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io: add WriteString support to MultiWriter
Fixes #11805 Change-Id: I081e16b869dc706bd847ee645bb902bc671c123f Reviewed-on: https://go-review.googlesource.com/12485 Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com> Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
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@ -52,6 +52,30 @@ func (t *multiWriter) Write(p []byte) (n int, err error) {
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return len(p), nil
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}
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var _ stringWriter = (*multiWriter)(nil)
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func (t *multiWriter) WriteString(s string) (n int, err error) {
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var p []byte // lazily initialized if/when needed
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for _, w := range t.writers {
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if sw, ok := w.(stringWriter); ok {
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n, err = sw.WriteString(s)
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} else {
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if p == nil {
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p = []byte(s)
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}
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n, err = w.Write(p)
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}
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if err != nil {
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return
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}
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if n != len(s) {
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err = ErrShortWrite
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return
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}
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}
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return len(s), nil
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}
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// MultiWriter creates a writer that duplicates its writes to all the
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// provided writers, similar to the Unix tee(1) command.
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func MultiWriter(writers ...Writer) Writer {
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@ -62,8 +62,59 @@ func TestMultiReader(t *testing.T) {
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}
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func TestMultiWriter(t *testing.T) {
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sha1 := sha1.New()
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sink := new(bytes.Buffer)
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// Hide bytes.Buffer's WriteString method:
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testMultiWriter(t, struct {
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Writer
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fmt.Stringer
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}{sink, sink})
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}
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func TestMultiWriter_String(t *testing.T) {
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testMultiWriter(t, new(bytes.Buffer))
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}
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// test that a multiWriter.WriteString calls results in at most 1 allocation,
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// even if multiple targets don't support WriteString.
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func TestMultiWriter_WriteStringSingleAlloc(t *testing.T) {
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var sink1, sink2 bytes.Buffer
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type simpleWriter struct { // hide bytes.Buffer's WriteString
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Writer
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}
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mw := MultiWriter(simpleWriter{&sink1}, simpleWriter{&sink2})
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allocs := int(testing.AllocsPerRun(1000, func() {
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WriteString(mw, "foo")
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}))
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if allocs != 1 {
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t.Errorf("num allocations = %d; want 1", allocs)
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}
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}
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type writeStringChecker struct{ called bool }
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func (c *writeStringChecker) WriteString(s string) (n int, err error) {
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c.called = true
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return len(s), nil
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}
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func (c *writeStringChecker) Write(p []byte) (n int, err error) {
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return len(p), nil
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}
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func TestMultiWriter_StringCheckCall(t *testing.T) {
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var c writeStringChecker
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mw := MultiWriter(&c)
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WriteString(mw, "foo")
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if !c.called {
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t.Error("did not see WriteString call to writeStringChecker")
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}
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}
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func testMultiWriter(t *testing.T, sink interface {
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Writer
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fmt.Stringer
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}) {
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sha1 := sha1.New()
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mw := MultiWriter(sha1, sink)
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sourceString := "My input text."
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