59 lines
1.7 KiB
Go
59 lines
1.7 KiB
Go
// Copyright 2018 Google Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package teelogger provides loggers which send their output to multiple
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// writers, like the tee(1) command.
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package teelogger
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import (
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"io"
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"io/ioutil"
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"log"
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"os"
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)
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type nonBlockingWriter struct {
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W chan<- string
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}
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func (w *nonBlockingWriter) Write(p []byte) (n int, _ error) {
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select {
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// Intentionally convert from byte slice ([]byte) to string because sending
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// a byte slice over a channel is not safe: it may point to new contents,
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// resulting in duplicate log lines showing up.
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case w.W <- string(p):
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default:
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// channel unavailable, ignore
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}
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return len(p), nil
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}
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// NewConsole returns a logger which returns to /dev/console and
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// os.Stderr. Writes to /dev/console are non-blocking, i.e. messages will be
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// discarded if /dev/console stalls (e.g. when enabling Scroll Lock on a HDMI
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// console).
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func NewConsole() *log.Logger {
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w := ioutil.Discard
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if console, err := os.OpenFile("/dev/console", os.O_RDWR, 0600); err == nil {
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ch := make(chan string, 1)
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go func() {
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for buf := range ch {
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console.Write([]byte(buf))
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}
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}()
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w = &nonBlockingWriter{W: ch}
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}
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return log.New(io.MultiWriter(os.Stderr, w), "", log.LstdFlags|log.Lshortfile)
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}
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