33 lines
762 B
Go
33 lines
762 B
Go
package main
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import "io"
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type prefixingWriter struct {
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prefix []byte
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writer io.Writer
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}
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func (pw *prefixingWriter) Write(p []byte) (int, error) {
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if len(p) == 0 {
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return 0, nil
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}
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// Perform an "atomic" write of a prefix and p to make sure that it doesn't interleave
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// sub-line when used concurrently with io.PipeWrite.
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n, err := pw.writer.Write(append(pw.prefix, p...))
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if n > len(p) {
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// To comply with the io.Writer interface requirements we must
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// return a number of bytes written from p (0 <= n <= len(p)),
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// so we are ignoring the length of the prefix here.
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return len(p), err
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}
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return n, err
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}
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func prefixWriter(prefix string, sink io.Writer) io.Writer {
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return &prefixingWriter{
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prefix: []byte(prefix),
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writer: sink,
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}
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}
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