      [0, 2],
+      [2, 2],
+      [0, 4],
+    ]) {
+      it(`should decode only the binary view bytes from ${start} to ${end}`, () => {
+        const bytes = Uint8Array.of(1, 2, 3, 4);
+        const view = bytes.subarray(start, end);
+        const decoded = decodePacket(view, "arraybuffer");
+
+        expect(decoded.type).to.eql("message");
+        expect(decoded.data).to.be.an(ArrayBuffer);
+        expect(areArraysEqual(decoded.data, view)).to.be(true);
+        expect(decoded.data.byteLength).to.eql(view.byteLength);
+      });
+    }
+
     it("should encode/decode a string", (done) => {
       const packet: Packet = { type: "message", data: "test" };
       encodePacket(packet, true, (encodedPacket) => {