From 920dc099c130e0ea23eb36becd157a95901aa5a2 Mon Sep 17 00:00:00 2001
From: Sergey Kandaurov <pluknet@nginx.com>
Date: Thu, 16 Oct 2025 15:22:56 +0000
Subject: The "multipath" parameter of the "listen" directive.

When configured, it enables Multipath TCP support on a listen socket.
As of now it works on Linux starting with Linux 5.6 and glibc 2.32,
where it is enabled with an IPPROTO_MPTCP socket(2) protocol.

To avoid EADDRINUSE errors in bind() and listen() when transitioning
between sockets with different protocols, SO_REUSEPORT is set on both
sockets.  See f7f1607bf for potential implications.

Based on previous work by Maxime Dourov and Anthony Doeraene.
---
 src/stream/ngx_stream.c             |  1 +
 src/stream/ngx_stream.h             |  1 +
 src/stream/ngx_stream_core_module.c | 19 +++++++++++++++++++
 3 files changed, 21 insertions(+)

(limited to 'src/stream')

diff --git a/src/stream/ngx_stream.c b/src/stream/ngx_stream.c
index b6eeb23af..508ce6082 100644
--- a/src/stream/ngx_stream.c
+++ b/src/stream/ngx_stream.c
@@ -1010,6 +1010,7 @@ ngx_stream_add_listening(ngx_conf_t *cf, ngx_stream_conf_addr_t *addr)
     ls->log.handler = ngx_accept_log_error;
 
     ls->type = addr->opt.type;
+    ls->protocol = addr->opt.protocol;
     ls->backlog = addr->opt.backlog;
     ls->rcvbuf = addr->opt.rcvbuf;
     ls->sndbuf = addr->opt.sndbuf;
diff --git a/src/stream/ngx_stream.h b/src/stream/ngx_stream.h
index dc05dc5ba..9bc689e99 100644
--- a/src/stream/ngx_stream.h
+++ b/src/stream/ngx_stream.h
@@ -62,6 +62,7 @@ typedef struct {
     int                            rcvbuf;
     int                            sndbuf;
     int                            type;
+    int                            protocol;
 #if (NGX_HAVE_SETFIB)
     int                            setfib;
 #endif
diff --git a/src/stream/ngx_stream_core_module.c b/src/stream/ngx_stream_core_module.c
index a09c7c634..6556c5a73 100644
--- a/src/stream/ngx_stream_core_module.c
+++ b/src/stream/ngx_stream_core_module.c
@@ -1202,6 +1202,19 @@ ngx_stream_core_listen(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
             continue;
         }
 
+        if (ngx_strcmp(value[i].data, "multipath") == 0) {
+#ifdef IPPROTO_MPTCP
+            lsopt.protocol = IPPROTO_MPTCP;
+            lsopt.set = 1;
+            lsopt.bind = 1;
+#else
+            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                               "multipath is not supported "
+                               "on this platform, ignored");
+#endif
+            continue;
+        }
+
         if (ngx_strcmp(value[i].data, "ssl") == 0) {
 #if (NGX_STREAM_SSL)
             lsopt.ssl = 1;
@@ -1338,6 +1351,12 @@ ngx_stream_core_listen(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
         }
 #endif
 
+#ifdef IPPROTO_MPTCP
+        if (lsopt.protocol == IPPROTO_MPTCP) {
+            return "\"multipath\" parameter is incompatible with \"udp\"";
+        }
+#endif
+
 #if (NGX_STREAM_SSL)
         if (lsopt.ssl) {
             return "\"ssl\" parameter is incompatible with \"udp\"";
-- 
cgit