dtee, implemented using sctp

output.txt

$ make LDLIBS=-lsctp sctp
g++     sctp.cpp  -lsctp -o sctp
$ ./sctp
flags 32896 assoc_id 0 stream 0 port 42417 len 20
flags 32896 assoc_id 0 stream 0 port 49898 len 20
flags 128 assoc_id 132 stream 0 port 42417 len 1 data o
flags 128 assoc_id 132 stream 0 port 42417 len 2 data OO
flags 128 assoc_id 134 stream 0 port 49898 len 1 data e
flags 128 assoc_id 134 stream 0 port 49898 len 2 data EE
flags 128 assoc_id 134 stream 0 port 49898 len 1 data e
flags 128 assoc_id 134 stream 0 port 49898 len 2 data EE
flags 128 assoc_id 132 stream 0 port 42417 len 1 data o
flags 128 assoc_id 132 stream 0 port 42417 len 2 data OO

sctp.cpp

#include <errno.h>
#include <netinet/in.h>
#include <netinet/sctp.h>
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>

#include <iostream>

int main() {
	int si = -1;
	int so = -1;
	int se = -1;
	struct sockaddr_in ai{};
	struct sockaddr_in ao{};
	struct sockaddr_in ae{};
	struct sockaddr_in am{};
	socklen_t li = sizeof(ai);
	socklen_t lo = sizeof(ao);
	socklen_t le = sizeof(ae);
	socklen_t lm;
	pid_t pid = getpid();
	struct sctp_event_subscribe ei{};

	ai.sin_family = AF_INET;
	ai.sin_addr.s_addr = htonl(0x7F000000 | (pid & 0xFFFFFF));

	ao.sin_family = AF_INET;
	ao.sin_addr.s_addr = htonl(0x7F000000 | (pid & 0xFFFFFF));

	ae.sin_family = AF_INET;
	ae.sin_addr.s_addr = htonl(0x7F000000 | (pid & 0xFFFFFF));

	si = socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);
	if (si == -1) {
		perror("socket");
		return 1;
	}

	so = socket(PF_INET, SOCK_STREAM, IPPROTO_SCTP);
	if (so == -1) {
		perror("socket");
		return 1;
	}

	se = socket(PF_INET, SOCK_STREAM, IPPROTO_SCTP);
	if (se == -1) {
		perror("socket");
		return 1;
	}

	if (bind(si, reinterpret_cast<struct sockaddr*>(&ai), sizeof(ai)) == -1) {
		perror("bind");
		return 1;
	}

	if (bind(so, reinterpret_cast<struct sockaddr*>(&ao), sizeof(ao)) == -1) {
		perror("bind");
		return 1;
	}

	if (bind(se, reinterpret_cast<struct sockaddr*>(&ae), sizeof(ae)) == -1) {
		perror("bind");
		return 1;
	}

	if (getsockname(si, reinterpret_cast<struct sockaddr*>(&ai), &li) == -1) {
		perror("getsockname");
		return 1;
	}

	if (getsockname(so, reinterpret_cast<struct sockaddr*>(&ao), &lo) == -1) {
		perror("getsockname");
		return 1;
	}

	if (getsockname(se, reinterpret_cast<struct sockaddr*>(&ae), &le) == -1) {
		perror("getsockname");
		return 1;
	}

	ei.sctp_association_event = 1;
	ei.sctp_data_io_event = 1;

	if (setsockopt(si, IPPROTO_SCTP, SCTP_EVENTS, &ei, sizeof(ei)) == -1) {
		perror("setsockopt");
		return 1;
	}

	if (listen(si, 2) == -1) {
		perror("listen");
		return 1;
	}

	if (connect(so, reinterpret_cast<struct sockaddr*>(&ai), lo) == -1) {
		perror("connect");
		return 1;
	}

	if (connect(se, reinterpret_cast<struct sockaddr*>(&ai), le) == -1) {
		perror("connect");
		return 1;
	}

	write(so, "o", 1);
	write(so, "OO", 2);
	write(so, "o", 1);
	write(so, "OO", 2);
	write(se, "e", 1);
	write(se, "EE", 2);
	write(se, "e", 1);
	write(se, "EE", 2);

	while (true) {
		char buf[4096] = { 0 };
		struct sctp_sndrcvinfo info{};
		int flags;
		int len;

		lm = sizeof(am);
		flags = 0;

		len = sctp_recvmsg(si, buf, sizeof(buf), reinterpret_cast<struct sockaddr *>(&am), &lm, &info, &flags);
		if (len == -1) {
			perror("sctp_recvmsg");
			return 1;
		}

		std::cout
			<< "flags " << flags
			<< " assoc_id " << info.sinfo_assoc_id
			<< " stream " << info.sinfo_stream
			<< " port " << am.sin_port
			<< " len " << len;

		if (!(flags & MSG_NOTIFICATION)) {
			if (len > 0)
				std::cout << " data ";

			for (int i = 0; i < len; i++ ) {
				std::cout << buf[i];
			}
		}

		std::cout << std::endl;
	}

	return 0;
}