Ok, code is as follow:

Code:
src/event/ngx_event_connect.c In ngx_event_connect_peer()

....................................
rc = connect(s, pc->sockaddr, pc->socklen);

if (rc == -1) {
err = ngx_socket_errno;


if (err != NGX_EINPROGRESS
#if (NGX_WIN32)
/* Winsock returns WSAEWOULDBLOCK (NGX_EAGAIN) */
&& err != NGX_EAGAIN
#endif
)
{
if (err == NGX_ECONNREFUSED
#if (NGX_LINUX)
/*
* Linux returns EAGAIN instead of ECONNREFUSED
* for unix sockets if listen queue is full
*/
|| err == NGX_EAGAIN
#endif
|| err == NGX_ECONNRESET
|| err == NGX_ENETDOWN
|| err == NGX_ENETUNREACH
|| err == NGX_EHOSTDOWN
|| err == NGX_EHOSTUNREACH)
{
level = NGX_LOG_ERR;
} else {
level = NGX_LOG_CRIT;
}

ngx_log_error(level, c->log, err, "connect() to %V failed",
pc->name);

ngx_close_connection(c);
pc->connection = NULL;

return NGX_DECLINED;
}
}

pc->local_socket = s; /* save socket fd after connect() */



Code:
src/http/ngx_http_upstream.c In ngx_http_upstream_process_header()

ssize_t n;
ngx_int_t rc;
ngx_connection_t *c;

ngx_peer_connection_t *pc;
u_char sa[NGX_SOCKADDRLEN];
socklen_t len;
u_char text[NGX_SOCKADDR_STRLEN];
u_char *p;
struct sockaddr_in *sin;


pc = &u->peer;

c = u->peer.connection;

ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0,
"http upstream process header");

c->log->action = "reading response header from upstream";

if (c->read->timedout) {
ngx_http_upstream_next(r, u, NGX_HTTP_UPSTREAM_FT_TIMEOUT);
return;
}

if (!u->request_sent && ngx_http_upstream_test_connect(c) != NGX_OK) {
ngx_http_upstream_next(r, u, NGX_HTTP_UPSTREAM_FT_ERROR);
return;
}
.........................................

/* getsockname by pc->local_socket which saved in ngx_event_connect_peer()*/

if (pc == NULL) {
return;
}
if (pc->local_socket) {
if (getsockname(pc->local_socket, (struct sockaddr *) &sa, &len) != -1) {
if (pc->local_sockaddr != NULL) {
ngx_memcpy(pc->local_sockaddr, &sa, len);

ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
"http upstream connect socket: %i",
pc->local_socket);
ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
"http upstream connect sa_family: %i",
pc->local_sockaddr->sa_family);
ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
"http upstream connect uri: %s", r->uri.data);
sin = (struct sockaddr_in *) sa;
p = (u_char *) &sin->sin_addr;
p = ngx_snprintf(text, NGX_SOCKADDR_STRLEN, "%ud.%ud.%ud.%ud:%d",
p[0], p[1], p[2], p[3], ntohs(sin->sin_port));
ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
"http upstream connect ip: %s", &text);
}
}
}


Code: src/http/ngx_http_upstream.c

static ngx_int_t
ngx_http_upstream_laddr_variable(ngx_http_request_t *r,
ngx_http_variable_value_t *v, uintptr_t data)
{

ngx_peer_connection_t *pc;
struct sockaddr_in *sin;
u_char sa[NGX_SOCKADDRLEN];
socklen_t len;
#if (NGX_HAVE_INET6)
ngx_uint_t i;
struct sockaddr_in6 *sin6;
#endif

ngx_str_t s;
u_char addr[NGX_SOCKADDR_STRLEN];

s.len = NGX_SOCKADDR_STRLEN;
s.data = addr;

if (r->upstream == NULL) {
return NGX_ERROR;
}

pc = &r->upstream->peer;
if (pc == NULL){
return NGX_ERROR;
}
if (pc->local_sockaddr == NULL) {
return NGX_ERROR;

s.len = ngx_sock_ntop(pc->local_sockaddr, s.data, s.len, 1);

s.data = ngx_pnalloc(r->pool, s.len);
if (s.data == NULL) {
return NGX_ERROR;
}


ngx_memcpy(s.data, addr, s.len);

v->len = s.len;
v->valid = 1;
v->no_cacheable = 0;
v->not_found = 0;
v->data = s.data;

return NGX_OK;
}