# package zlib
`import "compress/zlib"`
zlib包實現了對zlib格式壓縮數據的讀寫,參見[RFC 1950](http://tools.ietf.org/html/rfc1950)。
本包的實現提供了在讀取時解壓和寫入時壓縮的濾鏡。例如,將壓縮數據寫入一個bytes.Buffer:
```
var b bytes.Buffer
w := zlib.NewWriter(&b)
w.Write([]byte("hello, world\n"))
w.Close()
```
然后將數據讀取回來:
```
r, err := zlib.NewReader(&b)
io.Copy(os.Stdout, r)
r.Close()
```
## Index
* [Constants](#pkg-constants)
* [Variables](#pkg-variables)
* [func NewReader(r io.Reader) (io.ReadCloser, error)](#NewReader)
* [func NewReaderDict(r io.Reader, dict []byte) (io.ReadCloser, error)](#NewReaderDict)
* [type Writer](#Writer)
* [func NewWriter(w io.Writer) \*Writer](#NewWriter)
* [func NewWriterLevel(w io.Writer, level int) (\*Writer, error)](#NewWriterLevel)
* [func NewWriterLevelDict(w io.Writer, level int, dict []byte) (\*Writer, error)](#NewWriterLevelDict)
* [func (z \*Writer) Close() error](#Writer.Close)
* [func (z \*Writer) Flush() error](#Writer.Flush)
* [func (z \*Writer) Reset(w io.Writer)](#Writer.Reset)
* [func (z \*Writer) Write(p []byte) (n int, err error)](#Writer.Write)
### Examples
* [NewReader](#example-NewReader)
* [NewWriter](#example-NewWriter)
## Constants
```
const (
NoCompression = flate.NoCompression
BestSpeed = flate.BestSpeed
BestCompression = flate.BestCompression
DefaultCompression = flate.DefaultCompression
)
```
這些常量都是拷貝自flate包,因此導入"compress/zlib"后,就不必再導入"compress/flate"了。
## Variables
```
var (
// 當讀取的zlib數據的校驗和錯誤時,會返回ErrChecksum
ErrChecksum = errors.New("zlib: invalid checksum")
// 當讀取的zlib數據的目錄錯誤時,會返回ErrDictionary
ErrDictionary = errors.New("zlib: invalid dictionary")
// 當讀取的zlib數據的頭域錯誤時,會返回ErrHeader
ErrHeader = errors.New("zlib: invalid header")
)
```
## func [NewReader](https://github.com/golang/go/blob/master/src/compress/zlib/reader.go#L58 "View Source")
```
func NewReader(r io.Reader) (io.ReadCloser, error)
```
NewReader返回一個從r讀取并解壓數據的io.ReadCloser。其實現會緩沖輸入流的數據,并可能從r中讀取比需要的更多的數據。調用者有責任在讀取完畢后調用返回值的Close方法。
Example
```
buff := []byte{120, 156, 202, 72, 205, 201, 201, 215, 81, 40, 207,
47, 202, 73, 225, 2, 4, 0, 0, 255, 255, 33, 231, 4, 147}
b := bytes.NewReader(buff)
r, err := zlib.NewReader(b)
if err != nil {
panic(err)
}
io.Copy(os.Stdout, r)
```
Output:
```
hello, world
```
## func [NewReaderDict](https://github.com/golang/go/blob/master/src/compress/zlib/reader.go#L64 "View Source")
```
func NewReaderDict(r io.Reader, dict []byte) (io.ReadCloser, error)
```
NewReaderDict類似NewReader,但會使用預設的字典初始化返回的Reader。
如果壓縮數據沒有采用字典,本函數會忽略該參數。
## type [Writer](https://github.com/golang/go/blob/master/src/compress/zlib/writer.go#L26 "View Source")
```
type Writer struct {
// 內含隱藏或非導出字段
}
```
Writer將提供給它的數據壓縮后寫入下層io.Writer接口。
### func [NewWriter](https://github.com/golang/go/blob/master/src/compress/zlib/writer.go#L42 "View Source")
```
func NewWriter(w io.Writer) *Writer
```
NewWriter創建并返回一個Writer。寫入返回值的數據都會在壓縮后寫入w。
調用者有責任在結束寫入后調用返回值的Close方法。因為寫入的數據可能保存在緩沖中沒有刷新入下層。
Example
```
var b bytes.Buffer
w := zlib.NewWriter(&b)
w.Write([]byte("hello, world\n"))
w.Close()
fmt.Println(b.Bytes())
```
Output:
```
[120 156 202 72 205 201 201 215 81 40 207 47 202 73 225 2 4 0 0 255 255 33 231 4 147]
```
### func [NewWriterLevel](https://github.com/golang/go/blob/master/src/compress/zlib/writer.go#L53 "View Source")
```
func NewWriterLevel(w io.Writer, level int) (*Writer, error)
```
NewWriterLevel類似NewWriter但指定了壓縮水平而不是采用默認的DefaultCompression。
參數level可以是DefaultCompression、NoCompression或BestSpeed與BestCompression之間包括二者的任何整數。如果level合法,返回的錯誤值為nil。
### func [NewWriterLevelDict](https://github.com/golang/go/blob/master/src/compress/zlib/writer.go#L62 "View Source")
```
func NewWriterLevelDict(w io.Writer, level int, dict []byte) (*Writer, error)
```
NewWriterLevelDict類似NewWriterLevel但還指定了用于壓縮的字典。dict參數可以為nil;否則,在返回的Writer關閉之前,其內容不可被修改。
### func (\*Writer) [Reset](https://github.com/golang/go/blob/master/src/compress/zlib/writer.go#L76 "View Source")
```
func (z *Writer) Reset(w io.Writer)
```
Reset將w重置,丟棄當前的寫入狀態,并將下層輸出目標設為dst。效果上等價于將w設為使用dst和w的壓縮水平、字典重新調用NewWriterLevel或NewWriterLevelDict返回的\*Writer。
### func (\*Writer) [Write](https://github.com/golang/go/blob/master/src/compress/zlib/writer.go#L146 "View Source")
```
func (z *Writer) Write(p []byte) (n int, err error)
```
Write將p壓縮后寫入下層io.Writer接口。壓縮后的數據不一定會立刻刷新,除非Writer被關閉或者顯式的刷新。
### func (\*Writer) [Flush](https://github.com/golang/go/blob/master/src/compress/zlib/writer.go#L166 "View Source")
```
func (z *Writer) Flush() error
```
Flush將緩沖中的壓縮數據刷新到下層io.Writer接口中。
### func (\*Writer) [Close](https://github.com/golang/go/blob/master/src/compress/zlib/writer.go#L179 "View Source")
```
func (z *Writer) Close() error
```
調用Close會刷新緩沖并關閉w,但不會關閉下層io.Writer接口。
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