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Source file src/testing/iotest/reader.go

Documentation: testing/iotest

     1  // Copyright 2009 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 iotest implements Readers and Writers useful mainly for testing.
     6  package iotest
     7  
     8  import (
     9  	"errors"
    10  	"io"
    11  )
    12  
    13  // OneByteReader returns a Reader that implements
    14  // each non-empty Read by reading one byte from r.
    15  func OneByteReader(r io.Reader) io.Reader { return &oneByteReader{r} }
    16  
    17  type oneByteReader struct {
    18  	r io.Reader
    19  }
    20  
    21  func (r *oneByteReader) Read(p []byte) (int, error) {
    22  	if len(p) == 0 {
    23  		return 0, nil
    24  	}
    25  	return r.r.Read(p[0:1])
    26  }
    27  
    28  // HalfReader returns a Reader that implements Read
    29  // by reading half as many requested bytes from r.
    30  func HalfReader(r io.Reader) io.Reader { return &halfReader{r} }
    31  
    32  type halfReader struct {
    33  	r io.Reader
    34  }
    35  
    36  func (r *halfReader) Read(p []byte) (int, error) {
    37  	return r.r.Read(p[0 : (len(p)+1)/2])
    38  }
    39  
    40  // DataErrReader changes the way errors are handled by a Reader. Normally, a
    41  // Reader returns an error (typically EOF) from the first Read call after the
    42  // last piece of data is read. DataErrReader wraps a Reader and changes its
    43  // behavior so the final error is returned along with the final data, instead
    44  // of in the first call after the final data.
    45  func DataErrReader(r io.Reader) io.Reader { return &dataErrReader{r, nil, make([]byte, 1024)} }
    46  
    47  type dataErrReader struct {
    48  	r      io.Reader
    49  	unread []byte
    50  	data   []byte
    51  }
    52  
    53  func (r *dataErrReader) Read(p []byte) (n int, err error) {
    54  	// loop because first call needs two reads:
    55  	// one to get data and a second to look for an error.
    56  	for {
    57  		if len(r.unread) == 0 {
    58  			n1, err1 := r.r.Read(r.data)
    59  			r.unread = r.data[0:n1]
    60  			err = err1
    61  		}
    62  		if n > 0 || err != nil {
    63  			break
    64  		}
    65  		n = copy(p, r.unread)
    66  		r.unread = r.unread[n:]
    67  	}
    68  	return
    69  }
    70  
    71  var ErrTimeout = errors.New("timeout")
    72  
    73  // TimeoutReader returns ErrTimeout on the second read
    74  // with no data. Subsequent calls to read succeed.
    75  func TimeoutReader(r io.Reader) io.Reader { return &timeoutReader{r, 0} }
    76  
    77  type timeoutReader struct {
    78  	r     io.Reader
    79  	count int
    80  }
    81  
    82  func (r *timeoutReader) Read(p []byte) (int, error) {
    83  	r.count++
    84  	if r.count == 2 {
    85  		return 0, ErrTimeout
    86  	}
    87  	return r.r.Read(p)
    88  }
    89  

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