functional option MPTCP with --mptcp

docs/cmdline-opts/Makefile.inc

@@ -160,6 +160,7 @@ DPAGES = \
   max-redirs.md \
   max-time.md \
   metalink.md \
+  mptcp.md \
   negotiate.md \
   netrc-file.md \
   netrc-optional.md \

docs/cmdline-opts/mptcp.md

@@ -0,0 +1,37 @@
+---
+c: Copyright (C) Dorian Craps, <dorian.craps@student.vinci.be>
+SPDX-License-Identifier: curl
+Long: mptcp
+Added: 8.7.0
+Help: Enable Multipath TCP (MPTCP)
+Category: connection
+Multi: boolean
+See-also:
+  - tcp-fastopen
+Example:
+  - --mptcp $URL
+---
+
+# `--mptcp`
+
+Enables the use of Multipath TCP (MPTCP) for connections. MPTCP is an extension 
+to the standard TCP that allows multiple TCP streams over different network 
+paths between the same source and destination. This can enhance bandwidth and 
+improve reliability by using multiple paths simultaneously.
+
+MPTCP is beneficial in networks where multiple paths exist between clients and 
+servers, such as mobile networks where a device may switch between Wi-Fi and 
+cellular data or in wired networks with multiple ISPs.
+
+## Usage
+
+To use MPTCP for your connections, add the `--mptcp` option when using `curl`:
+
+## Requirements
+
+- Your operating system must support MPTCP, and it must be enabled.
+- The server you are connecting to must also support MPTCP.
+
+## Availability
+
+The `--mptcp` option is available starting from `curl` version 8.6.1.

docs/libcurl/curl_easy_setopt.md

@@ -423,6 +423,10 @@ Path to a Unix domain socket. See CURLOPT_UNIX_SOCKET_PATH(3)
 
 Path to an abstract Unix domain socket. See CURLOPT_ABSTRACT_UNIX_SOCKET(3)
 
+## CURLOPT_MPTCP
+
+Enable Multipath TCP (MPTCP). See CURLOPT_MPTCP(3)
+
 # NAMES and PASSWORDS OPTIONS (Authentication)
 
 ## CURLOPT_NETRC

docs/libcurl/opts/CURLOPT_MPTCP.md

@@ -0,0 +1,76 @@
+---
+c: Copyright (C) Dorian Craps, <dorian.craps@student.vinci.be>
+SPDX-License-Identifier: curl
+Title: CURLOPT_MPTCP
+Section: 3
+Source: libcurl
+See-also:
+  - tcp-fastopen (3)
+---
+
+# NAME
+
+CURLOPT_MPTCP - enable Multipath TCP
+
+# SYNOPSIS
+
+~~~c
+
+#include <curl/curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_MPTCP, long enable);
+~~~
+
+# DESCRIPTION
+
+Pass a long as parameter set to 1L to enable or 0 to disable.
+
+Multipath TCP (MPTCP) is an extension of TCP that allows multiple paths 
+to be used simultaneously by a single TCP connection, enhancing redundancy, 
+bandwidth, and potentially reducing latency. 
+It works by presenting a standard TCP interface to applications while 
+managing multiple underlying TCP connections.
+
+Enabling MPTCP can improve the performance and reliability of network requests, 
+particularly in environments where multiple network paths (e.g., WiFi and 
+cellular) are available.
+
+Note: MPTCP support depends on the underlying operating system and network 
+infrastructure. Not all networks support MPTCP, and its effectiveness will 
+vary based on the network configuration and conditions.
+
+# DEFAULT
+
+0
+
+# PROTOCOLS
+
+All
+
+# EXAMPLE
+
+~~~c
+
+int main(void)
+{
+  CURL *curl = curl_easy_init();
+  if(curl) {
+    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
+    curl_easy_setopt(curl, CURLOPT_MPTCP, 1L);
+    curl_easy_perform(curl);
+  }
+}
+~~~
+
+# AVAILABILITY
+
+Support for MPTCP in libcurl requires Linux 5.6 or later. 
+The feature's availability in libcurl can also depend 
+on the version of libcurl. Added in 8.7.0.
+
+# RETURN VALUE
+
+Returns CURLE_OK if MPTCP is successfully enabled for the connection,
+ otherwise returns an error code specific to the reason it could not be enabled, 
+ which might include lack of operating system support or libcurl not being built 
+ with MPTCP support.

docs/libcurl/symbols-in-versions

@@ -708,6 +708,7 @@ CURLOPT_MAXREDIRS               7.5
 CURLOPT_MIME_OPTIONS            7.81.0
 CURLOPT_MIMEPOST                7.56.0
 CURLOPT_MUTE                    7.1           7.8         7.15.5
+CURLOPT_MPTCP                   8.7.0
 CURLOPT_NETRC                   7.1
 CURLOPT_NETRC_FILE              7.11.0
 CURLOPT_NEW_DIRECTORY_PERMS     7.16.4

docs/options-in-versions

@@ -125,6 +125,7 @@
 --max-redirs                         7.5
 --max-time (-m)                      4.0
 --metalink                           7.27.0
+--mptcp                              8.7.0
 --negotiate                          7.10.6
 --netrc (-n)                         4.6
 --netrc-file                         7.21.5

include/curl/curl.h

@@ -2206,6 +2206,9 @@ typedef enum {
   /* millisecond version */
   CURLOPT(CURLOPT_SERVER_RESPONSE_TIMEOUT_MS, CURLOPTTYPE_LONG, 324),
 
+  /* Set MPTCP */
+  CURLOPT(CURLOPT_MPTCP, CURLOPTTYPE_LONG, 325),
+
   CURLOPT_LASTENTRY /* the last unused */
 } CURLoption;
 

lib/cf-socket.c

@@ -244,6 +244,10 @@ void Curl_sock_assign_addr(struct Curl_sockaddr_ex *dest,
     dest->socktype = SOCK_STREAM;
     dest->protocol = IPPROTO_IP;
     break;
+  case TRNSPRT_MPTCP:
+    dest->socktype = SOCK_STREAM;
+    dest->protocol = IPPROTO_MPTCP;
+    break;
   default: /* UDP and QUIC */
     dest->socktype = SOCK_DGRAM;
     dest->protocol = IPPROTO_UDP;
@@ -1601,7 +1605,12 @@ CURLcode Curl_cf_tcp_create(struct Curl_cfilter **pcf,
   if(!ctx) {
     result = CURLE_OUT_OF_MEMORY;
     goto out;
+  }  
+#ifdef __linux__
+  if (data->set.mptcp)  {
+     transport = TRNSPRT_MPTCP;
   }
+#endif
   cf_socket_ctx_init(ctx, ai, transport);
 
   result = Curl_cf_create(&cf, &Curl_cft_tcp, ctx);

lib/cf-socket.h

@@ -28,6 +28,10 @@
 #include "nonblock.h" /* for curlx_nonblock(), formerly Curl_nonblock() */
 #include "sockaddr.h"
 
+#ifndef IPPROTO_MPTCP
+#define IPPROTO_MPTCP 262
+#endif
+
 struct Curl_addrinfo;
 struct Curl_cfilter;
 struct Curl_easy;

lib/easyoptions.c

@@ -178,6 +178,7 @@ struct curl_easyoption Curl_easyopts[] = {
   {"MAX_SEND_SPEED_LARGE", CURLOPT_MAX_SEND_SPEED_LARGE, CURLOT_OFF_T, 0},
   {"MIMEPOST", CURLOPT_MIMEPOST, CURLOT_OBJECT, 0},
   {"MIME_OPTIONS", CURLOPT_MIME_OPTIONS, CURLOT_LONG, 0},
+  {"MPTCP", CURLOPT_MPTCP, CURLOT_LONG, 0},
   {"NETRC", CURLOPT_NETRC, CURLOT_VALUES, 0},
   {"NETRC_FILE", CURLOPT_NETRC_FILE, CURLOT_STRING, 0},
   {"NEW_DIRECTORY_PERMS", CURLOPT_NEW_DIRECTORY_PERMS, CURLOT_LONG, 0},
@@ -375,6 +376,6 @@ struct curl_easyoption Curl_easyopts[] = {
  */
 int Curl_easyopts_check(void)
 {
-  return ((CURLOPT_LASTENTRY%10000) != (324 + 1));
+  return ((CURLOPT_LASTENTRY%10000) != (325 + 1));
 }
 #endif

lib/setopt.c

@@ -2931,6 +2931,9 @@ CURLcode Curl_vsetopt(struct Curl_easy *data, CURLoption option, va_list param)
     result = CURLE_NOT_BUILT_IN;
 #endif
     break;
+  case  CURLOPT_MPTCP:
+    data->set.mptcp = TRUE;
+    break;  
   case CURLOPT_SSL_ENABLE_NPN:
     break;
   case CURLOPT_SSL_ENABLE_ALPN:

lib/urldata.h

@@ -788,6 +788,7 @@ struct ldapconninfo;
 #define TRNSPRT_UDP 4
 #define TRNSPRT_QUIC 5
 #define TRNSPRT_UNIX 6
+#define TRNSPRT_MPTCP 7
 
 /*
  * The connectdata struct contains all fields and variables that should be
@@ -1811,6 +1812,7 @@ struct UserDefined {
 #ifdef USE_WEBSOCKETS
   BIT(ws_raw_mode);
 #endif
+  bool mptcp; /* enable MPTCP support */
 };
 
 #ifndef CURL_DISABLE_MIME

src/tool_cfgable.c

@@ -45,6 +45,7 @@ void config_init(struct OperationConfig *config)
   config->http09_allowed = FALSE;
   config->ftp_skip_ip = TRUE;
   config->file_clobber_mode = CLOBBER_DEFAULT;
+  config->mptcp = FALSE;
   curlx_dyn_init(&config->postdata, MAX_FILE2MEMORY);
 }
 

src/tool_cfgable.h

@@ -298,6 +298,7 @@ struct OperationConfig {
   struct State state;             /* for create_transfer() */
   bool rm_partial;                /* on error, remove partially written output
                                      files */
+  bool mptcp;
 };
 
 struct GlobalConfig {

src/tool_getparam.c

@@ -199,6 +199,7 @@ typedef enum {
   C_MAX_REDIRS,
   C_MAX_TIME,
   C_METALINK,
+  C_MPTCP,
   C_NEGOTIATE,
   C_NETRC,
   C_NETRC_FILE,
@@ -480,6 +481,7 @@ static const struct LongShort aliases[]= {
   {"max-redirs",                 ARG_STRG, ' ', C_MAX_REDIRS},
   {"max-time",                   ARG_STRG, 'm', C_MAX_TIME},
   {"metalink",                   ARG_BOOL, ' ', C_METALINK},
+  {"mptcp",                      ARG_BOOL, ' ', C_MPTCP},
   {"negotiate",                  ARG_BOOL, ' ', C_NEGOTIATE},
   {"netrc",                      ARG_BOOL, 'n', C_NETRC},
   {"netrc-file",                 ARG_FILE, ' ', C_NETRC_FILE},
@@ -2742,6 +2744,9 @@ ParameterError getparameter(const char *flag, /* f or -long-flag */
         }
       }
       break;
+    case C_MPTCP: /* --mptcp */
+      config->mptcp = TRUE;
+      break;
     default: /* unknown flag */
       err = PARAM_OPTION_UNKNOWN;
       break;

src/tool_listhelp.c

@@ -378,6 +378,9 @@ const struct helptxt helptext[] = {
   {"    --metalink",
    "Process given URLs as metalink XML file",
    CURLHELP_MISC},
+  {"    --mptcp",
+   "Enable Multipath TCP (MPTCP)",
+   CURLHELP_CONNECTION},
   {"    --negotiate",
    "Use HTTP Negotiate (SPNEGO) authentication",
    CURLHELP_AUTH | CURLHELP_HTTP},

src/tool_operate.c

@@ -1291,6 +1291,9 @@ static CURLcode single_transfer(struct GlobalConfig *global,
         if(config->tcp_fastopen)
           my_setopt(curl, CURLOPT_TCP_FASTOPEN, 1L);
 
+        if(config->mptcp)
+          my_setopt(curl, CURLOPT_MPTCP, 1L);        
+
         /* where to store */
         my_setopt(curl, CURLOPT_WRITEDATA, per);
         my_setopt(curl, CURLOPT_INTERLEAVEDATA, per);