src/tac-pipe.c

   1 /* tac from a pipe.
   2
   3    Copyright (C) 1997-2024 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation, either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* FIXME */
  19 #include "assure.h"
  20
  21 /* FIXME: this is small for testing */
  22 #define BUFFER_SIZE (8)
  23
  24 #define LEN(X, I) ((X)->p[(I)].one_past_end - (X)->p[(I)].start)
  25 #define EMPTY(X) ((X)->n_bufs == 1 && LEN (X, 0) == 0)
  26
  27 #define ONE_PAST_END(X, I) ((X)->p[(I)].one_past_end)
  28
  29 struct Line_ptr
  30 {
  31   size_t i;
  32   char *ptr;
  33 };
  34 typedef struct Line_ptr Line_ptr;
  35
  36 struct B_pair
  37 {
  38   char *start;
  39   char *one_past_end;
  40 };
  41
  42 struct Buf
  43 {
  44   size_t n_bufs;
  45   struct obstack obs;
  46   struct B_pair *p;
  47 };
  48 typedef struct Buf Buf;
  49
  50 static bool
  51 buf_init_from_stdin (Buf *x, char eol_byte)
  52 {
  53   bool last_byte_is_eol_byte = true;
  54   bool ok = true;
  55
  56 #define OBS (&(x->obs))
  57   obstack_init (OBS);
  58
  59   while (true)
  60     {
  61       char *buf = malloc (BUFFER_SIZE);
  62
  63       if (buf == nullptr)
  64         {
  65           /* Fall back on the code that relies on a temporary file.
  66              Write all buffers to that file and free them.  */
  67           /* FIXME */
  68           ok = false;
  69           break;
  70         }
  71       idx_t bytes_read = full_read (STDIN_FILENO, buf, BUFFER_SIZE);
  72       if (bytes_read != BUFFER_SIZE && errno != 0)
  73         error (EXIT_FAILURE, errno, _("read error"));
  74
  75       {
  76         struct B_pair bp;
  77         bp.start = buf;
  78         bp.one_past_end = buf + bytes_read;
  79         obstack_grow (OBS, &bp, sizeof (bp));
  80       }
  81
  82       if (bytes_read != 0)
  83         last_byte_is_eol_byte = (buf[bytes_read - 1] == eol_byte);
  84
  85       if (bytes_read < BUFFER_SIZE)
  86         break;
  87     }
  88
  89   if (ok)
  90     {
  91       /* If the file was non-empty and lacked an EOL_BYTE at its end,
  92          then add a buffer containing just that one byte.  */
  93       if (!last_byte_is_eol_byte)
  94         {
  95           char *buf = malloc (1);
  96           if (buf == nullptr)
  97             {
  98               /* FIXME: just like above */
  99               ok = false;
 100             }
 101           else
 102             {
 103               struct B_pair bp;
 104               *buf = eol_byte;
 105               bp.start = buf;
 106               bp.one_past_end = buf + 1;
 107               obstack_grow (OBS, &bp, sizeof (bp));
 108             }
 109         }
 110     }
 111
 112   x->n_bufs = obstack_object_size (OBS) / sizeof (x->p[0]);
 113   x->p = (struct B_pair *) obstack_finish (OBS);
 114
 115   /* If there are two or more buffers and the last buffer is empty,
 116      then free the last one and decrement the buffer count.  */
 117   if (x->n_bufs >= 2
 118       && x->p[x->n_bufs - 1].start == x->p[x->n_bufs - 1].one_past_end)
 119     free (x->p[--(x->n_bufs)].start);
 120
 121   return ok;
 122 }
 123
 124 static void
 125 buf_free (Buf *x)
 126 {
 127   for (size_t i = 0; i < x->n_bufs; i++)
 128     free (x->p[i].start);
 129   obstack_free (OBS, nullptr);
 130 }
 131
 132 Line_ptr
 133 line_ptr_decrement (const Buf *x, const Line_ptr *lp)
 134 {
 135   Line_ptr lp_new;
 136
 137   if (lp->ptr > x->p[lp->i].start)
 138     {
 139       lp_new.i = lp->i;
 140       lp_new.ptr = lp->ptr - 1;
 141     }
 142   else
 143     {
 144       affirm (lp->i > 0);
 145       lp_new.i = lp->i - 1;
 146       lp_new.ptr = ONE_PAST_END (x, lp->i - 1) - 1;
 147     }
 148   return lp_new;
 149 }
 150
 151 Line_ptr
 152 line_ptr_increment (const Buf *x, const Line_ptr *lp)
 153 {
 154   Line_ptr lp_new;
 155
 156   affirm (lp->ptr <= ONE_PAST_END (x, lp->i) - 1);
 157   if (lp->ptr < ONE_PAST_END (x, lp->i) - 1)
 158     {
 159       lp_new.i = lp->i;
 160       lp_new.ptr = lp->ptr + 1;
 161     }
 162   else
 163     {
 164       affirm (lp->i < x->n_bufs - 1);
 165       lp_new.i = lp->i + 1;
 166       lp_new.ptr = x->p[lp->i + 1].start;
 167     }
 168   return lp_new;
 169 }
 170
 171 static bool
 172 find_bol (const Buf *x,
 173           const Line_ptr *last_bol, Line_ptr *new_bol, char eol_byte)
 174 {
 175   size_t i;
 176   Line_ptr tmp;
 177   char *last_bol_ptr;
 178
 179   if (last_bol->ptr == x->p[0].start)
 180     return false;
 181
 182   tmp = line_ptr_decrement (x, last_bol);
 183   last_bol_ptr = tmp.ptr;
 184   i = tmp.i;
 185   while (true)
 186     {
 187       char *nl = memrchr (x->p[i].start, last_bol_ptr, eol_byte);
 188       if (nl)
 189         {
 190           Line_ptr nl_pos;
 191           nl_pos.i = i;
 192           nl_pos.ptr = nl;
 193           *new_bol = line_ptr_increment (x, &nl_pos);
 194           return true;
 195         }
 196
 197       if (i == 0)
 198         break;
 199
 200       --i;
 201       last_bol_ptr = ONE_PAST_END (x, i);
 202     }
 203
 204   /* If last_bol->ptr didn't point at the first byte of X, then reaching
 205      this point means that we're about to return the line that is at the
 206      beginning of X.  */
 207   if (last_bol->ptr != x->p[0].start)
 208     {
 209       new_bol->i = 0;
 210       new_bol->ptr = x->p[0].start;
 211       return true;
 212     }
 213
 214   return false;
 215 }
 216
 217 static void
 218 print_line (FILE *out_stream, const Buf *x,
 219             const Line_ptr *bol, const Line_ptr *bol_next)
 220 {
 221   for (size_t i = bol->i; i <= bol_next->i; i++)
 222     {
 223       char *a = (i == bol->i ? bol->ptr : x->p[i].start);
 224       char *b = (i == bol_next->i ? bol_next->ptr : ONE_PAST_END (x, i));
 225       fwrite (a, 1, b - a, out_stream);
 226     }
 227 }
 228
 229 static bool
 230 tac_mem ()
 231 {
 232   Buf x;
 233   Line_ptr bol;
 234   char eol_byte = '\n';
 235
 236   if (! buf_init_from_stdin (&x, eol_byte))
 237     {
 238       buf_free (&x);
 239       return false;
 240     }
 241
 242   /* Special case the empty file.  */
 243   if (EMPTY (&x))
 244     return true;
 245
 246   /* Initially, point at one past the last byte of the file.  */
 247   bol.i = x.n_bufs - 1;
 248   bol.ptr = ONE_PAST_END (&x, bol.i);
 249
 250   while (true)
 251     {
 252       Line_ptr new_bol;
 253       if (! find_bol (&x, &bol, &new_bol, eol_byte))
 254         break;
 255       print_line (stdout, &x, &new_bol, &bol);
 256       bol = new_bol;
 257     }
 258   return true;
 259 }