// SPDX-License-Identifier: GPL-2.0

#define _GNU_SOURCE

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <string.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <unistd.h>
#include <time.h>

#include <sys/ioctl.h>
#include <sys/random.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/wait.h>

#include <netdb.h>
#include <netinet/in.h>

#include <linux/tcp.h>
#include <linux/sockios.h>

#ifndef IPPROTO_MPTCP
#define IPPROTO_MPTCP 262
#endif
#ifndef SOL_MPTCP
#define SOL_MPTCP 284
#endif

static int pf = AF_INET;
static int proto_tx = IPPROTO_MPTCP;
static int proto_rx = IPPROTO_MPTCP;

static void die_perror(const char *msg)
{
	perror(msg);
	exit(1);
}

static void die_usage(int r)
{
	fprintf(stderr, "Usage: mptcp_inq [-6] [ -t tcp|mptcp ] [ -r tcp|mptcp]\n");
	exit(r);
}

static void xerror(const char *fmt, ...)
{
	va_list ap;

	va_start(ap, fmt);
	vfprintf(stderr, fmt, ap);
	va_end(ap);
	fputc('\n', stderr);
	exit(1);
}

static const char *getxinfo_strerr(int err)
{
	if (err == EAI_SYSTEM)
		return strerror(errno);

	return gai_strerror(err);
}

static void xgetaddrinfo(const char *node, const char *service,
			 const struct addrinfo *hints,
			 struct addrinfo **res)
{
	int err = getaddrinfo(node, service, hints, res);

	if (err) {
		const char *errstr = getxinfo_strerr(err);

		fprintf(stderr, "Fatal: getaddrinfo(%s:%s): %s\n",
			node ? node : "", service ? service : "", errstr);
		exit(1);
	}
}

static int sock_listen_mptcp(const char * const listenaddr,
			     const char * const port)
{
	int sock = -1;
	struct addrinfo hints = {
		.ai_protocol = IPPROTO_TCP,
		.ai_socktype = SOCK_STREAM,
		.ai_flags = AI_PASSIVE | AI_NUMERICHOST
	};

	hints.ai_family = pf;

	struct addrinfo *a, *addr;
	int one = 1;

	xgetaddrinfo(listenaddr, port, &hints, &addr);
	hints.ai_family = pf;

	for (a = addr; a; a = a->ai_next) {
		sock = socket(a->ai_family, a->ai_socktype, proto_rx);
		if (sock < 0)
			continue;

		if (-1 == setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &one,
				     sizeof(one)))
			perror("setsockopt");

		if (bind(sock, a->ai_addr, a->ai_addrlen) == 0)
			break; /* success */

		perror("bind");
		close(sock);
		sock = -1;
	}

	freeaddrinfo(addr);

	if (sock < 0)
		xerror("could not create listen socket");

	if (listen(sock, 20))
		die_perror("listen");

	return sock;
}

static int sock_connect_mptcp(const char * const remoteaddr,
			      const char * const port, int proto)
{
	struct addrinfo hints = {
		.ai_protocol = IPPROTO_TCP,
		.ai_socktype = SOCK_STREAM,
	};
	struct addrinfo *a, *addr;
	int sock = -1;

	hints.ai_family = pf;

	xgetaddrinfo(remoteaddr, port, &hints, &addr);
	for (a = addr; a; a = a->ai_next) {
		sock = socket(a->ai_family, a->ai_socktype, proto);
		if (sock < 0)
			continue;

		if (connect(sock, a->ai_addr, a->ai_addrlen) == 0)
			break; /* success */

		die_perror("connect");
	}

	if (sock < 0)
		xerror("could not create connect socket");

	freeaddrinfo(addr);
	return sock;
}

static int protostr_to_num(const char *s)
{
	if (strcasecmp(s, "tcp") == 0)
		return IPPROTO_TCP;
	if (strcasecmp(s, "mptcp") == 0)
		return IPPROTO_MPTCP;

	die_usage(1);
	return 0;
}

static void parse_opts(int argc, char **argv)
{
	int c;

	while ((c = getopt(argc, argv, "h6t:r:")) != -1) {
		switch (c) {
		case 'h':
			die_usage(0);
			break;
		case '6':
			pf = AF_INET6;
			break;
		case 't':
			proto_tx = protostr_to_num(optarg);
			break;
		case 'r':
			proto_rx = protostr_to_num(optarg);
			break;
		default:
			die_usage(1);
			break;
		}
	}
}

/* wait up to timeout milliseconds */
static void wait_for_ack(int fd, int timeout, size_t total)
{
	int i;

	for (i = 0; i < timeout; i++) {
		int nsd, ret, queued = -1;
		struct timespec req;

		ret = ioctl(fd, TIOCOUTQ, &queued);
		if (ret < 0)
			die_perror("TIOCOUTQ");

		ret = ioctl(fd, SIOCOUTQNSD, &nsd);
		if (ret < 0)
			die_perror("SIOCOUTQNSD");

		if ((size_t)queued > total)
			xerror("TIOCOUTQ %u, but only %zu expected\n", queued, total);
		assert(nsd <= queued);

		if (queued == 0)
			return;

		/* wait for peer to ack rx of all data */
		req.tv_sec = 0;
		req.tv_nsec = 1 * 1000 * 1000ul; /* 1ms */
		nanosleep(&req, NULL);
	}

	xerror("still tx data queued after %u ms\n", timeout);
}

static void connect_one_server(int fd, int unixfd)
{
	size_t len, i, total, sent;
	char buf[4096], buf2[4096];
	ssize_t ret;

	len = rand() % (sizeof(buf) - 1);

	if (len < 128)
		len = 128;

	for (i = 0; i < len ; i++) {
		buf[i] = rand() % 26;
		buf[i] += 'A';
	}

	buf[i] = '\n';

	/* un-block server */
	ret = read(unixfd, buf2, 4);
	assert(ret == 4);

	assert(strncmp(buf2, "xmit", 4) == 0);

	ret = write(unixfd, &len, sizeof(len));
	assert(ret == (ssize_t)sizeof(len));

	ret = write(fd, buf, len);
	if (ret < 0)
		die_perror("write");

	if (ret != (ssize_t)len)
		xerror("short write");

	ret = read(unixfd, buf2, 4);
	assert(strncmp(buf2, "huge", 4) == 0);

	total = rand() % (16 * 1024 * 1024);
	total += (1 * 1024 * 1024);
	sent = total;

	ret = write(unixfd, &total, sizeof(total));
	assert(ret == (ssize_t)sizeof(total));

	wait_for_ack(fd, 5000, len);

	while (total > 0) {
		if (total > sizeof(buf))
			len = sizeof(buf);
		else
			len = total;

		ret = write(fd, buf, len);
		if (ret < 0)
			die_perror("write");
		total -= ret;

		/* we don't have to care about buf content, only
		 * number of total bytes sent
		 */
	}

	ret = read(unixfd, buf2, 4);
	assert(ret == 4);
	assert(strncmp(buf2, "shut", 4) == 0);

	wait_for_ack(fd, 5000, sent);

	ret = write(fd, buf, 1);
	assert(ret == 1);
	close(fd);
	ret = write(unixfd, "closed", 6);
	assert(ret == 6);

	close(unixfd);
}

static void get_tcp_inq(struct msghdr *msgh, unsigned int *inqv)
{
	struct cmsghdr *cmsg;

	for (cmsg = CMSG_FIRSTHDR(msgh); cmsg ; cmsg = CMSG_NXTHDR(msgh, cmsg)) {
		if (cmsg->cmsg_level == IPPROTO_TCP && cmsg->cmsg_type == TCP_CM_INQ) {
			memcpy(inqv, CMSG_DATA(cmsg), sizeof(*inqv));
			return;
		}
	}

	xerror("could not find TCP_CM_INQ cmsg type");
}

static void process_one_client(int fd, int unixfd)
{
	unsigned int tcp_inq;
	size_t expect_len;
	char msg_buf[4096];
	char buf[4096];
	char tmp[16];
	struct iovec iov = {
		.iov_base = buf,
		.iov_len = 1,
	};
	struct msghdr msg = {
		.msg_iov = &iov,
		.msg_iovlen = 1,
		.msg_control = msg_buf,
		.msg_controllen = sizeof(msg_buf),
	};
	ssize_t ret, tot;

	ret = write(unixfd, "xmit", 4);
	assert(ret == 4);

	ret = read(unixfd, &expect_len, sizeof(expect_len));
	assert(ret == (ssize_t)sizeof(expect_len));

	if (expect_len > sizeof(buf))
		xerror("expect len %zu exceeds buffer size", expect_len);

	for (;;) {
		struct timespec req;
		unsigned int queued;

		ret = ioctl(fd, FIONREAD, &queued);
		if (ret < 0)
			die_perror("FIONREAD");
		if (queued > expect_len)
			xerror("FIONREAD returned %u, but only %zu expected\n",
			       queued, expect_len);
		if (queued == expect_len)
			break;

		req.tv_sec = 0;
		req.tv_nsec = 1000 * 1000ul;
		nanosleep(&req, NULL);
	}

	/* read one byte, expect cmsg to return expected - 1 */
	ret = recvmsg(fd, &msg, 0);
	if (ret < 0)
		die_perror("recvmsg");

	if (msg.msg_controllen == 0)
		xerror("msg_controllen is 0");

	get_tcp_inq(&msg, &tcp_inq);

	assert((size_t)tcp_inq == (expect_len - 1));

	iov.iov_len = sizeof(buf);
	ret = recvmsg(fd, &msg, 0);
	if (ret < 0)
		die_perror("recvmsg");

	/* should have gotten exact remainder of all pending data */
	assert(ret == (ssize_t)tcp_inq);

	/* should be 0, all drained */
	get_tcp_inq(&msg, &tcp_inq);
	assert(tcp_inq == 0);

	/* request a large swath of data. */
	ret = write(unixfd, "huge", 4);
	assert(ret == 4);

	ret = read(unixfd, &expect_len, sizeof(expect_len));
	assert(ret == (ssize_t)sizeof(expect_len));

	/* peer should send us a few mb of data */
	if (expect_len <= sizeof(buf))
		xerror("expect len %zu too small\n", expect_len);

	tot = 0;
	do {
		iov.iov_len = sizeof(buf);
		ret = recvmsg(fd, &msg, 0);
		if (ret < 0)
			die_perror("recvmsg");

		tot += ret;

		get_tcp_inq(&msg, &tcp_inq);

		if (tcp_inq > expect_len - tot)
			xerror("inq %d, remaining %d total_len %d\n",
			       tcp_inq, expect_len - tot, (int)expect_len);

		assert(tcp_inq <= expect_len - tot);
	} while ((size_t)tot < expect_len);

	ret = write(unixfd, "shut", 4);
	assert(ret == 4);

	/* wait for hangup. Should have received one more byte of data. */
	ret = read(unixfd, tmp, sizeof(tmp));
	assert(ret == 6);
	assert(strncmp(tmp, "closed", 6) == 0);

	sleep(1);

	iov.iov_len = 1;
	ret = recvmsg(fd, &msg, 0);
	if (ret < 0)
		die_perror("recvmsg");
	assert(ret == 1);

	get_tcp_inq(&msg, &tcp_inq);

	/* tcp_inq should be 1 due to received fin. */
	assert(tcp_inq == 1);

	iov.iov_len = 1;
	ret = recvmsg(fd, &msg, 0);
	if (ret < 0)
		die_perror("recvmsg");

	/* expect EOF */
	assert(ret == 0);
	get_tcp_inq(&msg, &tcp_inq);
	assert(tcp_inq == 1);

	close(fd);
}

static int xaccept(int s)
{
	int fd = accept(s, NULL, 0);

	if (fd < 0)
		die_perror("accept");

	return fd;
}

static int server(int unixfd)
{
	int fd = -1, r, on = 1;

	switch (pf) {
	case AF_INET:
		fd = sock_listen_mptcp("127.0.0.1", "15432");
		break;
	case AF_INET6:
		fd = sock_listen_mptcp("::1", "15432");
		break;
	default:
		xerror("Unknown pf %d\n", pf);
		break;
	}

	r = write(unixfd, "conn", 4);
	assert(r == 4);

	alarm(15);
	r = xaccept(fd);

	if (-1 == setsockopt(r, IPPROTO_TCP, TCP_INQ, &on, sizeof(on)))
		die_perror("setsockopt");

	process_one_client(r, unixfd);

	return 0;
}

static int client(int unixfd)
{
	int fd = -1;

	alarm(15);

	switch (pf) {
	case AF_INET:
		fd = sock_connect_mptcp("127.0.0.1", "15432", proto_tx);
		break;
	case AF_INET6:
		fd = sock_connect_mptcp("::1", "15432", proto_tx);
		break;
	default:
		xerror("Unknown pf %d\n", pf);
	}

	connect_one_server(fd, unixfd);

	return 0;
}

static void init_rng(void)
{
	unsigned int foo;

	if (getrandom(&foo, sizeof(foo), 0) == -1) {
		perror("getrandom");
		exit(1);
	}

	srand(foo);
}

static pid_t xfork(void)
{
	pid_t p = fork();

	if (p < 0)
		die_perror("fork");
	else if (p == 0)
		init_rng();

	return p;
}

static int rcheck(int wstatus, const char *what)
{
	if (WIFEXITED(wstatus)) {
		if (WEXITSTATUS(wstatus) == 0)
			return 0;
		fprintf(stderr, "%s exited, status=%d\n", what, WEXITSTATUS(wstatus));
		return WEXITSTATUS(wstatus);
	} else if (WIFSIGNALED(wstatus)) {
		xerror("%s killed by signal %d\n", what, WTERMSIG(wstatus));
	} else if (WIFSTOPPED(wstatus)) {
		xerror("%s stopped by signal %d\n", what, WSTOPSIG(wstatus));
	}

	return 111;
}

int main(int argc, char *argv[])
{
	int e1, e2, wstatus;
	pid_t s, c, ret;
	int unixfds[2];

	parse_opts(argc, argv);

	e1 = socketpair(AF_UNIX, SOCK_DGRAM, 0, unixfds);
	if (e1 < 0)
		die_perror("pipe");

	s = xfork();
	if (s == 0)
		return server(unixfds[1]);

	close(unixfds[1]);

	/* wait until server bound a socket */
	e1 = read(unixfds[0], &e1, 4);
	assert(e1 == 4);

	c = xfork();
	if (c == 0)
		return client(unixfds[0]);

	close(unixfds[0]);

	ret = waitpid(s, &wstatus, 0);
	if (ret == -1)
		die_perror("waitpid");
	e1 = rcheck(wstatus, "server");
	ret = waitpid(c, &wstatus, 0);
	if (ret == -1)
		die_perror("waitpid");
	e2 = rcheck(wstatus, "client");

	return e1 ? e1 : e2;
}