1. const net = require('net'); 2. net.connect({port: 9999})
假如本机上没有监听9999端口，那么我们会获得以下输出。
1. events.js:170 2. throw er; // Unhandled 'error' event 3. ^ 4. 5. Error: connect ECONNREFUSED 127.0.0.1:9999 6. at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1088:14) 7. Emitted 'error' event at: 8. at emitErrorNT (internal/streams/destroy.js:91:8) 9. at emitErrorAndCloseNT (internal/streams/destroy.js:59:3) 10. at processTicksAndRejections (internal/process/task_queues.js:81:17)
我们简朴看一下connect的挪用流程。
1. const req = new TCPConnectWrap(); 2. req.oncomplete = afterConnect; 3. req.address = address; 4. req.port = port; 5. req.localAddress = localAddress; 6. req.localPort = localPort; 7. // 开始三次握手成立毗连 8. err = self._handle.connect(req, address, port);
接着我们看一下C++层connect的逻辑
1. err = req_wrap->Dispatch(uv_tcp_connect, 2. &wrap->handle_, 3. reinterpret_cast<const sockaddr*>(&addr), 4. AfterConnect);
C++层直接挪用Libuv的uv_tcp_connect，而且配置回调是AfterConnect。接着我们看libuv的实现。
1. do { 2. errno = 0; 3. // 非阻塞挪用 4. r = connect(uv__stream_fd(handle), addr, addrlen); 5. } while (r == -1 && errno == EINTR); 6. // 毗连错误，判定错误码 7. if (r == -1 && errno != 0) { 8. // 还在毗连中，不是错误，期待毗连完成，事件酿成可读 9. if (errno == EINPROGRESS) 10. ; /* not an error */ 11. else if (errno == ECONNREFUSED) 12. // 毗连被拒绝 13. handle->delayed_error = UV__ERR(ECONNREFUSED); 14. else 15. return UV__ERR(errno); 16. } 17. uv__req_init(handle->loop, req, UV_CONNECT); 18. req->cb = cb; 19. req->handle = (uv_stream_t*) handle; 20. QUEUE_INIT(&req->queue); 21. // 挂载到handle，期待可写事件 22. handle->connect_req = req; 23. uv__io_start(handle->loop, &handle->io_watcher, POLLOUT);
我们看到Libuv以异步的方法挪用操纵系统，然后把request挂载到handle中，而且注册期待可写事件，当毗连失败的时候，就会执行uv stream_io回调，我们看一下Libuv的处理惩罚（uv stream_io）。
1. getsockopt(uv__stream_fd(stream), 2. SOL_SOCKET, 3. SO_ERROR, 4. &error, 5. &errorsize); 6. error = UV__ERR(error); 7. if (req->cb) 8. req->cb(req, error);
获取错误信息后回调C++层的AfterConnect。
1. Local<Value> argv[5] = { 2. Integer::New(env->isolate(), status), 3. wrap->object(), 4. req_wrap->object(), 5. Boolean::New(env->isolate(), readable), 6. Boolean::New(env->isolate(), writable) 7. }; 8. 9. req_wrap->MakeCallback(env->oncomplete_string(), arraysize(argv), argv);
接着挪用JS层的oncomplete回调。
1. const ex = exceptionWithHostPort(status, 2. 'connect', 3. req.address, 4. req.port, 5. details); 6. if (details) { 7. ex.localAddress = req.localAddress; 8. ex.localPort = req.localPort; 9. } 10. // 销毁socket 11. self.destroy(ex);
exceptionWithHostPort结构错误信息，然后销毁socket而且以ex为参数触发error事件。我们看看uvExceptionWithHostPort的实现。
1. function uvExceptionWithHostPort(err, syscall, address, port) { 2. const [ code, uvmsg ] = uvErrmapGet(err) || uvUnmappedError; 3. const message = `${syscall} $[code]: ${uvmsg}`; 4. let details = ''; 5. 6. if (port && port > 0) { 7. details = ` ${address}:${port}`; 8. } else if (address) { 9. details = ` ${address}`; 10. } 11. const tmpLimit = Error.stackTraceLimit; 12. Error.stackTraceLimit = 0; 13. const ex = new Error(`${message}${details}`); 14. Error.stackTraceLimit = tmpLimit; 15. ex.code = code; 16. ex.errno = err; 17. ex.syscall = syscall; 18. ex.address = address; 19. if (port) { 20. ex.port = port; 21. } 22. // 获取挪用栈信息但不包罗当前挪用的函数uvExceptionWithHostPort，注入stack字段到ex中 23. Error.captureStackTrace(ex, excludedStackFn || uvExceptionWithHostPort); 24. return ex; 25. }
我们看到错误信息主要通过uvErrmapGet获取
1. function uvErrmapGet(name) { 2. uvBinding = lazyUv(); 3. if (!uvBinding.errmap) { 4. uvBinding.errmap = uvBinding.getErrorMap(); 5. } 6. return uvBinding.errmap.get(name); 7. } 8. 9. function lazyUv() { 10. if (!uvBinding) { 11. uvBinding = internalBinding('uv'); 12. } 13. return uvBinding; 14. }
继承往下看，uvErrmapGet挪用了C++层的uv模块的getErrorMap。
1. void GetErrMap(const FunctionCallbackInfo<Value>& args) { 2. Environment* env = Environment::GetCurrent(args); 3. Isolate* isolate = env->isolate(); 4. Local<Context> context = env->context(); 5. 6. Local<Map> err_map = Map::New(isolate); 7. // 从per_process::uv_errors_map中获取错误信息 8. size_t errors_len = arraysize(per_process::uv_errors_map); 9. // 赋值 10. for (size_t i = 0; i < errors_len; ++i) { 11. // map的键是 uv_errors_map每个元素中的value，值是name和message 12. const auto& error = per_process::uv_errors_map[i]; 13. Local<Value> arr[] = {OneByteString(isolate, error.name), 14. OneByteString(isolate, error.message)}; 15. if (err_map 16. ->Set(context, 17. Integer::New(isolate, error.value), 18. Array::New(isolate, arr, arraysize(arr))) 19. .IsEmpty()) { 20. return; 21. } 22. } 23. 24. args.GetReturnValue().Set(err_map); 25. }
我们看到错误信息存在per_process::uv_errors_map中，我们看一下uv_errors_map的界说。