Update to the C example #5

obonaventure · 2022-09-09T08:52:59Z

Code and README show how to detect that Multipath TCP is not enabled and fall back to regular TCP when Multipath TCP is not supported on the host.

…rtable manner and by falling back to TCP if used on a system that does not support Multipath TCP

… and fall back to TCP if Multipath TCP is not supported on this system

matttbe

thank you for the new update!

Some suggestions here and one sentence that looks wrong.

matttbe · 2022-09-09T08:57:00Z

c/README.md


-The [simple project](mptcphello.c) in this repository also illustrates how to automatically check with autoconf whether the compilation is on a Multipath TCP enabled host, see [configure.ac](configure.ac)
+Most networked applications abstract the creation of a TCP socket in a specific function that is called instead of calling [socket()](https://www.man7.org/linux/man-pages/man3/socket.3p.html) directly. This is a good opportunity to make the code portable and useable on hosts that support Multipath TCP or not. In practice, to efficiently enable Multipath TCP, your code should try to use Multipath TCP when creating the first TCP socket. If this socket is successfully created, then Multipath TCP is enabled on the host and you can continue to use Multipath TCP. Otherwise, the application is running on a host that does not yet support Multipath TCP. In this unfortunate case, you should fall back to regular TCP and always create TCP sockets. You might print an error message to encourage the user to upgrade his/her system to support Multipath TCP...


I'm not sure to understand the first sentence in this line here. I think some words are missing. Maybe:

In most network applications abstract, the creation of a TCP socket in a specific function is called instead of calling [socket()](https://www.man7.org/linux/man-pages/man3/socket.3p.html) directly.

matttbe · 2022-09-09T08:57:58Z

c/README.md

@@ -1,15 +1,17 @@
 # Using Multipath TCP in C


-It is pretty simple to use Multipath TCP with the C language. You simply need to pass IPPROTO_MPTCP as the third argument of the [socket()](https://www.man7.org/linux/man-pages/man3/socket.3p.html) system call. Make sure that IPPROTO_MPTCP is correctly defined and if you, define it as follows :
+It is pretty simple to use Multipath TCP with the C language. You simply need to pass IPPROTO_MPTCP as the third argument of the [socket()](https://www.man7.org/linux/man-pages/man3/socket.3p.html) system call. Make sure that IPPROTO_MPTCP is correctly defined and if not, define it as follows :


(do not hesitate to add backquotes around IPPROTO_MPTCP and any other non English words or non capitalised names)

matttbe · 2022-09-09T09:00:24Z

c/README.md

-The [simple project](mptcphello.c) in this repository also illustrates how to automatically check with autoconf whether the compilation is on a Multipath TCP enabled host, see [configure.ac](configure.ac)
+Most networked applications abstract the creation of a TCP socket in a specific function that is called instead of calling [socket()](https://www.man7.org/linux/man-pages/man3/socket.3p.html) directly. This is a good opportunity to make the code portable and useable on hosts that support Multipath TCP or not. In practice, to efficiently enable Multipath TCP, your code should try to use Multipath TCP when creating the first TCP socket. If this socket is successfully created, then Multipath TCP is enabled on the host and you can continue to use Multipath TCP. Otherwise, the application is running on a host that does not yet support Multipath TCP. In this unfortunate case, you should fall back to regular TCP and always create TCP sockets. You might print an error message to encourage the user to upgrade his/her system to support Multipath TCP...
+
+The [simple project](mptcphello.c) in this repository illustrates this strategy. If you want to automatically check with autoconf whether the compilation is on a Multipath TCP enabled host, see [configure.ac](configure.ac)


for the configure.ac, I would put big warnings to avoid doing that at compilation time except maybe to simplify tests (and still, I don't think it is a good idea to do that at the compilation time, even for tests but that's another story :) )

matttbe · 2022-09-09T09:00:55Z

c/mptcphello.c


+// IPPROTO_MPTCP is defined in <netinet/in.h> on recent kernels only


(it depends on the libc version in fact, not the kernel in fact but that's probably a detail)

matttbe · 2022-09-09T09:04:03Z

c/mptcphello.c

+    s = socket(domain, SOCK_STREAM, IPPROTO_MPTCP);
+    if(s==-1 && ( errno==EPROTONOSUPPORT || errno==ENOPROTOOPT) ) {
+      // Multipath TCP is not supported on this system
+      use_mptcp = false;


maybe good to re-add a clear error message?

fprintf(stderr, "Unable to create an MPTCP socket: " "your kernel probably don't support MPTCP yet, " "falling back to TCP for this socket and all the next ones.\n");

matttbe · 2022-09-09T09:05:39Z

c/mptcphello.c

+    }
+  }
+  // Multipath TCP is not supported on this system, return a TCP socket
+  return(socket(domain, SOCK_STREAM, IPPROTO_TCP));


(parenthesis not needed after the return)

matttbe · 2022-09-09T09:08:12Z

c/mptcphello.c

-    exit(0);
-  }
+
+  s = socket_create(AF_INET);


maybe good to check for errors?

if (s < 0) { fprintf(stderr, "Unable to create a socket\n"); exit(EXIT_FAILURE); } // do something useful with the socket close(s); return EXIT_SUCCESS;

matttbe · 2022-09-09T09:08:37Z

c/mptcphello.c

+  // do something useful with the socket
+
+  close(s);
+


(no need to have a return to avoid a warning? Or maybe only visible with -Wall?)

obonaventure added 3 commits September 8, 2022 16:01

Update of python example

ba4d8db

Example showing how to create Multipath TCP sockets in python in a po…

87ec170

…rtable manner and by falling back to TCP if used on a system that does not support Multipath TCP

New C example and README showing how to create a Multipath TCP socket…

20cde97

… and fall back to TCP if Multipath TCP is not supported on this system

matttbe requested changes Sep 9, 2022

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Update to the C example #5

Update to the C example #5

obonaventure commented Sep 9, 2022

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		The [simple project](mptcphello.c) in this repository also illustrates how to automatically check with autoconf whether the compilation is on a Multipath TCP enabled host, see [configure.ac](configure.ac)
		Most networked applications abstract the creation of a TCP socket in a specific function that is called instead of calling [socket()](https://www.man7.org/linux/man-pages/man3/socket.3p.html) directly. This is a good opportunity to make the code portable and useable on hosts that support Multipath TCP or not. In practice, to efficiently enable Multipath TCP, your code should try to use Multipath TCP when creating the first TCP socket. If this socket is successfully created, then Multipath TCP is enabled on the host and you can continue to use Multipath TCP. Otherwise, the application is running on a host that does not yet support Multipath TCP. In this unfortunate case, you should fall back to regular TCP and always create TCP sockets. You might print an error message to encourage the user to upgrade his/her system to support Multipath TCP...


		// IPPROTO_MPTCP is defined in <netinet/in.h> on recent kernels only

Update to the C example #5

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Update to the C example #5

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