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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// HTTP client. See RFC 2616.
// 
// This is the high-level Client interface.
// The low-level implementation is in transport.go.

package http

import (
        "encoding/base64"
        "errors"
        "fmt"
        "io"
        "net/url"
        "strings"
)

// A Client is an HTTP client. Its zero value (DefaultClient) is a usable client
// that uses DefaultTransport.
//
// The Client's Transport typically has internal state (cached
// TCP connections), so Clients should be reused instead of created as
// needed. Clients are safe for concurrent use by multiple goroutines.
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
        // returns that error instead of issue 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
}

// DefaultClient is the default Client and is used by Get, Head, and Post.
var DefaultClient = &Client{}

// RoundTripper is an interface representing the ability to execute a
// single HTTP transaction, obtaining the Response for a given Request.
//
// A RoundTripper must be safe for concurrent use by multiple
// goroutines.
type RoundTripper interface {
        // RoundTrip executes a single HTTP transaction, returning
        // the Response for the request req.  RoundTrip should not
        // attempt to interpret the response.  In particular,
        // RoundTrip must return err == nil if it obtained a response,
        // regardless of the response's HTTP status code.  A non-nil
        // err should be reserved for failure to obtain a response.
        // Similarly, RoundTrip should not attempt to handle
        // higher-level protocol details such as redirects,
        // authentication, or cookies.
        //
        // RoundTrip should not modify the request, except for
        // consuming the Body.  The request's URL and Header fields
        // are guaranteed to be initialized.
        RoundTrip(*Request) (*Response, error)
}

// Given a string of the form "host", "host:port", or "[ipv6::address]:port",
// return true if the string includes a port.
func hasPort(s string) bool { return strings.LastIndex(s, ":") > strings.LastIndex(s, "]") }

// Used in Send to implement io.ReadCloser by bundling together the
// bufio.Reader through which we read the response, and the underlying
// network connection.
type readClose struct {
        io.Reader
        io.Closer
}

// Do sends an HTTP request and returns an HTTP response, following
// policy (e.g. redirects, cookies, auth) as configured on the client.
//
// A non-nil response always contains a non-nil resp.Body.
//
// Callers should close resp.Body when done reading from it. If
// resp.Body is not closed, the Client's underlying RoundTripper
// (typically Transport) may not be able to re-use a persistent TCP
// connection to the server for a subsequent "keep-alive" request.
//
// Generally Get, Post, or PostForm will be used instead of Do.
func (c *Client) Do(req *Request) (resp *Response, err error) {
        if req.Method == "GET" || req.Method == "HEAD" {
                return c.doFollowingRedirects(req)
        }
        return send(req, c.Transport)
}

// send issues an HTTP request.  Caller should close resp.Body when done reading from it.
func send(req *Request, t RoundTripper) (resp *Response, err error) {
        if t == nil {
                t = DefaultTransport
                if t == nil {
                        err = errors.New("http: no Client.Transport or DefaultTransport")
                        return
                }
        }

        if req.URL == nil {
                return nil, errors.New("http: nil Request.URL")
        }

        if req.RequestURI != "" {
                return nil, errors.New("http: Request.RequestURI can't be set in client requests.")
        }

        // Most the callers of send (Get, Post, et al) don't need
        // Headers, leaving it uninitialized.  We guarantee to the
        // Transport that this has been initialized, though.
        if req.Header == nil {
                req.Header = make(Header)
        }

        if u := req.URL.User; u != nil {
                req.Header.Set("Authorization", "Basic "+base64.URLEncoding.EncodeToString([]byte(u.String())))
        }
        return t.RoundTrip(req)
}

// True if the specified HTTP status code is one for which the Get utility should
// automatically redirect.
func shouldRedirect(statusCode int) bool {
        switch statusCode {
        case StatusMovedPermanently, StatusFound, StatusSeeOther, StatusTemporaryRedirect:
                return true
        }
        return false
}

// Get issues a GET to the specified URL.  If the response is one of the following
// redirect codes, Get follows the redirect, up to a maximum of 10 redirects:
//
//    301 (Moved Permanently)
//    302 (Found)
//    303 (See Other)
//    307 (Temporary Redirect)
//
// Caller should close r.Body when done reading from it.
//
// Get is a wrapper around DefaultClient.Get.
func Get(url string) (r *Response, err error) {
        return DefaultClient.Get(url)
}

// Get issues a GET to the specified URL.  If the response is one of the
// following redirect codes, Get follows the redirect after calling the
// Client's CheckRedirect function.
//
//    301 (Moved Permanently)
//    302 (Found)
//    303 (See Other)
//    307 (Temporary Redirect)
//
// Caller should close r.Body when done reading from it.
func (c *Client) Get(url string) (r *Response, err error) {
        req, err := NewRequest("GET", url, nil)
        if err != nil {
                return nil, err
        }
        return c.doFollowingRedirects(req)
}

func (c *Client) doFollowingRedirects(ireq *Request) (r *Response, err error) {
        // TODO: if/when we add cookie support, the redirected request shouldn't
        // necessarily supply the same cookies as the original.
        var base *url.URL
        redirectChecker := c.CheckRedirect
        if redirectChecker == nil {
                redirectChecker = defaultCheckRedirect
        }
        var via []*Request

        if ireq.URL == nil {
                return nil, errors.New("http: nil Request.URL")
        }

        jar := c.Jar
        if jar == nil {
                jar = blackHoleJar{}
        }

        req := ireq
        urlStr := "" // next relative or absolute URL to fetch (after first request)
        for redirect := 0; ; redirect++ {
                if redirect != 0 {
                        req = new(Request)
                        req.Method = ireq.Method
                        req.Header = make(Header)
                        req.URL, err = base.Parse(urlStr)
                        if err != nil {
                                break
                        }
                        if len(via) > 0 {
                                // Add the Referer header.
                                lastReq := via[len(via)-1]
                                if lastReq.URL.Scheme != "https" {
                                        req.Header.Set("Referer", lastReq.URL.String())
                                }

                                err = redirectChecker(req, via)
                                if err != nil {
                                        break
                                }
                        }
                }

                for _, cookie := range jar.Cookies(req.URL) {
                        req.AddCookie(cookie)
                }
                urlStr = req.URL.String()
                if r, err = send(req, c.Transport); err != nil {
                        break
                }
                if c := r.Cookies(); len(c) > 0 {
                        jar.SetCookies(req.URL, c)
                }

                if shouldRedirect(r.StatusCode) {
                        r.Body.Close()
                        if urlStr = r.Header.Get("Location"); urlStr == "" {
                                err = errors.New(fmt.Sprintf("%d response missing Location header", r.StatusCode))
                                break
                        }
                        base = req.URL
                        via = append(via, req)
                        continue
                }
                return
        }

        method := ireq.Method
        err = &url.Error{
                Op:  method[0:1] + strings.ToLower(method[1:]),
                URL: urlStr,
                Err: err,
        }
        return
}

func defaultCheckRedirect(req *Request, via []*Request) error {
        if len(via) >= 10 {
                return errors.New("stopped after 10 redirects")
        }
        return nil
}

// Post issues a POST to the specified URL.
//
// Caller should close r.Body when done reading from it.
//
// Post is a wrapper around DefaultClient.Post
func Post(url string, bodyType string, body io.Reader) (r *Response, err error) {
        return DefaultClient.Post(url, bodyType, body)
}

// Post issues a POST to the specified URL.
//
// Caller should close r.Body when done reading from it.
func (c *Client) Post(url string, bodyType string, body io.Reader) (r *Response, err error) {
        req, err := NewRequest("POST", url, body)
        if err != nil {
                return nil, err
        }
        req.Header.Set("Content-Type", bodyType)
        r, err = send(req, c.Transport)
        if err == nil && c.Jar != nil {
                c.Jar.SetCookies(req.URL, r.Cookies())
        }
        return r, err
}

// PostForm issues a POST to the specified URL, 
// with data's keys and values urlencoded as the request body.
//
// Caller should close r.Body when done reading from it.
//
// PostForm is a wrapper around DefaultClient.PostForm
func PostForm(url string, data url.Values) (r *Response, err error) {
        return DefaultClient.PostForm(url, data)
}

// PostForm issues a POST to the specified URL, 
// with data's keys and values urlencoded as the request body.
//
// Caller should close r.Body when done reading from it.
func (c *Client) PostForm(url string, data url.Values) (r *Response, err error) {
        return c.Post(url, "application/x-www-form-urlencoded", strings.NewReader(data.Encode()))
}

// Head issues a HEAD to the specified URL.  If the response is one of the
// following redirect codes, Head follows the redirect after calling the
// Client's CheckRedirect function.
//
//    301 (Moved Permanently)
//    302 (Found)
//    303 (See Other)
//    307 (Temporary Redirect)
//
// Head is a wrapper around DefaultClient.Head
func Head(url string) (r *Response, err error) {
        return DefaultClient.Head(url)
}

// Head issues a HEAD to the specified URL.  If the response is one of the
// following redirect codes, Head follows the redirect after calling the
// Client's CheckRedirect function.
//
//    301 (Moved Permanently)
//    302 (Found)
//    303 (See Other)
//    307 (Temporary Redirect)
func (c *Client) Head(url string) (r *Response, err error) {
        req, err := NewRequest("HEAD", url, nil)
        if err != nil {
                return nil, err
        }
        return c.doFollowingRedirects(req)
}