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