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task/internal/output/prefixed.go

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package output
import (
"bytes"
"fmt"
"io"
"strings"
)
type Prefixed struct{}
func (Prefixed) WrapWriter(w io.Writer, prefix string) io.Writer {
return &prefixWriter{writer: w, prefix: prefix}
}
type prefixWriter struct {
writer io.Writer
prefix string
buff bytes.Buffer
}
func (pw *prefixWriter) Write(p []byte) (int, error) {
n, err := pw.buff.Write(p)
if err != nil {
return n, err
}
return n, pw.writeOutputLines(false)
}
func (pw *prefixWriter) Close() error {
return pw.writeOutputLines(true)
}
func (pw *prefixWriter) writeOutputLines(force bool) error {
for {
switch line, err := pw.buff.ReadString('\n'); err {
case nil:
if err = pw.writeLine(line); err != nil {
return err
}
case io.EOF:
// if this line was not a complete line, re-add to the buffer
if !force && !strings.HasSuffix(line, "\n") {
_, err = pw.buff.WriteString(line)
return err
}
return pw.writeLine(line)
default:
return err
}
}
}
func (pw *prefixWriter) writeLine(line string) error {
if line == "" {
return nil
}
if !strings.HasSuffix(line, "\n") {
line += "\n"
}
_, err := fmt.Fprintf(pw.writer, "[%s] %s", pw.prefix, line)
return err
}