/* Based on ipsvd utilities written by Gerrit Pape <pape@smarden.org>
 * which are released into public domain by the author.
 * Homepage: http://smarden.sunsite.dk/ipsvd/
 *
 * Copyright (C) 2007 Denis Vlasenko.
 *
 * Licensed under GPLv2, see file LICENSE in this tarball for details.
 */

/* Based on ipsvd ipsvd-0.12.1. This tcpsvd accepts all options
 * which are supported by one from ipsvd-0.12.1, but not all are
 * functional. See help text at the end of this file for details.
 *
 * Code inside "#ifdef SSLSVD" is for sslsvd and is currently unused.
 * Code inside #if 0" is parts of original tcpsvd which are not implemented
 * for busyboxed version.
 *
 * Output of verbose mode matches original (modulo bugs and
 * unimplemented stuff). Unnatural splitting of IP and PORT
 * is retained (personally I prefer one-value "IP:PORT" notation -
 * it is a natural string representation of struct sockaddr_XX).
 *
 * TCPORIGDST{IP,PORT} is busybox-specific addition
 */

#include <limits.h>
#include <linux/netfilter_ipv4.h> /* wants <limits.h> */
#include "busybox.h"
#include "ipsvd_perhost.h"

#ifdef SSLSVD
#include "matrixSsl.h"
#include "ssl_io.h"
#endif


static unsigned max_per_host; /* originally in ipsvd_check.c */
static unsigned cur_per_host;
static unsigned verbose;
static unsigned cnum;
static unsigned cmax = 30;

/* Must match getopt32 in main! */
enum {
	OPT_c = (1 << 0),
	OPT_C = (1 << 1),
	OPT_i = (1 << 2),
	OPT_x = (1 << 3),
	OPT_u = (1 << 4),
	OPT_l = (1 << 5),
	OPT_E = (1 << 6),
	OPT_b = (1 << 7),
	OPT_h = (1 << 8),
	OPT_p = (1 << 9),
	OPT_t = (1 << 10),
	OPT_v = (1 << 11),
	OPT_V = (1 << 12),
	OPT_U = (1 << 13), /* from here: sslsvd only */
	OPT_slash = (1 << 14),
	OPT_Z = (1 << 15),
	OPT_K = (1 << 16),
};

static void connection_status(void)
{
	printf("%s: info: status %u/%u\n", applet_name, cnum, cmax);
}

static void sig_term_handler(int sig)
{
	if (verbose)
		printf("%s: info: sigterm received, exit\n", applet_name);
	exit(0);
}

static void sig_child_handler(int sig)
{
	int wstat;
	int pid;

	while ((pid = wait_nohang(&wstat)) > 0) {
		if (max_per_host)
			ipsvd_perhost_remove(pid);
		if (cnum)
			cnum--;
		if (verbose) {
			/* Little bloated, but tries to give accurate info
			 * how child exited. Makes easier to spot segfaulting
			 * children etc... */
			unsigned e = 0;
			const char *cause = "?exit";
			if (WIFEXITED(wstat)) {
				cause++;
				e = WEXITSTATUS(wstat);
			} else if (WIFSIGNALED(wstat)) {
				cause = "signal";
				e = WTERMSIG(wstat);
			}
			printf("%s: info: end %d %s %d\n",
					applet_name, pid, cause, e);
		}
	}
	if (verbose)
		connection_status();
}

int tcpsvd_main(int argc, char **argv);
int tcpsvd_main(int argc, char **argv)
{
	char *str_c, *str_C, *str_b, *str_t;
	char *user;
	struct hcc *hccp;
	const char *instructs;
	char *msg_per_host = NULL;
	unsigned len_per_host = len_per_host; /* gcc */
	int need_hostnames, need_remote_ip;
	int pid;
	int sock;
	int conn;
	unsigned backlog = 20;
	union {
		struct sockaddr sa;
		struct sockaddr_in sin;
		USE_FEATURE_IPV6(struct sockaddr_in6 sin6;)
	} sock_adr;
	socklen_t sockadr_size;
	uint16_t local_port = local_port;
	uint16_t remote_port;
	char *local_hostname = NULL;
	char *remote_hostname = (char*)""; /* "" used if no -h */
	char *local_ip = local_ip; /* gcc */
	char *remote_ip = remote_ip; /* gcc */
	//unsigned iscdb = 0;		/* = option_mask32 & OPT_x (TODO) */
	//unsigned long timeout = 0;
#ifndef SSLSVD
	struct bb_uidgid_t ugid;
#endif

	/* 3+ args, -i at most once, -p implies -h, -v is counter */
	opt_complementary = "-3:?:i--i:ph:vv";
#ifdef SSLSVD
	getopt32(argc, argv, "c:C:i:x:u:l:Eb:hpt:vU:/:Z:K:",
		&str_c, &str_C, &instructs, &instructs, &user, &local_hostname,
		&str_b, &str_t, &ssluser, &root, &cert, &key, &verbose
	);
#else
	getopt32(argc, argv, "c:C:i:x:u:l:Eb:hpt:v",
		&str_c, &str_C, &instructs, &instructs, &user, &local_hostname,
		&str_b, &str_t, &verbose
	);
#endif
	if (option_mask32 & OPT_c)
		cmax = xatou_range(str_c, 1, INT_MAX);
	if (option_mask32 & OPT_C) { /* -C n[:message] */
		max_per_host = bb_strtou(str_C, &str_C, 10);
		if (str_C[0]) {
			if (str_C[0] != ':')
				bb_show_usage();
			msg_per_host = str_C + 1;
			len_per_host = strlen(msg_per_host);
		}
	}
	if (max_per_host > cmax)
		max_per_host = cmax;
	if (option_mask32 & OPT_u) {
		if (!get_uidgid(&ugid, user, 1))
			bb_error_msg_and_die("unknown user/group: %s", user);
	}
	if (option_mask32 & OPT_b)
		backlog = xatou(str_b);
//	if (option_mask32 & OPT_t) timeout = xatou(str_t);
#ifdef SSLSVD
	if (option_mask32 & OPT_U) ssluser = (char*)optarg; break;
	if (option_mask32 & OPT_slash) root = (char*)optarg; break;
	if (option_mask32 & OPT_Z) cert = (char*)optarg; break;
	if (option_mask32 & OPT_K) key = (char*)optarg; break;
#endif
	argv += optind;
	if (!argv[0][0] || LONE_CHAR(argv[0], '0'))
		argv[0] = (char*)"0.0.0.0";

	/* stdout is used for logging, don't buffer */
	setlinebuf(stdout);
	bb_sanitize_stdio(); /* fd# 1,2 must be opened */

	need_hostnames = verbose || !(option_mask32 & OPT_E);
	need_remote_ip = max_per_host || need_hostnames;

#ifdef SSLSVD
	sslser = user;
	client = 0;
	if ((getuid() == 0) && !(option_mask32 & OPT_u)) {
		xfunc_exitcode = 100;
		bb_error_msg_and_die("fatal: -U ssluser must be set when running as root");
	}
	if (option_mask32 & OPT_u)
		if (!uidgid_get(&sslugid, ssluser, 1)) {
			if (errno) {
				xfunc_exitcode = 100;
				bb_perror_msg_and_die("fatal: cannot get user/group: %s", ssluser);
			}
			xfunc_exitcode = 111;
			bb_error_msg_and_die("fatal: unknown user/group '%s'", ssluser);
		}
	if (!cert) cert = "./cert.pem";
	if (!key) key = cert;
	if (matrixSslOpen() < 0)
		fatal("cannot initialize ssl");
	if (matrixSslReadKeys(&keys, cert, key, 0, ca) < 0) {
		if (client)
			fatal("cannot read cert, key, or ca file");
		fatal("cannot read cert or key file");
	}
	if (matrixSslNewSession(&ssl, keys, 0, SSL_FLAGS_SERVER) < 0)
		fatal("cannot create ssl session");
#endif

	sig_block(SIGCHLD);
	signal(SIGCHLD, sig_child_handler);
	signal(SIGTERM, sig_term_handler);
	signal(SIGPIPE, SIG_IGN);

	if (max_per_host)
		ipsvd_perhost_init(cmax);

	local_port = bb_lookup_port(argv[1], "tcp", 0);
	sock = create_and_bind_stream_or_die(argv[0], local_port);
	xlisten(sock, backlog);
	/* ndelay_off(sock); - it is the default I think? */

#ifndef SSLSVD
	if (option_mask32 & OPT_u) {
		/* drop permissions */
		xsetgid(ugid.gid);
		xsetuid(ugid.uid);
	}
#endif
	close(0);

	if (verbose) {
		/* we do it only for ":port" cosmetics... oh well */
		len_and_sockaddr *lsa = xhost2sockaddr(argv[0], local_port);
		char *addr = xmalloc_sockaddr2dotted(&lsa->sa, lsa->len);

		printf("%s: info: listening on %s", applet_name, addr);
		free(addr);
#ifndef SSLSVD
		if (option_mask32 & OPT_u)
			printf(", uid %u, gid %u",
				(unsigned)ugid.uid, (unsigned)ugid.gid);
#endif
		puts(", starting");
	}

	/* The rest is a main accept() loop */

 again:
	hccp = NULL;

	while (cnum >= cmax)
		sig_pause(); /* wait for any signal (expecting SIGCHLD) */

	sockadr_size = sizeof(sock_adr);
	sig_unblock(SIGCHLD);
	conn = accept(sock, &sock_adr.sa, &sockadr_size);
	sig_block(SIGCHLD);
	if (conn == -1) {
		if (errno != EINTR)
			bb_perror_msg("accept");
		goto again;
	}

	if (max_per_host) {
		/* we drop connection immediately if cur_per_host > max_per_host
		 * (minimizing load under SYN flood) */
		remote_ip = xmalloc_sockaddr2dotted_noport(&sock_adr.sa, sockadr_size);
		cur_per_host = ipsvd_perhost_add(remote_ip, max_per_host, &hccp);
		if (cur_per_host > max_per_host) {
			free(remote_ip);
			/* ipsvd_perhost_add detected that max is exceeded
			 * (and did not store us in connection table) */
			if (msg_per_host) {
				ndelay_on(conn);
				/* don't test for errors */
				write(conn, msg_per_host, len_per_host);
			}
			close(conn);
			goto again;
		}
	}

	cnum++;
	if (verbose)
		connection_status();

	pid = fork();
	if (pid == -1) {
		bb_perror_msg("fork");
		close(conn);
		goto again;
	}
	if (pid != 0) {
		/* parent */
		close(conn);
		if (hccp)
			hccp->pid = pid;
		goto again;
	}

	/* Child: prepare env, log, and exec prog */

	close(sock);

	if (!max_per_host && need_remote_ip)
		remote_ip = xmalloc_sockaddr2dotted_noport(&sock_adr.sa, sizeof(sock_adr));
	/* else it is already done */

	remote_port = get_nport(&sock_adr.sa);
	remote_port = ntohs(remote_port);

	if (verbose) {
		pid = getpid();
		printf("%s: info: pid %d from %s\n", applet_name, pid, remote_ip);
	}

	if (need_hostnames && (option_mask32 & OPT_h)) {
		remote_hostname = xmalloc_sockaddr2host(&sock_adr.sa, sizeof(sock_adr));
		if (!remote_hostname) {
			bb_error_msg("warning: cannot look up hostname for %s", remote_ip);
			remote_hostname = (char*)"";
		}
	}

	sockadr_size = sizeof(sock_adr);
	/* Errors ignored (I'm not paranoid enough to imagine kernel
	 * which doesn't know local ip) */
	getsockname(conn, &sock_adr.sa, &sockadr_size);

	if (need_hostnames) {
		local_ip = xmalloc_sockaddr2dotted_noport(&sock_adr.sa, sockadr_size);
		local_port = get_nport(&sock_adr.sa);
		local_port = ntohs(local_port);
		if (!local_hostname) {
			local_hostname = xmalloc_sockaddr2host_noport(&sock_adr.sa, sockadr_size);
			if (!local_hostname)
				bb_error_msg_and_die("cannot look up local hostname for %s", local_ip);
		}
	}

	if (!(option_mask32 & OPT_E)) {
		/* setup ucspi env */

		/* Extract "original" destination addr:port
		 * from Linux firewall. Useful when you redirect
		 * an outbond connection to local handler, and it needs
		 * to know where it originally tried to connect */
		sockadr_size = sizeof(sock_adr);
		if (getsockopt(conn, SOL_IP, SO_ORIGINAL_DST, &sock_adr.sa, &sockadr_size) == 0) {
			char *ip = xmalloc_sockaddr2dotted_noport(&sock_adr.sa, sockadr_size);
			unsigned port = get_nport(&sock_adr.sa);
			port = ntohs(port);
			xsetenv("TCPORIGDSTIP", ip);
			xsetenv("TCPORIGDSTPORT", utoa(port));
			free(ip);
		}
		xsetenv("PROTO", "TCP");
		xsetenv("TCPLOCALIP", local_ip);
		xsetenv("TCPLOCALPORT", utoa(local_port));
		xsetenv("TCPLOCALHOST", local_hostname);
		xsetenv("TCPREMOTEIP", remote_ip);
		xsetenv("TCPREMOTEPORT", utoa(remote_port));
		if (option_mask32 & OPT_h) {
			xsetenv("TCPREMOTEHOST", remote_hostname);
		}
		xsetenv("TCPREMOTEINFO", "");
		/* additional */
		if (cur_per_host > 0)
			xsetenv("TCPCONCURRENCY", utoa(cur_per_host));
	}

#if 0
	if (instructs) {
		ac = ipsvd_check(iscdb, &inst, &match, (char*)instructs,
							remote_ip, remote_hostname, timeout);
		if (ac == -1) drop2("cannot check inst", remote_ip);
		if (ac == IPSVD_ERR) drop2("cannot read", (char*)instructs);
	} else
		ac = IPSVD_DEFAULT;
#endif

	if (max_per_host && verbose)
		printf("%s: info: concurrency %u %s %u/%u\n",
			applet_name, pid, remote_ip, cur_per_host, max_per_host);

	if (verbose) {
		printf("%s: info: start %u %s:%s :%s:%s:%u\n",
			applet_name, pid,
			local_hostname, local_ip,
			remote_hostname, remote_ip, (unsigned)remote_port);
#if 0
		switch(ac) {
		case IPSVD_DENY:
			printf("deny "); break;
		case IPSVD_DEFAULT:
		case IPSVD_INSTRUCT:
			printf("start "); break;
		case IPSVD_EXEC:
			printf("exec "); break;
		}
		...
		if (instructs) {
			printf(" ");
			if (iscdb) {
				printf((char*)instructs);
				printf("/");
			}
			outfix(match.s);
			if(inst.s && inst.len && (verbose > 1)) {
				printf(": ");
				printf(&inst);
			}
		}
		printf("\n");
#endif
	}

#if 0
	if (ac == IPSVD_DENY) {
		close(conn);
		_exit(100);
	}
	if (ac == IPSVD_EXEC) {
		args[0] = "/bin/sh";
		args[1] = "-c";
		args[2] = inst.s;
		args[3] = 0;
		run = args;
	} else
		run = argv + 2; /* below: we use argv+2 (was using run) */
#endif

	xmove_fd(conn, 0);
	dup2(0, 1);

	signal(SIGTERM, SIG_DFL);
	signal(SIGPIPE, SIG_DFL);
	signal(SIGCHLD, SIG_DFL);
	sig_unblock(SIGCHLD);

	argv += 2;
#ifdef SSLSVD
	strcpy(id, utoa(pid);
	ssl_io(0, argv);
#else
	BB_EXECVP(argv[0], argv);
#endif
	bb_perror_msg_and_die("exec '%s'", argv[0]);
}

/*
tcpsvd [-hpEvv] [-c n] [-C n:msg] [-b n] [-u user] [-l name]
	[-i dir|-x cdb] [ -t sec] host port prog

tcpsvd creates a TCP/IP socket, binds it to the address host:port,
and listens on the socket for incoming connections.

On each incoming connection, tcpsvd conditionally runs a program,
with standard input reading from the socket, and standard output
writing to the socket, to handle this connection. tcpsvd keeps
listening on the socket for new connections, and can handle
multiple connections simultaneously.

tcpsvd optionally checks for special instructions depending
on the IP address or hostname of the client that initiated
the connection, see ipsvd-instruct(5).

host
    host either is a hostname, or a dotted-decimal IP address,
    or 0. If host is 0, tcpsvd accepts connections to any local
    IP address.
    * busybox accepts IPv6 addresses and host:port pairs too
      In this case second parameter is ignored
port
    tcpsvd accepts connections to host:port. port may be a name
    from /etc/services or a number.
prog
    prog consists of one or more arguments. For each connection,
    tcpsvd normally runs prog, with file descriptor 0 reading from
    the network, and file descriptor 1 writing to the network.
    By default it also sets up TCP-related environment variables,
    see tcp-environ(5)
-i dir
    read instructions for handling new connections from the instructions
    directory dir. See ipsvd-instruct(5) for details.
    * ignored by busyboxed version
-x cdb
    read instructions for handling new connections from the constant database
    cdb. The constant database normally is created from an instructions
    directory by running ipsvd-cdb(8).
    * ignored by busyboxed version
-t sec
    timeout. This option only takes effect if the -i option is given.
    While checking the instructions directory, check the time of last access
    of the file that matches the clients address or hostname if any, discard
    and remove the file if it wasn't accessed within the last sec seconds;
    tcpsvd does not discard or remove a file if the user's write permission
    is not set, for those files the timeout is disabled. Default is 0,
    which means that the timeout is disabled.
    * ignored by busyboxed version
-l name
    local hostname. Do not look up the local hostname in DNS, but use name
    as hostname. This option must be set if tcpsvd listens on port 53
    to avoid loops.
-u user[:group]
    drop permissions. Switch user ID to user's UID, and group ID to user's
    primary GID after creating and binding to the socket. If user is followed
    by a colon and a group name, the group ID is switched to the GID of group
    instead. All supplementary groups are removed.
-c n
    concurrency. Handle up to n connections simultaneously. Default is 30.
    If there are n connections active, tcpsvd defers acceptance of a new
    connection until an active connection is closed.
-C n[:msg]
    per host concurrency. Allow only up to n connections from the same IP
    address simultaneously. If there are n active connections from one IP
    address, new incoming connections from this IP address are closed
    immediately. If n is followed by :msg, the message msg is written
    to the client if possible, before closing the connection. By default
    msg is empty. See ipsvd-instruct(5) for supported escape sequences in msg.

    For each accepted connection, the current per host concurrency is
    available through the environment variable TCPCONCURRENCY. n and msg
    can be overwritten by ipsvd(7) instructions, see ipsvd-instruct(5).
    By default tcpsvd doesn't keep track of connections.
-h
    Look up the client's hostname in DNS.
-p
    paranoid. After looking up the client's hostname in DNS, look up the IP
    addresses in DNS for that hostname, and forget about the hostname
    if none of the addresses match the client's IP address. You should
    set this option if you use hostname based instructions. The -p option
    implies the -h option.
    * ignored by busyboxed version
-b n
    backlog. Allow a backlog of approximately n TCP SYNs. On some systems n
    is silently limited. Default is 20.
-E
    no special environment. Do not set up TCP-related environment variables.
-v
    verbose. Print verbose messsages to standard output.
-vv
    more verbose. Print more verbose messages to standard output.
    * no difference between -v and -vv in busyboxed version
*/