1 files changed, 78 insertions, 0 deletions
diff --git a/packages/lsp/src/rpc.test.ts b/packages/lsp/src/rpc.test.ts
new file mode 100644
index 0000000..a03870f
--- /dev/null
+++ b/packages/lsp/src/rpc.test.ts
@@ -0,0 +1,78 @@
+import { describe, expect, it } from "vitest";
+import { JsonRpcConnection } from "./rpc.js";
+
+function makeConnection(): { conn: JsonRpcConnection; messages: string[] } {
+	const messages: string[] = [];
+	const conn = new JsonRpcConnection((bytes) => {
+		const decoded = new TextDecoder().decode(bytes);
+		// Extract JSON from the LSP-framed message
+		const headerEnd = decoded.indexOf("\r\n\r\n");
+		if (headerEnd !== -1) {
+			messages.push(decoded.slice(headerEnd + 4));
+		}
+	});
+	return { conn, messages };
+}
+
+function frameResponse(id: number, result: unknown): string {
+	return JSON.stringify({ jsonrpc: "2.0", id, result });
+}
+
+describe("rpc", () => {
+	it("sendRequest resolves by matching id", async () => {
+		const { conn, messages } = makeConnection();
+
+		const promise = conn.sendRequest("test/method", { key: "value" });
+		expect(messages).toHaveLength(1);
+
+		const rawSent = messages[0];
+		if (rawSent === undefined) throw new Error("expected a sent message");
+		const sent = JSON.parse(rawSent);
+		expect(sent.method).toBe("test/method");
+		expect(sent.params).toEqual({ key: "value" });
+		expect(sent.id).toBe(1);
+
+		conn.handleMessage(frameResponse(1, { ok: true }));
+		const result = await promise;
+		expect(result).toEqual({ ok: true });
+	});
+
+	it("onNotification dispatches by method", () => {
+		const { conn } = makeConnection();
+		let received: unknown = null;
+		conn.onNotification("test/notify", (params) => {
+			received = params;
+		});
+
+		conn.handleMessage(
+			JSON.stringify({ jsonrpc: "2.0", method: "test/notify", params: { data: 42 } }),
+		);
+		expect(received).toEqual({ data: 42 });
+	});
+
+	it("onRequest replies to a server-to-client request", async () => {
+		const { conn, messages } = makeConnection();
+
+		conn.onRequest("workspace/configuration", (params) => {
+			const { items } = params as { readonly items: readonly { readonly section?: string }[] };
+			return items.map(() => ({ setting: true }));
+		});
+
+		await conn.handleMessage(
+			JSON.stringify({
+				jsonrpc: "2.0",
+				id: 100,
+				method: "workspace/configuration",
+				params: { items: [{ section: "test" }] },
+			}),
+		);
+
+		// The response should be sent back
+		expect(messages).toHaveLength(1);
+		const rawResponse = messages[0];
+		if (rawResponse === undefined) throw new Error("expected a response message");
+		const response = JSON.parse(rawResponse);
+		expect(response.id).toBe(100);
+		expect(response.result).toEqual([{ setting: true }]);
+	});
+});