最近在阅读Golang源码时，有个地方没有看的很明白。认真思考了一下，本文作为记录总结。
看的源代码是
net/http/internal/chunked.go
// Writing to chunkedWriter translates to writing in HTTP chunked Transfer
// Encoding wire format to the underlying Wire chunkedWriter.
type chunkedWriter struct {
Wire io.Writer
}
// Write the contents of data as one chunk to Wire.
// NOTE: Note that the corresponding chunk-writing procedure in Conn.Write has
// a bug since it does not check for success of io.WriteString
func (cw *chunkedWriter) Write(data []byte) (n int, err error) {
// Don't send 0-length data. It looks like EOF for chunked encoding.
if len(data) == 0 {
return 0, nil
}
if _, err = fmt.Fprintf(cw.Wire, "%x\r\n", len(data)); err != nil {
return 0, err
}
if n, err = cw.Wire.Write(data); err != nil { // 这一行...
return
}
if n != len(data) {
err = io.ErrShortWrite
return
}
if _, err = io.WriteString(cw.Wire, "\r\n"); err != nil {
return
}
if bw, ok := cw.Wire.(*FlushAfterChunkWriter); ok {
err = bw.Flush()
}
return
}
chunkedWriter.Wire 是一个io.Writer， io.Writer是一个 interface.
type Writer interface {
Write(p []byte) (n int, err error)
}
卡住的点是， cw.Wire.Write(data) 的Write源代码在哪里呢? 我通过跳转并没有找到对应的代码位置。今天恰好看了goCN的推荐文章，连接在参考链接中。其中的代码实现是这样的：
package main
import (
"bytes"
"encoding/json"
"fmt"
"io"
)
type Person struct {
Id int
Name string
Age int
}
func (p *Person) Write(w io.Writer) {
b, _ := json.Marshal(*p)
w.Write(b)
}
func main() {
p := &Person{Id: 1, Name: "Joe", Age: 27}
var b bytes.Buffer
p.Write(&b)
fmt.Println(b.String())
}
看完这个例子我一下就明白了， cw.Wire 是io.Writer interface类型，只要某个类型或struct实现了Write方法,就实现了这个interface.
回到 chunkedWriter, 初始化chunkedWriter的时候,将 Wire初始化为 bytes.buffer 一类的实现了io.Writer interface的类型,这样就能使用到他们定义的Write方法了.Golang源码中有大量的这种运用.现在对interface又有更深的理解.
参考连接
https://medium.com/@as27/a-simple-beginners-tutorial-to-io-writer-in-golang-2a13bfefea02