github.com/4ad/go@v0.0.0-20161219182952-69a12818b605/src/io/multi.go (about)

     1  // Copyright 2010 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package io
     6  
     7  type multiReader struct {
     8  	readers []Reader
     9  }
    10  
    11  func (mr *multiReader) Read(p []byte) (n int, err error) {
    12  	for len(mr.readers) > 0 {
    13  		// Optimization to flatten nested multiReaders (Issue 13558)
    14  		if len(mr.readers) == 1 {
    15  			if r, ok := mr.readers[0].(*multiReader); ok {
    16  				mr.readers = r.readers
    17  				continue
    18  			}
    19  		}
    20  		n, err = mr.readers[0].Read(p)
    21  		if err == EOF {
    22  			mr.readers = mr.readers[1:]
    23  		}
    24  		if n > 0 || err != EOF {
    25  			if err == EOF && len(mr.readers) > 0 {
    26  				// Don't return EOF yet. More readers remain.
    27  				err = nil
    28  			}
    29  			return
    30  		}
    31  	}
    32  	return 0, EOF
    33  }
    34  
    35  // MultiReader returns a Reader that's the logical concatenation of
    36  // the provided input readers. They're read sequentially. Once all
    37  // inputs have returned EOF, Read will return EOF.  If any of the readers
    38  // return a non-nil, non-EOF error, Read will return that error.
    39  func MultiReader(readers ...Reader) Reader {
    40  	r := make([]Reader, len(readers))
    41  	copy(r, readers)
    42  	return &multiReader{r}
    43  }
    44  
    45  type multiWriter struct {
    46  	writers []Writer
    47  }
    48  
    49  func (t *multiWriter) Write(p []byte) (n int, err error) {
    50  	for _, w := range t.writers {
    51  		n, err = w.Write(p)
    52  		if err != nil {
    53  			return
    54  		}
    55  		if n != len(p) {
    56  			err = ErrShortWrite
    57  			return
    58  		}
    59  	}
    60  	return len(p), nil
    61  }
    62  
    63  var _ stringWriter = (*multiWriter)(nil)
    64  
    65  func (t *multiWriter) WriteString(s string) (n int, err error) {
    66  	var p []byte // lazily initialized if/when needed
    67  	for _, w := range t.writers {
    68  		if sw, ok := w.(stringWriter); ok {
    69  			n, err = sw.WriteString(s)
    70  		} else {
    71  			if p == nil {
    72  				p = []byte(s)
    73  			}
    74  			n, err = w.Write(p)
    75  		}
    76  		if err != nil {
    77  			return
    78  		}
    79  		if n != len(s) {
    80  			err = ErrShortWrite
    81  			return
    82  		}
    83  	}
    84  	return len(s), nil
    85  }
    86  
    87  // MultiWriter creates a writer that duplicates its writes to all the
    88  // provided writers, similar to the Unix tee(1) command.
    89  func MultiWriter(writers ...Writer) Writer {
    90  	w := make([]Writer, len(writers))
    91  	copy(w, writers)
    92  	return &multiWriter{w}
    93  }