apps/web/imgsrv/imgsrv.c

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/*!***************************************************************************
*! FILE NAME  : imgsrv.c
*! DESCRIPTION: Simple and fast HTTP server to send camera still images
*! Copyright (C) 2007 Elphel, Inc.
*! -----------------------------------------------------------------------------**
*!  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 3 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, see <http://www.gnu.org/licenses/>.
*! -----------------------------------------------------------------------------**
*!
*!  $Log: imgsrv.c,v $
*!  Revision 1.14  2008/04/22 22:14:56  elphel
*!  Added malloc failures handling, syslog logging of such events
*!
*!  Revision 1.13  2008/04/16 20:30:33  elphel
*!  added optional fps reduction to multipart JPEGs
*!
*!  Revision 1.11  2008/04/07 09:13:35  elphel
*!  Changes related to new Exif generation/processing
*!
*!  Revision 1.10  2008/03/22 04:39:53  elphel
*!  remove complaints about "&_time=..."
*!
*!  Revision 1.9  2007/12/03 08:28:45  elphel
*!  Multiple changes, mostly cleanup
*!
*!  Revision 1.8  2007/11/16 08:56:19  elphel
*!  Added support for 2 additional commands to check circbuf usage
*!
*!  Revision 1.7  2007/11/04 23:25:16  elphel
*!  removed extra (used during debug) munmap that caused segfault after sending "img" (so no /nxt/save)
*!
*!  Revision 1.6  2007/11/04 05:47:40  elphel
*!  Cleaned up from debug code inserted to fight mmap/caching bug (fixed by now)
*!
*!  Revision 1.5  2007/11/01 18:59:37  elphel
*!  debugging mmap/caching problems
*!
*!  Revision 1.4  2007/10/30 16:56:06  elphel
*!  release 7.1.4.5 - working on "can not find 0xffff in frame parameters" bug. Temporary fix
*!
*!  Revision 1.3  2007/10/27 00:55:32  elphel
*!  untested revision - need to go
*!
*!  Revision 1.2  2007/10/11 06:42:28  elphel
*!  Fixed bug - /meta command should return trivial xml file, not 1x1 pixel gif
*!
*!  Revision 1.1.1.1  2007/10/02 19:44:54  elphel
*!  This is a fresh tree based on elphel353-2.10
*!
*!  Revision 1.4  2007/10/02 19:44:54  elphel
*!  More functionality (buffer manipulation commands, clean interface, xml responces)
*!
*!  Revision 1.3  2007/09/29 16:21:25  elphel
*!  removed IOCTL usage from /dev/circbuf, improved comments, other minor changes
*!
*!  Revision 1.2  2007/09/25 23:35:16  elphel
*!  added Exif initialization, made it to work in background mode
*!
*!  Revision 1.1  2007/09/23 06:49:10  elphel
*!  Simple web server designed for particular task - serving camera JPEG images. It is faster, than through any of the web servers tested. Only some of the functionality is implemented (no Exif yet, no synchronization with the camera)
*!
*!
*/ 
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
//#include <ctype.h>
//#include <getopt.h>
#include <time.h>
#include <string.h>
#include <syslog.h>

#include <netinet/in.h>
#include <sys/mman.h>           /* mmap */
#include <sys/ioctl.h>

#include <asm/elphel/c313a.h>
#include <asm/elphel/exifa.h>
#include <asm/elphel/ext353.h>
#include <asm/byteorder.h>

#define D(x)
//#define D(x) fprintf(stderr,"%s:%d:",__FILE__,__LINE__);x

//#define USEHTTP10(x)
#define USEHTTP10(x) x

// HEADER_SIZE is defined to be larger than actual header (later - with EXIF)  to use compile-time buffer
#define JPEG_HEADER_SIZE    0x26f // will not change

#define TRAILER_SIZE   0x02
#define MAP_OPTIONS MAP_FILE|MAP_PRIVATE

unsigned long * ccam_dma_buf;           /* mmapped array */

char trailer[TRAILER_SIZE] = {0xff,0xd9};

const char url_args[]="This server supports sequence of commands entered in the URL (separated by \"/\", case sensitive )\n" \
                      "executing them from left to right as they appear in the URL\n" \
                      "img -      send image at the current pointer (if it is first command - use last acquired image, if none availabe - send 1x1 gif)\n" \
                      "bimg -     same as above, but save the whole image in the memory before sending - useful to avoid overruns with slow connection \n" \
                      "mimg[n] -  send images as a multipart JPEG (all commands after will be ignored), possible to specify optional fps reduction\n" \
                      "           i.e. mimg4 - skip 3 frames for each frame output (1/4 fps) \n" \
                      "bmimg[n] - same as above, buffered\n" \
                      "pointers - send XML-formatted data about frames available in the camera circular buffer)\n\n" \
                      "Any of the 5 commands above can appear only once in the URL string, the second instance will be ignored. If none of the 5\n" \
                      "are present in the URL 1x1 pixel gif will be returned to the client after executing the URL command.\n\n" \
                      "torp -   set frame pointer to global read pointer, maintained by the camera driver. If frame at that pointer\n" \
                      "         is invalid, use scnd (see below)\n" \
                      "towp -   set frame pointer to hardware write pointer - position where next frame will be aquired\n" \
                      "prev -   move to previous frame in buffer, nop if there are none\n" \
                      "next -   move to the next frame in buffer (will stop at write pointer, see towp above)\n" \
                      "last -   move to the most recently acquired frame, or to write pointer if there are none.\n" \
                      "         this command is implied at the start of the url command sequence.\n" \
                      "first -  move to the oldest frame still available in the buffer. It is not safe to rely on it if\n" \
                      "         more frames are expected - data might be overwritten at any moment and the output will be corrupted.\n" \
                      "second - move to the second oldest frame in the buffer - somewhat safer than \"first\" - there will be time for\n" \
                      "         \"next\" command at least before frame data (and pointer structures) will be overwritten.\n" \
                      "save   - save current frame pointer as a global read pointer that holds it values between server requests.\n" \
                      "         This pointer is shared between all the clients and applications that use it.\n" \
                      "wait   - Wait until there will be a frame at current pointer ready\n";
int  sendImage (int bufferImageData, int fd_circ, int use_Exif);
void sendBuffer(void * buffer, int len);
void listener_loop(int port);
void errorMsgXML(char * msg);
int  framePointersXML(int fd_circ);
int  out1x1gif(void);

int framePointersXML(int fd_circ) {
  const char SensParsFileName[]="/dev/sensorpars";
  unsigned long * imageParamsR;
  int fd_sens, senspars_size;
  char s[256]; // 136;
  char * compressor_state;
  int p, wp, rp;
  int nf=0;
  int nfl=0;
  int buf_free, buf_used;
  int save_p; 



   fd_sens = open(SensParsFileName, O_RDWR);
   if (fd_sens<0) { // check control OK
      D(fprintf (stderr,"Error opening %s\n", SensParsFileName));
      return -2;
   }
   senspars_size=lseek(fd_sens,0,SEEK_END);
   imageParamsR = (unsigned long *) mmap(0, senspars_size, PROT_READ, MAP_SHARED, fd_sens, 0);
   if((int)imageParamsR == -1) {
     D(fprintf (stderr,"Error in mmap of %s\n",SensParsFileName));
     close(fd_sens);
     return -3;
   }


  save_p=lseek(fd_circ,0,SEEK_CUR); 
  rp=lseek(fd_circ,CIRCLSEEK_TORP,SEEK_END); 
  wp=lseek(fd_circ,CIRCLSEEK_TOWP,SEEK_END); 
  p=wp;
  while ((p>=0) & (nf<500)) {
   if (p==rp) nfl=nf;
   p=lseek(fd_circ,CIRCLSEEK_PREV,SEEK_END);
   nf++;
  }
  buf_free=imageParamsR[P_FREECIRCBUF];
  buf_used=imageParamsR[P_CIRCBUFSIZE]-imageParamsR[P_FREECIRCBUF];
  compressor_state=(imageParamsR[P_CAMSEQSTATE]==CAMSEQ_RUN)?"running":
                     ((imageParamsR[P_CAMSEQSTATE]==CAMSEQ_SINGLE)?"acquiring":
                      ((imageParamsR[P_CAMSEQSTATE]==CAMSEQ_STOP)?"stoppping":
                       ((imageParamsR[P_CAMSEQSTATE]==CAMSEQ_JPEG)?"stopped":
                        ((imageParamsR[P_CAMSEQSTATE]==CAMSEQ_OFF)?"reset":"other"))));


  lseek(fd_circ,save_p,SEEK_SET); 
  buf_free=lseek(fd_circ,CIRCLSEEK_FREE,SEEK_END); 
  lseek(fd_circ,save_p,SEEK_SET); 
  buf_used=lseek(fd_circ,CIRCLSEEK_USED,SEEK_END); 
  lseek(fd_circ,save_p,SEEK_SET); 

  sprintf (s,"<?xml version=\"1.0\"?>\n" \
             "<frame_pointers>\n" \
             "  <this>%d</this>\n" \
             "  <write>%d</write>\n" \
             "  <read>%d</read>\n" \
             "  <frames>%d</frames>\n" \
             "  <left>%d</left>\n" \
             "  <free>%d</free>\n" \
             "  <used>%d</used>\n" \
             "  <compressor_state>\"%s\"</compressor_state>\n" \
             "</frame_pointers>\n",
              save_p,
              wp,
              rp,
              nf-1,
              nfl,
              buf_free,
              buf_used,
              compressor_state);
   D(fprintf (stderr,">%s< [%d bytes]",s,strlen(s)));
   printf("HTTP/1.0 200 OK\n");
   printf("Server: Elphel Imgsrv\n");
   printf("Content-Length: %d\n",strlen(s));
   printf("Content-Type: text/xml\n");
   printf("Pragma: no-cache\n");
   printf("\n");
   printf(s);
   close(fd_sens); 
   return 0; 
}
//fwrite (&cbuffer[offset],1,bytesLeft,stdout);
int out1x1gif(void) {
 char s[]="HTTP/1.0 200 OK\n" \
          "Server: Elphel Imgsrv\n" \
          "Content-Length: 35\n" \
          "Content-Type: image/gif\n" \
          "\n" \
          "GIF87a\x01\x00\x01\x00\x80\x01\x00\x00\x00\x00" \
          "\xff\xff\xff\x2c\x00\x00\x00\x00\x01\x00\x01\x00\x00\x02\x02\x4c" \
          "\x01\x00\x3b";
          fwrite (s,1,sizeof(s),stdout); 
   return 0; 
 }

void errorMsgXML(char * msg) {
  char s[1024]; // was 701 acrtually
    sprintf (s,"<?xml version=\"1.0\"?>\n" \
             "<frame_params>\n" \
             "<error>%s</error>\n" \
             "</frame_params>\n",msg);
  D(fprintf (stderr,">%s< [%d bytes]",s,strlen(s)));
  printf("HTTP/1.0 200 OK\n");
  printf("Server: Elphel Imgsrv\n");
  printf("Content-Length: %d\n",strlen(s));
  printf("Content-Type: text/xml\n");
  printf("Pragma: no-cache\n");
  printf("\n");
  printf(s);
}




int  sendImage (int bufferImageData, int fd_circ, int use_Exif) {
   const char HeadFileName[]="/dev/jpeghead";
   const char ExifFileName[]="/dev/exif_exif";
//   char jpegHeader [JPEG_HEADER_SIZE];
   int  exifDataSize=0;
   int  frameParamPointer=0;
   struct frame_params_t frame_params;
   int buff_size;
//   unsigned long * ccam_dma_buf;           /* mmapped array */
//   volatile unsigned long * ccam_dma_buf;           /* mmapped array */
   int jpeg_len;   //bytes
   int jpeg_start; // bytes
   int fd_head;
   int fd_exif;
   int head_size;
   int jpeg_full_size, jpeg_this_size;
   char * jpeg_copy;
   int l,i;
   jpeg_start=lseek(fd_circ,0,SEEK_CUR); //get the current read pointer
   D(fprintf(stderr,"jpeg_start= (long)=0x%x\n",jpeg_start>>2));
   fd_head = open(HeadFileName, O_RDWR);
   if (fd_head<0) { // check control OK
     fprintf (stderr,"Error opening %s\n", HeadFileName);
     return -1;
   }
   head_size=lseek(fd_head,0,SEEK_END);
   if (head_size>JPEG_HEADER_SIZE) {
     fprintf(stderr,"%s:%d: Too big JPEG header (%d > %d)",__FILE__,__LINE__,head_size, JPEG_HEADER_SIZE );
     close (fd_head);
     return -2;
   }
    buff_size=lseek(fd_circ,0,SEEK_END);
    lseek(fd_circ, jpeg_start, SEEK_SET);
    D(fprintf(stderr,"position (longs)=0x%x\n", (int) lseek(fd_circ,0,SEEK_CUR)>>2));
//#define MAP_OPTIONS MAP_FILE|MAP_PRIVATE

/*
   ccam_dma_buf = (unsigned long *) mmap(0, buff_size, PROT_READ, MAP_SHARED, fd_circ, 0);
   if((int)ccam_dma_buf == -1) {
     fprintf(stderr, "Error in mmap\n");
     close (fd_head);
//     close(fd_circ); - caller opened, caller - to close
     return -3;
   }
*/
//   char exifData [MAX_EXIF_SIZE];
//   int  exifDataSize=0;
   frameParamPointer=jpeg_start-32;
//   if (exifIndexPointer<0) exifIndexPointer+=buff_size;
   if (frameParamPointer<0) frameParamPointer+=buff_size;
//   memcpy (&frame_exif, (unsigned long * ) &ccam_dma_buf[exifIndexPointer>>2],8);
   memcpy (&frame_params, (unsigned long * ) &ccam_dma_buf[frameParamPointer>>2],32);
//   jpeg_len=frame_exif.frame_length;
   jpeg_len=frame_params.frame_length;
//   if (frame_exif.signffff !=0xffff) {
   if (frame_params.signffff !=0xffff) {
//     fprintf(stderr, "wrong signature - %d\r\n",(int) frame_exif.signffff);
     fprintf(stderr, "wrong signature - %d\r\n",(int) frame_params.signffff);
     close (fd_head);
     return -4;
   }

   if (use_Exif) {
//     D(fprintf(stderr,"frame_exif.meta_index=0x%x\n",(int) frame_exif.meta_index));
     D(fprintf(stderr,"frame_params.meta_index=0x%x\n",(int) frame_params.meta_index));
     fd_exif = open(ExifFileName, O_RDONLY);
     if (fd_exif<0) { // check control OK
       fprintf (stderr,"Error opening %s\n", ExifFileName);
       close (fd_head);
       return -5;
     }
     exifDataSize=lseek(fd_exif,1,SEEK_END); // at the beginning of page 1 - position == page length
     if (exifDataSize < 0) exifDataSize=0; // error from lseek;
     if (!exifDataSize) close(fd_exif);
   } else {
//      frame_exif.meta_index=0;
      frame_params.meta_index=0;
      fd_exif=-1;
   }
   if (exifDataSize>0 ) {
     lseek(fd_head,jpeg_start+1,SEEK_END); 
   }


   jpeg_full_size=jpeg_len+head_size+2+exifDataSize;
//   if (bufferImageData) jpeg_copy=malloc(jpeg_full_size);           /// header+frame
//   else                 jpeg_copy=malloc(head_size+exifDataSize);   /// only header
   if (bufferImageData) jpeg_this_size=jpeg_full_size;           
   else                 jpeg_this_size=head_size+exifDataSize;   
   jpeg_copy=malloc(jpeg_this_size);
   if (!jpeg_copy) {
      syslog(LOG_ERR, "%s:%d malloc (%d) failed", __FILE__,__LINE__,jpeg_this_size);
      for (i=0;i<10;i++) {
         usleep(((jpeg_this_size & 0x3ff) + 5) * 100); // up to 0.1 sec
         jpeg_copy=malloc(jpeg_this_size);
         if (jpeg_copy) break;
         syslog(LOG_ERR, "%s:%d malloc (%d) failed", __FILE__,__LINE__,jpeg_this_size);
      }
      if (!jpeg_copy) {
        syslog(LOG_ERR, "%s:%d malloc (%d) failed 10 times - giving up", __FILE__,__LINE__,jpeg_this_size);
        exit (1);
      }
    }

   lseek(fd_head,0,0);
   read (fd_head,&jpeg_copy[exifDataSize],head_size);
   close (fd_head);
   if (exifDataSize>0) {
       memcpy (jpeg_copy,&jpeg_copy[exifDataSize],2); 
//       lseek(fd_exif,frame_exif.meta_index,SEEK_END); //! select meta page to use (matching frame)
       lseek(fd_exif,frame_params.meta_index,SEEK_END); 
       read (fd_exif,&jpeg_copy[2],exifDataSize);  
       close(fd_exif);
   }
   printf("Content-Type: image/jpeg\n");
   if (bufferImageData) { 
     l=head_size+exifDataSize;
     if ((jpeg_start+jpeg_len) > buff_size) { // two segments
       memcpy (&jpeg_copy[l], (unsigned long * ) &ccam_dma_buf[jpeg_start>>2],buff_size-jpeg_start);
       l+=buff_size-jpeg_start;
       memcpy (&jpeg_copy[l],(unsigned long * ) &ccam_dma_buf[0],jpeg_len-(buff_size-jpeg_start));
     } else {  
       memcpy (&jpeg_copy[l],(unsigned long * ) &ccam_dma_buf[jpeg_start>>2],jpeg_len);
     }
     memcpy (&jpeg_copy[jpeg_len+head_size+exifDataSize],trailer,2);
     printf("Content-Length: %d\n",jpeg_full_size);
     printf("\n");
     sendBuffer(jpeg_copy, jpeg_full_size);
   } else { 
     printf("Content-Length: %d\n",jpeg_full_size);
     printf("\n");
     sendBuffer(jpeg_copy, head_size+exifDataSize); //JPEG+Exif
     if ((jpeg_start+jpeg_len) > buff_size) { // two segments
        sendBuffer((void *) &ccam_dma_buf[jpeg_start>>2], buff_size-jpeg_start);
        sendBuffer((void *) &ccam_dma_buf[0], jpeg_len-(buff_size-jpeg_start));
     } else { // single segment
        sendBuffer((void *) &ccam_dma_buf[jpeg_start>>2], jpeg_len);
     }
     sendBuffer(trailer,2);
   }
   free(jpeg_copy);
   return 0;

}


void sendBuffer(void * buffer, int len) {
   int  bytesLeft=len;
   int  offset=0;
   int  bytesWritten;
   char * cbuffer= (char *) buffer;
D(fprintf (stderr,"buffer=%p, len=%d\n",buffer, len));
   while (bytesLeft>0) {
D(fprintf (stderr," --bytesLeft=%d\n",bytesLeft));

      bytesWritten= fwrite (&cbuffer[offset],1,bytesLeft,stdout);
      bytesLeft-=   bytesWritten;
      offset+=      bytesWritten;
   }
}




void listener_loop(int port)
{
   char errormsg[1024];
   const char circbufFileName[]="/dev/circbuf";
   int fd_circ;
   int this_p; 
   int rslt;
   int buf_images=0;
   char buf [1024];
   int len=0;
   char * cp, *cp1, *cp2;
   int slow,skip; // reduce frame rate by slow
   int sent2socket=-1; // 1 - img, 2 - meta, 3 - pointers
   struct sockaddr_in sock;
   int res;
   int one=1;
   int buff_size;
   memset((char *)&sock, 0, sizeof(sock));
   sock.sin_port = htons(port);
   sock.sin_family = AF_INET;
   res = socket(AF_INET, SOCK_STREAM, 0);
   setsockopt(res,SOL_SOCKET,SO_REUSEADDR,(char *)&one,sizeof(one));
   bind(res, (struct sockaddr * ) &sock,sizeof(sock));
   listen(res, 10);
   int exif_enable=1;
   while (1) {
     int fd;
     fd = accept(res,NULL,0);
     if (fd == -1) continue;
     signal(SIGCHLD, SIG_IGN); // no zombies, please!

     if (fork() == 0) {
       close(res);
       fflush(stdout);
       fflush(stderr);
       dup2(fd, 0);
       dup2(fd, 1);
       close(fd);
       if (fgets(buf, sizeof(buf)-1, stdin)) len=strlen(buf);
       cp=buf;
       strsep(&cp, "/?"); // ignore everything before first "/" or "?"
       if (cp) {
         cp1=strchr(cp,' ');
         if (cp1) cp1[0]='\0';
       } 
       if (!cp || (strlen(cp)==0)) { 
         printf("HTTP/1.0 200 OK\n");
         printf("Server: Elphel Imgsrv\n");
         printf("Content-Length: %d\n",strlen(url_args));
         printf("Content-Type: text/plain\n");
         printf("\n");
         printf(url_args);
         fflush(stdout);
        _exit(0);
       }
       fd_circ = open(circbufFileName, O_RDWR);
       if (fd_circ<0) { // check control OK
         fprintf (stderr,"Error opening %s\n", circbufFileName);
         out1x1gif();
         fflush(stdout);
        _exit(0);
       }
       buff_size=lseek(fd_circ,0,SEEK_END);
       ccam_dma_buf = (unsigned long *) mmap(0, buff_size, PROT_READ, MAP_SHARED, fd_circ, 0);
       if((int)ccam_dma_buf == -1) {
          fprintf(stderr, "Error in mmap\n");
          close(fd_circ); // - caller opened, caller - to close
          out1x1gif();
          fflush(stdout);
         _exit(0);
       }
       this_p=lseek(fd_circ,CIRCLSEEK_LAST,SEEK_END);
       while ((cp1=strsep(&cp, "/?&"))) {
        if (strchr("0123456789",cp1[0])) {
          this_p= lseek(fd_circ,strtol(cp1, NULL, 10),SEEK_SET);
        } else if ((strcmp(cp1, "img")==0) || (strcmp(cp1, "bimg")==0)) {
          if (sent2socket>0) break; 
          if (lseek(fd_circ,CIRCLSEEK_READY,SEEK_END)<0) 
            rslt=out1x1gif();
          else {
           printf("HTTP/1.0 200 OK\n");
           printf("Server: Elphel Imgsrv\n");
           printf("Expires: 0\n");
           printf("Pragma: no-cache\n");
           buf_images= (strcmp(cp1, "img")==0)?0:1;
           rslt=sendImage (buf_images, fd_circ, exif_enable); 
          }
          sent2socket=1;
          if (rslt<0) {
            if (sent2socket==1) out1x1gif();
            else {
               sprintf(errormsg,"sendImage error = %d (%s:line %d)",rslt,__FILE__,__LINE__);
               errorMsgXML(errormsg);
            }
          }
          fflush(stdout); 

        } else if ((strncmp(cp1, "mimg",4)==0) || (strncmp(cp1, "bmimg",5)==0) || (strncmp(cp1, "mbimg",5)==0)) {
          if (sent2socket>0) break; 
          if (lseek(fd_circ,CIRCLSEEK_READY,SEEK_END)<0) 
            rslt=out1x1gif();
          else {
//int  sendImage (int bufferImageData, int fd_circ, int use_Exif)
//TODO:
           buf_images= (strncmp(cp1, "mimg",4)==0)?0:1;
           cp2=cp1+(buf_images?5:4);
           slow=strtol(cp2, NULL, 10);
           if (slow < 1) slow =1;

           printf("HTTP/1.0 200 OK\n");
           printf("Server: Elphel Imgsrv\n");
           printf("Expires: 0\n");
           printf("Pragma: no-cache\n");
           printf("Content-Type: multipart/x-mixed-replace;boundary=ElphelMultipartJPEGBoundary\n");
           rslt=0;
           while (rslt>=0) {
             printf("\n--ElphelMultipartJPEGBoundary\n");
             rslt=sendImage (buf_images, fd_circ, exif_enable); 
             fflush(stdout);
             if (rslt>=0) for (skip=0;skip<slow;skip++) {
               this_p=lseek(fd_circ,CIRCLSEEK_NEXT, SEEK_END);
               if ((lseek(fd_circ,CIRCLSEEK_VALID,SEEK_END) >= 0) && 
                   (lseek(fd_circ,CIRCLSEEK_READY,SEEK_END) <  0) && 
                   (lseek(fd_circ,CIRCLSEEK_VALID,SEEK_END) >= 0))   
                    this_p=lseek(fd_circ,CIRCLSEEK_WAIT,SEEK_END);
               else this_p=lseek(fd_circ,CIRCLSEEK_LAST, SEEK_END);
             }
           }
          _exit(0);
          }
        } else if (strcmp(cp1, "pointers")==0)   {
          if (sent2socket>0) break; 
          framePointersXML(fd_circ); 
          sent2socket=3;
          fflush(stdout); 
        } else if (strcmp(cp1, "noexif")==0)   {
          exif_enable=0;
        } else if (strcmp(cp1, "exif")==0)   {
          exif_enable=1;
        } else if (strcmp(cp1, "torp")==0)   {
          this_p=lseek(fd_circ,CIRCLSEEK_TORP, SEEK_END);
        } else if (strcmp(cp1, "towp")==0)   {
          this_p=lseek(fd_circ,CIRCLSEEK_TOWP, SEEK_END);
        } else if (strcmp(cp1, "prev")==0)   {
          this_p=lseek(fd_circ,CIRCLSEEK_PREV, SEEK_END);
        } else if (strcmp(cp1, "next")==0)   {
          this_p=lseek(fd_circ,CIRCLSEEK_NEXT, SEEK_END);
        } else if (strcmp(cp1, "last")==0)   {
          this_p=lseek(fd_circ,CIRCLSEEK_LAST, SEEK_END);
        } else if (strcmp(cp1, "first")==0)  {
          this_p=lseek(fd_circ,CIRCLSEEK_FIRST,SEEK_END);
        } else if (strcmp(cp1, "second")==0) {
          this_p=lseek(fd_circ,CIRCLSEEK_SCND, SEEK_END);
        } else if (strcmp(cp1, "save")==0)   {
          this_p=lseek(fd_circ,CIRCLSEEK_SETP,SEEK_END);
        } else if (strcmp(cp1, "wait")==0)   {
               if ((lseek(fd_circ,CIRCLSEEK_VALID,SEEK_END) >= 0) && 
                   (lseek(fd_circ,CIRCLSEEK_READY,SEEK_END) <  0) && 
                   (lseek(fd_circ,CIRCLSEEK_VALID,SEEK_END) >= 0))   
                  this_p=lseek(fd_circ,CIRCLSEEK_WAIT,SEEK_END);
/*
          if (((dbg_test1=(lseek(fd_circ,CIRCLSEEK_VALID,SEEK_END))) >= 0) && //! no sense to wait if the pointer is invalid
              (((dbg_test2=lseek(fd_circ,CIRCLSEEK_READY,SEEK_END))) <0))     //! or the frame is already ready
                 this_p=lseek(fd_circ,CIRCLSEEK_WAIT,SEEK_END);
                 dbg_test3=this_p;
*/
        } else {
          if (cp1[0]!='_') fprintf(stderr,"Unrecognized URL command: \"%s\" - ignoring\n",cp1); 
        }
     } 
     if (sent2socket<=0) { 
       out1x1gif();
       fflush(stdout);
     }

     fflush(stdout); // probably it is not needed anymore, just in case
      _exit(0);
    } // end of child process
    close(fd); // parent
  } // while (1)
}

int main(int argc, char *argv[])
{
     const char usage[]=   "Usage:\n%s -p <port_number>\n" \
                           "Start image server, bind it to port <port_number>\n";

     int port;
     if ((argc < 3) || (strcasecmp(argv[1], "-p"))) {
     printf (usage,argv[0]);
     printf (url_args);
     return 0;
   }
   port=strtol(argv[2], NULL, 10);
   if (!port) {printf ("Invalid port number %d\n", port); return -1;}
   signal(SIGCHLD, SIG_IGN); // no zombies, please!
   if (fork() == 0) { // child
     listener_loop(port);
      _exit(0); // should not get here?
    } // end of child process
   return 0;
}

---