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Source file src/io/multi.go

  // Copyright 2010 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package io
  
  type eofReader struct{}
  
  func (eofReader) Read([]byte) (int, error) {
  	return 0, EOF
  }
  
  type multiReader struct {
  	readers []Reader
  }
  
  func (mr *multiReader) Read(p []byte) (n int, err error) {
  	for len(mr.readers) > 0 {
  		// Optimization to flatten nested multiReaders (Issue 13558).
  		if len(mr.readers) == 1 {
  			if r, ok := mr.readers[0].(*multiReader); ok {
  				mr.readers = r.readers
  				continue
  			}
  		}
  		n, err = mr.readers[0].Read(p)
  		if err == EOF {
  			// Use eofReader instead of nil to avoid nil panic
  			// after performing flatten (Issue 18232).
  			mr.readers[0] = eofReader{} // permit earlier GC
  			mr.readers = mr.readers[1:]
  		}
  		if n > 0 || err != EOF {
  			if err == EOF && len(mr.readers) > 0 {
  				// Don't return EOF yet. More readers remain.
  				err = nil
  			}
  			return
  		}
  	}
  	return 0, EOF
  }
  
  // MultiReader returns a Reader that's the logical concatenation of
  // the provided input readers. They're read sequentially. Once all
  // inputs have returned EOF, Read will return EOF.  If any of the readers
  // return a non-nil, non-EOF error, Read will return that error.
  func MultiReader(readers ...Reader) Reader {
  	r := make([]Reader, len(readers))
  	copy(r, readers)
  	return &multiReader{r}
  }
  
  type multiWriter struct {
  	writers []Writer
  }
  
  func (t *multiWriter) Write(p []byte) (n int, err error) {
  	for _, w := range t.writers {
  		n, err = w.Write(p)
  		if err != nil {
  			return
  		}
  		if n != len(p) {
  			err = ErrShortWrite
  			return
  		}
  	}
  	return len(p), nil
  }
  
  var _ stringWriter = (*multiWriter)(nil)
  
  func (t *multiWriter) WriteString(s string) (n int, err error) {
  	var p []byte // lazily initialized if/when needed
  	for _, w := range t.writers {
  		if sw, ok := w.(stringWriter); ok {
  			n, err = sw.WriteString(s)
  		} else {
  			if p == nil {
  				p = []byte(s)
  			}
  			n, err = w.Write(p)
  		}
  		if err != nil {
  			return
  		}
  		if n != len(s) {
  			err = ErrShortWrite
  			return
  		}
  	}
  	return len(s), nil
  }
  
  // MultiWriter creates a writer that duplicates its writes to all the
  // provided writers, similar to the Unix tee(1) command.
  func MultiWriter(writers ...Writer) Writer {
  	w := make([]Writer, len(writers))
  	copy(w, writers)
  	return &multiWriter{w}
  }
  

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