How to send a request through a specific interface?

Question

linux

Hi all!
The server has 4 interfaces on which the Internet hangs eth0 eth1 eth2 eth3
The task is to write software that will make requests through a specific interface.
In general, the question is, how to send a curl request through a specific interface?
I write in golang, but that's not the point, I think

Answer 1

I have two addresses on the server on the same interface, to send a request with curl from the desired address, I use
Where NNNN is the IP address from which to send the request.
And man tells us that you can also specify the name of the interface there, a quote from man

--interface <name>                                                                                                                                                                    
              Perform an operation using a specified interface. You can enter interface name, IP address or host name. An example could look like:
                                                                                                                                                                                             
               curl --interface eth0

Answer 2

Do you mean TCP/UDP requests? Then you just need to configure the routing accordingly, the OS network stack will figure out where to send the packets.

Answer 3

I didn’t check it, but in fact the network works like this ...
https://golang.org/pkg/net/#Interface - from here we take the addresses
https://golang.org/pkg/net/#DialTCP - here as the 2nd parameter ( laddr - local address) insert one of the addresses to choose from and get a connection through the selected interface.
Correct if wrong.