sliding_window.c

   1 /*
   2  * Licensed under a two-clause BSD-style license.
   3  * See LICENSE for details.
   4  */
   5
   6 #include "git-compat-util.h"
   7 #include "sliding_window.h"
   8 #include "line_buffer.h"
   9 #include "strbuf.h"
  10
  11 static int input_error(struct line_buffer *file)
  12 {
  13         if (!buffer_ferror(file))
  14                 return error("delta preimage ends early");
  15         return error("cannot read delta preimage: %s", strerror(errno));
  16 }
  17
  18 static int skip_or_whine(struct line_buffer *file, off_t gap)
  19 {
  20         if (buffer_skip_bytes(file, gap) != gap)
  21                 return input_error(file);
  22         return 0;
  23 }
  24
  25 static int read_to_fill_or_whine(struct line_buffer *file,
  26                                 struct strbuf *buf, size_t width)
  27 {
  28         buffer_read_binary(file, buf, width - buf->len);
  29         if (buf->len != width)
  30                 return input_error(file);
  31         return 0;
  32 }
  33
  34 static int check_overflow(off_t a, size_t b)
  35 {
  36         if (b > maximum_signed_value_of_type(off_t))
  37                 return error("unrepresentable length in delta: "
  38                                 "%"PRIuMAX" > OFF_MAX", (uintmax_t) b);
  39         if (signed_add_overflows(a, (off_t) b))
  40                 return error("unrepresentable offset in delta: "
  41                                 "%"PRIuMAX" + %"PRIuMAX" > OFF_MAX",
  42                                 (uintmax_t) a, (uintmax_t) b);
  43         return 0;
  44 }
  45
  46 int move_window(struct sliding_view *view, off_t off, size_t width)
  47 {
  48         off_t file_offset;
  49         assert(view);
  50         assert(view->width <= view->buf.len);
  51         assert(!check_overflow(view->off, view->buf.len));
  52
  53         if (check_overflow(off, width))
  54                 return -1;
  55         if (off < view->off || off + width < view->off + view->width)
  56                 return error("invalid delta: window slides left");
  57
  58         file_offset = view->off + view->buf.len;
  59         if (off < file_offset) {
  60                 /* Move the overlapping region into place. */
  61                 strbuf_remove(&view->buf, 0, off - view->off);
  62         } else {
  63                 /* Seek ahead to skip the gap. */
  64                 if (skip_or_whine(view->file, off - file_offset))
  65                         return -1;
  66                 strbuf_setlen(&view->buf, 0);
  67         }
  68
  69         if (view->buf.len > width)
  70                 ; /* Already read. */
  71         else if (read_to_fill_or_whine(view->file, &view->buf, width))
  72                 return -1;
  73
  74         view->off = off;
  75         view->width = width;
  76         return 0;
  77 }