blob: 783bd98c8b4148b0b7529e695a4b55daaec37715 [file] [log] [blame]
// Copyright 2014 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.
package internal
import (
// HTTPClient is the context key to use with's
// WithValue function to associate an *http.Client value with a context.
var HTTPClient ContextKey
// ContextKey is just an empty struct. It exists so HTTPClient can be
// an immutable public variable with a unique type. It's immutable
// because nobody else can create a ContextKey, being unexported.
type ContextKey struct{}
// ContextClientFunc is a func which tries to return an *http.Client
// given a Context value. If it returns an error, the search stops
// with that error. If it returns (nil, nil), the search continues
// down the list of registered funcs.
type ContextClientFunc func(context.Context) (*http.Client, error)
var contextClientFuncs []ContextClientFunc
func RegisterContextClientFunc(fn ContextClientFunc) {
contextClientFuncs = append(contextClientFuncs, fn)
func ContextClient(ctx context.Context) (*http.Client, error) {
if ctx != nil {
if hc, ok := ctx.Value(HTTPClient).(*http.Client); ok {
return hc, nil
for _, fn := range contextClientFuncs {
c, err := fn(ctx)
if err != nil {
return nil, err
if c != nil {
return c, nil
return http.DefaultClient, nil
func ContextTransport(ctx context.Context) http.RoundTripper {
hc, err := ContextClient(ctx)
// This is a rare error case (somebody using nil on App Engine).
if err != nil {
return ErrorTransport{err}
return hc.Transport
// ErrorTransport returns the specified error on RoundTrip.
// This RoundTripper should be used in rare error cases where
// error handling can be postponed to response handling time.
type ErrorTransport struct{ Err error }
func (t ErrorTransport) RoundTrip(*http.Request) (*http.Response, error) {
return nil, t.Err