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 } 36
