I want to integrate ReCAPTCHA to my GAE Golang web application. In order to verify a captcha, I need to get user's IP address. How can I fetch user's IP address from a form post?
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4 Answers
inside your handler function call r.RemoteAddr to receive ip:port
like this:
func renderIndexPage(w http.ResponseWriter, r *http.Request) { ip := strings.Split(r.RemoteAddr,":")[0] } update 02/15/2017 as @Aigars Matulis pointed out, in current version there is already a function todo this
ip, _, _ := net.SplitHostPort(r.RemoteAddr) 
3 Comments
bsr
+1 For completeness, I had issue as I used localhost in my url. see the discussion here. groups.google.com/forum/#!topic/golang-nuts/rqo1--qR-8Y
fmt.Println.MKO
yes localhost is always special, and I guess you use a mac who resolves ipv6, which causes localhost and ip problems since years
Greivin López
Add the end what worked for me was to just use "r.RemoteAddr".
The answers above neglect to check if user's IP is forwarded by a proxy. In a lot of cases, the IP that you will find in the RemoteAddr is the IP of a proxy that is forwarding the user's request to you - not the user's IP address!
A more accurate solution would look like this:
package main import ( "net" "net/http" ) func GetIP(r *http.Request) string { if ipProxy := r.Header.Get("X-FORWARDED-FOR"); len(ipProxy) > 0 { return ipProxy } ip, _, _ := net.SplitHostPort(r.RemoteAddr) return ip } 
3 Comments
sv_lane
This answer suggests that X-Forwarded-For can be a list: stackoverflow.com/a/27235620/214070
Eran Chetzroni
@orcaman this is indeed true, if a request is passed through multiple proxies, like in Elastic Load Balancer in AWS, to content will be a list of IPs. the left most ip should be the client IP. You can find more info here docs.aws.amazon.com/ElasticLoadBalancing/latest/DeveloperGuide/…
Patrick Boos
When logging an IP address. Make sure to log both RemoteAddr AND X-Forwarded-For. Reason? A hacker can always set the X-Forwarded-For header ;-). On the other hand. A hacker will most likely use TOR or another way to hide his IP.
This worked for me. I run go in 8081 and made a request from port 8080.
fmt.Printf("r: %+v\n", r) // Print all fields that you get in request Output:
r: &{Method:POST URL:/email Proto:HTTP/1.1 ProtoMajor:1 ProtoMinor:1 Header:map[User-Agent:[Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_1) AppleWebKit/602.2.11 (KHTML, like Gecko) Version/10.0.1 Safari/602.2.11] Accept-Language:[en-us] Accept-Encoding:[gzip, deflate] Connection:[keep-alive] Accept:[/] Referer:[http://127.0.0.1:8080/] Content-Length:[9] Content-Type:[application/x-www-form-urlencoded; charset=UTF-8] Origin:[http://127.0.0.1:8080]] Body:0xc420012800 ContentLength:9 TransferEncoding:[] Close:false Host:127.0.0.1:8081 Form:map[] PostForm:map[] MultipartForm: Trailer:map[] RemoteAddr:127.0.0.1:62232 RequestURI:/email TLS: Cancel: Response: ctx:0xc420017860}
The Referer and Origin have my client IP.
ip := r.Referer() // Get Referer value fmt.Println(ip) // print ip Output:
