Golang : How to get HTTP request header information?

Alright, as a webmaster sometimes we want to know about our visitors and then alert us if there is any visitor that match certain profile.

For example, we want to know where the visitor from and which client he/she or it(bot) is using. Fortunately, HTTP request header will provide us the information we want with header fields - RemoteAddr and User-Agent. If the IP address was banned by you, then tell your server to do something about it.

This code example below will demonstrate how to retrieve the HTTP request header information such as this :

 {
 "Method": "GET",
 "URL": {
 "Scheme": "",
 "Opaque": "",
 "User": null,
 "Host": "",
 "Path": "/favicon.ico",
 "RawQuery": "",
 "Fragment": ""
 },
 "Proto": "HTTP/1.1",
 "ProtoMajor": 1,
 "ProtoMinor": 1,
 "Header": {
 "Accept": [
 "*/*"
 ],
 "Accept-Encoding": [
 "gzip, deflate, sdch"
 ],
 "Accept-Language": [
 "en-US,en;q=0.8"
 ],
 "Connection": [
 "keep-alive"
 ],
 "Cookie": [
 "__utma=72123530.124214442.1438251812.1438251812.1438274470.2; __utmc=72123530; __utmz=72123530.1438251812.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none)"
 ],
 "User-Agent": [
 "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.99 Safari/537.36"
 ]
 },
 "Body": {
 "Closer": {
 "Reader": null
 }
 },
 "ContentLength": 0,
 "TransferEncoding": null,
 "Close": false,
 "Host": "example.com:8080",
 "Form": null,
 "PostForm": null,
 "MultipartForm": null,
 "Trailer": null,
 "RemoteAddr": "121.122.88.158:65075",
 "RequestURI": "/favicon.ico",
 "TLS": null
 }

and output the result in JSON format to terminal and web page.

 package main

 import (
 "fmt"
 "net/http"
 "encoding/json"
 )

 func Home(w http.ResponseWriter, r *http.Request) {

 // out JSON format
 // see - https://www.socketloop.com/tutorials/golang-http-response-json-encoded-data

 byte, err := json.Marshal(r)

 if err != nil {
 return
 }

 w.Header().Set("Content-Type", "application/json")
 fmt.Fprint(w, string(byte))

 fmt.Println(string(byte))
 }

 func main() {
 http.HandleFunc("/", Home)
 http.ListenAndServe(":8080", nil)
 }

run this code and point your browser to the main page. You should be able to see the JSON formatted HTTP request header result about your visitor.

What if you want to extract User-Agent only?

Then narrow down to the field you want to extract to

 r.Header.Get("User-Agent")

For example :

 package main

 import (
 "fmt"
 "net/http"
 "encoding/json"
 )

 func Home(w http.ResponseWriter, r *http.Request) {

 // out JSON format
 // see - https://www.socketloop.com/tutorials/golang-http-response-json-encoded-data

 byte, err := json.Marshal(r.Header.Get("User-Agent")) // <-------- here !

 if err != nil {
 return
 }

 w.Header().Set("Content-Type", "application/json")
 fmt.Fprint(w, string(byte))

 fmt.Println(string(byte))
 }

 func main() {
 http.HandleFunc("/", Home)
 http.ListenAndServe(":8080", nil)
 }

References :

https://www.socketloop.com/tutorials/get-client-ip-address

https://www.socketloop.com/tutorials/golang-http-response-json-encoded-data