src/getline.h

   1 /*
   2  * Copyright © 2024 Nick Bowler
   3  *
   4  * getline-like function which removes trailing newline (if any).
   5  *
   6  * If HAVE_GETLINE is not defined (or defined to 0) then a standard C
   7  * implementation is used.  Othewrise, the POSIX getline function
   8  * is called.
   9  *
  10  * This program is free software: you can redistribute it and/or modify
  11  * it under the terms of the GNU General Public License as published by
  12  * the Free Software Foundation, either version 3 of the License, or
  13  * (at your option) any later version.
  14  *
  15  * This program is distributed in the hope that it will be useful,
  16  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  17  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18  * GNU General Public License for more details.
  19  *
  20  * You should have received a copy of the GNU General Public License
  21  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  22  */
  23 #ifndef DX_GETLINE_H_
  24 #define DX_GETLINE_H_
  25
  26 /*
  27  * On some very old preprocessors (e.g., VAX C) -Dinline= defines inline to 1,
  28  * so when not using a config header detect and work around the problem here.
  29  */
  30 #if !HAVE_CONFIG_H && (inline - 1 == 0)
  31 #  undef inline
  32 #  define inline
  33 #endif
  34
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <string.h>
  38 #include <limits.h>
  39
  40 /*
  41  * Size of the initial buffer allocated internally by the fallback
  42  * implementation when *linebuf is NULL.
  43  */
  44 #ifndef DX_GETLINE_INITIAL_ALLOC
  45 #  define DX_GETLINE_INITIAL_ALLOC 75
  46 #endif
  47
  48 enum {
  49         DX_GETLINE_OK     =  1,
  50         DX_GETLINE_EOF    =  0,
  51         DX_GETLINE_ERROR  = -1,
  52         DX_GETLINE_ENOMEM = -2
  53 };
  54
  55 /*
  56  * Wrapper around getline with standard C fallback.
  57  *
  58  * Note that for portability to some getline implementations (e.g., FreeBSD)
  59  * both *linebuf and *n should be set to zero on the initial call.
  60  *
  61  * If pre-allocating a buffer, ensure that its size is more than 1 byte,
  62  * otherwise AIX 7.2 getline fails to work correctly.
  63  *
  64  * Returns 1 (DX_GETLINE_OK) if a line was read or 0 (DX_GETLINE_EOF) if
  65  * no line could be read because the end of file was reached.
  66  *
  67  * On failure, returns a negative value.  If the C library input call failed
  68  * then the return value is DX_GETLINE_ERROR and the reason for the failure
  69  * should be available in errno.
  70  *
  71  * For the standard C fallback only, a return value of DX_GETLINE_ENOMEM
  72  * indicates that the buffer allocation could not be expanded to fit the
  73  * input line.
  74  */
  75 static inline int dx_getline(char **linebuf, size_t *n, FILE *f)
  76 {
  77 #if HAVE_GETLINE
  78         ssize_t rc;
  79
  80         if ((rc = getline(linebuf, n, f)) < 0) {
  81                 if (ferror(f))
  82                         return DX_GETLINE_ERROR;
  83                 return DX_GETLINE_EOF;
  84         }
  85
  86         if (rc-- && (*linebuf)[rc] == '\n')
  87                 (*linebuf)[rc] = '\0';
  88
  89         return DX_GETLINE_OK;
  90 #else
  91         char *work = *linebuf;
  92         size_t pos = 0;
  93         size_t sz;
  94
  95         if (!work) {
  96                 sz = DX_GETLINE_INITIAL_ALLOC;
  97                 goto initial_alloc;
  98         }
  99
 100         for (sz = *n;;) {
 101                 if (!fgets(&work[pos], sz - pos, f)) {
 102                         if (ferror(f))
 103                                 return DX_GETLINE_ERROR;
 104
 105                         return pos ? DX_GETLINE_OK : DX_GETLINE_EOF;
 106                 }
 107
 108                 pos += strlen(&work[pos]);
 109                 if (work[pos-1] == '\n') {
 110                         work[pos-1] = '\0';
 111                         return DX_GETLINE_OK;
 112                 }
 113
 114                 if (sz > INT_MAX/2 || sz > ((size_t)-1)/4)
 115                         break;
 116
 117                 sz = ((sz*4) + 2) / 3;
 118 initial_alloc:
 119                 work = realloc(work, sz);
 120                 if (!work)
 121                         break;
 122                 *linebuf = work;
 123                 *n = sz;
 124         }
 125
 126         return DX_GETLINE_ENOMEM;
 127 #endif
 128 }
 129
 130 #endif