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log_prefixer.go
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/
log_prefixer.go
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package service
import (
"bufio"
"bytes"
"fmt"
"io"
)
const prefixCommandMaxLen = 16
const prefixCutCommandSuffix = "..."
// LogPrefixer implements `io.writer` interface and adds prefix to each output line.
type LogPrefixer struct {
writer io.Writer
prefix []byte
}
// NewLogPrefixer initializes log prefixer.
func NewLogPrefixer(writer io.Writer, command string) *LogPrefixer {
logPrefixer := &LogPrefixer{writer: writer}
logPrefixer.prefix = logPrefixer.prefixForCommand(command)
return logPrefixer
}
func (p *LogPrefixer) Write(data []byte) (int, error) {
reader := bufio.NewReader(bytes.NewReader(data))
var line []byte
var err error
var bytesWritten int
for {
line, err = reader.ReadBytes('\n')
// There can be data to write in `line` even if `io.EOF` error is returned.
// Exit immediately only in case of unexpected error.
if err != nil && err != io.EOF {
return bytesWritten, err
}
if len(line) > 0 {
_, writeErr := p.writer.Write(p.prefix)
if writeErr != nil {
return bytesWritten, writeErr
}
n, writeErr := p.writer.Write(line)
bytesWritten += n
if writeErr != nil {
return bytesWritten, writeErr
}
}
if err == io.EOF {
break
}
}
return bytesWritten, nil
}
func (p *LogPrefixer) prefixForCommand(command string) []byte {
if len(command) > prefixCommandMaxLen {
command = command[:prefixCommandMaxLen]
command += prefixCutCommandSuffix
}
prefix := fmt.Sprintf("{%s} ", command)
return []byte(prefix)
}