Add an InMemoryTransport

src/inMemory.ts

@@ -0,0 +1,54 @@
+import { Transport } from "./shared/transport.js";
+import { JSONRPCMessage } from "./types.js";
+
+/**
+ * In-memory transport for creating clients and servers that talk to each other within the same process.
+ */
+export class InMemoryTransport implements Transport {
+  private _otherTransport?: InMemoryTransport;
+  private _messageQueue: JSONRPCMessage[] = [];
+
+  onclose?: () => void;
+  onerror?: (error: Error) => void;
+  onmessage?: (message: JSONRPCMessage) => void;
+
+  /**
+   * Creates a pair of linked in-memory transports that can communicate with each other. One should be passed to a Client and one to a Server.
+   */
+  static createLinkedPair(): [InMemoryTransport, InMemoryTransport] {
+    const clientTransport = new InMemoryTransport();
+    const serverTransport = new InMemoryTransport();
+    clientTransport._otherTransport = serverTransport;
+    serverTransport._otherTransport = clientTransport;
+    return [clientTransport, serverTransport];
+  }
+
+  async start(): Promise<void> {
+    // Process any messages that were queued before start was called
+    while (this._messageQueue.length > 0) {
+      const message = this._messageQueue.shift();
+      if (message) {
+        this.onmessage?.(message);
+      }
+    }
+  }
+
+  async close(): Promise<void> {
+    const other = this._otherTransport;
+    this._otherTransport = undefined;
+    await other?.close();
+    this.onclose?.();
+  }
+
+  async send(message: JSONRPCMessage): Promise<void> {
+    if (!this._otherTransport) {
+      throw new Error("Not connected");
+    }
+
+    if (this._otherTransport.onmessage) {
+      this._otherTransport.onmessage(message);
+    } else {
+      this._otherTransport._messageQueue.push(message);
+    }
+  }
+}