[PATCH 2 of 4] HTTP: added MPTCP support

[Dourov Maxime]

# HG changeset patch
# User maxime <mux99 at live.be>
# Date 1713355399 -7200
#      Wed Apr 17 14:03:19 2024 +0200
# Node ID 69e3909234d76c6888fba539f9bbbecc9858a7ab
# Parent  b7cbe9281f9d6911fd40a894ebc4ac2d701d8fa4
HTTP: added MPTCP support.

Multipath TCP (MPTCP), standardized in RFC8684 [1], is a TCP extension
that enables a TCP connection to use different paths.

Multipath TCP has been used for several use cases. On smartphones, MPTCP
enables seamless handovers between cellular and Wi-Fi networks while
preserving established connections. This use-case is what pushed Apple
to use MPTCP since 2013 in multiple applications [2]. On dual-stack
hosts, Multipath TCP enables the TCP connection to automatically use the
best performing path, either IPv4 or IPv6. If one path fails, MPTCP
automatically uses the other path.

To benefit from MPTCP, both the client and the server have to support
it. Multipath TCP is a backward-compatible TCP extension that is enabled
by default on recent Linux distributions (Debian, Ubuntu, Redhat, ...).
Multipath TCP is included in the Linux kernel since version 5.6 [3].
To use it on Linux, an application must explicitly enable it when
creating the socket. No need to change anything else in the application.

Even if MPTCP is supported by different OS, only Linux supports the
`IPPROTO_MPTCP` protocol, which is why this feature is currently
limited to Linux only.

This patch adds a new parameter 'mptcp' to the  'listen' directive
in the HTTP module.

Link: https://www.rfc-editor.org/rfc/rfc8684.html [1]
Link: https://www.tessares.net/apples-mptcp-story-so-far/ [2]
Link: https://www.mptcp.dev [3]

diff --git a/contrib/vim/syntax/nginx.vim b/contrib/vim/syntax/nginx.vim
--- a/contrib/vim/syntax/nginx.vim
+++ b/contrib/vim/syntax/nginx.vim
@@ -65,7 +65,7 @@ syn match ngxListenComment '#.*$'
     \ contained
     \ nextgroup=@ngxListenParams skipwhite skipempty
 syn keyword ngxListenOptions contained
-    \ default_server ssl quic proxy_protocol
+    \ default_server ssl quic proxy_protocol mptcp
     \ setfib fastopen backlog rcvbuf sndbuf accept_filter deferred bind
     \ ipv6only reuseport so_keepalive
     \ nextgroup=@ngxListenParams skipwhite skipempty
diff --git a/src/http/ngx_http.c b/src/http/ngx_http.c
--- a/src/http/ngx_http.c
+++ b/src/http/ngx_http.c
@@ -1845,6 +1845,7 @@ ngx_http_add_listening(ngx_conf_t *cf, n
 #endif
 
     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/http/ngx_http_core_module.c b/src/http/ngx_http_core_module.c
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -20,6 +20,10 @@ typedef struct {
 #define NGX_HTTP_REQUEST_BODY_FILE_ON     1
 #define NGX_HTTP_REQUEST_BODY_FILE_CLEAN  2
 
+#ifndef IPPROTO_MPTCP
+#define IPPROTO_MPTCP 262
+#endif
+
 
 static ngx_int_t ngx_http_core_auth_delay(ngx_http_request_t *r);
 static void ngx_http_core_auth_delay_handler(ngx_http_request_t *r);
@@ -4049,6 +4053,13 @@ ngx_http_core_listen(ngx_conf_t *cf, ngx
         }
 #endif
 
+#if (NGX_LINUX)
+        if (ngx_strcmp(value[n].data, "mptcp") == 0) {
+            lsopt.protocol = IPPROTO_MPTCP;
+            continue;
+        }
+#endif
+
         if (ngx_strncmp(value[n].data, "backlog=", 8) == 0) {
             lsopt.backlog = ngx_atoi(value[n].data + 8, value[n].len - 8);
             lsopt.set = 1;
@@ -4351,6 +4362,11 @@ ngx_http_core_listen(ngx_conf_t *cf, ngx
         if (lsopt.proxy_protocol) {
             return "\"proxy_protocol\" parameter is incompatible with \"quic\"";
         }
+#if (NGX_LINUX)
+        if (lsopt.protocol == IPPROTO_MPTCP) {
+             return "\"mptcp\" parameter is incompatible with \"quic\"";
+        }
+#endif
     }
 
     for (n = 0; n < u.naddrs; n++) {
diff --git a/src/http/ngx_http_core_module.h b/src/http/ngx_http_core_module.h
--- a/src/http/ngx_http_core_module.h
+++ b/src/http/ngx_http_core_module.h
@@ -88,6 +88,7 @@ typedef struct {
     int                        rcvbuf;
     int                        sndbuf;
     int                        type;
+    int                        protocol;
 #if (NGX_HAVE_SETFIB)
     int                        setfib;
 #endif