获取Http跳转和地址兼小谈GoDoc

在Go语言中，一直比较好奇如何进行跳转控制，最近正好看了下gocrawl的源码，结合GoDoc，解决了这个疑惑：

type Client struct {
        // Transport specifies the mechanism by which individual
        // HTTP requests are made.
        // If nil, DefaultTransport is used.
        Transport RoundTripper

        // CheckRedirect specifies the policy for handling redirects.
        // If CheckRedirect is not nil, the client calls it before
        // following an HTTP redirect. The arguments req and via are
        // the upcoming request and the requests made already, oldest
        // first. If CheckRedirect returns an error, the Client's Get
        // method returns both the previous Response and
        // CheckRedirect's error (wrapped in a url.Error) instead of
        // issuing the Request req.
        //
        // If CheckRedirect is nil, the Client uses its default policy,
        // which is to stop after 10 consecutive requests.
        CheckRedirect func(req *Request, via []*Request) error

        // Jar specifies the cookie jar.
        // If Jar is nil, cookies are not sent in requests and ignored
        // in responses.
        Jar CookieJar
}

具体案例如下：

func httpReq(url string) (int, string, error){
    client := &http.Client{CheckRedirect: func(req *http.Request, via []*http.Request) error {
        return errors.New("Redirected!")
    }}

    resp, err := client.Get(url)
    defer resp.Body.Close()
    redir := ""
    if (resp.StatusCode > 300 && resp.StatusCode < 400) {
        redir = resp.Header.Get("Location")
    }

    return resp.StatusCode, redir, err
}

如同上面提到的，GoDoc工具是Go语言中内置的一个文档查看工具，可以使用

godoc -http=:8080
在本地8080端口打开了一个和golang.org相似的网站，考虑到golang.org经常被墙的问题，这个还是蛮有用的。GoDoc优点是相对golang.org，godoc生成的文件还包含了自己安装的包文件的文档（前提是提供）。

当然也可以命令行下使用：

godoc fmt Println
这样就查看了fmt.Println的使用方法。