fix: properly encode empty buffer in base64 encoding (#131)

An empty buffer was encoded into `bundefined` instead of `b`
(reproduced on Chrome v108 / Ubuntu).

Co-authored-by: Mauricio Narvaez <nvz@fb.com>

lib/encodePacket.browser.ts

@@ -45,7 +45,7 @@ const encodeBlobAsBase64 = (
   const fileReader = new FileReader();
   fileReader.onload = function() {
     const content = (fileReader.result as string).split(",")[1];
-    callback("b" + content);
+    callback("b" + (content || ""));
   };
   return fileReader.readAsDataURL(data);
 };

test/browser.ts

@@ -97,6 +97,18 @@ describe("engine.io-parser (browser only)", () => {
           done();
         });
       });
+
+      it("should encode/decode a string + a 0-length ArrayBuffer payload", done => {
+        const packets: Packet[] = [
+          { type: "message", data: "test" },
+          { type: "message", data: createArrayBuffer([]) }
+        ];
+        encodePayload(packets, payload => {
+          expect(payload).to.eql("4test\x1eb");
+          expect(decodePayload(payload, "arraybuffer")).to.eql(packets);
+          done();
+        });
+      });
     }
   });
 });