聊聊golang的zap的WriteSyncer

序

本文主要研究一下golang的zap的WriteSyncer

WriteSyncer

zap@v1.16.0/zapcore/write_syncer.go

type WriteSyncer interface {
    io.Writer
    Sync() error
}

WriteSyncer内嵌了io.Writer接口，定义了Sync方法

Writer

/usr/local/go/src/io/io.go

type Writer interface {
    Write(p []byte) (n int, err error)
}

Writer接口定义了Write方法

lockedWriteSyncer

zap@v1.16.0/zapcore/write_syncer.go

type lockedWriteSyncer struct {
    sync.Mutex
    ws WriteSyncer
}

func Lock(ws WriteSyncer) WriteSyncer {
    if _, ok := ws.(*lockedWriteSyncer); ok {
        // no need to layer on another lock
        return ws
    }
    return &lockedWriteSyncer{ws: ws}
}

func (s *lockedWriteSyncer) Write(bs []byte) (int, error) {
    s.Lock()
    n, err := s.ws.Write(bs)
    s.Unlock()
    return n, err
}

func (s *lockedWriteSyncer) Sync() error {
    s.Lock()
    err := s.ws.Sync()
    s.Unlock()
    return err
}

lockedWriteSyncer定义了sync.Mutex及WriteSyncer属性，它实现了WriteSyncer接口，它对Write和Sync方法都加了锁，内部委托的WriteSyncer；Lock方法用于创建lockedWriteSyncer

multiWriteSyncer

zap@v1.16.0/zapcore/write_syncer.go

type multiWriteSyncer []WriteSyncer

func NewMultiWriteSyncer(ws ...WriteSyncer) WriteSyncer {
    if len(ws) == 1 {
        return ws[0]
    }
    // Copy to protect against https://github.com/golang/go/issues/7809
    return multiWriteSyncer(append([]WriteSyncer(nil), ws...))
}

func (ws multiWriteSyncer) Write(p []byte) (int, error) {
    var writeErr error
    nWritten := 0
    for _, w := range ws {
        n, err := w.Write(p)
        writeErr = multierr.Append(writeErr, err)
        if nWritten == 0 && n != 0 {
            nWritten = n
        } else if n < nWritten {
            nWritten = n
        }
    }
    return nWritten, writeErr
}

func (ws multiWriteSyncer) Sync() error {
    var err error
    for _, w := range ws {
        err = multierr.Append(err, w.Sync())
    }
    return err
}

multiWriteSyncer为[]WriteSyncer类型，它实现了WriteSyncer接口，其Write方法会遍历multiWriteSyncer挨个执行其w.Write，然后会用multierr.Append(writeErr, err)来包装err；其Sync方法会遍历multiWriteSyncer，挨个执行w.Sync()，然后会用multierr.Append(writeErr, err)来包装err；NewMultiWriteSyncer方法用于创建multiWriteSyncer

CombineWriteSyncers

zap@v1.16.0/writer.go

func CombineWriteSyncers(writers ...zapcore.WriteSyncer) zapcore.WriteSyncer {
    if len(writers) == 0 {
        return zapcore.AddSync(ioutil.Discard)
    }
    return zapcore.Lock(zapcore.NewMultiWriteSyncer(writers...))
}

func Open(paths ...string) (zapcore.WriteSyncer, func(), error) {
    writers, close, err := open(paths)
    if err != nil {
        return nil, nil, err
    }

    writer := CombineWriteSyncers(writers...)
    return writer, close, nil
}

func open(paths []string) ([]zapcore.WriteSyncer, func(), error) {
    writers := make([]zapcore.WriteSyncer, 0, len(paths))
    closers := make([]io.Closer, 0, len(paths))
    close := func() {
        for _, c := range closers {
            c.Close()
        }
    }

    var openErr error
    for _, path := range paths {
        sink, err := newSink(path)
        if err != nil {
            openErr = multierr.Append(openErr, fmt.Errorf("couldn't open sink %q: %v", path, err))
            continue
        }
        writers = append(writers, sink)
        closers = append(closers, sink)
    }
    if openErr != nil {
        close()
        return writers, nil, openErr
    }

    return writers, close, nil
}

CombineWriteSyncers方法会先使用zapcore.NewMultiWriteSyncer(writers...)创建multiWriteSyncer，在通过Lock创建lockedWriteSyncer；Open方法根据paths创建zapcore.WriteSyncer，最后通过CombineWriteSyncers来创建带锁的multiWriteSyncer

Sink

zap@v1.16.0/sink.go

type Sink interface {
    zapcore.WriteSyncer
    io.Closer
}

Sink接口内嵌了zapcore.WriteSyncer及io.Closer接口

Closer

/usr/local/go/src/io/io.go

type Closer interface {
    Close() error
}

Closer接口定义了Close方法

nopCloserSink

type nopCloserSink struct{ zapcore.WriteSyncer }

func (nopCloserSink) Close() error { return nil }

nopCloserSink内嵌了zapcore.WriteSyncer，其Close方法为空操作

newSink

zap@v1.16.0/sink.go

var (
    _sinkMutex     sync.RWMutex
    _sinkFactories map[string]func(*url.URL) (Sink, error) // keyed by scheme
)

func init() {
    resetSinkRegistry()
}

func resetSinkRegistry() {
    _sinkMutex.Lock()
    defer _sinkMutex.Unlock()

    _sinkFactories = map[string]func(*url.URL) (Sink, error){
        schemeFile: newFileSink,
    }
}

func newSink(rawURL string) (Sink, error) {
    u, err := url.Parse(rawURL)
    if err != nil {
        return nil, fmt.Errorf("can't parse %q as a URL: %v", rawURL, err)
    }
    if u.Scheme == "" {
        u.Scheme = schemeFile
    }

    _sinkMutex.RLock()
    factory, ok := _sinkFactories[u.Scheme]
    _sinkMutex.RUnlock()
    if !ok {
        return nil, &errSinkNotFound{u.Scheme}
    }
    return factory(u)
}

newSink方法解析url，然后通过scheme找到对应的factory，调用factory创建Sink；_sinkFactories默认注册了newFileSink

newFileSink

zap@v1.16.0/sink.go

func newFileSink(u *url.URL) (Sink, error) {
    if u.User != nil {
        return nil, fmt.Errorf("user and password not allowed with file URLs: got %v", u)
    }
    if u.Fragment != "" {
        return nil, fmt.Errorf("fragments not allowed with file URLs: got %v", u)
    }
    if u.RawQuery != "" {
        return nil, fmt.Errorf("query parameters not allowed with file URLs: got %v", u)
    }
    // Error messages are better if we check hostname and port separately.
    if u.Port() != "" {
        return nil, fmt.Errorf("ports not allowed with file URLs: got %v", u)
    }
    if hn := u.Hostname(); hn != "" && hn != "localhost" {
        return nil, fmt.Errorf("file URLs must leave host empty or use localhost: got %v", u)
    }
    switch u.Path {
    case "stdout":
        return nopCloserSink{os.Stdout}, nil
    case "stderr":
        return nopCloserSink{os.Stderr}, nil
    }
    return os.OpenFile(u.Path, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0666)
}

newFileSink针对stdout创建nopCloserSink{os.Stdout}，针对stderr创建nopCloserSink{os.Stderr}，非以上两者则返回os.OpenFile(u.Path, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0666)；*os.File拥有Write、Sync、Close方法，实现了Sink接口

实例

func sinkDemo() {
    sink, cleanup, err := zap.Open("stdout", "/tmp/out1", "/tmp/out2")
    if err == nil {
        defer cleanup()
    }

    sink.Write([]byte("hello"))
    sink.Write([]byte("world"))
}

输出

helloworld

同时/tmp/out1，/tmp/out2也都有输出

小结

• WriteSyncer内嵌了io.Writer接口，定义了Sync方法；它有lockedWriteSyncer、multiWriteSyncer两个实现，同时CombineWriteSyncers创建是带lock的multiWriteSyncer
• Sink接口内嵌了zapcore.WriteSyncer及io.Closer接口；*os.File拥有Write、Sync、Close方法，实现了Sink接口；nopCloserSink内嵌了zapcore.WriteSyncer，其Close方法为空操作；FileSink则是基于文件的sink
• zap.Open先通过newSink创建fileSink的zapcore.WriteSyncer，再通过CombineWriteSyncers将这些fileSink包装为带锁的multiWriteSyncer

doc

• zap