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annotate tfo/find-is-hdr.c @ 72:afebef67e8d4 default tip

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tmo/CSD-tests: document Experiment 7
author Mychaela Falconia <falcon@freecalypso.org>
date Thu, 28 Nov 2024 02:53:59 +0000
parents 98c0881c2af0
children
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Mychaela Falconia <falcon@freecalypso.org>
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1 /*
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2 * This program reads a binary file containing a G.711 PCM stream capture
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Mychaela Falconia <falcon@freecalypso.org>
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3 * and looks for an IS_Header pattern as defined in ETSI TS 101 504
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4 * (GSM 08.62) section A.1.2. The objective is to analyze PCM streams
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Mychaela Falconia <falcon@freecalypso.org>
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5 * originating from extant commercial GSM network operators and see if
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6 * they implement in-band TFO.
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7 */
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8
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9 #include <sys/types.h>
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10 #include <sys/file.h>
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11 #include <sys/stat.h>
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12 #include <sys/mman.h>
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13 #include <stdio.h>
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14 #include <stdlib.h>
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15 #include <unistd.h>
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16
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17 static char *pcmfile;
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18 static size_t pcm_file_size;
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19 static u_char *filemap;
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20
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21 static const u_char hdr_pattern[20] = {0, 1, 0, 1, 0, 1, 1, 0, 1, 0,
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22 0, 1, 1, 0, 1, 0, 1, 0, 0, 1};
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23
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24 static void
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25 mmap_pcm_file()
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26 {
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27 int fd;
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28 struct stat st;
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29
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30 fd = open(pcmfile, O_RDONLY);
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31 if (fd < 0) {
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32 perror(pcmfile);
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33 exit(1);
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34 }
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35 fstat(fd, &st);
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36 if (!S_ISREG(st.st_mode)) {
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37 fprintf(stderr, "error: %s is not a regular file\n", pcmfile);
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38 exit(1);
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39 }
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40 pcm_file_size = st.st_size;
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41 if (pcm_file_size < 320) {
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42 fprintf(stderr, "error: %s is too short\n", pcmfile);
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43 exit(1);
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44 }
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45 filemap = mmap(NULL, pcm_file_size, PROT_READ, MAP_PRIVATE, fd, 0L);
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46 if (filemap == MAP_FAILED) {
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47 perror("mmap");
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48 exit(1);
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49 }
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50 close(fd);
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51 }
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52
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53 static void
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54 try_offset(offset)
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55 size_t offset;
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56 {
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57 unsigned n;
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58
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59 for (n = 0; n < 20; n++) {
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60 if ((filemap[offset + n * 16] & 1) != hdr_pattern[n])
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61 return;
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62 }
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63 printf("Found IS_Header at offset %lu (0x%lx)\n", (u_long) offset,
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64 (u_long) offset);
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65 }
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66
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67 main(argc, argv)
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68 char **argv;
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69 {
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70 size_t offset, endoff;
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71
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72 if (argc != 2) {
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73 fprintf(stderr, "usage: %s pcm-capture-file\n", argv[0]);
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74 exit(1);
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75 }
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76 pcmfile = argv[1];
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77 mmap_pcm_file();
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78 endoff = pcm_file_size - 320;
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79 for (offset = 0; offset <= endoff; offset++)
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80 try_offset(offset);
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81 exit(0);
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82 }