cext: use modern buffer protocol in patches()

PyObject_AsCharBuffer() is part of the "Old Buffer Protocol," which
has been deprecated for years. Let's port away from it.

PyBuffer_GetBuffer() must be paired with PyBuffer_Release(), hence the
added "goto cleanup" in a failure case.

We don't bump the extension version because the API has not changed.

Differential Revision: https://phab.mercurial-scm.org/D4840

mercurial/cext/mpatch.c

@@ -1,201 +1,204 b''
 /*
  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 "bitmanipulation.h"
 #include "compat.h"
 #include "mpatch.h"
 #include "util.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;
+	Py_buffer buffer;
 	int r = 0;
 	char *out;
-	Py_ssize_t len, outlen, inlen;
+	Py_ssize_t len, outlen;
 
 	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))
+	if (PyObject_GetBuffer(text, &buffer, PyBUF_CONTIG_RO)) {
 		return NULL;
+	}
 
 	patch = mpatch_fold(bins, cpygetitem, 0, len);
 	if (!patch) { /* error already set or memory error */
 		if (!PyErr_Occurred())
 			PyErr_NoMemory();
-		return NULL;
+		result = NULL;
+		goto cleanup;
 	}
 
-	outlen = mpatch_calcsize(inlen, patch);
+	outlen = mpatch_calcsize(buffer.len, 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);
 	/* clang-format off */
 	{
 		Py_BEGIN_ALLOW_THREADS
-		r = mpatch_apply(out, in, inlen, patch);
+		r = mpatch_apply(out, buffer.buf, buffer.len, patch);
 		Py_END_ALLOW_THREADS
 	}
 	/* clang-format on */
 	if (r < 0) {
 		Py_DECREF(result);
 		result = NULL;
 	}
 cleanup:
 	mpatch_lfree(patch);
+	PyBuffer_Release(&buffer);
 	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, PY23("ls#", "ly#"), &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},
 };
 
 static const int version = 1;
 
 #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.cext.mpatch.mpatchError", NULL, NULL);
 	Py_INCREF(mpatch_Error);
 	PyModule_AddObject(m, "mpatchError", mpatch_Error);
 	PyModule_AddIntConstant(m, "version", version);
 
 	return m;
 }
 #else
 PyMODINIT_FUNC initmpatch(void)
 {
 	PyObject *m;
 	m = Py_InitModule3("mpatch", methods, mpatch_doc);
 	mpatch_Error =
 	    PyErr_NewException("mercurial.cext.mpatch.mpatchError", NULL, NULL);
 	PyModule_AddIntConstant(m, "version", version);
 }
 #endif