Determine IP to which HTTP request was addressed in http.Handler

Question

I have the following setup:

The request is made to the server using one of its IP addresses - let's say either 192.168.0.1(on eth0) or 192.168.0.2(on eth1). The server is listening on all addresses on the local machine (e.g. http.ListenAndServe(":8080", nil)).

How can I determine in the server code from the request which network interface (or IP address) it was sent to?

req.Host contains the host name for the server. Moreover, I can't see anything in the request headers.

I would edit the question as the fact your Go code is a proxy is irrelevant to the question. The question is basically "how do I know the local address of a TCP connection which is carrying out an HTTP request being processed?" — kostix
– kostix, Commented Jul 1, 2020 at 14:40

sev3ryn · Accepted Answer · 2020-07-01 14:15:29Z

3

ok, I figured out this for http library source code - incoming address is stored in request context under http.LocalAddrContextKey key. So to extract incomming IP address you need to do

r.Context().Value(http.LocalAddrContextKey)

answered Jul 1, 2020 at 14:15

sev3ryn

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3 Comments

kostix Over a year ago

I'd look at the ConnContext callback of the http.Server: its second argument is a net.Conn of the client's connection, so one could probably call LocalAddr() on it and actually populate the context.

kostix Over a year ago

@Flimzy, no it works as expected: <play.golang.org/p/zTBqVQuZtFL> (I did a series of curl -s http://address_or_hostname:8080/ calls; this is a Debian box with two known IPv4 localhost addresses, one IPv6 localhost address and a C-class address on a private LAN).

kostix Over a year ago

(Verified that the OP's method works identically). So I'd mark the answer as accepted (this is OK on StackOverflow).

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