go下载

今天处理GO下载的时候遇到一个问题：如果调用readall去读取response，会造成很大的内存消耗，并且无法获取下载的进度。

直到搜到ioutil.ReadAll(httpResponse.Body) memory consumption，才解决了我的问题。

package main
import (
    "fmt"
    "io"
    "net/http"
    "os"
)
func main() {
    url := "http://dl.360safe.com/setup.exe"
    resp, _ := http.Get(url)
    filename := "setup.exe"
    f, _ := os.OpenFile(filename, os.O_CREATE|os.O_RDWR|os.O_TRUNC, 0644)
    n, err := copyBuffer(f, resp.Body, nil)
    if err != nil {
        fmt.Println(err, n)
    }
}
func copyBuffer(dst io.Writer, src io.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.(io.WriterTo); ok {
        return wt.WriteTo(dst)
    }
    // Similarly, if the writer has a ReadFrom method, use it to do the copy.
    if rt, ok := dst.(io.ReaderFrom); ok {
        return rt.ReadFrom(src)
    }
    if buf == nil {
        buf = make([]byte, 1024*1024)
    }
    for {
        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 = io.ErrShortWrite
                break
            }
        }
        if er == io.EOF {
            break
        }
        if er != nil {
            err = er
            break
        }
    }
    return written, err
}

其中copyBuffer的written就可以解决下载进度的问题，并且使用了io.copy打通了读和写的通道，很优雅的解决了问题。