vcs-svn: learn to maintain a sliding view of a file
Each section of a Subversion-format delta only requires examining (and
keeping in random-access memory) a small portion of the preimage. At
any moment, this portion starts at a certain file offset and has a
well-defined length, and as the delta is applied, the portion advances
from the beginning to the end of the preimage. Add a move_window
function to keep track of this view into the preimage.
You can use it like this:
buffer_init(f, NULL);
struct sliding_view window = SLIDING_VIEW_INIT(f);
move_window(&window, 3, 7); /* (1) */
move_window(&window, 5, 5); /* (2) */
move_window(&window, 12, 2); /* (3) */
strbuf_release(&window.buf);
buffer_deinit(f);
The data structure is called sliding_view instead of _window to
prevent confusion with svndiff0 Windows.
In this example, (1) reads 10 bytes and discards the first 3;
(2) discards the first 2, which are not needed any more; and (3) skips
2 bytes and reads 2 new bytes to work with.
When move_window returns, the file position indicator is at position
window->off + window->width and the data from positions window->off to
the current file position are stored in window->buf.
This function performs only sequential access from the input file and
never seeks, so it can be safely used on pipes and sockets.
On end-of-file, move_window silently reads less than the caller
requested. On other errors, it prints a message and returns -1.
Helped-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
2011-01-03 04:54:58 +01:00
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/*
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* Licensed under a two-clause BSD-style license.
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* See LICENSE for details.
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*/
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#include "git-compat-util.h"
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#include "sliding_window.h"
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#include "line_buffer.h"
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#include "strbuf.h"
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static int input_error(struct line_buffer *file)
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{
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if (!buffer_ferror(file))
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return error("delta preimage ends early");
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return error("cannot read delta preimage: %s", strerror(errno));
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}
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static int skip_or_whine(struct line_buffer *file, off_t gap)
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{
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if (buffer_skip_bytes(file, gap) != gap)
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return input_error(file);
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return 0;
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}
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static int read_to_fill_or_whine(struct line_buffer *file,
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struct strbuf *buf, size_t width)
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{
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buffer_read_binary(file, buf, width - buf->len);
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if (buf->len != width)
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return input_error(file);
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return 0;
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}
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2012-02-02 12:06:01 +01:00
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static int check_offset_overflow(off_t offset, uintmax_t len)
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vcs-svn: learn to maintain a sliding view of a file
Each section of a Subversion-format delta only requires examining (and
keeping in random-access memory) a small portion of the preimage. At
any moment, this portion starts at a certain file offset and has a
well-defined length, and as the delta is applied, the portion advances
from the beginning to the end of the preimage. Add a move_window
function to keep track of this view into the preimage.
You can use it like this:
buffer_init(f, NULL);
struct sliding_view window = SLIDING_VIEW_INIT(f);
move_window(&window, 3, 7); /* (1) */
move_window(&window, 5, 5); /* (2) */
move_window(&window, 12, 2); /* (3) */
strbuf_release(&window.buf);
buffer_deinit(f);
The data structure is called sliding_view instead of _window to
prevent confusion with svndiff0 Windows.
In this example, (1) reads 10 bytes and discards the first 3;
(2) discards the first 2, which are not needed any more; and (3) skips
2 bytes and reads 2 new bytes to work with.
When move_window returns, the file position indicator is at position
window->off + window->width and the data from positions window->off to
the current file position are stored in window->buf.
This function performs only sequential access from the input file and
never seeks, so it can be safely used on pipes and sockets.
On end-of-file, move_window silently reads less than the caller
requested. On other errors, it prints a message and returns -1.
Helped-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
2011-01-03 04:54:58 +01:00
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{
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2012-02-02 11:59:23 +01:00
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if (len > maximum_signed_value_of_type(off_t))
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vcs-svn: learn to maintain a sliding view of a file
Each section of a Subversion-format delta only requires examining (and
keeping in random-access memory) a small portion of the preimage. At
any moment, this portion starts at a certain file offset and has a
well-defined length, and as the delta is applied, the portion advances
from the beginning to the end of the preimage. Add a move_window
function to keep track of this view into the preimage.
You can use it like this:
buffer_init(f, NULL);
struct sliding_view window = SLIDING_VIEW_INIT(f);
move_window(&window, 3, 7); /* (1) */
move_window(&window, 5, 5); /* (2) */
move_window(&window, 12, 2); /* (3) */
strbuf_release(&window.buf);
buffer_deinit(f);
The data structure is called sliding_view instead of _window to
prevent confusion with svndiff0 Windows.
In this example, (1) reads 10 bytes and discards the first 3;
(2) discards the first 2, which are not needed any more; and (3) skips
2 bytes and reads 2 new bytes to work with.
When move_window returns, the file position indicator is at position
window->off + window->width and the data from positions window->off to
the current file position are stored in window->buf.
This function performs only sequential access from the input file and
never seeks, so it can be safely used on pipes and sockets.
On end-of-file, move_window silently reads less than the caller
requested. On other errors, it prints a message and returns -1.
Helped-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
2011-01-03 04:54:58 +01:00
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return error("unrepresentable length in delta: "
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2012-02-02 12:06:01 +01:00
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"%"PRIuMAX" > OFF_MAX", len);
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2012-02-02 11:59:23 +01:00
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if (signed_add_overflows(offset, (off_t) len))
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vcs-svn: learn to maintain a sliding view of a file
Each section of a Subversion-format delta only requires examining (and
keeping in random-access memory) a small portion of the preimage. At
any moment, this portion starts at a certain file offset and has a
well-defined length, and as the delta is applied, the portion advances
from the beginning to the end of the preimage. Add a move_window
function to keep track of this view into the preimage.
You can use it like this:
buffer_init(f, NULL);
struct sliding_view window = SLIDING_VIEW_INIT(f);
move_window(&window, 3, 7); /* (1) */
move_window(&window, 5, 5); /* (2) */
move_window(&window, 12, 2); /* (3) */
strbuf_release(&window.buf);
buffer_deinit(f);
The data structure is called sliding_view instead of _window to
prevent confusion with svndiff0 Windows.
In this example, (1) reads 10 bytes and discards the first 3;
(2) discards the first 2, which are not needed any more; and (3) skips
2 bytes and reads 2 new bytes to work with.
When move_window returns, the file position indicator is at position
window->off + window->width and the data from positions window->off to
the current file position are stored in window->buf.
This function performs only sequential access from the input file and
never seeks, so it can be safely used on pipes and sockets.
On end-of-file, move_window silently reads less than the caller
requested. On other errors, it prints a message and returns -1.
Helped-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
2011-01-03 04:54:58 +01:00
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return error("unrepresentable offset in delta: "
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"%"PRIuMAX" + %"PRIuMAX" > OFF_MAX",
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2012-02-02 12:06:01 +01:00
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(uintmax_t) offset, len);
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vcs-svn: learn to maintain a sliding view of a file
Each section of a Subversion-format delta only requires examining (and
keeping in random-access memory) a small portion of the preimage. At
any moment, this portion starts at a certain file offset and has a
well-defined length, and as the delta is applied, the portion advances
from the beginning to the end of the preimage. Add a move_window
function to keep track of this view into the preimage.
You can use it like this:
buffer_init(f, NULL);
struct sliding_view window = SLIDING_VIEW_INIT(f);
move_window(&window, 3, 7); /* (1) */
move_window(&window, 5, 5); /* (2) */
move_window(&window, 12, 2); /* (3) */
strbuf_release(&window.buf);
buffer_deinit(f);
The data structure is called sliding_view instead of _window to
prevent confusion with svndiff0 Windows.
In this example, (1) reads 10 bytes and discards the first 3;
(2) discards the first 2, which are not needed any more; and (3) skips
2 bytes and reads 2 new bytes to work with.
When move_window returns, the file position indicator is at position
window->off + window->width and the data from positions window->off to
the current file position are stored in window->buf.
This function performs only sequential access from the input file and
never seeks, so it can be safely used on pipes and sockets.
On end-of-file, move_window silently reads less than the caller
requested. On other errors, it prints a message and returns -1.
Helped-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
2011-01-03 04:54:58 +01:00
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return 0;
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}
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int move_window(struct sliding_view *view, off_t off, size_t width)
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{
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off_t file_offset;
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assert(view);
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assert(view->width <= view->buf.len);
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2012-02-02 11:59:23 +01:00
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assert(!check_offset_overflow(view->off, view->buf.len));
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vcs-svn: learn to maintain a sliding view of a file
Each section of a Subversion-format delta only requires examining (and
keeping in random-access memory) a small portion of the preimage. At
any moment, this portion starts at a certain file offset and has a
well-defined length, and as the delta is applied, the portion advances
from the beginning to the end of the preimage. Add a move_window
function to keep track of this view into the preimage.
You can use it like this:
buffer_init(f, NULL);
struct sliding_view window = SLIDING_VIEW_INIT(f);
move_window(&window, 3, 7); /* (1) */
move_window(&window, 5, 5); /* (2) */
move_window(&window, 12, 2); /* (3) */
strbuf_release(&window.buf);
buffer_deinit(f);
The data structure is called sliding_view instead of _window to
prevent confusion with svndiff0 Windows.
In this example, (1) reads 10 bytes and discards the first 3;
(2) discards the first 2, which are not needed any more; and (3) skips
2 bytes and reads 2 new bytes to work with.
When move_window returns, the file position indicator is at position
window->off + window->width and the data from positions window->off to
the current file position are stored in window->buf.
This function performs only sequential access from the input file and
never seeks, so it can be safely used on pipes and sockets.
On end-of-file, move_window silently reads less than the caller
requested. On other errors, it prints a message and returns -1.
Helped-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
2011-01-03 04:54:58 +01:00
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2012-02-02 11:59:23 +01:00
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if (check_offset_overflow(off, width))
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vcs-svn: learn to maintain a sliding view of a file
Each section of a Subversion-format delta only requires examining (and
keeping in random-access memory) a small portion of the preimage. At
any moment, this portion starts at a certain file offset and has a
well-defined length, and as the delta is applied, the portion advances
from the beginning to the end of the preimage. Add a move_window
function to keep track of this view into the preimage.
You can use it like this:
buffer_init(f, NULL);
struct sliding_view window = SLIDING_VIEW_INIT(f);
move_window(&window, 3, 7); /* (1) */
move_window(&window, 5, 5); /* (2) */
move_window(&window, 12, 2); /* (3) */
strbuf_release(&window.buf);
buffer_deinit(f);
The data structure is called sliding_view instead of _window to
prevent confusion with svndiff0 Windows.
In this example, (1) reads 10 bytes and discards the first 3;
(2) discards the first 2, which are not needed any more; and (3) skips
2 bytes and reads 2 new bytes to work with.
When move_window returns, the file position indicator is at position
window->off + window->width and the data from positions window->off to
the current file position are stored in window->buf.
This function performs only sequential access from the input file and
never seeks, so it can be safely used on pipes and sockets.
On end-of-file, move_window silently reads less than the caller
requested. On other errors, it prints a message and returns -1.
Helped-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
2011-01-03 04:54:58 +01:00
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return -1;
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if (off < view->off || off + width < view->off + view->width)
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return error("invalid delta: window slides left");
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2011-05-27 11:07:44 +02:00
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if (view->max_off >= 0 && view->max_off < off + width)
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return error("delta preimage ends early");
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vcs-svn: learn to maintain a sliding view of a file
Each section of a Subversion-format delta only requires examining (and
keeping in random-access memory) a small portion of the preimage. At
any moment, this portion starts at a certain file offset and has a
well-defined length, and as the delta is applied, the portion advances
from the beginning to the end of the preimage. Add a move_window
function to keep track of this view into the preimage.
You can use it like this:
buffer_init(f, NULL);
struct sliding_view window = SLIDING_VIEW_INIT(f);
move_window(&window, 3, 7); /* (1) */
move_window(&window, 5, 5); /* (2) */
move_window(&window, 12, 2); /* (3) */
strbuf_release(&window.buf);
buffer_deinit(f);
The data structure is called sliding_view instead of _window to
prevent confusion with svndiff0 Windows.
In this example, (1) reads 10 bytes and discards the first 3;
(2) discards the first 2, which are not needed any more; and (3) skips
2 bytes and reads 2 new bytes to work with.
When move_window returns, the file position indicator is at position
window->off + window->width and the data from positions window->off to
the current file position are stored in window->buf.
This function performs only sequential access from the input file and
never seeks, so it can be safely used on pipes and sockets.
On end-of-file, move_window silently reads less than the caller
requested. On other errors, it prints a message and returns -1.
Helped-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
2011-01-03 04:54:58 +01:00
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file_offset = view->off + view->buf.len;
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if (off < file_offset) {
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/* Move the overlapping region into place. */
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strbuf_remove(&view->buf, 0, off - view->off);
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} else {
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/* Seek ahead to skip the gap. */
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if (skip_or_whine(view->file, off - file_offset))
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return -1;
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strbuf_setlen(&view->buf, 0);
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}
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if (view->buf.len > width)
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; /* Already read. */
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else if (read_to_fill_or_whine(view->file, &view->buf, width))
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return -1;
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view->off = off;
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view->width = width;
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return 0;
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}
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