Commonize on port-connected behavior for compressors and decompressors (part of the refactor for issue #44)

archive/common.js

@@ -0,0 +1,40 @@
+/**
+ * common.js
+ *
+ * Provides common functionality for compressing and decompressing.
+ *
+ * Licensed under the MIT License
+ *
+ * Copyright(c) 2023 Google Inc.
+ */
+
+// Requires the following JavaScript features: MessageChannel, MessagePort, and dynamic imports.
+
+/**
+ * Connects a host to a compress/decompress implementation via MessagePorts. The implementation must
+ * have an exported connect() function that accepts a MessagePort. If the runtime support Workers
+ * (e.g. web browsers, deno), imports the implementation inside a Web Worker. Otherwise, it
+ * dynamically imports the implementation inside the current JS context (node, bun).
+ * @param {string} implFilename The compressor/decompressor implementation filename relative to this
+ *     path (e.g. './unzip.js').
+ * @returns {Promise<MessagePort>} The Promise resolves to the MessagePort connected to the
+ *     implementation that the host should use.
+ */
+export async function getConnectedPort(implFilename) {
+  const messageChannel = new MessageChannel();
+  const hostPort = messageChannel.port1;
+  const implPort = messageChannel.port2;
+
+  if (typeof Worker === 'undefined') {
+    const implModule = await import(`${implFilename}`);
+    await implModule.connect(implPort);
+    return hostPort;
+  }
+  
+  return new Promise((resolve, reject) => {
+    const workerScriptPath = new URL(`./webworker-wrapper.js`, import.meta.url).href;
+    const worker = new Worker(workerScriptPath, { type: 'module' });
+    worker.postMessage({ implSrc: implFilename }, [implPort]);
+    resolve(hostPort);
+  });
+}