golang语言渐入佳境[19]-从go源代码读懂interface接口

1

func Get(url string) (resp *Response, err error)

12
3
4
5
6
7
8
9

type Response struct {
        Status     string // e.g. "200 OK"
        StatusCode int    // e.g. 200
        Proto      string // e.g. "HTTP/1.0"
        ProtoMajor int    // e.g. 1        ProtoMinor int    // e.g. 0
        Header Header

        Body io.ReadCloser

12
3
4

type ReadCloser interface {
        Reader
        Closer
}

12
3

type Reader interface {
        Read(p []byte) (n int, err error)
}

12
3

type Closer interface {
        Close() error
}

12
3
4
5
6
7
8
9
10
1112
13
14
15
16
17
18
19
20
21

package main

import (
	"net/http"
	"fmt"
	"os"
)

func main(){
	resp,err := http.Get("http://tmall.com")

	if err !=nil{
		fmt.Println("Error:",err)
		os.Exit(1)
	}
  //设置大一点，read方法不会自动的扩容。
	bs:=make([]byte,99999)
  //read函数将读取到的数据放入到bs中。
	resp.Body.Read(bs)
	fmt.Println(string(bs))
}

12
3

type Writer interface {
        Write(p []byte) (n int, err error)
}

12
3
4
5
6
7
8
9
10
1112
13
14
15
16
17
18
19
20

package main

import (
	"net/http"
	"fmt"
	"os"
	"io"
)

func main(){
	resp,err := http.Get("http://tmall.com")

	if err !=nil{
		fmt.Println("Error:",err)
		os.Exit(1)
	}

	//读取resp.Body中的信息，写到os.Stdout中。os.Stdout实现了write接口，resp.Body实现了read接口。
	io.Copy(os.Stdout,resp.Body)
}

12
3
4
5
6
7
8
9
10
1112
13
14
15
16
17
18
19
20
2122
23
24
25
26
27
28
29
30
3132
33
34
35
36
37
38
39
40
4142
43
44
45
46
47
48
49
50
5152
53
54
55
56
57
58

func Copy(dst Writer, src Reader) (written int64, err error) {
	return copyBuffer(dst, src, nil)
}

---------
func CopyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) {
	if buf != nil && len(buf) == 0 {
		panic("empty buffer in io.CopyBuffer")
	}
	return copyBuffer(dst, src, buf)
}
---------
func copyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) {
	// If the reader has a WriteTo method, use it to do the copy.
	// Avoids an allocation and a copy.
	if wt, ok := src.(WriterTo); ok {
		return wt.WriteTo(dst)
	}
	// Similarly, if the writer has a ReadFrom method, use it to do the copy.
	if rt, ok := dst.(ReaderFrom); ok {
		return rt.ReadFrom(src)
	}
	size := 32 * 1024  
	if l, ok := src.(*LimitedReader); ok && int64(size) > l.N {
		if l.N < 1 {
			size = 1		} else {
			size = int(l.N)
		}
	}
	if buf == nil {
		buf = make([]byte, size)//分配
	}
	for {   //疯狂读取并写入
		nr, er := src.Read(buf)
		if nr > 0 {
			nw, ew := dst.Write(buf[0:nr])
			if nw > 0 {
				written += int64(nw)
			}
			if ew != nil {
				err = ew
				break
			}
			if nr != nw {
				err = ErrShortWrite
				break
			}
		}
		if er != nil {
			if er != EOF {
				err = er
			}
			break
		}
	}
	return written, err
}

12
3
4
5
6
7
8
9
10
1112
13
14
15
16
17
18
19
20
2122
23
24
25
26
27
28
29
30
31

package main

import (
	"net/http"
	"fmt"
	"os"
	"io"
)


type logWriter struct{}

func main(){
	resp,err := http.Get("http://tmall.com")

	if err !=nil{
		fmt.Println("Error:",err)
		os.Exit(1)
	}

	lw:= logWriter{}

  //读取resp.Body中的信息，写到os.Stdout中。os.Stdout实现了write接口，resp.Body实现了read接口。
	io.Copy(lw,resp.Body)
}

func (logWriter) Write(bs []byte)(int,error){
	fmt.Println(string(bs))
	fmt.Println("Just wrote this many bytes",len(bs))
	return len(bs),nil
}