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// Copyright 2016 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 gensupport
import (
// Hook is the type of a function that is called once before each HTTP request
// that is sent by a generated API. It returns a function that is called after
// the request returns.
// Hooks are not called if the context is nil.
type Hook func(ctx context.Context, req *http.Request) func(resp *http.Response)
var hooks []Hook
// RegisterHook registers a Hook to be called before each HTTP request by a
// generated API. Hooks are called in the order they are registered. Each
// hook can return a function; if it is non-nil, it is called after the HTTP
// request returns. These functions are called in the reverse order.
// RegisterHook should not be called concurrently with itself or SendRequest.
func RegisterHook(h Hook) {
hooks = append(hooks, h)
// SendRequest sends a single HTTP request using the given client.
// If ctx is non-nil, it calls all hooks, then sends the request with
// req.WithContext, then calls any functions returned by the hooks in
// reverse order.
func SendRequest(ctx context.Context, client *http.Client, req *http.Request) (*http.Response, error) {
// Disallow Accept-Encoding because it interferes with the automatic gzip handling
// done by the default http.Transport. See
if _, ok := req.Header["Accept-Encoding"]; ok {
return nil, errors.New("google api: custom Accept-Encoding headers not allowed")
if ctx == nil {
return client.Do(req)
// Call hooks in order of registration, store returned funcs.
post := make([]func(resp *http.Response), len(hooks))
for i, h := range hooks {
fn := h(ctx, req)
post[i] = fn
// Send request.
resp, err := send(ctx, client, req)
// Call returned funcs in reverse order.
for i := len(post) - 1; i >= 0; i-- {
if fn := post[i]; fn != nil {
return resp, err
func send(ctx context.Context, client *http.Client, req *http.Request) (*http.Response, error) {
if client == nil {
client = http.DefaultClient
resp, err := client.Do(req.WithContext(ctx))
// If we got an error, and the context has been canceled,
// the context's error is probably more useful.
if err != nil {
select {
case <-ctx.Done():
err = ctx.Err()
return resp, err
// DecodeResponse decodes the body of res into target. If there is no body,
// target is unchanged.
func DecodeResponse(target interface{}, res *http.Response) error {
if res.StatusCode == http.StatusNoContent {
return nil
return json.NewDecoder(res.Body).Decode(target)