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git/vcs-svn/sliding_window.h

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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>
14 years ago
#ifndef SLIDING_WINDOW_H_
#define SLIDING_WINDOW_H_
#include "strbuf.h"
struct sliding_view {
struct line_buffer *file;
off_t off;
size_t width;
vcs-svn: cap number of bytes read from sliding view Introduce a "max_off" field in struct sliding_view, roughly representing a maximum number of bytes that can be read from "file". If it is set to a nonnegative integer, a call to move_window() attempting to put the right endpoint beyond that offset will return an error instead. The idea is to use this when applying Subversion-format deltas to prevent reads past the end of the preimage (which has known length). Without such a check, corrupt deltas would cause svn-fe to block indefinitely when data in the input pipe is exhausted. Inspired-by: Ramkumar Ramachandra <artagnon@gmail.com> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
14 years ago
off_t max_off; /* -1 means unlimited */
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>
14 years ago
struct strbuf buf;
};
vcs-svn: cap number of bytes read from sliding view Introduce a "max_off" field in struct sliding_view, roughly representing a maximum number of bytes that can be read from "file". If it is set to a nonnegative integer, a call to move_window() attempting to put the right endpoint beyond that offset will return an error instead. The idea is to use this when applying Subversion-format deltas to prevent reads past the end of the preimage (which has known length). Without such a check, corrupt deltas would cause svn-fe to block indefinitely when data in the input pipe is exhausted. Inspired-by: Ramkumar Ramachandra <artagnon@gmail.com> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
14 years ago
#define SLIDING_VIEW_INIT(input, len) { (input), 0, 0, (len), STRBUF_INIT }
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>
14 years ago
extern int move_window(struct sliding_view *view, off_t off, size_t width);
#endif