深入解析golang bufio

bufio 包介绍

bufio包实现了有缓冲的I/O。它包装一个io.Reader或io.Writer接口对象，创建另一个也实现了该接口，且同时还提供了缓冲和一些文本I/O的帮助函数的对象。

golang bufio

bufio

WriteBufferSizeTransport.dialConn

	tr := &http.Transport{
		WriteBufferSize:     64 * 1024,
	}

	pconn.br = bufio.NewReaderSize(pconn, t.readBufferSize())
	pconn.bw = bufio.NewWriterSize(persistConnWriter{pconn}, t.writeBufferSize())

使用bufio进行写

bufio.NewWriterWriterbufio.NewWriterSizeWriter

Writerbufnwr

type Writer struct {
	err error
	buf []byte
	n   int
	wr  io.Writer
}

bufio.Writer

缓存中满数据
缓存中仍有空间
待写入的数据大于缓存的大小

缓存中满数据

当缓存中满数据时，会执行写操作。

缓存中仍有空间

Flush()

待写入的数据大于缓存的大小

由于此时缓存无法缓存足够的数据，此时会跳过缓存直接执行写操作

type Writer int
func (*Writer) Write(p []byte) (n int, err error) {
	fmt.Printf("Writing: %s\n", p)
	return len(p), nil
}
func main() {
	w := new(Writer)
	bw1 := bufio.NewWriterSize(w, 4)
	// Case 1: Writing to buffer until full
	bw1.Write([]byte{'1'})
	bw1.Write([]byte{'2'})
	bw1.Write([]byte{'3'})
	bw1.Write([]byte{'4'}) // write - buffer is full
	// Case 2: Buffer has space
    bw1.Write([]byte{'5'}) //此时buffer中无法容纳更多的数据，执行写操作，写入 []byte{'1','2','3','4'}
	err = bw1.Flush() // forcefully write remaining
	if err != nil {
		panic(err)
	}
	// Case 3: (too) large write for buffer
	// Will skip buffer and write directly
	bw1.Write([]byte("12345")) //buffer不足，直接执行写操作
//结果：
Writing: 1234
Writing: 5
Writing: 12345

缓存重用

ResetWritern

wr := new(Writer)
bw := bufio.NewWriterSize(wr,2) 
bw.Reset(wr)

获取缓存的可用空间数

Available()len(Writer.buf)-Writer.n

使用bufio进行读

WriterReaderNewReaderReaderNewReaderSizeReaderReaderr

type Reader struct {
	buf          []byte
	rd           io.Reader // reader provided by the client
	r, w         int       // buf read and write positions
	err          error
	lastByte     int // last byte read for UnreadByte; -1 means invalid
	lastRuneSize int // size of last rune read for UnreadRune; -1 means invalid
}

Peek

该方法会返回buf中的前n个字节的内容，但与Read操作不同的是，它不会消费缓存中的数据，即不会增加数据偏移量，因此通常也会用于判断是否读取结束(EOF)。通常有如下几种情况：

如果peak的值小于缓存大小，则返回相应的内容
如果peak的值大于缓存大小，则返回bufio.ErrBufferFull错误
如果peak的值包含EOF且小于缓存大小，则返回EOF

Read

pp

func (b *Reader) Read(p []byte) (n int, err error)

ReadSlice

delimdelimio.ErrBufferFull

func (b *Reader) ReadSlice(delim byte) (line []byte, err error)

delim','1234,

r := strings.NewReader("1234,567")
rb := bufio.NewReaderSize(r, 20)
fmt.Println(rb.ReadSlice(','))
// 结果：[49 50 51 52 44] <nil>

// Because the data returned from ReadSlice will be overwritten
// by the next I/O operation, most clients should use
// ReadBytes or ReadString instead.

ReadLine

ReadLine() (line []byte, isPrefix bool, err error)

ReadLineReadSlice\n\r\nio.ErrBufferFullisPrefixtrue

ReadBytes

ReadSlicedelimReadBytesio.EOF

func (b *Reader) ReadBytes(delim byte) ([]byte, error)

Scanner

scanner可以不断将数据读取到缓存(默认64*1024字节)。

    rb := strings.NewReader("12345678901234567890")
	scanner := bufio.NewScanner(rb)
	for scanner.Scan() {
		fmt.Printf("Token (Scanner): %q\n", scanner.Text())
	}
	// 结果：Token (Scanner): "12345678901234567890"

参考

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