aprsfeed.c

// Process AX.25 frames containing APRS data, feed to APRS2 network
// Copyright 2018-2023, Phil Karn, KA9Q

#define _GNU_SOURCE 1
#include <assert.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdint.h>

#include <locale.h>
#include <errno.h>
#include <sys/socket.h>
#include <netdb.h>
#include <math.h>
#include <ctype.h>
#if __linux__
#include <bsd/string.h>
#else
#include <string.h>
#endif
#include <sysexits.h>

#include "multicast.h"
#include "ax25.h"
#include "misc.h"

char *Mcast_address_text = "ax25.mcast.local";
char *Host = "noam.aprs2.net";
char *Port = "14580";
char *User;
char *Passcode;
char *Logfilename;
FILE *Logfile;
const char *App_path;
int Verbose;

int Input_fd = -1;
int Network_fd = -1;

pthread_t Read_thread;
void *netreader(void *arg);

int main(int argc,char *argv[]){
  App_path = argv[0];
  // Quickly drop root if we have it
  // The sooner we do this, the fewer options there are for abuse
  if(seteuid(getuid()) != 0)
    fprintf(stderr,"seteuid: %s\n",strerror(errno));
  
  setlocale(LC_ALL,getenv("LANG"));
  setlinebuf(stdout);

  int c;
  while((c = getopt(argc,argv,"u:p:I:vh:f:V")) != EOF){
    switch(c){
    case 'f':
      Logfilename = optarg;
      Verbose = 0;
      break;
    case 'u':
      User = optarg;
      break;
    case 'v':
      if(!Logfilename)
	Verbose++;
      break;
    case 'h':
      Host = optarg;
      break;
    case 'p':
      Passcode = optarg;
      break;
    case 'I':
      Mcast_address_text = optarg;
      break;
    case 'V':
      VERSION();
      exit(EX_OK);
    default:
      fprintf(stderr,"Usage: %s -u user [-p passcode] [-v] [-I mcast_address][-h host]\n",argv[0]);
      exit(EX_USAGE);
    }
  }
  // Set up multicast input
  {
    struct sockaddr_storage sock;
    resolve_mcast(Mcast_address_text,&sock,DEFAULT_RTP_PORT,NULL,0);
    Input_fd = listen_mcast(&sock,NULL);
  }
  if(Input_fd == -1){
    fprintf(stderr,"Can't set up multicast input from %s\n",Mcast_address_text);
    exit(EX_IOERR);
  }

  if(Logfilename)
    Logfile = fopen(Logfilename,"a");
  else if(Verbose)
    Logfile = stdout;

  if(Logfile){
    setlinebuf(Logfile);
    fprintf(Logfile,"APRS feeder program by KA9Q\n");
  }
  if(User == NULL){
    fprintf(stderr,"Must specify -u User\n");
    exit(EX_USAGE);
  }
  if(!Passcode){
    // Calculate trivial hash authenticator
    int hash = 0x73e2;
    char callsign[11];
    strlcpy(callsign,User,sizeof(callsign));
    char *cp;
    if((cp = strchr(callsign,'-')) != NULL)
      *cp = '\0';
    
    int const len = strlen(callsign);

    for(int i=0; i<len; i += 2){
      hash ^= toupper(callsign[i]) << 8;
      hash ^= toupper(callsign[i+1]);
    }
    hash &= 0x7fff;
    if(asprintf(&Passcode,"%d",hash) < 0){
      fprintf(stderr,"Unexpected error in computing passcode\n");
      exit(EX_SOFTWARE);
    }
  }

  while(true) {
    // Resolve the APRS network server
    struct addrinfo hints;
    memset(&hints,0,sizeof(hints));
    hints.ai_family = PF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;
    hints.ai_flags = AI_CANONNAME|AI_ADDRCONFIG;
    
    struct addrinfo *results = NULL;
    int ecode;
    // Try a few times in case we come up before the resolver is quite ready
    for(int tries=0; tries < 10; tries++){
      if((ecode = getaddrinfo(Host,Port,&hints,&results)) == 0)
	break;
      usleep(500000); // 500 ms
    }
    if(ecode != 0){
      fprintf(stderr,"Can't getaddrinfo(%s,%s): %s\n",Host,Port,gai_strerror(ecode));
      usleep(5000000); // 5 sec
      continue; // Keep trying
    }
    struct addrinfo *resp;
    for(resp = results; resp != NULL; resp = resp->ai_next){
      if((Network_fd = socket(resp->ai_family,resp->ai_socktype,resp->ai_protocol)) < 0)
	continue;
      if(connect(Network_fd,resp->ai_addr,resp->ai_addrlen) == 0)
	break;
      close(Network_fd); Network_fd = -1;
    }
    if(resp == NULL){
      fprintf(stderr,"Can't connect to server %s:%s\n",Host,Port);
      sleep(600); // 5 minutes
      freeaddrinfo(results);
      resp = results = NULL;
      continue;
    }
    if(Logfile)
      fprintf(Logfile,"Connected to APRS server %s port %s\n",resp->ai_canonname,Port);
  
    freeaddrinfo(results);
    resp = results = NULL;

    FILE *network = fdopen(Network_fd,"w+");
    setlinebuf(network);
    
    pthread_create(&Read_thread,NULL,netreader,NULL);
    
    // Log into the network
    if(fprintf(network,"user %s pass %s vers KA9Q-aprs 1.0\r\n",User,Passcode) <= 0){
      // error
      fclose(network); network = NULL;
      sleep(600); // 5 minutes;
      continue;
    }
    uint8_t packet[PKTSIZE];
    int size;
    while((size = recv(Input_fd,packet,sizeof(packet),0)) > 0){
      struct rtp_header rtp_header;
      uint8_t const *dp = packet;
      
      dp = ntoh_rtp(&rtp_header,dp);
      size -= dp - packet;
      
      if(rtp_header.pad){
	// Remove padding
	size -= dp[size-1];
	rtp_header.pad = 0;
      }

      if(size <= 0)
	continue;  // Bogus RTP header?
      
      if(rtp_header.type != AX25_pt)
	continue; // Wrong type
      
      if(Logfile){
	// Emit local timestamp
	char result[1024];

	fprintf(Logfile,"%s ssrc %u seq %d",
		format_gpstime(result,sizeof(result),gps_time_ns()),
		rtp_header.ssrc,rtp_header.seq);
      }
      
      // Parse incoming AX.25 frame
      struct ax25_frame frame;
      if(ax25_parse(&frame,dp,size) < 0){
	if(Logfile)
	  fprintf(Logfile," Unparsable packet\n");
	continue;
      }
      
      // Construct TNC2-style monitor string for APRS reporting
      char monstring[PKTSIZE]; // Should be large enough for any legal AX.25 frame; we'll assert this periodically
      int sspace = sizeof(monstring);
      int infolen = 0;
      int is_tcpip = 0;
      {
	memset(monstring,0,sizeof(monstring));
	char *cp = monstring;
	{
	  int w = snprintf(cp,sspace,"%s>%s",frame.source,frame.dest);
	  cp += w; sspace -= w;
	  assert(sspace > 0);
	}
	for(int i=0;i<frame.ndigi;i++){
	  // if "TCPIP" appears, this frame came off the Internet and should not be sent back to it
	  if(strcmp(frame.digipeaters[i].name,"TCPIP") == 0)
	    is_tcpip = 1;
	  int const w = snprintf(cp,sspace,",%s%s",frame.digipeaters[i].name,frame.digipeaters[i].h ? "*" : "");
	  cp += w; sspace -= w;
	  assert(sspace > 0);
	}
	{
	  // qAR means a bidirectional i-gate, qAO means receive-only
	  //    w = snprintf(cp,sspace,",qAR,%s",User);
	  int const w = snprintf(cp,sspace,",qAO,%s",User);
	  cp += w; sspace -= w;
	  *cp++ = ':'; sspace--;
	  assert(sspace > 0);
	}      
	for(int i=0; i < frame.info_len; i++){
	  char const c = frame.information[i] & 0x7f; // Strip parity in monitor strings
	  if(c != '\r' && c != '\n' && c != '\0'){
	    // Strip newlines, returns and nulls (we'll add a cr-lf later)
	    *cp++ = c;
	    sspace--;
	    infolen++;
	    assert(sspace > 0);
	  }
	}
	*cp++ = '\0';
	sspace--;
      }      
      assert(sizeof(monstring) - sspace - 1 == strlen(monstring));
      if(Logfile)
	fprintf(Logfile," %s\n",monstring);
      
      if(frame.control != 0x03 || frame.type != 0xf0){
	if(Logfile)
	  fprintf(Logfile," Not relaying: invalid ax25 ctl/protocol\n");
	continue;
      }
      if(infolen == 0){
	if(Logfile)
	  fprintf(Logfile," Not relaying: empty I field\n");
	continue;
      }
      if(is_tcpip){
	if(Logfile)
	  fprintf(Logfile," Not relaying: Internet relayed packet\n");
	continue;
      }
      if(frame.information[0] == '{'){
	if(Logfile)
	  fprintf(Logfile," Not relaying: third party traffic\n");	
	continue;
      }
      
      // Send to APRS network with appended crlf
      if(fprintf(network,"%s\r\n",monstring) <= 0){
	// error!
	fclose(network); network = NULL;
	goto retry; // Try to reopen the network connection
      }
    }
  retry:;
    pthread_cancel(Read_thread);
    pthread_join(Read_thread,NULL);
  }
}
// Just read and echo responses from server
void *netreader(void *arg){
  pthread_setname("aprs-read");

  char *line = NULL;
  size_t linecap = 0;
  ssize_t linelen;
  // Create our own stream; there seem to be problems sharing a common stream among threads
  FILE *network = fdopen(Network_fd,"r");

  while((linelen = getline(&line,&linecap,network)) > 0){
    if(Logfile)
      fwrite(line,linelen,1,Logfile);
  }
  FREE(line);
  return NULL;
}