Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I found one other question from 2017 about accessing Linux SocketCAN sockets from Perl, but there weren't any replies that I could make sense of. One that suggested using pack/unpack to modify the socket type parameter to the IO::Socket call. I have no idea how to make use of that, but after the passage of time, I wonder if someone has come up with a more straightforward solution. Like the previous poster, I have been able to use the linux candump tool with a Perl wrapper, but I was hoping for something a little cleaner. Perl is my weapon of choice for ad hoc scripts to acquire and process data, and this is the first time I've found no direct method to do what I want it to do.

My present use case is to capture data from an Arduino sending on a MCP2515 CAnbus module and receiving on a RPi with a CANbus interface that works well in Linux as far as I can tell. In the fullness of time, I'd like to create an intelligent sniffer that can capture specific data from a busy CANbus that is part of a control system in a particle accelerator lab.

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Re: Access socketCAN from Perl
by bliako (Abbot) on Jul 19, 2023 at 00:01 UTC
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      I'm not really familiar with XS wrappers, but on the surface, it appears to provide similar functionality to using a child process and filesystem sematics to read or write. Is there more to it than that? My present scheme looks like this: 
          open( CAN, "candump|" ); 

    while( <CAN> ){ 
            # Process captue data here...
        }

      [download]
      Do I get anything more by using XS Wrappers? Ultimately, I'd like to have the socket access so I can use it to perform both reads and writes to the CANbus.
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        What I provided *writes* to the CANbus. When I say "wrapper" I don't mean shelling or piping out from perl but calling the can-util functions directly.

        If you are familiar with C, have a look at cansend.c (of the distribution I posted) and particularly the cansend(...) function. You will see there how to open the socketCAN and write to it. In candump.c, of can-utils distribution, you will see how they open the socketCAN for reading and read from it (and print to stdout).

        If you are familiar with C, again, I suggest that you build up a small library, following can-utils's code, where you provide funcionality like socketCAN_open(interface), socketCAN_close(socket), socketCAN_read(socket), socketCAN_write(socker, data). Then you proceed implementing your sniffer in C utilising these functions.

        FInally, write the XS wrapper to call your function. But here you have a major problem: you need to poll the CANbus at regular intervals and when it has data you need to push that back to Perl somehow. One way to do this is via a user-specified Perl callback which is called whenever the bus has data. That's possible and in Net::Ncap you can see how they do it (their XS code is at https://metacpan.org/release/MSISK/Net-Ncap-1.01/source). Others here may have better ideas

        The other way is via pure-perl, opening a Socket (in Perl) and do all I describe above in Perl. BUT I don't think they have implemented the socket type AF_CAN which is already specified in include/linux/can.h. So how do you open the socketCAN? Hmm. perhaps posting an issue at https://rt.cpan.org/Public/Dist/Display.html?Name=Socket and ask them what their plan is for socketCAN. Or better, post a patch for AF_CAN to be covered.

        Finally, what you have suggested and doing already (piping out to candump) is OK, AFAIC. Although it may suffer if you aim for realtime performance.

        So, depending on your C experience and time to invest, chose your route. I suggest the 1st route: building your C library (and don't worry too much about XS as I and others here can help you, and with C obviously). The 2nd route is mostly effortless and ready to use now, as you have already tried it. Check its realtime performance. Edit: Either way you chose, if you have the time, please post an issue about socketCAN at the Socket's bug tracker (Or I can do it sometime in the future).

        bw, bliako

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