lib/other/getgrent.c

   1 /*      getgrent(), getgrgid(), getgrnam() - group file routines
   2  *
   3  *                                                      Author: Kees J. Bot
   4  *                                                              31 Jan 1994
   5  */
   6 #define nil 0
   7 #define open _open
   8 #define fcntl _fcntl
   9 #define read _read
  10 #define close _close
  11 #include <sys/types.h>
  12 #include <grp.h>
  13 #include <string.h>
  14 #include <stdlib.h>
  15 #include <unistd.h>
  16 #include <fcntl.h>
  17
  18 #define arraysize(a)    (sizeof(a) / sizeof((a)[0]))
  19 #define arraylimit(a)   ((a) + arraysize(a))
  20
  21 static char GROUP[]= "/etc/group";      /* The group file. */
  22 static const char *grfile;              /* Current group file. */
  23
  24 static char buf[1024];                  /* Read buffer. */
  25 static char grline[512];                /* One line from the group file. */
  26 static struct group entry;              /* Entry to fill and return. */
  27 static char *members[64];               /* Group members with the entry. */
  28 static int grfd= -1;                    /* Filedescriptor to the file. */
  29 static char *bufptr;                    /* Place in buf. */
  30 static ssize_t buflen= 0;               /* Remaining characters in buf. */
  31 static char *lineptr;                   /* Place in the line. */
  32
  33 void endgrent(void)
  34 /* Close the group file. */
  35 {
  36         if (grfd >= 0) {
  37                 (void) close(grfd);
  38                 grfd= -1;
  39                 buflen= 0;
  40         }
  41 }
  42
  43 int setgrent(void)
  44 /* Open the group file. */
  45 {
  46         if (grfd >= 0) endgrent();
  47
  48         if (grfile == nil) grfile= GROUP;
  49
  50         if ((grfd= open(grfile, O_RDONLY)) < 0) return -1;
  51         (void) fcntl(grfd, F_SETFD, fcntl(grfd, F_GETFD) | FD_CLOEXEC);
  52         return 0;
  53 }
  54
  55 void setgrfile(const char *file)
  56 /* Prepare for reading an alternate group file. */
  57 {
  58         endgrent();
  59         grfile= file;
  60 }
  61
  62 static int getline(void)
  63 /* Get one line from the group file, return 0 if bad or EOF. */
  64 {
  65         lineptr= grline;
  66
  67         do {
  68                 if (buflen == 0) {
  69                         if ((buflen= read(grfd, buf, sizeof(buf))) <= 0)
  70                                 return 0;
  71                         bufptr= buf;
  72                 }
  73
  74                 if (lineptr == arraylimit(grline)) return 0;
  75                 buflen--;
  76         } while ((*lineptr++ = *bufptr++) != '\n');
  77
  78         lineptr= grline;
  79         return 1;
  80 }
  81
  82 static char *scan_punct(int punct)
  83 /* Scan for a field separator in a line, return the start of the field. */
  84 {
  85         char *field= lineptr;
  86         char *last;
  87
  88         for (;;) {
  89                 last= lineptr;
  90                 if (*lineptr == 0) return nil;
  91                 if (*lineptr == '\n') break;
  92                 if (*lineptr++ == punct) break;
  93                 if (lineptr[-1] == ':') return nil;     /* :::,,,:,,,? */
  94         }
  95         *last= 0;
  96         return field;
  97 }
  98
  99 struct group *getgrent(void)
 100 /* Read one entry from the group file. */
 101 {
 102         char *p;
 103         char **mem;
 104
 105         /* Open the file if not yet open. */
 106         if (grfd < 0 && setgrent() < 0) return nil;
 107
 108         /* Until a good line is read. */
 109         for (;;) {
 110                 if (!getline()) return nil;     /* EOF or corrupt. */
 111
 112                 if ((entry.gr_name= scan_punct(':')) == nil) continue;
 113                 if ((entry.gr_passwd= scan_punct(':')) == nil) continue;
 114                 if ((p= scan_punct(':')) == nil) continue;
 115                 entry.gr_gid= strtol(p, nil, 0);
 116
 117                 entry.gr_mem= mem= members;
 118                 if (*lineptr != '\n') {
 119                         do {
 120                                 if ((*mem= scan_punct(',')) == nil) goto again;
 121                                 if (mem < arraylimit(members) - 1) mem++;
 122                         } while (*lineptr != 0);
 123                 }
 124                 *mem= nil;
 125                 return &entry;
 126         again:;
 127         }
 128 }
 129
 130 struct group *getgrgid(_mnx_Gid_t gid)
 131 /* Return the group file entry belonging to the user-id. */
 132 {
 133         struct group *gr;
 134
 135         endgrent();
 136         while ((gr= getgrent()) != nil && gr->gr_gid != gid) {}
 137         endgrent();
 138         return gr;
 139 }
 140
 141 struct group *getgrnam(const char *name)
 142 /* Return the group file entry belonging to the user name. */
 143 {
 144         struct group *gr;
 145
 146         endgrent();
 147         while ((gr= getgrent()) != nil && strcmp(gr->gr_name, name) != 0) {}
 148         endgrent();
 149         return gr;
 150 }