text: // Copyright 2011 Google Inc. All rights reserved.
  // Use of this source code is governed by the Apache 2.0
  // license that can be found in the LICENSE file.
  
  // Package urlfetch provides an http.RoundTripper implementation
  // for fetching URLs via App Engine's urlfetch service.
  package urlfetch // import "google.golang.org/appengine/urlfetch"
  
  import (
  	"errors"
  	"fmt"
  	"io"
  	"io/ioutil"
  	"net/http"
  	"net/url"
  	"strconv"
  	"strings"
  	"time"
  
  	"github.com/golang/protobuf/proto"
  	"golang.org/x/net/context"
  
  	"google.golang.org/appengine/internal"
  	pb "google.golang.org/appengine/internal/urlfetch"
  )
  
  // Transport is an implementation of http.RoundTripper for
  // App Engine. Users should generally create an http.Client using
  // this transport and use the Client rather than using this transport
  // directly.
  type Transport struct {
  	Context context.Context
  
  	// Controls whether the application checks the validity of SSL certificates
  	// over HTTPS connections. A value of false (the default) instructs the
  	// application to send a request to the server only if the certificate is
  	// valid and signed by a trusted certificate authority (CA), and also
  	// includes a hostname that matches the certificate. A value of true
  	// instructs the application to perform no certificate validation.
  	AllowInvalidServerCertificate bool
  }
  
  // Verify statically that *Transport implements http.RoundTripper.
  var _ http.RoundTripper = (*Transport)(nil)
  
  // Client returns an *http.Client using a default urlfetch Transport. This
  // client will have the default deadline of 5 seconds, and will check the
  // validity of SSL certificates.
  //
  // Any deadline of the provided context will be used for requests through this client;
  // if the client does not have a deadline then a 5 second default is used.
  func Client(ctx context.Context) *http.Client {
  	return &http.Client{
  		Transport: &Transport{
  			Context: ctx,
  		},
  	}
  }
  
  type bodyReader struct {
  	content   []byte
  	truncated bool
  	closed    bool
  }
  
  // ErrTruncatedBody is the error returned after the final Read() from a
  // response's Body if the body has been truncated by App Engine's proxy.
  var ErrTruncatedBody = errors.New("urlfetch: truncated body")
  
  func statusCodeToText(code int) string {
  	if t := http.StatusText(code); t != "" {
  		return t
  	}
  	return strconv.Itoa(code)
  }
  
  func (br *bodyReader) Read(p []byte) (n int, err error) {
  	if br.closed {
  		if br.truncated {
  			return 0, ErrTruncatedBody
  		}
  		return 0, io.EOF
  	}
  	n = copy(p, br.content)
  	if n > 0 {
  		br.content = br.content[n:]
  		return
  	}
  	if br.truncated {
  		br.closed = true
  		return 0, ErrTruncatedBody
  	}
  	return 0, io.EOF
  }
  
  func (br *bodyReader) Close() error {
  	br.closed = true
  	br.content = nil
  	return nil
  }
  
  // A map of the URL Fetch-accepted methods that take a request body.
  var methodAcceptsRequestBody = map[string]bool{
  	"POST":  true,
  	"PUT":   true,
  	"PATCH": true,
  }
  
  // urlString returns a valid string given a URL. This function is necessary because
  // the String method of URL doesn't correctly handle URLs with non-empty Opaque values.
  // See http://code.google.com/p/go/issues/detail?id=4860.
  func urlString(u *url.URL) string {
  	if u.Opaque == "" || strings.HasPrefix(u.Opaque, "//") {
  		return u.String()
  	}
  	aux := *u
  	aux.Opaque = "//" + aux.Host + aux.Opaque
  	return aux.String()
  }
  
  // RoundTrip issues a single HTTP request and returns its response. Per the
  // http.RoundTripper interface, RoundTrip only returns an error if there
  // was an unsupported request or the URL Fetch proxy fails.
  // Note that HTTP response codes such as 5xx, 403, 404, etc are not
  // errors as far as the transport is concerned and will be returned
  // with err set to nil.
  func (t *Transport) RoundTrip(req *http.Request) (res *http.Response, err error) {
  	methNum, ok := pb.URLFetchRequest_RequestMethod_value[req.Method]
  	if !ok {
  		return nil, fmt.Errorf("urlfetch: unsupported HTTP method %q", req.Method)
  	}
  
  	method := pb.URLFetchRequest_RequestMethod(methNum)
  
  	freq := &pb.URLFetchRequest{
  		Method:                        &method,
  		Url:                           proto.String(urlString(req.URL)),
  		FollowRedirects:               proto.Bool(false), // http.Client's responsibility
  		MustValidateServerCertificate: proto.Bool(!t.AllowInvalidServerCertificate),
  	}
  	if deadline, ok := t.Context.Deadline(); ok {
  		freq.Deadline = proto.Float64(deadline.Sub(time.Now()).Seconds())
  	}
  
  	for k, vals := range req.Header {
  		for _, val := range vals {
  			freq.Header = append(freq.Header, &pb.URLFetchRequest_Header{
  				Key:   proto.String(k),
  				Value: proto.String(val),
  			})
  		}
  	}
  	if methodAcceptsRequestBody[req.Method] && req.Body != nil {
  		// Avoid a []byte copy if req.Body has a Bytes method.
  		switch b := req.Body.(type) {
  		case interface {
  			Bytes() []byte
  		}:
  			freq.Payload = b.Bytes()
  		default:
  			freq.Payload, err = ioutil.ReadAll(req.Body)
  			if err != nil {
  				return nil, err
  			}
  		}
  	}
  
  	fres := &pb.URLFetchResponse{}
  	if err := internal.Call(t.Context, "urlfetch", "Fetch", freq, fres); err != nil {
  		return nil, err
  	}
  
  	res = &http.Response{}
  	res.StatusCode = int(*fres.StatusCode)
  	res.Status = fmt.Sprintf("%d %s", res.StatusCode, statusCodeToText(res.StatusCode))
  	res.Header = make(http.Header)
  	res.Request = req
  
  	// Faked:
  	res.ProtoMajor = 1
  	res.ProtoMinor = 1
  	res.Proto = "HTTP/1.1"
  	res.Close = true
  
  	for _, h := range fres.Header {
  		hkey := http.CanonicalHeaderKey(*h.Key)
  		hval := *h.Value
  		if hkey == "Content-Length" {
  			// Will get filled in below for all but HEAD requests.
  			if req.Method == "HEAD" {
  				res.ContentLength, _ = strconv.ParseInt(hval, 10, 64)
  			}
  			continue
  		}
  		res.Header.Add(hkey, hval)
  	}
  
  	if req.Method != "HEAD" {
  		res.ContentLength = int64(len(fres.Content))
  	}
  
  	truncated := fres.GetContentWasTruncated()
  	res.Body = &bodyReader{content: fres.Content, truncated: truncated}
  	return
  }
  
  func init() {
  	internal.RegisterErrorCodeMap("urlfetch", pb.URLFetchServiceError_ErrorCode_name)
  	internal.RegisterTimeoutErrorCode("urlfetch", int32(pb.URLFetchServiceError_DEADLINE_EXCEEDED))
  }
  