Debugging HTTP Client requests with Go
Sometimes when you're integrating with APIs or web services, you need to debug the HTTP requests/responses that are occuring.
In some toolchains it's part of configuration, but in Go it's unfortunately not part of the standard library to globally turn on logging for the http.Client.
That being said, the Go standard library has net/http/httputil has the handy helper methods httputil.DumpRequestOut and httputil.DumpResponse which we can use alongside an implementation of http.RoundTripper to provide a logging HTTP client.
We can wrap this together with:
package main
import (
"fmt"
"log"
"net/http"
"net/http/httputil"
"net/url"
)
type loggingTransport struct{}
func (s *loggingTransport) RoundTrip(r *http.Request) (*http.Response, error) {
bytes, _ := httputil.DumpRequestOut(r, true)
resp, err := http.DefaultTransport.RoundTrip(r)
// err is returned after dumping the response
respBytes, _ := httputil.DumpResponse(resp, true)
bytes = append(bytes, respBytes...)
fmt.Printf("%s\n", bytes)
return resp, err
}
func main() {
client := http.Client{
Transport: &loggingTransport{},
}
baseUrl := "https://..." // this would be filled in with i.e. a Request Bin style application
resp, err := client.PostForm(baseUrl, url.Values{
"name": {"foo"},
"content": {"baz", "bing"},
})
if err != nil {
log.Fatal(err)
}
defer resp.Body.Close()
fmt.Printf("resp.Status: %v\n", resp.Status)
resp, err = client.Get(must(url.JoinPath(baseUrl, "/user")))
if err != nil {
log.Fatal(err)
}
defer resp.Body.Close()
fmt.Printf("resp.Status: %v\n", resp.Status)
// preferably don't mutate the global client!
http.DefaultClient = &client
resp, err = http.DefaultClient.Get(must(url.JoinPath(baseUrl, "/from-default-client")))
if err != nil {
log.Fatal(err)
}
defer resp.Body.Close()
fmt.Printf("resp.Status: %v\n", resp.Status)
}
func must(s string, err error) string {
if err != nil {
log.Fatal(err)
}
return s
}
This then outputs:
Example output
POST / HTTP/1.1
Host: enzzopego73pb.x.pipedream.net
User-Agent: Go-http-client/1.1
Content-Length: 33
Content-Type: application/x-www-form-urlencoded
Accept-Encoding: gzip
content=baz&content=bing&name=fooHTTP/2.0 200 OK
Content-Length: 16
Access-Control-Allow-Origin: *
Content-Type: application/json; charset=utf-8
Date: Sat, 11 Mar 2023 10:06:43 GMT
X-Pd-Status: sent to primary
X-Powered-By: Express
{"success":true}
resp.Status: 200 OK
GET /user HTTP/1.1
Host: enzzopego73pb.x.pipedream.net
User-Agent: Go-http-client/1.1
Accept-Encoding: gzip
HTTP/2.0 200 OK
Content-Length: 16
Access-Control-Allow-Origin: *
Content-Type: application/json; charset=utf-8
Date: Sat, 11 Mar 2023 10:06:43 GMT
X-Pd-Status: sent to primary
X-Powered-By: Express
{"success":true}
resp.Status: 200 OK
GET /from-default-client HTTP/1.1
Host: enzzopego73pb.x.pipedream.net
User-Agent: Go-http-client/1.1
Accept-Encoding: gzip
HTTP/2.0 200 OK
Content-Length: 16
Access-Control-Allow-Origin: *
Content-Type: application/json; charset=utf-8
Date: Sat, 11 Mar 2023 10:06:43 GMT
X-Pd-Status: sent to primary
X-Powered-By: Express
{"success":true}
resp.Status: 200 OK
