48 lines
1.1 KiB
Go
48 lines
1.1 KiB
Go
// Package logonce implements an io.Writer facade that only performs distinct
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// writes. This can be used by log.Loggers as they're guaranteed to make a
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// single Write method call for each message. This is useful for loggers that
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// print useful information about unexpected conditions that aren't fatal in
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// code.
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package logonce
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import (
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"io"
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"log"
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"os"
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)
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// A default logger similar to the default logger in the log package.
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var Stderr *log.Logger
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func init() {
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// This should emulate the default logger in the log package where
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// possible. No time flag so that messages don't differ by time. Code
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// debug information is useful.
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Stderr = log.New(Writer(os.Stderr), "logonce: ", log.Lshortfile)
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}
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type writer struct {
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w io.Writer
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writes map[string]struct{}
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}
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func (w writer) Write(p []byte) (n int, err error) {
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s := string(p)
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if _, ok := w.writes[s]; ok {
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return
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}
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n, err = w.w.Write(p)
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if n != len(s) {
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s = string(p[:n])
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}
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w.writes[s] = struct{}{}
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return
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}
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func Writer(w io.Writer) io.Writer {
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return writer{
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w: w,
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writes: make(map[string]struct{}),
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}
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}
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