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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multiWriteSyncerCombineWriteSyncers
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
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