function spawnDlvDapServerProcess()

in src/goDebugFactory.ts [479:599]
94 lines of code
23 McCabe index (conditional complexity)

function spawnDlvDapServerProcess(
	launchAttachArgs: vscode.DebugConfiguration,
	host: string,
	port: number,
	log: (msg: string) => void,
	logErr: (msg: string) => void,
	logConsole: (msg: string) => void
): Promise<ChildProcess> {
	const { dlvArgs, dlvPath, dir, env } = getSpawnConfig(launchAttachArgs, logErr);
	// env does not include process.env. Construct the new env for process spawning
	// by combining process.env.
	const envForSpawn = env ? Object.assign({}, process.env, env) : undefined;

	dlvArgs.push(`--listen=${host}:${port}`);

	const onWindows = process.platform === 'win32';

	if (!onWindows) {
		dlvArgs.push('--log-dest=3');
	}

	const logDest = launchAttachArgs.logDest;
	if (typeof logDest === 'number') {
		logErr(`Using a file descriptor for 'logDest' (${logDest}) is not allowed.\n`);
		throw new Error('Using a file descriptor for `logDest` is not allowed.');
	}
	if (logDest && !path.isAbsolute(logDest)) {
		logErr(
			`Using a relative path for 'logDest' (${logDest}) is not allowed.\nSee https://code.visualstudio.com/docs/editor/variables-reference if you want workspace-relative path.\n`
		);
		throw new Error('Using a relative path for `logDest` is not allowed');
	}
	if (logDest && onWindows) {
		logErr(
			'Using `logDest` or `--log-dest` is not supported on windows yet. See https://github.com/golang/vscode-go/issues/1472.'
		);
		throw new Error('Using `logDest` on windows is not allowed');
	}

	const logDestStream = logDest ? fs.createWriteStream(logDest) : undefined;

	logConsole(`Starting: ${dlvPath} ${dlvArgs.join(' ')} from ${dir}\n`);

	// TODO(hyangah): In module-module workspace mode, the program should be build in the super module directory
	// where go.work (gopls.mod) file is present. Where dlv runs determines the build directory currently. Two options:
	//  1) launch dlv in the super-module module directory and adjust launchArgs.cwd (--wd).
	//  2) introduce a new buildDir launch attribute.
	return new Promise<ChildProcess>((resolve, reject) => {
		const p = spawn(dlvPath, dlvArgs, {
			cwd: dir,
			env: envForSpawn,
			stdio: onWindows ? ['pipe', 'pipe', 'pipe'] : ['pipe', 'pipe', 'pipe', 'pipe'] // --log-dest=3 if !onWindows.
		});
		let started = false;
		const timeoutToken: NodeJS.Timer = setTimeout(() => {
			logConsole(`Delve DAP server (PID: ${p.pid}) is not responding`);
			reject(new Error('timed out while waiting for DAP server to start'));
		}, 30_000);

		const stopWaitingForServerToStart = () => {
			clearTimeout(timeoutToken);
			started = true;
			resolve(p);
		};

		p.stdout.on('data', (chunk) => {
			const msg = chunk.toString();
			if (!started && msg.startsWith('DAP server listening at:')) {
				stopWaitingForServerToStart();
			}
			log(msg);
		});
		p.stderr.on('data', (chunk) => {
			logErr(chunk.toString());
		});
		p.stdio[3]?.on('data', (chunk) => {
			const msg = chunk.toString();
			if (!started && msg.startsWith('DAP server listening at:')) {
				stopWaitingForServerToStart();
			}
			if (logDestStream) {
				// always false on windows.
				// write to the specified file.
				logDestStream?.write(chunk, (err) => {
					if (err) {
						logConsole(`Error writing to ${logDest}: ${err}, log may be incomplete.`);
					}
				});
			} else {
				logConsole(msg);
			}
		});
		p.stdio[3]?.on('close', () => {
			// always false on windows.
			logDestStream?.end();
		});

		p.on('close', (code, signal) => {
			// TODO: should we watch 'exit' instead?

			// NOTE: log messages here may not appear in DEBUG CONSOLE if the termination of
			// the process was triggered by debug adapter's dispose when dlv dap doesn't
			// respond to disconnect on time. In that case, it's possible that the session
			// is in the middle of teardown and DEBUG CONSOLE isn't accessible. Check
			// Go Debug output channel.
			if (typeof code === 'number') {
				// The process exited on its own.
				logConsole(`dlv dap (${p.pid}) exited with code: ${code}\n`);
			} else if (code === null && signal) {
				logConsole(`dlv dap (${p.pid}) was killed by signal: ${signal}\n`);
			} else {
				logConsole(`dlv dap (${p.pid}) terminated with code: ${code} signal: ${signal}\n`);
			}
		});
		p.on('error', (err) => {
			if (err) {
				logConsole(`Error: ${err}\n`);
			}
		});
	});
}