Where does $remote_addr come from?

[B.R.]

I am curious: apart from a training prospective at code digging, what was
the goal?
In other words, where did you expect the IP address to come from, if not
from a system network socket?

Have a nice week-end,
---
*B. R.*

On Sat, Feb 4, 2017 at 12:02 AM, Paul Nickerson <pnickerson at cashstar.com>
wrote:

> > Reading that file, the next likely looking line is:
> >             c->addr_text.len = ngx_sock_ntop(c->sockaddr, c->socklen,
> >                                              c->addr_text.data,
> >                                              ls->addr_text_max_len, 0);
>
> Thank you for the boost. From what you said, it looks like the variable is
> constructed from c->sockaddr
>
> src/event/ngx_event_accept.c
> line 167
> c->sockaddr = ngx_palloc(c->pool, socklen);
>
> I chased that down, and it looks like ngx_palloc only allocates some
> memory; it doesn't fill it. Moving on.
>
> line 173
> ngx_memcpy(c->sockaddr, &sa, socklen);
>
> It looks like ngx_memcpy is a wrapper around the standard C library
> function memcpy. For memcpy(A, B, C), it copies to destination A from
> source B, and it does amount C. So now I want to know where &sa comes from.
>
> line 70
> s = accept(lc->fd, &sa.sockaddr, &socklen);
>
> Here, &sa.sockaddr is being sent into something. I think &sa.sockaddr
> becomes c->sockaddr, so I chase this.
>
> Bash
> man 2 accept
>
> accept is a Linux system call: "accept a connection on a socket"
> int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);
>
> "The argument addr is a pointer to a sockaddr structure.  This
> structure is filled in with the address of the peer socket, as known
> to the communications layer.  The exact format of the address
> returned addr is determined by the socket's address family (see
> socket(2) and the respective protocol man pages).  When addr is NULL,
> nothing is filled in; in this case, addrlen is not used, and should
> also be NULL."
>
> And so, the answer to my question appears to be: $remote_addr is
> constructed from "struct sockaddr *addr" of the "accept" Linux system call.
> It is the address of the peer socket.
>
> I am going to read through socket(2) and the respective protocol man
> pages, but at this point we're outside of NGINX, and so the scope of this
> mailing list.
> Thank you again for your help.
>
>  ~ Paul Nickerson
>
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