1 files changed, 132 insertions, 0 deletions
diff --git a/packages/lsp/src/rpc.ts b/packages/lsp/src/rpc.ts
new file mode 100644
index 0000000..45adf42
--- /dev/null
+++ b/packages/lsp/src/rpc.ts
@@ -0,0 +1,132 @@
+/**
+ * JSON-RPC connection over an injected write function.
+ *
+ * Provides sendRequest (correlated by id), sendNotification, onRequest,
+ * and onNotification. The caller feeds decoded JSON messages via `handleMessage`.
+ */
+
+import { encode } from "./framing.js";
+
+export type WriteFn = (bytes: Uint8Array) => void;
+
+export interface PendingRequest {
+	readonly resolve: (value: unknown) => void;
+	readonly reject: (reason: unknown) => void;
+}
+
+export type RequestHandler = (params: unknown) => unknown | Promise<unknown>;
+export type NotificationHandler = (params: unknown) => void;
+
+export interface JsonRpcMessage {
+	readonly jsonrpc: "2.0";
+	readonly id?: number | string | undefined;
+	readonly method?: string | undefined;
+	readonly params?: unknown;
+	readonly result?: unknown;
+	readonly error?:
+		| { readonly code: number; readonly message: string; readonly data?: unknown }
+		| undefined;
+}
+
+export class JsonRpcConnection {
+	private nextId = 1;
+	private pending = new Map<number | string, PendingRequest>();
+	private requestHandlers = new Map<string, RequestHandler>();
+	private notificationHandlers = new Map<string, NotificationHandler>();
+	private write: WriteFn;
+
+	constructor(write: WriteFn) {
+		this.write = write;
+	}
+
+	sendRequest(method: string, params?: unknown): Promise<unknown> {
+		const id = this.nextId++;
+		const msg: JsonRpcMessage = { jsonrpc: "2.0", id, method, params };
+		return new Promise((resolve, reject) => {
+			this.pending.set(id, { resolve, reject });
+			this.sendMessage(msg);
+		});
+	}
+
+	sendNotification(method: string, params?: unknown): void {
+		const msg: JsonRpcMessage = { jsonrpc: "2.0", method, params };
+		this.sendMessage(msg);
+	}
+
+	onRequest(method: string, handler: RequestHandler): void {
+		this.requestHandlers.set(method, handler);
+	}
+
+	onNotification(method: string, handler: NotificationHandler): void {
+		this.notificationHandlers.set(method, handler);
+	}
+
+	async handleMessage(json: string): Promise<void> {
+		const msg = JSON.parse(json) as JsonRpcMessage;
+		const { id, method } = msg;
+
+		if (id !== undefined && method !== undefined) {
+			await this.handleIncomingRequest(id, method, msg.params);
+		} else if (method !== undefined) {
+			this.handleIncomingNotification(method, msg.params);
+		} else if (id !== undefined) {
+			this.handleResponse(id, msg);
+		}
+	}
+
+	private sendMessage(msg: JsonRpcMessage): void {
+		this.write(encode(JSON.stringify(msg)));
+	}
+
+	private handleResponse(id: number | string, msg: JsonRpcMessage): void {
+		const entry = this.pending.get(id);
+		if (!entry) return;
+		this.pending.delete(id);
+		if (msg.error) {
+			entry.reject(new Error(msg.error.message));
+		} else {
+			entry.resolve(msg.result);
+		}
+	}
+
+	private async handleIncomingRequest(
+		id: number | string,
+		method: string,
+		params: unknown,
+	): Promise<void> {
+		const handler = this.requestHandlers.get(method);
+		if (!handler) {
+			this.sendMessage({
+				jsonrpc: "2.0",
+				id,
+				error: { code: -32601, message: `Method not found: ${method}` },
+			});
+			return;
+		}
+		try {
+			const result = await handler(params);
+			this.sendMessage({ jsonrpc: "2.0", id, result });
+		} catch (err: unknown) {
+			const message = err instanceof Error ? err.message : String(err);
+			this.sendMessage({
+				jsonrpc: "2.0",
+				id,
+				error: { code: -32603, message },
+			});
+		}
+	}
+
+	private handleIncomingNotification(method: string, params: unknown): void {
+		const handler = this.notificationHandlers.get(method);
+		if (handler) {
+			handler(params);
+		}
+	}
+
+	dispose(): void {
+		for (const entry of this.pending.values()) {
+			entry.reject(new Error("Connection closed"));
+		}
+		this.pending.clear();
+	}
+}