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 (
   8         "io"
   9         "os"
  10 )
  11
  12 // TruncateWriter returns a Writer that writes to w
  13 // but stops silently after n bytes.
  14 func TruncateWriter(w io.Writer, n int64) io.Writer {
  15         return &truncateWriter{w, n}
  16 }
  17
  18 type truncateWriter struct {
  19         w io.Writer
  20         n int64
  21 }
  22
  23 func (t *truncateWriter) Write(p []byte) (n int, err os.Error) {
  24         if t.n <= 0 {
  25                 return len(p), nil
  26         }
  27         // real write
  28         n = len(p)
  29         if int64(n) > t.n {
  30                 n = int(t.n)
  31         }
  32         n, err = t.w.Write(p[0:n])
  33         t.n -= int64(n)
  34         if err == nil {
  35                 n = len(p)
  36         }
  37         return
  38 }