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// Copyright 2018 Google Inc.
//
// 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.
// Package linewriter provides an io.Writer which calls an emitter on each line.
package linewriter
import (
"bytes"
"sync"
)
// Writer is an io.Writer which buffers input, flushing
// individual lines through an emitter function.
type Writer struct {
// the mutex locks buf.
sync.Mutex
// buf holds the data we haven't emitted yet.
buf bytes.Buffer
// emit is used to flush individual lines.
emit func(p []byte)
}
// NewWriter creates a Writer which emits using emitter.
// The emitter must not retain p. It may change after emitter returns.
func NewWriter(emitter func(p []byte)) *Writer {
return &Writer{emit: emitter}
}
// Write implements io.Writer.Write.
// It calls emit on each line of input, not including the newline.
// Write may be called concurrently.
func (w *Writer) Write(p []byte) (int, error) {
w.Lock()
defer w.Unlock()
total := 0
for len(p) > 0 {
emit := true
i := bytes.IndexByte(p, '\n')
if i < 0 {
// No newline, we will buffer everything.
i = len(p)
emit = false
}
n, err := w.buf.Write(p[:i])
if err != nil {
return total, err
}
total += n
p = p[i:]
if emit {
// Skip the newline, but still count it.
p = p[1:]
total++
w.emit(w.buf.Bytes())
w.buf.Reset()
}
}
return total, nil
}
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