Introduce MPTCP

src/anet.c

@@ -573,7 +573,26 @@ static int anetV6Only(char *err, int s) {
     return ANET_OK;
 }
 
-static int _anetTcpServer(char *err, int port, char *bindaddr, int af, int backlog) {
+/* Until glibc 2.39, getaddrinfo with hints.ai_protocol of IPPROTO_MPTCP leads error.
+ * Use hints.ai_protocol IPPROTO_IP (0) or IPPROTO_TCP (6) to resolve address and overwrite
+ * it when MPTCP is enabled.
+ * Ref: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/net/mptcp/mptcp_connect.c
+ */
+static int anetTcpGetProtocol(char *err, int ai_protocol, int mptcp) {
+    if (mptcp) {
+#ifdef IPPROTO_MPTCP
+        UNUSED(err);
+        return IPPROTO_MPTCP;
+    }
+#else
+        anetSetError(err, "MPTCP is not supported on this platform");
+        return ANET_ERR;
+    }
+#endif
+    return ai_protocol;
+}
+
+static int _anetTcpServer(char *err, int port, char *bindaddr, int af, int backlog, int mptcp) {
     int s = -1, rv;
     char _port[6]; /* strlen("65535") */
     struct addrinfo hints, *servinfo, *p;
@@ -591,7 +610,10 @@ static int _anetTcpServer(char *err, int port, char *bindaddr, int af, int backl
         return ANET_ERR;
     }
     for (p = servinfo; p != NULL; p = p->ai_next) {
-        if ((s = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1) continue;
+        rv = anetTcpGetProtocol(err, p->ai_protocol, mptcp);
+        if (rv == ANET_ERR) goto error;
+
+        if ((s = socket(p->ai_family, p->ai_socktype, rv)) == -1) continue;
 
         if (af == AF_INET6 && anetV6Only(err, s) == ANET_ERR) goto error;
         if (anetSetReuseAddr(err, s) == ANET_ERR) goto error;
@@ -611,12 +633,12 @@ static int _anetTcpServer(char *err, int port, char *bindaddr, int af, int backl
     return s;
 }
 
-int anetTcpServer(char *err, int port, char *bindaddr, int backlog) {
-    return _anetTcpServer(err, port, bindaddr, AF_INET, backlog);
+int anetTcpServer(char *err, int port, char *bindaddr, int backlog, int mptcp) {
+    return _anetTcpServer(err, port, bindaddr, AF_INET, backlog, mptcp);
 }
 
-int anetTcp6Server(char *err, int port, char *bindaddr, int backlog) {
-    return _anetTcpServer(err, port, bindaddr, AF_INET6, backlog);
+int anetTcp6Server(char *err, int port, char *bindaddr, int backlog, int mptcp) {
+    return _anetTcpServer(err, port, bindaddr, AF_INET6, backlog, mptcp);
 }
 
 int anetUnixServer(char *err, char *path, mode_t perm, int backlog, char *group) {

src/anet.h

@@ -54,8 +54,8 @@
 int anetTcpNonBlockConnect(char *err, const char *addr, int port);
 int anetTcpNonBlockBestEffortBindConnect(char *err, const char *addr, int port, const char *source_addr);
 int anetResolve(char *err, char *host, char *ipbuf, size_t ipbuf_len, int flags);
-int anetTcpServer(char *err, int port, char *bindaddr, int backlog);
-int anetTcp6Server(char *err, int port, char *bindaddr, int backlog);
+int anetTcpServer(char *err, int port, char *bindaddr, int backlog, int mptcp);
+int anetTcp6Server(char *err, int port, char *bindaddr, int backlog, int mptcp);
 int anetUnixServer(char *err, char *path, mode_t perm, int backlog, char *group);
 int anetTcpAccept(char *err, int serversock, char *ip, size_t ip_len, int *port);
 int anetUnixAccept(char *err, int serversock);

src/config.c

@@ -3276,6 +3276,7 @@ standardConfig static_configs[] = {
     createIntConfig("timeout", NULL, MODIFIABLE_CONFIG, 0, INT_MAX, server.maxidletime, 0, INTEGER_CONFIG, NULL, NULL), /* Default client timeout: infinite */
     createIntConfig("replica-announce-port", "slave-announce-port", MODIFIABLE_CONFIG, 0, 65535, server.replica_announce_port, 0, INTEGER_CONFIG, NULL, NULL),
     createIntConfig("tcp-backlog", NULL, IMMUTABLE_CONFIG, 0, INT_MAX, server.tcp_backlog, 511, INTEGER_CONFIG, NULL, NULL), /* TCP listen backlog. */
+    createBoolConfig("mptcp", NULL, IMMUTABLE_CONFIG, server.mptcp, 0, NULL, NULL),                                          /* Multipath TCP. */
     createIntConfig("cluster-port", NULL, IMMUTABLE_CONFIG, 0, 65535, server.cluster_port, 0, INTEGER_CONFIG, NULL, NULL),
     createIntConfig("cluster-announce-bus-port", NULL, MODIFIABLE_CONFIG, 0, 65535, server.cluster_announce_bus_port, 0, INTEGER_CONFIG, NULL, updateClusterAnnouncedPort), /* Default: Use +10000 offset. */
     createIntConfig("cluster-announce-port", NULL, MODIFIABLE_CONFIG, 0, 65535, server.cluster_announce_port, 0, INTEGER_CONFIG, NULL, updateClusterAnnouncedPort),         /* Use server.port */

src/server.c

@@ -2651,10 +2651,10 @@ int listenToPort(connListener *sfd) {
         if (optional) addr++;
         if (strchr(addr, ':')) {
             /* Bind IPv6 address. */
-            sfd->fd[sfd->count] = anetTcp6Server(server.neterr, port, addr, server.tcp_backlog);
+            sfd->fd[sfd->count] = anetTcp6Server(server.neterr, port, addr, server.tcp_backlog, server.mptcp);
         } else {
             /* Bind IPv4 address. */
-            sfd->fd[sfd->count] = anetTcpServer(server.neterr, port, addr, server.tcp_backlog);
+            sfd->fd[sfd->count] = anetTcpServer(server.neterr, port, addr, server.tcp_backlog, server.mptcp);
         }
         if (sfd->fd[sfd->count] == ANET_ERR) {
             int net_errno = errno;

src/server.h

@@ -1612,6 +1612,7 @@ struct valkeyServer {
     int port;                              /* TCP listening port */
     int tls_port;                          /* TLS listening port */
     int tcp_backlog;                       /* TCP listen() backlog */
+    int mptcp;                             /* Use Multipath TCP */
     char *bindaddr[CONFIG_BINDADDR_MAX];   /* Addresses we should bind to */
     int bindaddr_count;                    /* Number of addresses in server.bindaddr[] */
     char *bind_source_addr;                /* Source address to bind on for outgoing connections */

tests/unit/introspection.tcl

@@ -661,6 +661,7 @@ start_server {tags {"introspection"}} {
             rdbchecksum
             daemonize
             tcp-backlog
+            mptcp
             always-show-logo
             syslog-enabled
             cluster-enabled

valkey.conf

@@ -147,6 +147,15 @@ port 6379
 # in order to get the desired effect.
 tcp-backlog 511
 
+# Multipath TCP
+#
+# Multipath TCP (MPTCP) allows a single transport connection to use multiple network
+# interfaces or paths. MPTCP is useful for applications like bandwidth aggregation,
+# failover, and more resilient connections.
+# Note that MPTCP is supported in the official Linux kernel starting with version 5.6.
+#
+# mptcp yes
+
 # Unix socket.
 #
 # Specify the path for the Unix socket that will be used to listen for