serval-dna/overlay_mdp.c

/*
Copyright (C) 2010-2012 Paul Gardner-Stephen, Serval Project.
 
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
 
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
 
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
*/

#include "serval.h"
#include <sys/stat.h>

int mdp_abstract_socket=-1;
int mdp_named_socket=-1;
int overlay_mdp_setup_sockets()
{
  struct sockaddr_un name;
  int len;
  
  name.sun_family = AF_UNIX;
  
#ifndef HAVE_LINUX_IF_H
  /* Abstrack name space (i.e., non-file represented) unix domain sockets are a
     linux-only thing. */
  mdp_abstract_socket = -1;
#else
  if (mdp_abstract_socket==-1) {
    /* Abstract name space unix sockets is a special Linux thing, which is
       convenient for us because Android is Linux, but does not have a shared
       writable path that is on a UFS partition, so we cannot use traditional
       named unix domain sockets. So the abstract name space gives us a solution. */
    name.sun_path[0]=0;
    /* XXX The 100 should be replaced with the actual maximum allowed.
       Apparently POSIX requires it to be at least 100, but I would still feel
       more comfortable with using the appropriate constant. */
    snprintf(&name.sun_path[1],100,"org.servalproject.mesh.overlay.mdp");
    len = 1+strlen(&name.sun_path[1]) + sizeof(name.sun_family);
    
    mdp_abstract_socket = socket(AF_UNIX, SOCK_DGRAM, 0);
    if (mdp_abstract_socket>-1) {
      int dud=0;
      int r=bind(mdp_abstract_socket, (struct sockaddr *)&name, len);
      if (r) { dud=1; r=0; WHY("bind() of abstract name space socket failed (not an error on non-linux systems"); }
      if (dud) {
	close(mdp_abstract_socket);
	mdp_abstract_socket=-1;
	WHY("Could not open abstract name-space socket (only a problem on Linux).");
      }
    }
  }
#endif
  if (mdp_named_socket==-1) {
    char *instancepath=serval_instancepath();
    if (strlen(instancepath)>85) return WHY("Instance path too long to allow construction of named unix domain socket.");
    snprintf(&name.sun_path[0],100,"%s/mdp.socket",instancepath);
    unlink(&name.sun_path[0]);
    len = 0+strlen(&name.sun_path[0]) + sizeof(name.sun_family)+1;
    mdp_named_socket = socket(AF_UNIX, SOCK_DGRAM, 0);
    if (mdp_named_socket>-1) {
      int dud=0;
      int r=bind(mdp_named_socket, (struct sockaddr *)&name, len);
      if (r) { dud=1; r=0; WHY("bind() of named unix domain socket failed"); }
      if (dud) {
	close(mdp_named_socket);
	mdp_named_socket=-1;
	WHY("Could not open named unix domain socket.");
      }
    }
  }

  return 0;
  
}

int overlay_mdp_get_fds(struct pollfd *fds,int *fdcount,int fdmax)
{
  /* Make sure sockets are open */
  overlay_mdp_setup_sockets();

  if ((*fdcount)>=fdmax) return -1;
  if (mdp_abstract_socket>-1)
    {
      if (1||debug&DEBUG_IO) {
	fprintf(stderr,"MDP abstract name space socket is poll() slot #%d (fd %d)\n",
		*fdcount,mdp_abstract_socket);
      }
      fds[*fdcount].fd=mdp_abstract_socket;
      fds[*fdcount].events=POLLIN;
      (*fdcount)++;
    }
  if ((*fdcount)>=fdmax) return -1;
  if (mdp_named_socket>-1)
    {
      if (1||debug&DEBUG_IO) {
	fprintf(stderr,"MDP named unix domain socket is poll() slot #%d (fd %d)\n",
		*fdcount,mdp_named_socket);
      }
      fds[*fdcount].fd=mdp_named_socket;
      fds[*fdcount].events=POLLIN;
      (*fdcount)++;
    }


  return 0;
}

#define MDP_MAX_BINDINGS 100
#define MDP_MAX_SOCKET_NAME_LEN 110
int mdp_bindings_initialised=0;
sockaddr_mdp mdp_bindings[MDP_MAX_BINDINGS];
char mdp_bindings_sockets[MDP_MAX_BINDINGS][MDP_MAX_SOCKET_NAME_LEN];
int mdp_bindings_socket_name_lengths[MDP_MAX_BINDINGS];

int overlay_mdp_reply_error(int sock,
			    struct sockaddr_un *recvaddr,int recvaddrlen,
			    int error_number,char *message)
{
  overlay_mdp_frame mdpreply;

  mdpreply.packetTypeAndFlags=MDP_ERROR;
  mdpreply.error.error=error_number;
  if (error_number==0||message)
    snprintf(&mdpreply.error.message[0],128,"%s",message?message:"Success");
  else
    snprintf(&mdpreply.error.message[0],128,"Error code #%d",error_number);
  mdpreply.error.message[127]=0;
  int replylen=4+4+strlen(mdpreply.error.message)+1;
  errno=0;
  int r=sendto(sock,(char *)&mdpreply,replylen,0,
	       (struct sockaddr *)recvaddr,recvaddrlen);
  if (r<0) { 
    perror("sendto"); 
    WHY("sendto() failed when sending MDP reply"); 
    printf("sock=%d, r=%d\n",sock,r);
    return -1;
  }
  return 0;  
}

int overlay_mdp_reply_ok(int sock,
			 struct sockaddr_un *recvaddr,int recvaddrlen,
			 char *message)
{
  return overlay_mdp_reply_error(sock,recvaddr,recvaddrlen,0,message);
}

int overlay_mdp_process_bind_request(int sock,overlay_mdp_frame *mdp,
				     struct sockaddr_un *recvaddr,int recvaddrlen)
{
  int i;
  if (!mdp_bindings_initialised) {
    /* Mark all slots as unused */
    for(i=0;i<MDP_MAX_BINDINGS;i++) mdp_bindings[i].port=0;
    mdp_bindings_initialised=1;
  }

  /* See if binding already exists */
  int found=-1;
  int free=-1;
  for(i=0;i<MDP_MAX_BINDINGS;i++) {
    /* Look for duplicate bindings */
    if (mdp_bindings[i].port==mdp->bind.port_number)
      if (!memcmp(mdp_bindings[i].sid,mdp->bind.sid,SID_SIZE))
	{ found=i; break; }
    /* Look for free slots in case we need one */
    if ((free==-1)&&(mdp_bindings[i].port==0)) free=i;
  }
 
  /* Binding was found.  See if it is us, if so, then all is well,
     else we check flags to see if we should override the existing binding. */
  if (found>-1) {
    if (mdp_bindings_socket_name_lengths[found]==recvaddrlen)
      if (!memcmp(mdp_bindings_sockets[found],recvaddr->sun_path,recvaddrlen))
	{
	  fprintf(stderr,"Identical binding exists");
	  return overlay_mdp_reply_ok(sock,recvaddr,recvaddrlen,"Port bound (actually, it was already bound to you)");
	}
    /* Okay, so there is an existing binding.  Either replace it (if requested) or
       return an error */
    if (!(mdp->packetTypeAndFlags&MDP_FORCE))
      {
	fprintf(stderr,"Port already in use.\n");
	return overlay_mdp_reply_error(sock,recvaddr,recvaddrlen,3,
				       "Port already in use");
      }
    else {
      /* Cause existing binding to be replaced.
	 XXX - We should notify the existing binding holder that their binding
	 has been snaffled. */
      WHY("Warn socket holder about port-snatch");
      free=found;
    }
  }

  /* Okay, so no binding exists.  Make one, and return success.
     If we have too many bindings, we should return an error.
     XXX - We don't find out when the socket responsible for a binding has died,
     so stale bindings can hang around.  We really need a solution to this, e.g., 
     probing the sockets periodically (by sending an MDP NOOP frame perhaps?) and
     destroying any socket that reports an error.
  */
  if (free==-1) {
    /* XXX Should we probe for stale bindings here and now, since this is when
       we want the spare slots ? */
    WHY("Should probe existing bindings to see if any can be freed");
    fprintf(stderr,"No free port binding slots.  Close other connections and try again?");
    return overlay_mdp_reply_error(sock,recvaddr,recvaddrlen,4,"All binding slots in use. Close old connections and try again, or increase MDP_MAX_BINDINGS.");
  }

  /* Okay, record binding and report success */
  mdp_bindings[free].port=mdp->bind.port_number;
  memcpy(&mdp_bindings[free].sid[0],&mdp->bind.sid[0],SID_SIZE);
  mdp_bindings_socket_name_lengths[free]=recvaddrlen-2;
  memcpy(&mdp_bindings_sockets[free][0],&recvaddr->sun_path[0],
	 mdp_bindings_socket_name_lengths[free]);
  fprintf(stderr,"Port bound\n");
  return overlay_mdp_reply_ok(sock,recvaddr,recvaddrlen,"Port bound");
}

int overlay_saw_mdp_frame(int interface,overlay_frame *f,long long now)
{
  return WHY("Not implemented");
}

int overlay_mdp_poll()
{
  unsigned char buffer[16384];
  int ttl;
  unsigned char recvaddrbuffer[1024];
  struct sockaddr *recvaddr=(struct sockaddr *)&recvaddrbuffer[0];
  socklen_t recvaddrlen=sizeof(recvaddrbuffer);
  struct sockaddr_un *recvaddr_un=NULL;

  if (mdp_named_socket>-1) {
    ttl=-1;
    bzero((void *)recvaddrbuffer,sizeof(recvaddrbuffer));
    fcntl(mdp_named_socket, F_SETFL, 
	  fcntl(mdp_named_socket, F_GETFL, NULL)|O_NONBLOCK); 
    int len = recvwithttl(mdp_named_socket,buffer,sizeof(buffer),&ttl,
			  recvaddr,&recvaddrlen);
    recvaddr_un=(struct sockaddr_un *)recvaddr;

    if (len>0) {
      /* Look at overlay_mdp_frame we have received */
      overlay_mdp_frame *mdp=(overlay_mdp_frame *)&buffer[0];
      switch(mdp->packetTypeAndFlags&MDP_TYPE_MASK) {
      case MDP_TX: /* Send payload */
	break;
      case MDP_BIND: /* Bind to port */
	return overlay_mdp_process_bind_request(mdp_named_socket,mdp,
						recvaddr_un,recvaddrlen);
	break;
      default:
	/* Client is not allowed to send any other frame type */
	WHY("Illegal frame type.");
	mdp->packetTypeAndFlags=MDP_ERROR;
	mdp->error.error=2;
	snprintf(mdp->error.message,128,"Illegal request type.  Clients may use only MDP_TX or MDP_BIND.");
	int len=4+4+strlen(mdp->error.message)+1;
	errno=0;
	int e=sendto(mdp_named_socket,mdp,len,0,(struct sockaddr *)recvaddr,recvaddrlen);
	
	perror("sendto");
      }
    }

    fcntl(mdp_named_socket, F_SETFL, 
	  fcntl(mdp_named_socket, F_GETFL, NULL)&(~O_NONBLOCK)); 
  }

  if (!(random()&0xff)) WHY("Not implemented");
  return -1;
}

int mdp_client_socket=-1;
int overlay_mdp_dispatch(overlay_mdp_frame *mdp,int flags,int timeout_ms)
{
  int len=4;
  char mdp_temporary_socket[1024];
  mdp_temporary_socket[0]=0;
 
  /* Minimise frame length to save work and prevent accidental disclosure of
     memory contents. */
  switch(mdp->packetTypeAndFlags)
    {
    case MDP_TX: len=4+sizeof(mdp->out)+mdp->out.payload_length; break;
    case MDP_RX: len=4+sizeof(mdp->in)+mdp->out.payload_length; break;
    case MDP_BIND: len=4+4; break;
    case MDP_ERROR: len=4+4+strlen(mdp->error.message)+1; break;
    default:
      return WHY("Illegal MDP frame type.");
    }

  if (mdp_client_socket==-1) {
    /* Open socket to MDP server (thus connection is always local) */
    WHY("Use of abstract name space socket for Linux not implemented");
    
    mdp_client_socket = socket(AF_UNIX, SOCK_DGRAM, 0);
    if (mdp_client_socket < 0) {
      perror("socket");
      return WHY("Could not open socket to MDP server");
    }

    /* We must bind to a temporary file name */
    snprintf(mdp_temporary_socket,1024,"%s/mdp-client.socket",serval_instancepath());
    unlink(mdp_temporary_socket);    
    struct sockaddr_un name;
    name.sun_family = AF_UNIX;
    snprintf(&name.sun_path[0],100,"%s",mdp_temporary_socket);
    int len = 1+strlen(&name.sun_path[0]) + sizeof(name.sun_family)+1;
    int r=bind(mdp_client_socket, (struct sockaddr *)&name, len);
    if (r) {
      WHY("Could not bind MDP client socket to file name");
      perror("bind");
      return -1;
    }
  }

  /* Construct name of socket to send to. */
  char mdp_socket_name[101];
  mdp_socket_name[100]=0;
  snprintf(mdp_socket_name,100,"%s/mdp.socket",serval_instancepath());
  if (mdp_socket_name[100]) {
    if (mdp_temporary_socket[0]) unlink(mdp_temporary_socket);
    return WHY("instance path is too long (unix domain named sockets have a short maximum path length)");
  }
  struct sockaddr_un name;
  name.sun_family = AF_UNIX;
  strcpy(name.sun_path, mdp_socket_name); 

  int result=sendto(mdp_client_socket, mdp, len, 0,
		    (struct sockaddr *)&name, sizeof(struct sockaddr_un));
  if (result<0) {
    mdp->packetTypeAndFlags=MDP_ERROR;
    mdp->error.error=1;
    snprintf(mdp->error.message,128,"Error sending frame to MDP server.");
    /* Clear socket so that we have the chance of reconnecting */
    mdp_client_socket=-1;
    if (mdp_temporary_socket[0]) unlink(mdp_temporary_socket);
    return -1;
  } else {
    WHY("packet sent");
    if (!(flags&MDP_AWAITREPLY)) { 
      if (mdp_temporary_socket[0]) unlink(mdp_temporary_socket);
      return 0;
    }
  }

  /* Wait for a reply until timeout */
  struct pollfd fds[1];
  int fdcount=1;
  fds[0].fd=mdp_client_socket; fds[0].events=POLLIN;
  result = poll(fds,fdcount,timeout_ms);
  if (result==0) {
    /* Timeout */
    mdp->packetTypeAndFlags=MDP_ERROR;
    mdp->error.error=1;
    snprintf(mdp->error.message,128,"Timeout waiting for reply to MDP packet (packet was successfully sent).");
    if (mdp_temporary_socket[0]) unlink(mdp_temporary_socket);
    return -1;
  }

  /* Check if reply available */
  unsigned char replybuffer[2048];
  fcntl(mdp_client_socket, F_SETFL, 
	fcntl(mdp_client_socket, F_GETFL, NULL)|O_NONBLOCK); 
  int ttl=-1;
  unsigned char recvaddrbuffer[1024];
  struct sockaddr *recvaddr=(struct sockaddr *)recvaddrbuffer;
  unsigned int recvaddrlen=sizeof(recvaddrbuffer);
  struct sockaddr_un *recvaddr_un;
  len = recvwithttl(mdp_client_socket,replybuffer,sizeof(replybuffer),&ttl,
			recvaddr,&recvaddrlen);
  recvaddr_un=(struct sockaddr_un *)recvaddr;
  if (len>0) {
    /* Make sure recvaddr matches who we sent it to */
    if (strcmp(mdp_socket_name,recvaddr_un->sun_path)) {
      /* Okay, reply was PROBABLY not from the server, but on OSX if the path
	 has a symlink in it, it is resolved in the reply path, but might not
	 be in the request path (mdp_socket_name), thus we need to stat() and
	 compare inode numbers etc */
      struct stat sb1,sb2;
      if (stat(mdp_socket_name,&sb1)) return WHY("stat(mdp_socket_name) failed, so could not verify that reply came from MDP server");
      if (stat(recvaddr_un->sun_path,&sb2)) return WHY("stat(ra->sun_path) failed, so could not verify that reply came from MDP server");
      if ((sb1.st_ino!=sb2.st_ino)||(sb1.st_dev!=sb2.st_dev))
	return WHY("Reply did not come from server");
    }

    /* If all is well, examine result and return error code provided */
    overlay_mdp_frame *mdpreply=(overlay_mdp_frame *)&replybuffer[0];
    WHY("Got a reply from server");
    
  }

  if (mdp_temporary_socket[0]) unlink(mdp_temporary_socket);
  return WHY("Not implemented");
}