MINOR: mux/server: Add 'proto' keyword to force the multiplexer's protocol

For now, it is parsed but not used. Tests are done on it to check if the side
and the mode are compatible with the server's definition.

doc/configuration.txt

@@ -11669,6 +11669,15 @@ port <port>
   inetd for instance. This parameter is ignored if the "check" parameter is not
   set. See also the "addr" parameter.
 
+proto <name>
+
+  Forces the multiplexer's protocol to use for the outgoing connections to this
+  server. It must be compatible with the mode of the backend (TCP or HTTP). It
+  must also be usable on the backend side. The list of available protocols is
+  reported in haproxy -vv.
+  Idea behind this optipon is to bypass the selection of the best multiplexer's
+  protocol for all connections established to this server.
+
 redir <prefix>
   The "redir" parameter enables the redirection mode for all GET and HEAD
   requests addressing this server. This means that instead of having HAProxy

include/types/server.h

@@ -205,6 +205,7 @@ struct server {
 	char *rdr_pfx;				/* the redirection prefix */
 
 	struct proxy *proxy;			/* the proxy this server belongs to */
+	struct mux_proto_list *mux_proto;       /* the mux to use for all outgoing connections (specified by the "proto" keyword) */
 	int served;				/* # of active sessions currently being served (ie not pending) */
 	int cur_sess;				/* number of currently active sessions (including syn_sent) */
 	unsigned maxconn, minconn;		/* max # of active sessions (0 = unlimited), min# for dynamic limit. */

src/cfgparse.c

@@ -8769,7 +8769,7 @@ out_uri_auth_compat:
 			}
 		}
 
-		/* Check the mux protocols, if any, for each listener
+		/* Check the mux protocols, if any, for each listener and server
 		 * attached to the current proxy */
 		list_for_each_entry(bind_conf, &curproxy->conf.bind, by_fe) {
 			int mode = (1 << (curproxy->mode == PR_MODE_HTTP));
@@ -8785,6 +8785,20 @@ out_uri_auth_compat:
 				cfgerr++;
 			}
 		}
+		for (newsrv = curproxy->srv; newsrv; newsrv = newsrv->next) {
+			int mode = (1 << (curproxy->mode == PR_MODE_HTTP));
+
+			if (!newsrv->mux_proto)
+				continue;
+			if (!(newsrv->mux_proto->mode & mode)) {
+				ha_alert("config : %s '%s' : MUX protocol '%.*s' is not usable for server '%s' at [%s:%d].\n",
+					 proxy_type_str(curproxy), curproxy->id,
+					 (int)newsrv->mux_proto->token.len,
+					 newsrv->mux_proto->token.ptr,
+					 newsrv->id, newsrv->conf.file, newsrv->conf.line);
+				cfgerr++;
+			}
+		}
 	}
 
 	/***********************************************************/

src/server.c

@@ -32,6 +32,7 @@
 #include <proto/applet.h>
 #include <proto/cli.h>
 #include <proto/checks.h>
+#include <proto/connection.h>
 #include <proto/port_range.h>
 #include <proto/protocol.h>
 #include <proto/queue.h>
@@ -499,6 +500,29 @@ static int inline srv_enable_pp_flags(struct server *srv, unsigned int flags)
 	srv->pp_opts |= flags;
 	return 0;
 }
+/* parse the "proto" server keyword */
+static int srv_parse_proto(char **args, int *cur_arg,
+			   struct proxy *px, struct server *newsrv, char **err)
+{
+	struct ist proto;
+
+	if (!*args[*cur_arg + 1]) {
+		memprintf(err, "'%s' : missing value", args[*cur_arg]);
+		return ERR_ALERT | ERR_FATAL;
+	}
+	proto = ist2(args[*cur_arg + 1], strlen(args[*cur_arg + 1]));
+	newsrv->mux_proto = get_mux_proto(proto);
+	if (!newsrv->mux_proto) {
+		memprintf(err, "'%s' :  unknown MUX protocol '%s'", args[*cur_arg], args[*cur_arg+1]);
+		return ERR_ALERT | ERR_FATAL;
+	}
+	else if (!(newsrv->mux_proto->side & PROTO_SIDE_BE)) {
+		memprintf(err, "'%s' :  MUX protocol '%s' cannot be used for outgoing connections",
+			  args[*cur_arg], args[*cur_arg+1]);
+		return ERR_ALERT | ERR_FATAL;
+	}
+	return 0;
+}
 
 /* parse the "proxy-v2-options" */
 static int srv_parse_proxy_v2_options(char **args, int *cur_arg,
@@ -1179,6 +1203,7 @@ static struct srv_kw_list srv_kws = { "ALL", { }, {
 	{ "no-send-proxy-v2",    srv_parse_no_send_proxy_v2,    0,  1 }, /* Disable use of PROXY V2 protocol */
 	{ "non-stick",           srv_parse_non_stick,           0,  1 }, /* Disable stick-table persistence */
 	{ "observe",             srv_parse_observe,             1,  1 }, /* Enables health adjusting based on observing communication with the server */
+	{ "proto",               srv_parse_proto,               1,  1 }, /* Set the proto to use for all outgoing connections */
 	{ "proxy-v2-options",    srv_parse_proxy_v2_options,    1,  1 }, /* options for send-proxy-v2 */
 	{ "redir",               srv_parse_redir,               1,  1 }, /* Enable redirection mode */
 	{ "send-proxy",          srv_parse_send_proxy,          0,  1 }, /* Enforce use of PROXY V1 protocol */
@@ -1584,6 +1609,8 @@ static void srv_settings_cpy(struct server *srv, struct server *src, int srv_tmp
 #ifdef TCP_USER_TIMEOUT
 	srv->tcp_ut = src->tcp_ut;
 #endif
+	srv->mux_proto = src->mux_proto;
+
 	if (srv_tmpl)
 		srv->srvrq = src->srvrq;
 }