libgo/go/testing/iotest/writer.go

   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
   6
   7 import "io"
   8
   9 // TruncateWriter returns a Writer that writes to w
  10 // but stops silently after n bytes.
  11 func TruncateWriter(w io.Writer, n int64) io.Writer {
  12         return &truncateWriter{w, n}
  13 }
  14
  15 type truncateWriter struct {
  16         w io.Writer
  17         n int64
  18 }
  19
  20 func (t *truncateWriter) Write(p []byte) (n int, err error) {
  21         if t.n <= 0 {
  22                 return len(p), nil
  23         }
  24         // real write
  25         n = len(p)
  26         if int64(n) > t.n {
  27                 n = int(t.n)
  28         }
  29         n, err = t.w.Write(p[0:n])
  30         t.n -= int64(n)
  31         if err == nil {
  32                 n = len(p)
  33         }
  34         return
  35 }