Go-HTTP-RedirectHandler

這是一個建立於 的文章，其中的資訊可能已經有所發展或是發生改變。

Keywords: HandlerFunc, RedirectHandler, Redirect

前言

在Go-http-HandlerFunc()函數中，詳細介紹了HandlerFunc，所以本文換個方式來講：從外往裡一層層剝離，即先講使用者層面的API或使用方法，然後再介紹涉及的內部實現細節。

RedirectHandler實現代碼

func Redirect(w ResponseWriter, r *Request, urlStr string, code int) {    // Skipped now ...}// Redirect to a fixed URLtype redirectHandler struct {    url  string    code int}func (rh *redirectHandler) ServeHTTP(w ResponseWriter, r *Request) {    Redirect(w, r, rh.url, rh.code)}// RedirectHandler returns a request handler that redirects// each request it receives to the given url using the given// status code.//// The provided code should be in the 3xx range and is usually// StatusMovedPermanently, StatusFound or StatusSeeOther.func RedirectHandler(url string, code int) Handler {    return &redirectHandler{url, code}}

慣用法

使用者可以看到的介面就是：

func RedirectHandler(url string, code int) Handler

樣本

TODO 待補充

type redirectHandler

上面的原始碼中，給出了type redirectHandler的定義。——redirectHandler也是Handler介面的一個實現。

Redirect()

redirectHandler具體類用到了Redirect()函數，原始碼如下：

// Redirect replies to the request with a redirect to url,// which may be a path relative to the request path.//// The provided code should be in the 3xx range and is usually// StatusMovedPermanently, StatusFound or StatusSeeOther.func Redirect(w ResponseWriter, r *Request, urlStr string, code int) {    if u, err := url.Parse(urlStr); err == nil {        // If url was relative, make absolute by        // combining with request path.        // The browser would probably do this for us,        // but doing it ourselves is more reliable.        // NOTE(rsc): RFC 2616 says that the Location        // line must be an absolute URI, like        // "http://www.google.com/redirect/",        // not a path like "/redirect/".        // Unfortunately, we don't know what to        // put in the host name section to get the        // client to connect to us again, so we can't        // know the right absolute URI to send back.        // Because of this problem, no one pays attention        // to the RFC; they all send back just a new path.        // So do we.        if u.Scheme == "" && u.Host == "" {            oldpath := r.URL.Path            if oldpath == "" { // should not happen, but avoid a crash if it does                oldpath = "/"            }            // no leading http://server            if urlStr == "" || urlStr[0] != '/' {                // make relative path absolute                olddir, _ := path.Split(oldpath)                urlStr = olddir + urlStr            }            var query string            if i := strings.Index(urlStr, "?"); i != -1 {                urlStr, query = urlStr[:i], urlStr[i:]            }            // clean up but preserve trailing slash            trailing := strings.HasSuffix(urlStr, "/")            urlStr = path.Clean(urlStr)            if trailing && !strings.HasSuffix(urlStr, "/") {                urlStr += "/"            }            urlStr += query        }    }    w.Header().Set("Location", urlStr)    w.WriteHeader(code)    // RFC 2616 recommends that a short note "SHOULD" be included in the    // response because older user agents may not understand 301/307.    // Shouldn't send the response for POST or HEAD; that leaves GET.    if r.Method == "GET" {        note := "<a href=\"" + htmlEscape(urlStr) + "\">" + statusText[code] + "</a>.\n"        fmt.Fprintln(w, note)    }}var htmlReplacer = strings.NewReplacer(    "&", "&amp;",    "<", "&lt;",    ">", "&gt;",    // "&#34;" is shorter than "&quot;".    `"`, "&#34;",    // "&#39;" is shorter than "&apos;" and apos was not in HTML until HTML5.    "'", "&#39;",)func htmlEscape(s string) string {    return htmlReplacer.Replace(s)}

待詳細解釋