annotate mercurial/mpatch.c @ 35616:706aa203b396

fileset: add a lightweight file filtering language

This patch was inspired by one that Jun Wu authored for the fb-experimental
repo, to avoid using matcher for efficiency[1].  We want a way to specify what
files will be converted to LFS at commit time.  And per discussion, we also want
to specify what files to skip, text diff, or merge in another config option.
The current `lfs.threshold` config option could not satisfy complex needs.  I'm
putting it in a core package because Augie floated the idea of also using it for
narrow and sparse.

Yuya suggested farming out to fileset.parse(), which added support for more
symbols.  The only fileset element not supported here is 'negate'.  (List isn't
supported by filesets either.)  I also changed the 'always' token to the 'all()'
predicate for consistency, and introduced 'none()' to improve readability in a
future tracked file based config.  The extension operator was changed from '.'
to '**', to match how recursive path globs are specified.  Finally, I changed
the path matcher from '/' to 'path:' at Yuya's suggestion, for consistency with
matcher.  Unfortunately, ':' is currently reserved in filesets, so this has to
be quoted to be processed as a string instead of a symbol[2].  We should
probably revisit that, because it's seriously ugly.  But it's only used by an
experimental extension, and I think using a file based config for LFS may drive
some more tweaks, so I'm settling for this for now.

I reserved all of the glob characters in fileset except '.' and '_' for the
extension test because those are likely valid extension characters.

Sample filter settings:

  all()                        # everything
  size(">20MB")                # larger than 20MB
  !**.txt                      # except for .txt files
  **.zip | **.tar.gz | **.7z   # some types of compressed files
  "path:bin"                   # files under "bin" in the project root

[1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-December/109387.html
[2] https://www.mercurial-scm.org/pipermail/mercurial-devel/2018-January/109729.html

/*
 mpatch.c - efficient binary patching for Mercurial

 This implements a patch algorithm that's O(m + nlog n) where m is the
 size of the output and n is the number of patches.

 Given a list of binary patches, it unpacks each into a hunk list,
 then combines the hunk lists with a treewise recursion to form a
 single hunk list. This hunk list is then applied to the original
 text.

 The text (or binary) fragments are copied directly from their source
 Python objects into a preallocated output string to avoid the
 allocation of intermediate Python objects. Working memory is about 2x
 the total number of hunks.

 Copyright 2005, 2006 Matt Mackall <[e-mail]>

 This software may be used and distributed according to the terms
 of the GNU General Public License, incorporated herein by reference.
*/

#include <stdlib.h>
#include <string.h>

#include "bitmanipulation.h"
#include "compat.h"
#include "mpatch.h"

static struct mpatch_flist *lalloc(ssize_t size)
{
	struct mpatch_flist *a = NULL;

	if (size < 1)
		size = 1;

	a = (struct mpatch_flist *)malloc(sizeof(struct mpatch_flist));
	if (a) {
		a->base = (struct mpatch_frag *)malloc(
		    sizeof(struct mpatch_frag) * size);
		if (a->base) {
			a->head = a->tail = a->base;
			return a;
		}
		free(a);
	}
	return NULL;
}

void mpatch_lfree(struct mpatch_flist *a)
{
	if (a) {
		free(a->base);
		free(a);
	}
}

static ssize_t lsize(struct mpatch_flist *a)
{
	return a->tail - a->head;
}

/* move hunks in source that are less cut to dest, compensating
   for changes in offset. the last hunk may be split if necessary.
*/
static int gather(struct mpatch_flist *dest, struct mpatch_flist *src, int cut,
                  int offset)
{
	struct mpatch_frag *d = dest->tail, *s = src->head;
	int postend, c, l;

	while (s != src->tail) {
		if (s->start + offset >= cut)
			break; /* we've gone far enough */

		postend = offset + s->start + s->len;
		if (postend <= cut) {
			/* save this hunk */
			offset += s->start + s->len - s->end;
			*d++ = *s++;
		} else {
			/* break up this hunk */
			c = cut - offset;
			if (s->end < c)
				c = s->end;
			l = cut - offset - s->start;
			if (s->len < l)
				l = s->len;

			offset += s->start + l - c;

			d->start = s->start;
			d->end = c;
			d->len = l;
			d->data = s->data;
			d++;
			s->start = c;
			s->len = s->len - l;
			s->data = s->data + l;

			break;
		}
	}

	dest->tail = d;
	src->head = s;
	return offset;
}

/* like gather, but with no output list */
static int discard(struct mpatch_flist *src, int cut, int offset)
{
	struct mpatch_frag *s = src->head;
	int postend, c, l;

	while (s != src->tail) {
		if (s->start + offset >= cut)
			break;

		postend = offset + s->start + s->len;
		if (postend <= cut) {
			offset += s->start + s->len - s->end;
			s++;
		} else {
			c = cut - offset;
			if (s->end < c)
				c = s->end;
			l = cut - offset - s->start;
			if (s->len < l)
				l = s->len;

			offset += s->start + l - c;
			s->start = c;
			s->len = s->len - l;
			s->data = s->data + l;

			break;
		}
	}

	src->head = s;
	return offset;
}

/* combine hunk lists a and b, while adjusting b for offset changes in a/
   this deletes a and b and returns the resultant list. */
static struct mpatch_flist *combine(struct mpatch_flist *a,
                                    struct mpatch_flist *b)
{
	struct mpatch_flist *c = NULL;
	struct mpatch_frag *bh, *ct;
	int offset = 0, post;

	if (a && b)
		c = lalloc((lsize(a) + lsize(b)) * 2);

	if (c) {

		for (bh = b->head; bh != b->tail; bh++) {
			/* save old hunks */
			offset = gather(c, a, bh->start, offset);

			/* discard replaced hunks */
			post = discard(a, bh->end, offset);

			/* insert new hunk */
			ct = c->tail;
			ct->start = bh->start - offset;
			ct->end = bh->end - post;
			ct->len = bh->len;
			ct->data = bh->data;
			c->tail++;
			offset = post;
		}

		/* hold on to tail from a */
		memcpy(c->tail, a->head, sizeof(struct mpatch_frag) * lsize(a));
		c->tail += lsize(a);
	}

	mpatch_lfree(a);
	mpatch_lfree(b);
	return c;
}

/* decode a binary patch into a hunk list */
int mpatch_decode(const char *bin, ssize_t len, struct mpatch_flist **res)
{
	struct mpatch_flist *l;
	struct mpatch_frag *lt;
	int pos = 0;

	/* assume worst case size, we won't have many of these lists */
	l = lalloc(len / 12 + 1);
	if (!l)
		return MPATCH_ERR_NO_MEM;

	lt = l->tail;

	while (pos >= 0 && pos < len) {
		lt->start = getbe32(bin + pos);
		lt->end = getbe32(bin + pos + 4);
		lt->len = getbe32(bin + pos + 8);
		lt->data = bin + pos + 12;
		pos += 12 + lt->len;
		if (lt->start > lt->end || lt->len < 0)
			break; /* sanity check */
		lt++;
	}

	if (pos != len) {
		mpatch_lfree(l);
		return MPATCH_ERR_CANNOT_BE_DECODED;
	}

	l->tail = lt;
	*res = l;
	return 0;
}

/* calculate the size of resultant text */
ssize_t mpatch_calcsize(ssize_t len, struct mpatch_flist *l)
{
	ssize_t outlen = 0, last = 0;
	struct mpatch_frag *f = l->head;

	while (f != l->tail) {
		if (f->start < last || f->end > len) {
			return MPATCH_ERR_INVALID_PATCH;
		}
		outlen += f->start - last;
		last = f->end;
		outlen += f->len;
		f++;
	}

	outlen += len - last;
	return outlen;
}

int mpatch_apply(char *buf, const char *orig, ssize_t len,
                 struct mpatch_flist *l)
{
	struct mpatch_frag *f = l->head;
	int last = 0;
	char *p = buf;

	while (f != l->tail) {
		if (f->start < last || f->end > len) {
			return MPATCH_ERR_INVALID_PATCH;
		}
		memcpy(p, orig + last, f->start - last);
		p += f->start - last;
		memcpy(p, f->data, f->len);
		last = f->end;
		p += f->len;
		f++;
	}
	memcpy(p, orig + last, len - last);
	return 0;
}

/* recursively generate a patch of all bins between start and end */
struct mpatch_flist *
mpatch_fold(void *bins, struct mpatch_flist *(*get_next_item)(void *, ssize_t),
            ssize_t start, ssize_t end)
{
	ssize_t len;

	if (start + 1 == end) {
		/* trivial case, output a decoded list */
		return get_next_item(bins, start);
	}

	/* divide and conquer, memory management is elsewhere */
	len = (end - start) / 2;
	return combine(mpatch_fold(bins, get_next_item, start, start + len),
	               mpatch_fold(bins, get_next_item, start + len, end));
}