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// Copyright 2015-2016 Luke Shumaker
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//go:generate make
package sd_daemon
import (
"bytes"
"io"
"log/syslog"
"os"
"strings"
"sync"
)
// A Logger writes "<N>"-prefixed lines to an io.Writer, where N is a
// syslog priority number. It implements mostly the same interface as
// syslog.Writer.
//
// You probably don't need any instance of this other than the
// constant "Log", which uses os.Stderr as the writer. It is
// implemented as a struct rather than a set of functions so that it
// can be passed around as an implementation of an interface.
//
// Each logging operation makes a single call to the underlying
// Writer's Write method. A single logging operation may be multiple
// lines; each line will have the prefix, and they will all be written
// in the same Write. A Logger can be used simultaneously from
// multiple goroutines; it guarantees to serialize access to the
// Writer.
type Logger struct {
mu sync.Mutex
out io.Writer
buf []byte
}
// NewLogger creates a new Logger.
func NewLogger(w io.Writer) *Logger {
return &Logger{out: w}
}
// Log is a Logger whose interface is very similar to syslog.Writer,
// but writes to os.Stderr under the assumption that stderr is
// forwarded to syslog (or journald).
//
// You are encouraged to use stderr unless you have a good reason to
// talk to syslog or journald directly.
var Log = NewLogger(os.Stderr)
// Cheap version of
//
// *buf = append(*buf, fmt.Sprintf("<%d>", n)...)
func appendPrefix(buf []byte, n syslog.Priority) []byte {
var b [21]byte // 21 = (floor(log_10(2^63-1))+1) + len("<>")
b[len(b)-1] = '>'
i := len(b) - 2
for n >= 10 {
b[i] = byte('0' + n%10)
n = n / 10
i--
}
b[i] = byte('0' + n)
i--
b[i] = '<'
return append(buf, b[i:]...)
}
// WriteString writes a message with the specified priority to the
// log.
func (l *Logger) WriteString(pri syslog.Priority, msg string) (n int, err error) {
l.mu.Lock()
defer l.mu.Unlock()
msg = strings.TrimSuffix(msg, "\n")
// The following is a cheap version of:
//
// prefix := fmt.Sprintf("<%d>", pri)
// buf := prefix + strings.Replace(msg, "\n", "\n"+prefix, -1)
// return io.WriteString(l.out, buf)
l.buf = l.buf[:0]
l.buf = appendPrefix(l.buf, pri) // possible allocation
prefix := l.buf
nlines := strings.Count(msg, "\n") + 1
n = len(msg) + len(prefix)*nlines + 1
if cap(l.buf) < n {
l.buf = make([]byte, len(l.buf), n) // allocation
copy(l.buf, prefix)
}
for nlines > 1 {
nl := strings.IndexByte(msg, '\n')
l.buf = append(l.buf, msg[:nl+1]...)
l.buf = append(l.buf, prefix...)
msg = msg[nl+1:]
nlines--
}
l.buf = append(l.buf, msg...)
l.buf = append(l.buf, '\n')
return l.out.Write(l.buf)
}
// WriteString writes a message with the specified priority to the
// log.
func (l *Logger) WriteBytes(pri syslog.Priority, msg []byte) (n int, err error) {
// Copy/pasted from WriteString and
// * `strings.` -> `bytes.`
// * `"\n"` -> `[]byte{'\n'}`
l.mu.Lock()
defer l.mu.Unlock()
msg = bytes.TrimSuffix(msg, []byte{'\n'})
l.buf = l.buf[:0]
l.buf = appendPrefix(l.buf, pri) // possible allocation
prefix := l.buf
nlines := bytes.Count(msg, []byte{'\n'}) + 1
n = len(msg) + len(prefix)*nlines + 1
if cap(l.buf) < n {
l.buf = make([]byte, len(l.buf), n) // allocation
copy(l.buf, prefix)
}
for nlines > 1 {
nl := bytes.IndexByte(msg, '\n')
l.buf = append(l.buf, msg[:nl+1]...)
l.buf = append(l.buf, prefix...)
msg = msg[nl+1:]
nlines--
}
l.buf = append(l.buf, msg...)
l.buf = append(l.buf, '\n')
return l.out.Write(l.buf)
}
type loggerWriter struct {
log *Logger
pri syslog.Priority
}
func (lw loggerWriter) Write(p []byte) (n int, err error) {
return lw.log.WriteBytes(lw.pri, p)
}
// Writer returns an io.Writer that writes messages with the specified
// priority to the log.
func (l *Logger) Writer(pri syslog.Priority) io.Writer {
return loggerWriter{log: l, pri: pri}
}
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