golang http client 关闭重用连接两种方法

时间：02-16来源：作者：点击数：13

同事有个模块会定期获取宿主机上的所有容器信息，代码中使用http client 请求docker engine获取容器信息。运行后收到用户反馈，程序导致系统fd泄漏,修复后代码如下，比原来代码多了一句 req.Close=true

    client := &http.Client{
        Timeout: time.Duration(timeout) * time.Millisecond,
        Transport: &http.Transport{
            Dial: unixDial,
        },
    }

    req, err := http.NewRequest("GET", url, nil)
    if err != nil {
        return nil, fmt.Errorf("NewRequest(): url = %s, err = %s", url, err)
    }

    req.Close = true // fd leak without setting this
    resp, err := client.Do(req)
    ...

因为我自己有个清理容器数据的代码也有类似逻辑。代码如下，但是这个清理容器的模块是运行一次就退出的（磁盘资源紧张时才运行）所以没有这个问题。

  tr := &http.Transport{Dial: fakeDial, } 
    client := &http.Client{Transport: tr}
    resp, err := client.Get("http://localhost/containers/json")
    if err != nil {
        return nil, err
    }
    defer resp.Body.Close()

翻了下源码发现这段注释

    // Close indicates whether to close the connection after
    // replying to this request (for servers) or after sending this
    // request and reading its response (for clients).
    //
    // For server requests, the HTTP server handles this automatically
    // and this field is not needed by Handlers.
    //
    // For client requests, setting this field prevents re-use of
    // TCP connections between requests to the same hosts, as if
    // Transport.DisableKeepAlives were set.
    Close bool

http 1.1默认是保持keep-alive 的，所以如果每次请求都new 一个xin的client，就会造成fd泄漏。按照注释，在new client时，把keep-alive 设置为disable 就可以解决这个问题。修改后代码如下

  tr := &http.Transport{Dial: fakeDial, DisableKeepAlives: true}
    client := &http.Client{Transport: tr}
    resp, err := client.Get("http://localhost/containers/json")
    if err != nil {
        return nil, err
    }
    defer resp.Body.Close()