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sync_writer.go

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package tools

import "io"

// closeFn is the type of func Close() in the io.Closer interface.

type closeFn func() error

// syncFn is the type of func Sync() in the *os.File implementation.

type syncFn func() error

// SyncWriter provides a wrapper around an io.Writer that synchronizes all

// write after they occur, if the underlying writer supports synchronization.

type SyncWriter struct {

w io.Writer

closeFn closeFn

syncFn syncFn

}

// NewSyncWriter returns a new instance of the *SyncWriter that sends all writes

// to the given io.Writer.

func NewSyncWriter(w io.Writer) *SyncWriter {

sw := &SyncWriter{

w: w,

}

if sync, ok := w.(interface {

Sync() error

}); ok {

sw.syncFn = sync.Sync

} else {

sw.syncFn = func() error { return nil }

}

if close, ok := w.(io.Closer); ok {

sw.closeFn = close.Close

} else {

sw.closeFn = func() error { return nil }

}

return sw

}

// Write will write to the file and perform a Sync() if writing succeeds.

func (w *SyncWriter) Write(b []byte) error {

if _, err := w.w.Write(b); err != nil {

return err

}

return w.syncFn()

}

// Close will call Close() on the underlying file

func (w *SyncWriter) Close() error {

return w.closeFn()

}