Golang bytes.buffer

原文链接：https://www.kancloud.cn/digest/batu-go/153538

bytes.buffer是一个缓冲byte类型的缓冲器存放着都是byte
Buffer 是 bytes 包中的一个 type Buffer struct{…}

A buffer is a variable-sized buffer of bytes with Read and Write methods. The zero value for Buffer is an empty buffer ready to use.
（是一个变长的 buffer，具有 Read 和Write 方法。 Buffer 的 零值 是一个 空的 buffer，但是可以使用）
Buffer 就像一个集装箱容器，可以存东西，取东西（存取数据）

• 创建 一个 Buffer （其实底层就是一个 []byte， 字节切片）
• 向其中写入数据 (Write mtheods)
• 从其中读取数据 (Write methods)

创建 Buffer缓冲器

var b bytes.Buffer  //直接定义一个 Buffer 变量，而不用初始化
b.Writer([]byte("Hello ")) // 可以直接使用

b1 := new(bytes.Buffer)   //直接使用 new 初始化，可以直接使用
// 其它两种定义方式
func NewBuffer(buf []byte) *Buffer
func NewBufferString(s string) *Buffer

NewBuffer

// NewBuffer creates and initializes a new Buffer using buf as its initial
// contents.  It is intended to prepare a Buffer to read existing data.  It
// can also be used to size the internal buffer for writing. To do that,
// buf should have the desired capacity but a length of zero.
//
// In most cases, new(Buffer) (or just declaring a Buffer variable) is
// sufficient to initialize a Buffer.
func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} }

• NewBuffer使用buf作为参数初始化Buffer，
• Buffer既可以被读也可以被写
• 如果是读Buffer，buf需填充一定的数据
• 如果是写，buf需有一定的容量(capacity)，当然也可以通过new(Buffer)来初始化Buffer。另外一个方法NewBufferString用一个string来初始化可读Buffer，并用string的内容填充Buffer.

func IntToBytes(n int) []byte {
    x := int32(n)
    //创建一个内容是[]byte的slice的缓冲器
    //与bytes.NewBufferString("")等效
    bytesBuffer := bytes.NewBuffer([]byte{})
    binary.Write(bytesBuffer, binary.BigEndian, x)
    return bytesBuffer.Bytes()
}

NewBufferString

• 方法NewBufferString用一个string来初始化可读Buffer，并用string的内容填充Buffer.
• 用法和NewBuffer没有太大区别

// NewBufferString creates and initializes a new Buffer using string s as its
// initial contents. It is intended to prepare a buffer to read an existing
// string.
//
// In most cases, new(Buffer) (or just declaring a Buffer variable) is
// sufficient to initialize a Buffer.
func NewBufferString(s string) *Buffer {
    return &Buffer{buf: []byte(s)}
}

func TestBufferString(){
    buf1:=bytes.NewBufferString("swift")
    buf2:=bytes.NewBuffer([]byte("swift"))
    buf3:=bytes.NewBuffer([]byte{'s','w','i','f','t'})
    fmt.Println("===========以下buf1,buf2,buf3等效=========")
    fmt.Println("buf1:", buf1)
    fmt.Println("buf2:", buf2)
    fmt.Println("buf3:", buf3)
    fmt.Println("===========以下创建空的缓冲器等效=========")
    buf4:=bytes.NewBufferString("")
    buf5:=bytes.NewBuffer([]byte{})
    fmt.Println("buf4:", buf4)
    fmt.Println("buf5:", buf5)
}

输出：

===========以下buf1,buf2,buf3等效=========
buf1: swift
buf2: swift
buf3: swift
===========以下创建空的缓冲器等效=========
buf4:
buf5:

向 Buffer 中写入数据

Write

把字节切片 p 写入到buffer中去。

// Write appends the contents of p to the buffer, growing the buffer as
// needed. The return value n is the length of p; err is always nil. If the
// buffer becomes too large, Write will panic with ErrTooLarge.
func (b *Buffer) Write(p []byte) (n int, err error) {
    b.lastRead = opInvalid
    m := b.grow(len(p))
    return copy(b.buf[m:], p), nil
}

fmt.Println("===========以下通过Write把swift写入Learning缓冲器尾部=========")
    newBytes := []byte("swift")
    //创建一个内容Learning的缓冲器
    buf := bytes.NewBuffer([]byte("Learning"))
    //打印为Learning
    fmt.Println(buf.String())
    //将newBytes这个slice写到buf的尾部
    buf.Write(newBytes)
    fmt.Println(buf.String())

打印：

===========以下通过Write把swift写入Learning缓冲器尾部=========
Learning
Learningswift

WriteString

使用WriteString方法，将一个字符串放到缓冲器的尾部

// WriteString appends the contents of s to the buffer, growing the buffer as
// needed. The return value n is the length of s; err is always nil. If the
// buffer becomes too large, WriteString will panic with ErrTooLarge.
func (b *Buffer) WriteString(s string) (n int, err error) {
    b.lastRead = opInvalid
    m := b.grow(len(s))
    return copy(b.buf[m:], s), nil
}

    fmt.Println("===========以下通过WriteString把swift写入Learning缓冲器尾部=========")
    newString := "swift"
    //创建一个string内容Learning的缓冲器
    buf := bytes.NewBufferString("Learning")
    //打印为Learning
    fmt.Println(buf.String())
    //将newString这个string写到buf的尾部
    buf.WriteString(newString)
    fmt.Println(buf.String())

打印：

===========以下通过Write把swift写入Learning缓冲器尾部=========
Learning
Learningswift

WriteByte

将一个byte类型的数据放到缓冲器的尾部

// WriteByte appends the byte c to the buffer, growing the buffer as needed.
// The returned error is always nil, but is included to match bufio.Writer's
// WriteByte. If the buffer becomes too large, WriteByte will panic with
// ErrTooLarge.
func (b *Buffer) WriteByte(c byte) error {
    b.lastRead = opInvalid
    m := b.grow(1)
    b.buf[m] = c
    return nil
}

fmt.Println("===========以下通过WriteByte把!写入Learning缓冲器尾部=========")
    var newByte byte = '!'
    //创建一个string内容Learning的缓冲器
    buf := bytes.NewBufferString("Learning")
    //打印为Learning
    fmt.Println(buf.String())
    //将newString这个string写到buf的尾部
    buf.WriteByte(newByte)
    fmt.Println(buf.String())

打印：

===========以下通过WriteByte把swift写入Learning缓冲器尾部=========
Learning
Learning!

WriteRune

将一个rune类型的数据放到缓冲器的尾部

// WriteRune appends the UTF-8 encoding of Unicode code point r to the
// buffer, returning its length and an error, which is always nil but is
// included to match bufio.Writer's WriteRune. The buffer is grown as needed;
// if it becomes too large, WriteRune will panic with ErrTooLarge.
func (b *Buffer) WriteRune(r rune) (n int, err error) {
    if r < utf8.RuneSelf {
        b.WriteByte(byte(r))
        return 1, nil
    }
    n = utf8.EncodeRune(b.runeBytes[0:], r)
    b.Write(b.runeBytes[0:n])
    return n, nil
}

    fmt.Println("===========以下通过WriteRune把"好"写入Learning缓冲器尾部=========")
    var newRune = '好'
    //创建一个string内容Learning的缓冲器
    buf := bytes.NewBufferString("Learning")
    //打印为Learning
    fmt.Println(buf.String())
    //将newString这个string写到buf的尾部
    buf.WriteRune(newRune)
    fmt.Println(buf.String())

打印：

===========以下通过WriteRune把”好”写入Learning缓冲器尾部=========
Learning
Learning好

完整示例

package main

import (
    "bytes"
    "encoding/binary"
    "fmt"
)

func main() {
    //newBuffer 整形转换成字节
    var n int = 10000
    intToBytes := IntToBytes(n)
    fmt.Println("==========int to bytes========")
    fmt.Println(intToBytes)
    //NewBufferString
    TestBufferString()
    //write
    BufferWrite()
    //WriteString
    BufferWriteString()
    //WriteByte
    BufferWriteByte()
    //WriteRune
    BufferWriteRune()

}

func IntToBytes(n int) []byte {
    x := int32(n)
    //创建一个内容是[]byte的slice的缓冲器
    //与bytes.NewBufferString("")等效
    bytesBuffer := bytes.NewBuffer([]byte{})
    binary.Write(bytesBuffer, binary.BigEndian, x)
    return bytesBuffer.Bytes()
}

func TestBufferString(){
    buf1:=bytes.NewBufferString("swift")
    buf2:=bytes.NewBuffer([]byte("swift"))
    buf3:=bytes.NewBuffer([]byte{'s','w','i','f','t'})
    fmt.Println("===========以下buf1,buf2,buf3等效=========")
    fmt.Println("buf1:", buf1)
    fmt.Println("buf2:", buf2)
    fmt.Println("buf3:", buf3)
    fmt.Println("===========以下创建空的缓冲器等效=========")
    buf4:=bytes.NewBufferString("")
    buf5:=bytes.NewBuffer([]byte{})
    fmt.Println("buf4:", buf4)
    fmt.Println("buf5:", buf5)
}

func BufferWrite(){
    fmt.Println("===========以下通过Write把swift写入Learning缓冲器尾部=========")
    newBytes := []byte("swift")
    //创建一个内容Learning的缓冲器
    buf := bytes.NewBuffer([]byte("Learning"))
    //打印为Learning
    fmt.Println(buf.String())
    //将newBytes这个slice写到buf的尾部
    buf.Write(newBytes)
    fmt.Println(buf.String())
}

func BufferWriteString(){
    fmt.Println("===========以下通过Write把swift写入Learning缓冲器尾部=========")
    newString := "swift"
    //创建一个string内容Learning的缓冲器
    buf := bytes.NewBufferString("Learning")
    //打印为Learning
    fmt.Println(buf.String())
    //将newString这个string写到buf的尾部
    buf.WriteString(newString)
    fmt.Println(buf.String())
}

func BufferWriteByte(){
    fmt.Println("===========以下通过WriteByte把swift写入Learning缓冲器尾部=========")
    var newByte byte = '!'
    //创建一个string内容Learning的缓冲器
    buf := bytes.NewBufferString("Learning")
    //打印为Learning
    fmt.Println(buf.String())
    //将newString这个string写到buf的尾部
    buf.WriteByte(newByte)
    fmt.Println(buf.String())
}

func BufferWriteRune(){
    fmt.Println("===========以下通过WriteRune把"好"写入Learning缓冲器尾部=========")
    var newRune = '好'
    //创建一个string内容Learning的缓冲器
    buf := bytes.NewBufferString("Learning")
    //打印为Learning
    fmt.Println(buf.String())
    //将newString这个string写到buf的尾部
    buf.WriteRune(newRune)
    fmt.Println(buf.String())
}

向 Buffer 中读取数据

Read

给Read方法一个容器p，读完后，p就满了，缓冲器相应的减少了，返回的n为成功读的数量

// Read reads the next len(p) bytes from the buffer or until the buffer
// is drained.  The return value n is the number of bytes read.  If the
// buffer has no data to return, err is io.EOF (unless len(p) is zero);
// otherwise it is nil.
func (b *Buffer) Read(p []byte) (n int, err error) {}

func Read(){
    bufs := bytes.NewBufferString("Learning swift.")
    fmt.Println(bufs.String())

    //声明一个空的slice,容量为8
    l := make([]byte, 8)
    //把bufs的内容读入到l内,因为l容量为8,所以只读了8个过来
    bufs.Read(l)
    fmt.Println("::bufs缓冲器内容::")
    fmt.Println(bufs.String())
    //空的l被写入了8个字符,所以为 Learning
    fmt.Println("::l的slice内容::")
    fmt.Println(string(l))
    //把bufs的内容读入到l内,原来的l的内容被覆盖了
    bufs.Read(l)
    fmt.Println("::bufs缓冲器被第二次读取后剩余的内容::")
    fmt.Println(bufs.String())
    fmt.Println("::l的slice内容被覆盖,由于bufs只有7个了,因此最后一个g被留下来了::")
    fmt.Println(string(l))

}

打印：

=======Read=======
Learning swift.
::bufs缓冲器内容::
swift.
::l的slice内容::
Learning
::bufs缓冲器被第二次读取后剩余的内容::

::l的slice内容被覆盖::
swift.g

ReadByte

返回缓冲器头部的第一个byte，缓冲器头部第一个byte被拿掉

// ReadByte reads and returns the next byte from the buffer.
// If no byte is available, it returns error io.EOF.
func (b *Buffer) ReadByte() (c byte, err error) {}

func ReadByte(){
    bufs := bytes.NewBufferString("Learning swift.")
    fmt.Println(bufs.String())
    //读取第一个byte,赋值给b
    b, _ := bufs.ReadByte()
    fmt.Println(bufs.String())
    fmt.Println(string(b))
}

打印：

=======ReadByte===
Learning swift.
earning swift.
L

ReadRune

ReadRune和ReadByte很像
返回缓冲器头部的第一个rune，缓冲器头部第一个rune被拿掉

// ReadRune reads and returns the next UTF-8-encoded
// Unicode code point from the buffer.
// If no bytes are available, the error returned is io.EOF.
// If the bytes are an erroneous UTF-8 encoding, it
// consumes one byte and returns U+FFFD, 1.
func (b *Buffer) ReadRune() (r rune, size int, err error) {}

func ReadRune(){
    bufs := bytes.NewBufferString("学swift.")
    fmt.Println(bufs.String())

    //读取第一个rune,赋值给r
    r,z,_ := bufs.ReadRune()
    //打印中文"学",缓冲器头部第一个被拿走
    fmt.Println(bufs.String())
    //打印"学","学"作为utf8储存占3个byte
    fmt.Println("r=",string(r),",z=",z)

}

ReadBytes

ReadBytes需要一个byte作为分隔符，读的时候从缓冲器里找第一个出现的分隔符（delim），找到后，把从缓冲器头部开始到分隔符之间的所有byte进行返回，作为byte类型的slice，返回后，缓冲器也会空掉一部分

// ReadBytes reads until the first occurrence of delim in the input,
// returning a slice containing the data up to and including the delimiter.
// If ReadBytes encounters an error before finding a delimiter,
// it returns the data read before the error and the error itself (often io.EOF).
// ReadBytes returns err != nil if and only if the returned data does not end in
// delim.
func (b *Buffer) ReadBytes(delim byte) (line []byte, err error) {}

func ReadBytes(){
    bufs := bytes.NewBufferString("现在开始 Learning swift.")
    fmt.Println(bufs.String())

    var delim byte = 'L'
    line, _ := bufs.ReadBytes(delim)
    fmt.Println(bufs.String())
    fmt.Println(string(line))
}

打印：

=======ReadBytes==
现在开始 Learning swift.
earning swift.
现在开始 L

ReadString

ReadString需要一个byte作为分隔符，读的时候从缓冲器里找第一个出现的分隔符（delim），找到后，把从缓冲器头部开始到分隔符之间的所有byte进行返回，作为字符串，返回后，缓冲器也会空掉一部分
和ReadBytes类似

// ReadString reads until the first occurrence of delim in the input,
// returning a string containing the data up to and including the delimiter.
// If ReadString encounters an error before finding a delimiter,
// it returns the data read before the error and the error itself (often io.EOF).
// ReadString returns err != nil if and only if the returned data does not end
// in delim.
func (b *Buffer) ReadString(delim byte) (line string, err error) {}

ReadFrom

从一个实现io.Reader接口的r，把r里的内容读到缓冲器里，n返回读的数量

// ReadFrom reads data from r until EOF and appends it to the buffer, growing
// the buffer as needed. The return value n is the number of bytes read. Any
// error except io.EOF encountered during the read is also returned. If the
// buffer becomes too large, ReadFrom will panic with ErrTooLarge.
func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) {}

func ReadFrom(){
    //test.txt 内容是 "未来"
    file, _ := os.Open("learngo/bytes/text.txt")
    buf := bytes.NewBufferString("Learning swift.")
    buf.ReadFrom(file)              //将text.txt内容追加到缓冲器的尾部
    fmt.Println(buf.String())
}

打印：

=======ReadFrom===
Learning swift.未来

Reset

将数据清空，没有数据可读

// Reset resets the buffer so it has no content.
// b.Reset() is the same as b.Truncate(0).
func (b *Buffer) Reset() { b.Truncate(0) }

func Reset(){
    bufs := bytes.NewBufferString("现在开始 Learning swift.")
    fmt.Println(bufs.String())

    bufs.Reset()
    fmt.Println("::已经清空了bufs的缓冲内容::")
    fmt.Println(bufs.String())
}

打印：

=======Reset======
现在开始 Learning swift.
::已经清空了bufs的缓冲内容::

string

将未读取的数据返回成 string

// String returns the contents of the unread portion of the buffer
// as a string.  If the Buffer is a nil pointer, it returns "<nil>".
func (b *Buffer) String() string {}