Golang : Get HTTP protocol version example

Upgraded socketloop.com's NGINX web server to serve via HTTP/2 and wanted to find out if Golang can detect the HTTP/2 protocol version. However, at this moment (Go 1.5), Golang's client will always return protocol version HTTP/1.1

From https://golang.org/pkg/net/http/#Request :

 // The protocol version for incoming requests.
 // Client requests always use HTTP/1.1.

Pretty sure HTTP/2 detection is available at https://godoc.org/golang.org/x/net/http2#ClientConn, but better to wait till it is incorporated into Go 1.6.

Here is a simple example on how to find out the protocol version use by the client in making request to server.

 package main

 import (
 "fmt"
 "net/http"
 "os"
 )

 func main() {

 client := &http.Client{}

 url := "https://www.google.com"

 resp, err := client.Get(url) // can use http directly instead of client

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 // get protocol version
 protocol := resp.Request.Proto

 fmt.Println("URL is : ", url)
 fmt.Println("Protocol is : ", protocol)

 }

Sample outputs :

URL is : //www.socketloop.com

Protocol is : <----- missing protocol!

URL is : https://www.socketloop.com

Protocol is : HTTP/1.1

URL is : http://www.google.com

Protocol is : HTTP/1.1

URL is : https://www.google.com

Protocol is : HTTP/1.1

Apparently, attempt to get protocol version from NON-HTTPS (//www.socketloop.com) version of socketloop.com will return empty string. Upon further investigation with curl -I command, Golang's net/http.Request.Proto will only returns value if the HTTP status code is 200 - OK.

>curl -I //www.socketloop.com

HTTP/1.1 301 Moved Permanently

>curl -I https://www.socketloop.com

HTTP/1.1 200 OK

Tried to improve the protocol detection by getting Request header information from the final/effective URL, but it seems that after resolving to the final/effective URL, the protocol variable will still be returned as empty string. (See how to get the HTTP status code https://www.socketloop.com/tutorials/golang-intercept-and-compare-http-response-code-example)

Hence, it is best to check for the protocol string length first before displaying the version.

 package main

 import (
 "fmt"
 "net/http"
 "os"
 )

 func main() {

 client := &http.Client{}

 url := "//www.socketloop.com" // has 301 redirect

 resp, err := client.Get(url)

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 // get protocol version
 protocol := resp.Request.Proto

 if len(protocol) > 0 {
 fmt.Println("URL is : ", url)
 fmt.Println("Protocol is : ", protocol)
 } else {
 fmt.Println("URL is : ", url)
 fmt.Println("Unable to determine protocol version. Check URL with curl -I to see if HTTP status code is 301")
 fmt.Println("Golang will resolve to the final/effective URL and will not return HTTP status 301, but 200. However, it will still return empty string for Proto ")
 }

 }

Output :

With 301 redirect :

URL is : //www.socketloop.com

Unable to determine protocol version. Check URL with curl -I to see if HTTP status code is 301

Golang will resolve to the final/effective URL and will not return HTTP status 301, but 200. However, it will still return empty string for Proto

and with 200 - OK :