root/vcs-svn/sliding_window.c

DEFINITIONS

1. input_error
2. skip_or_whine
3. read_to_fill_or_whine
4. check_offset_overflow
5. move_window

/*
 * Licensed under a two-clause BSD-style license.
 * See LICENSE for details.
 */

#include "git-compat-util.h"
#include "sliding_window.h"
#include "line_buffer.h"
#include "strbuf.h"

static int input_error(struct line_buffer *file)
{
        if (!buffer_ferror(file))
                return error("delta preimage ends early");
        return error("cannot read delta preimage: %s", strerror(errno));
}

static int skip_or_whine(struct line_buffer *file, off_t gap)
{
        if (buffer_skip_bytes(file, gap) != gap)
                return input_error(file);
        return 0;
}

static int read_to_fill_or_whine(struct line_buffer *file,
                                struct strbuf *buf, size_t width)
{
        buffer_read_binary(file, buf, width - buf->len);
        if (buf->len != width)
                return input_error(file);
        return 0;
}

static int check_offset_overflow(off_t offset, uintmax_t len)
{
        if (len > maximum_signed_value_of_type(off_t))
                return error("unrepresentable length in delta: "
                                "%"PRIuMAX" > OFF_MAX", len);
        if (signed_add_overflows(offset, (off_t) len))
                return error("unrepresentable offset in delta: "
                                "%"PRIuMAX" + %"PRIuMAX" > OFF_MAX",
                                (uintmax_t) offset, len);
        return 0;
}

int move_window(struct sliding_view *view, off_t off, size_t width)
{
        off_t file_offset;
        assert(view);
        assert(view->width <= view->buf.len);
        assert(!check_offset_overflow(view->off, view->buf.len));

        if (check_offset_overflow(off, width))
                return -1;
        if (off < view->off || off + width < view->off + view->width)
                return error("invalid delta: window slides left");
        if (view->max_off >= 0 && view->max_off < off + (off_t) width)
                return error("delta preimage ends early");

        file_offset = view->off + view->buf.len;
        if (off < file_offset) {
                /* Move the overlapping region into place. */
                strbuf_remove(&view->buf, 0, off - view->off);
        } else {
                /* Seek ahead to skip the gap. */
                if (skip_or_whine(view->file, off - file_offset))
                        return -1;
                strbuf_setlen(&view->buf, 0);
        }

        if (view->buf.len > width)
                ; /* Already read. */
        else if (read_to_fill_or_whine(view->file, &view->buf, width))
                return -1;

        view->off = off;
        view->width = width;
        return 0;
}