SCTP messaging between two threads

[mikedilger]

Is there any way to communicate over SCTP (over UDP) on localhost between two threads in the same program? My use case is a test suite. I'm wrapping usrsctp for the rust language.

I would presume the two threads would need to be working with different UDP encapsulation ports. But I also presume usrsctp_init() is called only once and the structures are shared by all the threads, thus not having separate ports to communicate to each other over.

I tried just using the default 9899 for both threads, but using the same SCTP address/port in both bind() in the server thread, and connect() in the client thread, but nothing happens (and wireshark shows no activity).

[velichkov]

Hi @mikedilger,

I just implemented a unit test for the application I'm working on, similar to what you've described above and it works.

I've used only one UDP port (the default 9899), called usrsctp_init only once, bind server to a port on all interface and called connect to the Server's SCTP port (no need to bind the client).

Here is excerpt from the tshark -i any -f "port 9899" -V output

Internet Protocol Version 4, Src: 127.0.0.1 (127.0.0.1), Dst: 127.0.0.1 (127.0.0.1)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..00 = Explicit Congestion Notification: Not-ECT (Not ECN-Capable Transport) (0x00)
    Total Length: 156
    Identification: 0xb2b7 (45751)
    Flags: 0x02 (Don't Fragment)
        0... .... = Reserved bit: Not set
        .1.. .... = Don't fragment: Set
        ..0. .... = More fragments: Not set
    Fragment offset: 0
    Time to live: 64
    Protocol: UDP (17)
    Header checksum: 0x8997 [validation disabled]
        [Good: False]
        [Bad: False]
    Source: 127.0.0.1 (127.0.0.1)
    Destination: 127.0.0.1 (127.0.0.1)
User Datagram Protocol, Src Port: sctp-tunneling (9899), Dst Port: sctp-tunneling (9899)
    Source port: sctp-tunneling (9899)
    Destination port: sctp-tunneling (9899)
    Length: 136
    Checksum: 0xfe9b [validation disabled]
        [Good Checksum: False]
        [Bad Checksum: False]
Stream Control Transmission Protocol, Src Port: 64839 (64839), Dst Port: 58707 (58707)
    Source port: 64839
    Destination port: 58707

  1 0.000000000    127.0.0.1 -> 127.0.0.1    SCTP 172 INIT 
  2 0.000083330    127.0.0.1 -> 127.0.0.1    SCTP 492 INIT_ACK 
  3 0.000152627    127.0.0.1 -> 127.0.0.1    SCTP 400 COOKIE_ECHO 
  4 0.000233159    127.0.0.1 -> 127.0.0.1    SCTP 60 COOKIE_ACK 
  5 0.000349945    127.0.0.1 -> 127.0.0.1    SCTP 84 DATA 
  6 0.000540295    127.0.0.1 -> 127.0.0.1    SCTP 72 SACK 
  7 0.002164253    127.0.0.1 -> 127.0.0.1    SCTP 80 DATA 

[mikedilger]

Thanks for running that test. I'll investigate further when I get time to work on this again, but at this point it sounds like I must be doing something wrong on my side.