MINOR: listener: add so_name sample fetch

Add a sample fetch for the name of a bind. This can be useful to
take decisions when PROXY protocol is used and we can't rely on dst,
such as the sample config below.

  defaults
    mode http
  listen bar
    bind 127.0.0.1:1111
    server s1 127.0.1.1:1234 send-proxy

  listen foo
    bind 127.0.1.1:1234 name foo accept-proxy
    http-request return status 200 hdr dst %[dst] if { dst 127.0.1.1 }

doc/configuration.txt

@@ -15449,6 +15449,11 @@ so_id : integer
   in frontends involving many "bind" lines, or to stick all users coming via a
   same socket to the same server.
 
+so_name : string
+  Returns a string containing the current listening socket's name, as defined
+  with name on a "bind" line. It can serve the same purposes as so_id but with
+  strings instead of integers.
+
 src : ip
   This is the source IPv4 address of the client of the session. It is of type
   IP and works on both IPv4 and IPv6 tables. On IPv6 tables, IPv4 addresses are

reg-tests/sample_fetches/so_name.vtc

@@ -0,0 +1,22 @@
+varnishtest "so_name sample fetche Test"
+
+#REQUIRE_VERSION=2.2
+
+feature ignore_unknown_macro
+
+haproxy h1 -conf {
+    defaults
+        mode http
+
+    frontend fe
+        bind "fd@${fe}" name foo
+        http-request return status 200 hdr so-name %[so_name]
+
+} -start
+
+client c1 -connect ${h1_fe_sock} {
+    txreq -url "/"
+    rxresp
+    expect resp.status == 200
+    expect resp.http.so-name == "foo"
+} -run

src/listener.c

@@ -1290,6 +1290,18 @@ smp_fetch_so_id(const struct arg *args, struct sample *smp, const char *kw, void
 	smp->data.u.sint = smp->sess->listener->luid;
 	return 1;
 }
+static int
+smp_fetch_so_name(const struct arg *args, struct sample *smp, const char *kw, void *private)
+{
+	smp->data.u.str.area = smp->sess->listener->name;
+	if (!smp->data.u.str.area)
+		return 0;
+
+	smp->data.type = SMP_T_STR;
+	smp->flags = SMP_F_CONST;
+	smp->data.u.str.data = strlen(smp->data.u.str.area);
+	return 1;
+}
 
 /* parse the "accept-proxy" bind keyword */
 static int bind_parse_accept_proxy(char **args, int cur_arg, struct proxy *px, struct bind_conf *conf, char **err)
@@ -1526,6 +1538,7 @@ static int cfg_parse_tune_listener_mq(char **args, int section_type, struct prox
 static struct sample_fetch_kw_list smp_kws = {ILH, {
 	{ "dst_conn", smp_fetch_dconn, 0, NULL, SMP_T_SINT, SMP_USE_FTEND, },
 	{ "so_id",    smp_fetch_so_id, 0, NULL, SMP_T_SINT, SMP_USE_FTEND, },
+	{ "so_name",  smp_fetch_so_name, 0, NULL, SMP_T_STR, SMP_USE_FTEND, },
 	{ /* END */ },
 }};