Bun adapter for csharp-ls to work with Claude Code LSP (fixes workDoneProgress/registerCapability issues)

csharp-ls

#!/usr/bin/env bun
/**
 * LSP Adapter for csharp-ls
 *
 * Proxies LSP messages between Claude Code and csharp-ls,
 * handling unsupported methods that crash csharp-ls.
 *
 * Intercepts (responds with null to csharp-ls, doesn't forward to Claude):
 * - window/workDoneProgress/create -> progress token creation
 * - window/workDoneProgress/cancel -> progress cancellation
 * - client/registerCapability -> dynamic capability registration
 *
 * Passes through (Claude Code handles these):
 * - workspace/configuration -> Claude Code returns config
 * - Everything else
 */

import { spawn } from "bun";
import { dirname, join } from "path";

const DEBUG = process.env.LSP_ADAPTER_DEBUG === "1";

// Find the original csharp-ls binary (sibling to this script)
const SCRIPT_DIR = dirname(Bun.main);
const CSHARP_LS_ORIGINAL = join(SCRIPT_DIR, "csharp-ls-original");

function log(...args: any[]) {
	if (DEBUG) {
		console.error("[ADAPTER]", ...args);
	}
}

// LSP Message parser state
class LspParser {
	private buffer = Buffer.alloc(0);
	private contentLength = -1;

	parse(chunk: Buffer): Array<{ header: string; body: any }> {
		this.buffer = Buffer.concat([this.buffer, chunk]);
		const messages: Array<{ header: string; body: any }> = [];

		while (true) {
			if (this.contentLength === -1) {
				// Looking for Content-Length header
				const headerEnd = this.buffer.indexOf("\r\n\r\n");
				if (headerEnd === -1) break;

				const header = this.buffer.subarray(0, headerEnd).toString();
				const match = header.match(/Content-Length:\s*(\d+)/i);
				if (!match) {
					log("Invalid header:", header);
					break;
				}

				this.contentLength = parseInt(match[1], 10);
				this.buffer = this.buffer.subarray(headerEnd + 4);
			}

			if (this.buffer.length < this.contentLength) break;

			const bodyStr = this.buffer.subarray(0, this.contentLength).toString();
			this.buffer = this.buffer.subarray(this.contentLength);
			this.contentLength = -1;

			try {
				const body = JSON.parse(bodyStr);
				messages.push({
					header: `Content-Length: ${bodyStr.length}\r\n\r\n`,
					body
				});
			} catch (e) {
				log("Failed to parse JSON:", bodyStr);
			}
		}

		return messages;
	}
}

function encodeMessage(body: any): Buffer {
	const content = JSON.stringify(body);
	const header = `Content-Length: ${Buffer.byteLength(content)}\r\n\r\n`;
	return Buffer.from(header + content);
}

// Methods we intercept and handle ourselves (respond with null, don't forward to Claude)
const INTERCEPTED_METHODS = new Set([
	"window/workDoneProgress/create",
	"window/workDoneProgress/cancel",
	"client/registerCapability",
]);

async function main() {
	log("Starting csharp-ls adapter...");

	// Spawn the real csharp-ls (original binary renamed, sibling to this script)
	const csharpLs = spawn([CSHARP_LS_ORIGINAL], {
		stdin: "pipe",
		stdout: "pipe",
		stderr: "inherit",
	});

	log("Spawned csharp-ls, pid:", csharpLs.pid);

	const clientParser = new LspParser(); // Claude Code -> Adapter
	const serverParser = new LspParser(); // csharp-ls -> Adapter

	// Pending requests from server that we need to respond to
	const pendingServerRequests = new Map<number | string, string>();

	// Forward stdin (from Claude Code) to csharp-ls
	(async () => {
		const reader = Bun.stdin.stream().getReader();
		while (true) {
			const { done, value } = await reader.read();
			if (done) {
				log("Client stdin closed");
				csharpLs.stdin.end();
				break;
			}

			const messages = clientParser.parse(Buffer.from(value));
			for (const msg of messages) {
				log("CLIENT ->", msg.body.method || msg.body.id);
				// Pass all client messages through unchanged
				csharpLs.stdin.write(encodeMessage(msg.body));
			}

			if (messages.length === 0 && value.length > 0) {
				// Partial message, buffer is handling it
			}
		}
	})();

	// Forward stdout (from csharp-ls) to Claude Code, intercepting specific methods
	(async () => {
		const reader = csharpLs.stdout.getReader();
		while (true) {
			const { done, value } = await reader.read();
			if (done) {
				log("Server stdout closed");
				break;
			}

			const messages = serverParser.parse(Buffer.from(value));
			for (const msg of messages) {
				const { body } = msg;

				// Check if this is a request we should intercept
				if (body.method && INTERCEPTED_METHODS.has(body.method)) {
					log("INTERCEPT <-", body.method, "id:", body.id);

					// Send success response back to csharp-ls
					if (body.id !== undefined) {
						const response = {
							jsonrpc: "2.0",
							id: body.id,
							result: null
						};
						csharpLs.stdin.write(encodeMessage(response));
						log("INTERCEPT ->", "response for", body.method);
					}
					// Don't forward to client
					continue;
				}

				log("SERVER ->", body.method || `response:${body.id}`);
				// Forward to Claude Code
				process.stdout.write(encodeMessage(body));
			}
		}
	})();

	// Handle process termination
	process.on("SIGINT", () => {
		log("SIGINT received, killing csharp-ls");
		csharpLs.kill();
		process.exit(0);
	});

	process.on("SIGTERM", () => {
		log("SIGTERM received, killing csharp-ls");
		csharpLs.kill();
		process.exit(0);
	});

	// Wait for csharp-ls to exit
	const exitCode = await csharpLs.exited;
	log("csharp-ls exited with code:", exitCode);
	process.exit(exitCode);
}

main().catch((err) => {
	console.error("[ADAPTER] Fatal error:", err);
	process.exit(1);
});