view mercurial/mpatch_module.c @ 31793:69d8fcf20014

help: document bundle specifications

I softly formalized the concept of a "bundle specification" a while
ago when I was working on clone bundles and stream clone bundles and
wanted a more robust way to define what exactly is in a bundle file.

The concept has existed for a while. Since it is part of the clone
bundles feature and exposed to the user via the "-t" argument to
`hg bundle`, it is something we need to support for the long haul.

After the 4.1 release, I heard a few people comment that they didn't
realize you could generate zstd bundles with `hg bundle`. I'm
partially to blame for not documenting it in bundle's docstring.

Additionally, I added a hacky, experimental feature for controlling
the compression level of bundles in 76104a4899ad. As the commit
message says, I went with a quick and dirty solution out of time
constraints. Furthermore, I wanted to eventually store this
configuration in the "bundlespec" so it could be made more flexible.

Given:

a) bundlespecs are here to stay
b) we don't have great documentation over what they are, despite being
   a user-facing feature
c) the list of available compression engines and their behavior isn't
   exposed
d) we need an extensible place to modify behavior of compression
   engines

I want to move forward with formalizing bundlespecs as a user-facing
feature. This commit does that by introducing a "bundlespec" help
page. Leaning on the just-added compression engine documentation
and API, the topic also conveniently lists available compression
engines and details about them. This makes features like zstd
bundle compression more discoverable. e.g. you can now
`hg help -k zstd` and it lists the "bundlespec" topic.

/*
 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.
*/

#define PY_SSIZE_T_CLEAN
#include <Python.h>
#include <stdlib.h>
#include <string.h>

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

static char mpatch_doc[] = "Efficient binary patching.";
static PyObject *mpatch_Error;

static void setpyerr(int r)
{
	switch (r) {
	case MPATCH_ERR_NO_MEM:
		PyErr_NoMemory();
		break;
	case MPATCH_ERR_CANNOT_BE_DECODED:
		PyErr_SetString(mpatch_Error, "patch cannot be decoded");
		break;
	case MPATCH_ERR_INVALID_PATCH:
		PyErr_SetString(mpatch_Error, "invalid patch");
		break;
	}
}

struct mpatch_flist *cpygetitem(void *bins, ssize_t pos)
{
	const char *buffer;
	struct mpatch_flist *res;
	ssize_t blen;
	int r;

	PyObject *tmp = PyList_GetItem((PyObject*)bins, pos);
	if (!tmp)
		return NULL;
	if (PyObject_AsCharBuffer(tmp, &buffer, (Py_ssize_t*)&blen))
		return NULL;
	if ((r = mpatch_decode(buffer, blen, &res)) < 0) {
		if (!PyErr_Occurred())
			setpyerr(r);
		return NULL;
	}
	return res;
}

static PyObject *
patches(PyObject *self, PyObject *args)
{
	PyObject *text, *bins, *result;
	struct mpatch_flist *patch;
	const char *in;
	int r = 0;
	char *out;
	Py_ssize_t len, outlen, inlen;

	if (!PyArg_ParseTuple(args, "OO:mpatch", &text, &bins))
		return NULL;

	len = PyList_Size(bins);
	if (!len) {
		/* nothing to do */
		Py_INCREF(text);
		return text;
	}

	if (PyObject_AsCharBuffer(text, &in, &inlen))
		return NULL;

	patch = mpatch_fold(bins, cpygetitem, 0, len);
	if (!patch) { /* error already set or memory error */
		if (!PyErr_Occurred())
			PyErr_NoMemory();
		return NULL;
	}

	outlen = mpatch_calcsize(inlen, patch);
	if (outlen < 0) {
		r = (int)outlen;
		result = NULL;
		goto cleanup;
	}
	result = PyBytes_FromStringAndSize(NULL, outlen);
	if (!result) {
		result = NULL;
		goto cleanup;
	}
	out = PyBytes_AsString(result);
	if ((r = mpatch_apply(out, in, inlen, patch)) < 0) {
		Py_DECREF(result);
		result = NULL;
	}
cleanup:
	mpatch_lfree(patch);
	if (!result && !PyErr_Occurred())
		setpyerr(r);
	return result;
}

/* calculate size of a patched file directly */
static PyObject *
patchedsize(PyObject *self, PyObject *args)
{
	long orig, start, end, len, outlen = 0, last = 0, pos = 0;
	Py_ssize_t patchlen;
	char *bin;

	if (!PyArg_ParseTuple(args, "ls#", &orig, &bin, &patchlen))
		return NULL;

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

	if (pos != patchlen) {
		if (!PyErr_Occurred())
			PyErr_SetString(mpatch_Error, "patch cannot be decoded");
		return NULL;
	}

	outlen += orig - last;
	return Py_BuildValue("l", outlen);
}

static PyMethodDef methods[] = {
	{"patches", patches, METH_VARARGS, "apply a series of patches\n"},
	{"patchedsize", patchedsize, METH_VARARGS, "calculed patched size\n"},
	{NULL, NULL}
};

#ifdef IS_PY3K
static struct PyModuleDef mpatch_module = {
	PyModuleDef_HEAD_INIT,
	"mpatch",
	mpatch_doc,
	-1,
	methods
};

PyMODINIT_FUNC PyInit_mpatch(void)
{
	PyObject *m;

	m = PyModule_Create(&mpatch_module);
	if (m == NULL)
		return NULL;

	mpatch_Error = PyErr_NewException("mercurial.mpatch.mpatchError",
					  NULL, NULL);
	Py_INCREF(mpatch_Error);
	PyModule_AddObject(m, "mpatchError", mpatch_Error);

	return m;
}
#else
PyMODINIT_FUNC
initmpatch(void)
{
	Py_InitModule3("mpatch", methods, mpatch_doc);
	mpatch_Error = PyErr_NewException("mercurial.mpatch.mpatchError",
					  NULL, NULL);
}
#endif