How to trace http.Client with httptrace in Go - http

Question

Per this doc, we can trace http.Client with httptrace in this way
t := &transport{}
req, _ := http.NewRequest("GET", "https://google.com", nil)
trace := &httptrace.ClientTrace{
GotConn: t.GotConn,
}
req = req.WithContext(httptrace.WithClientTrace(req.Context(), trace))
client := &http.Client{Transport: t}
For google API client, here are the one wrapper codes
func NewWithClient(jsonKey []byte, cli *http.Client) (*Client, error) {
if cli == nil {
return nil, fmt.Errorf("client is nil")
}
ctx := context.WithValue(context.Background(), oauth2.HTTPClient, cli)
conf, err := google.JWTConfigFromJSON(jsonKey, androidpublisher.AndroidpublisherScope)
if err != nil {
return nil, err
}
service, err := androidpublisher.NewService(ctx, option.WithHTTPClient(conf.Client(ctx)))
if err != nil {
return nil, err
}
return &Client{service}, err
}
We want to apply httptrace to the http.Client argument of NewWithClient to do HTTP trace.
What we have tried
type TraceTransport struct {
}
var traceTransport = &TraceTransport{}
var trace = &httptrace.ClientTrace{
GotConn: traceTransport.GotConn,
}
func (t *TraceTransport) RoundTrip(req *http.Request) (*http.Response, error) {
return http.DefaultTransport.RoundTrip(req)
}
func (t *TraceTransport) GotConn(info httptrace.GotConnInfo) {
fmt.Printf("Connection reused for %v \n", info.Reused)
}
type ClientWrapper struct {
defaultClient *http.Client
}
var clientWrapperTrace = &httptrace.ClientTrace{GotConn: traceTransport.GotConn}
func (c *ClientWrapper) Do(req *http.Request) (*http.Response, error) {
req = req.WithContext(httptrace.WithClientTrace(req.Context(), clientWrapperTrace))
return c.defaultClient.Do(req)
}
func NewClientTrace(jsonKey []byte) (*Client, error) {
cli := &http.Client{
Transport: traceTransport,
Timeout: time.Duration(10) * time.Second,
}
cliWrapper := &ClientWrapper{defaultClient: cli}
ctx := context.WithValue(context.Background(), oauth2.HTTPClient, cliWrapper)
conf, err := google.JWTConfigFromJSON(jsonKey, androidpublisher.AndroidpublisherScope)
if err != nil {
return nil, err
}
service, err := androidpublisher.NewService(ctx, option.WithHTTPClient(conf.Client(ctx)))
if err != nil {
return nil, err
}
return &Client{service}, err
}
type Client struct {
service *androidpublisher.Service
}
func (c *Client) VerifyProduct(
ctx context.Context,
packageName string,
productID string,
token string,
) (*androidpublisher.ProductPurchase, error) {
ps := androidpublisher.NewPurchasesProductsService(c.service)
result, err := ps.Get(packageName, productID, token).Context(ctx).Do()
return result, err
}
// test codes
c, err := NewClientTrace([]byte(privateKey))
if err != nil {
return
}
packageName := "package.name"
productID := "product_id"
token := "xxxxx"
r, err := c.VerifyProduct(context.Background(), packageName, productID, token)
However, it is failed to trace http.Client, There is no output of GotConn. Could someone help us to figure out the issue of the above codes?

Answer 1

Requests from google/oauth2 are not traceable by httptrace. your ClientWrapper passed with context.WithValue will be ignored here, and oauth2 has it's own http.Client, it just use the Transport method of *http.Client from context.Value.
Requests from androidpublisher can be traced by httptrace like this:
ctx := httptrace.WithClientTrace(context.Background(), clientWrapperTrace)
r, err := c.VerifyProduct(ctx, packageName, productID, token)
If you just want to count the requests, i think overwrite the http.Client.Transport is a easy way.
type TraceTransport struct {
}
func (t *TraceTransport) RoundTrip(req *http.Request) (*http.Response, error) {
fmt.Printf("RoundTrip hook %v\n", req.URL)
return http.DefaultTransport.RoundTrip(req)
}
func NewClientTrace(jsonKey []byte) (*Client, error) {
cli := &http.Client{Transport: &TraceTransport{}}
ctx := context.WithValue(context.Background(), oauth2.HTTPClient, cli)
// ...
service, err := androidpublisher.NewService(ctx, option.WithHTTPClient(conf.Client(ctx)))
// ....
}