Improve PNG decompression implementation

package.json

@@ -41,9 +41,10 @@
   "dependencies": {
     "@xmldom/xmldom": "^0.9.8",
     "bson": "^7.0.0",
+    "buffer": "^6.0.3",
     "cbor-js": "^0.1.0",
     "eventemitter3": "^5.0.1",
-    "pngparse": "^2.0.0",
+    "fast-png": "^7.0.1",
     "uuid": "^13.0.0",
     "ws": "^8.0.0"
   },

src/core/SocketAdapter.ts

@@ -11,6 +11,7 @@ import {
 } from "../types/protocol.js";
 import { deserialize } from "bson";
 import type { WebSocket as WsWebSocket } from "ws";
+import decompressPng from "../util/decompressPng.js";
 
 export type RequiredSocketInterface = Pick<
   WebSocket | RTCDataChannel | WsWebSocket,
@@ -157,27 +158,11 @@ export default class SocketAdapter {
     callback: (message: RosbridgeMessage) => void,
   ) {
     if (isRosbridgePngMessage(message)) {
-      const pngCallback = (data: unknown) => {
-        if (isRosbridgeMessage(data)) {
-          callback(data);
-        } else {
-          throw new Error("Decompressed PNG data was invalid!");
-        }
-      };
-      // If in Node.js..
-      if (typeof window === "undefined") {
-        import("../util/decompressPng.js")
-          .then(({ default: decompressPng }) => {
-            decompressPng(message.data, pngCallback);
-          })
-          .catch(console.error);
+      const decoded = decompressPng(message.data);
+      if (isRosbridgeMessage(decoded)) {
+        callback(decoded);
       } else {
-        // if in browser..
-        import("../util/shim/decompressPng.js")
-          .then(({ default: decompressPng }) => {
-            decompressPng(message.data, pngCallback);
-          })
-          .catch(console.error);
+        throw new Error("Received invalid message in PNG data!");
       }
     } else {
       callback(message);

src/util/decompressPng.ts

@@ -3,28 +3,34 @@
  * @author Ramon Wijnands - rayman747@hotmail.com
  */
 
-import pngparse from "pngparse";
+import { decode } from "fast-png";
+import { Buffer } from "buffer";
+
+const textDecoder = new TextDecoder();
 
 /**
  * If a message was compressed as a PNG image (a compression hack since
  * gzipping over WebSockets * is not supported yet), this function decodes
  * the "image" as a Base64 string.
  *
  * @param data - An object containing the PNG data.
- * @param callback - Function with the following params:
  */
-export default function decompressPng(
-  data: string,
-  callback: (data: unknown) => void,
-) {
+export default function decompressPng(data: string): unknown {
   const buffer = Buffer.from(data, "base64");
 
-  pngparse.parse(buffer, function (err, data) {
-    if (err || !(data instanceof Object) || !("data" in data)) {
-      throw new Error("Cannot process PNG encoded message ");
-    } else {
-      const jsonData = String(data.data);
-      callback(JSON.parse(jsonData));
-    }
-  });
+  const decoded = tryDecodeBuffer(buffer);
+
+  try {
+    return JSON.parse(textDecoder.decode(decoded.data));
+  } catch (error) {
+    throw new Error("Error parsing PNG JSON contents", { cause: error });
+  }
+}
+
+function tryDecodeBuffer(buffer: Buffer) {
+  try {
+    return decode(buffer);
+  } catch (error) {
+    throw new Error("Error decoding buffer", { cause: error });
+  }
 }

test/examples/topic-listener.example.ts

@@ -1,4 +1,4 @@
-import { describe, it, expect } from "vitest";
+import { describe, it, expect, vi } from "vitest";
 import * as ROSLIB from "../../src/RosLib.js";
 
 const ros = new ROSLIB.Ros({
@@ -45,4 +45,22 @@ describe("Topics Example", function () {
 
       topic.on("unsubscribe", done);
     }));
-}, 1000);
+
+  // TODO: reenable when rosbridge is fixed in ROS 2
+  it.skip("Listening to a PNG-compressed topic", async () => {
+    const topic = ros.Topic<{ data: string }>({
+      name: "/png_test",
+      messageType: "std_msgs/String",
+      compression: "png",
+    });
+    const callback = vi.fn();
+    topic.subscribe(callback);
+
+    topic.publish({ data: "some message that will be PNG-compressed" });
+    await vi.waitFor(() => {
+      expect(callback).toHaveBeenCalledWith({
+        data: "some message that will be PNG-compressed",
+      });
+    });
+  });
+});