| // Copyright 2018 The gVisor Authors. |
| // |
| // 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" |
| |
| "gvisor.dev/gvisor/pkg/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 |
| } |