/*
  Clear Channel Sametime Proxy Utility
  The Meanwhile Project

  This is a tool which can act as a proxy between a client and a
  sametime server, which will force all channels to be created without
  any encryption method. This makes reverse-engineering much, much
  easier.

  It also outputs the messages sent to and from the client to stdout
  as hex pairs. If compiled with USE_HEXDUMP, output will be printed
  via `hexdump -C`
  
  All it really does is nab all Channel Create messages, strip the
  offered ciphers portion from the message and replace it with an
  empty ciphers list.

  Christopher O'Brien <siege@preoccupied.net>
*/


#include <netinet/in.h>
#include <netdb.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>

#include <glib.h>
#include <glib/glist.h>

#include <mw_common.h>
#include <mw_message.h>


struct proxy_side {
  int sock;
  GIOChannel *chan;
  gint chan_io;

  guchar *buf;
  gsize buf_size;
  gsize buf_recv;

  void (*forward)(const guchar *buf, gsize len);
};


static struct proxy_side client;
static struct proxy_side server;


static void hexdump(const char *txt, const guchar *buf, gsize len) {
  FILE *fp;

  if(txt) fprintf(stdout, "\n%s\n", txt);
  fflush(stdout);

  fp = popen("hexdump -C", "w");
  fwrite(buf, len, 1, fp);
  fflush(fp);
  pclose(fp);
}


static void put_msg(struct mwMessage *msg, struct mwOpaque *o) {
  struct mwPutBuffer *b;

  b = mwPutBuffer_new();
  mwMessage_put(b, msg);
  mwPutBuffer_finalize(o, b);
  
  b = mwPutBuffer_new();
  mwOpaque_put(b, o);
  mwOpaque_clear(o);
  mwPutBuffer_finalize(o, b);
}


static void side_buf_free(struct proxy_side *s) {
  g_free(s->buf);
  s->buf = NULL;
  s->buf_size = 0;
  s->buf_recv = 0;
}


static void munge_redir() {
  struct mwMessage *msg;
  struct mwOpaque o = { 0, 0 };

  msg = mwMessage_new(mwMessage_LOGIN_CONTINUE);
  put_msg(msg, &o);
  mwMessage_free(msg);

  server.forward(o.data, o.len);

  mwOpaque_clear(&o);
}


static void munge_create(struct proxy_side *side,
			 struct mwMsgChannelCreate *msg) {

  struct mwOpaque o = { 0, 0 };
  GList *l;

  for(l = msg->encrypt.items; l; l = l->next) {
    mwEncryptItem_clear(l->data);
    g_free(l->data);
  }
  g_list_free(msg->encrypt.items);
  msg->encrypt.items = NULL;

  msg->encrypt.mode = 0x00;
  msg->encrypt.extra = 0x00;
  msg->encrypt.flag = FALSE;

  put_msg(MW_MESSAGE(msg), &o);
  side->forward(o.data, o.len);
  mwOpaque_clear(&o);
}


static void side_process(struct proxy_side *s, const guchar *buf, gsize len) {
  struct mwOpaque o = { .len = len, .data = (guchar *) buf };
  struct mwGetBuffer *b;
  guint16 type;

  if(! len) return;

  b = mwGetBuffer_wrap(&o);
  type = guint16_peek(b);

  switch(type) {
  case mwMessage_LOGIN_REDIRECT:
    munge_redir();
    break;

  case mwMessage_CHANNEL_CREATE:
    {
      struct mwMessage *msg = mwMessage_get(b);
      munge_create(s, (struct mwMsgChannelCreate *) msg);
      mwMessage_free(msg);
      break;
    }
    
  default:
    {
      struct mwPutBuffer *pb = mwPutBuffer_new();
      struct mwOpaque po = { 0, 0 };
      mwOpaque_put(pb, &o);
      mwPutBuffer_finalize(&po, pb);
      s->forward(po.data, po.len);
      mwOpaque_clear(&po);
    }
  }

  mwGetBuffer_free(b);
}


#define ADVANCE(b, n, count) { b += count; n -= count; }


/* handle input to complete an existing buffer */
static gsize side_recv_cont(struct proxy_side *s, const guchar *b, gsize n) {

  gsize x = s->buf_size - s->buf_recv;

  if(n < x) {
    memcpy(s->buf+s->buf_recv, b, n);
    s->buf_recv += n;
    return 0;
    
  } else {
    memcpy(s->buf+s->buf_recv, b, x);
    ADVANCE(b, n, x);
    
    if(s->buf_size == 4) {
      struct mwOpaque o = { .len = 4, .data = s->buf };
      struct mwGetBuffer *gb = mwGetBuffer_wrap(&o);
      x = guint32_peek(gb);
      mwGetBuffer_free(gb);

      if(n < x) {
	guchar *t;
	x += 4;
	t = (guchar *) g_malloc(x);
	memcpy(t, s->buf, 4);
	memcpy(t+4, b, n);
	
	side_buf_free(s);
	
	s->buf = t;
	s->buf_size = x;
	s->buf_recv = n + 4;
	return 0;
	
      } else {
	side_buf_free(s);
	side_process(s, b, x);
	ADVANCE(b, n, x);
      }
      
    } else {
      side_process(s, s->buf+4, s->buf_size-4);
      side_buf_free(s);
    }
  }

  return n;
}


/* handle input when there's nothing previously buffered */
static gsize side_recv_empty(struct proxy_side *s, const guchar *b, gsize n) {
  struct mwOpaque o = { .len = n, .data = (guchar *) b };
  struct mwGetBuffer *gb;
  gsize x;

  if(n < 4) {
    s->buf = (guchar *) g_malloc0(4);
    memcpy(s->buf, b, n);
    s->buf_size = 4;
    s->buf_recv = n;
    return 0;
  }
  
  gb = mwGetBuffer_wrap(&o);
  x = guint32_peek(gb);
  mwGetBuffer_free(gb);
  if(! x) return n - 4;

  if(n < (x + 4)) {

    x += 4;
    s->buf = (guchar *) g_malloc(x);
    memcpy(s->buf, b, n);
    s->buf_size = x;
    s->buf_recv = n;
    return 0;
    
  } else {
    ADVANCE(b, n, 4);
    side_process(s, b, x);
    ADVANCE(b, n, x);

    return n;
  }
}


static gsize side_recv(struct proxy_side *s, const guchar *b, gsize n) {

  if(n && (s->buf_size == 0) && (*b & 0x80)) {
    ADVANCE(b, n, 1);
  }

  if(n == 0) {
    return 0;

  } else if(s->buf_size > 0) {
    return side_recv_cont(s, b, n);

  } else {
    return side_recv_empty(s, b, n);
  }
}


static void feed_buf(struct proxy_side *side, const guchar *buf, gsize n) {
  guchar *b = (guchar *) buf;
  gsize remain = 0;
  
  g_return_if_fail(side != NULL);

  while(n > 0) {
    remain = side_recv(side, b, n);
    b += (n - remain);
    n = remain;
  }
}


static int read_recv(struct proxy_side *side) {
  guchar buf[2048];
  int len;

  len = read(side->sock, buf, 2048);
  if(len > 0) feed_buf(side, buf, (gsize) len);

  return len;
}


static void done() {
  close(client.sock);
  close(server.sock);
  exit(0);
}


static gboolean read_cb(GIOChannel *chan,
			GIOCondition cond,
			gpointer data) {

  struct proxy_side *side = data;
  int ret = 0;

  if(cond & G_IO_IN) {
    ret = read_recv(side);
    if(ret > 0) return TRUE;
  }

  if(side->sock) {
    g_source_remove(side->chan_io);
    close(side->sock);
    side->sock = 0;
    side->chan = NULL;
    side->chan_io = 0;
  }

  done();
  
  return FALSE;
}


static void client_cb(const guchar *buf, gsize len) {
  if(server.sock) {
    hexdump("client -> server", buf, len);
    write(server.sock, buf, len);
  }
}


static gboolean listen_cb(GIOChannel *chan,
			  GIOCondition cond,
			  gpointer data) {

  struct sockaddr_in rem;
  guint len = sizeof(rem);
  struct proxy_side *side = data;
  int sock;
  
  sock = accept(side->sock, (struct sockaddr *) &rem, &len);
  g_assert(sock > 0);

  g_source_remove(side->chan_io);
  side->sock = sock;
  side->chan = g_io_channel_unix_new(sock);
  side->chan_io = g_io_add_watch(side->chan, G_IO_IN | G_IO_ERR | G_IO_HUP,
				 read_cb, side);

  return FALSE;
}


static void init_client(int port) {
  /* start listening on the local port specifier */

  struct sockaddr_in sin;
  int sock;

  sock = socket(PF_INET, SOCK_STREAM, 0);
  g_assert(sock >= 0);

  memset(&sin, 0, sizeof(struct sockaddr_in));
  sin.sin_family = PF_INET;
  sin.sin_port = htons(port);
  sin.sin_addr.s_addr = htonl(INADDR_ANY);

  if(bind(sock, (struct sockaddr *)&sin, sizeof(sin)) < 0)
    g_assert_not_reached();

  if(listen(sock, 1) < 0)
    g_assert_not_reached();

  client.forward = client_cb;
  client.sock = sock;
  client.chan = g_io_channel_unix_new(sock);
  client.chan_io = g_io_add_watch(client.chan, G_IO_IN | G_IO_ERR | G_IO_HUP,
				  listen_cb, &client);
}


static void server_cb(const guchar *buf, gsize len) {
  if(client.sock) {
    hexdump("server -> client", buf, len);
    write(client.sock, buf, len);
  }
}


/* address lookup used by init_sock */
static void init_sockaddr(struct sockaddr_in *addr,
			  const char *host, int port) {

  struct hostent *hostinfo;

  addr->sin_family = AF_INET;
  addr->sin_port = htons (port);
  hostinfo = gethostbyname(host);
  if(hostinfo == NULL) {
    fprintf(stderr, "Unknown host %s.\n", host);
    exit(1);
  }
  addr->sin_addr = *(struct in_addr *) hostinfo->h_addr;
}


static void init_server(const char *host, int port) {
  /* connect to server on host/port */
  struct sockaddr_in srvrname;
  int sock;

  sock = socket(PF_INET, SOCK_STREAM, 0);
  if(sock < 0) {
    fprintf(stderr, "socket failure");
    exit(1);
  }
  
  init_sockaddr(&srvrname, host, port);
  connect(sock, (struct sockaddr *)&srvrname, sizeof(srvrname));

  server.forward = server_cb;
  server.sock = sock;
  server.chan = g_io_channel_unix_new(sock);
  server.chan_io = g_io_add_watch(server.chan, G_IO_IN | G_IO_ERR | G_IO_HUP,
				  read_cb, &server);
}


int main(int argc, char *argv[]) {
  char *host = NULL;
  int client_port = 0, server_port = 0;

  memset(&client, 0, sizeof(struct proxy_side));
  memset(&server, 0, sizeof(struct proxy_side));

  if(argc > 1) {
    char *z;

    host = argv[1];
    z = host;

    host = strchr(z, ':');
    if(host) *host++ = '\0';
    client_port = atoi(z);

    z = strchr(host, ':');
    if(z) *z++ = '\0';
    server_port = atoi(z);
  }

  if(!host || !*host || !client_port || !server_port) {
    fprintf(stderr,
	    ( " Usage: %s local_port:remote_host:remote_port\n"
	      " Creates a locally-running sametime proxy which enforces"
	      " unencrypted channels\n" ),
	    argv[0]);
    exit(1);
  }

  /* @todo create signal handlers to cleanup sockets */

  init_client(client_port);
  init_server(host, server_port);

  g_main_loop_run(g_main_loop_new(NULL, FALSE)); 
  return 0;
}