path: root/source3/python/py_tdbpack.c

/* -*- c-file-style: "python"; indent-tabs-mode: nil; -*-
	 
   Python wrapper for Samba tdb pack/unpack functions
   Copyright (C) Martin Pool 2002


   NOTE PYTHON STYLE GUIDE
   http://www.python.org/peps/pep-0007.html
   
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/



#include "Python.h"

static PyObject * pytdbpack_number(char ch, PyObject *val_iter, PyObject *packed_list);
static PyObject * pytdbpack_str_850(PyObject *val_iter, PyObject *packed_list);
static PyObject * pytdbpack_buffer(PyObject *val_iter, PyObject *packed_list);

static PyObject *pytdbunpack_item(char, char **pbuf, int *plen, PyObject *);

static PyObject *pytdbpack_data(const char *format_str,
				     PyObject *val_seq,
				     PyObject *val_list);

static void pack_le_uint32(unsigned long val_long, unsigned char *pbuf);


static PyObject *pytdbpack_bad_type(char ch,
				    const char *expected,
				    PyObject *val_obj);

static const char * pytdbpack_docstring =
"Convert between Python values and Samba binary encodings.

This module is conceptually similar to the standard 'struct' module, but it
uses both a different binary format and a different description string.

Samba's encoding is based on that used inside DCE-RPC and SMB: a
little-endian, unpadded, non-self-describing binary format.  It is intended
that these functions be as similar as possible to the routines in Samba's
tdb/tdbutil module, with appropriate adjustments for Python datatypes.

Python strings are used to specify the format of data to be packed or
unpacked.

Strings are always stored in codepage 850.  Unicode objects are translated
to cp850; plain strings are assumed to be in latin-1 and are also
translated.

This may be a problem in the future if it is different to the Samba codepage.
It might be better to have the caller do the conversion, but that would conflict
with existing CMI code.

tdbpack format strings:

    'f':  NULL-terminated string in codepage 850

    'P':  same as 'f'

    'd':  4 byte little-endian unsigned number

    'w':  2 byte little-endian unsigned number

    'P': \"Pointer\" value -- in the subset of DCERPC used by Samba, this is
          really just an \"exists\" or \"does not exist\" flag.  The boolean
          value of the Python object is used.
    
    'B': 4-byte LE length, followed by that many bytes of binary data.
         Corresponds to a Python integer giving the length, followed by a byte
         string of the appropriate length.

    '$': Special flag indicating that the preceding format code should be
         repeated while data remains.  This is only supported for unpacking.

    Every code corresponds to a single Python object, except 'B' which
    corresponds to two values (length and contents), and '$', which produces
    however many make sense.
";


static char const pytdbpack_doc[] = 
"pack(format, values) -> buffer
Pack Python objects into Samba binary format according to format string.

arguments:
    format -- string of tdbpack format characters
    values -- sequence of value objects corresponding 1:1 to format characters

returns:
    buffer -- string containing packed data

raises:
    IndexError -- if there are too few values for the format
    ValueError -- if any of the format characters is illegal
    TypeError  -- if the format is not a string, or values is not a sequence,
        or any of the values is of the wrong type for the corresponding
        format character

notes:
    For historical reasons, it is not an error to pass more values than are consumed
    by the format.
";


static char const pytdbunpack_doc[] =
"unpack(format, buffer) -> (values, rest)
Unpack Samba binary data according to format string.

arguments:
    format -- string of tdbpack characters
    buffer -- string of packed binary data

returns:
    2-tuple of:
        values -- sequence of values corresponding 1:1 to format characters
        rest -- string containing data that was not decoded, or '' if the
            whole string was consumed

raises:
    IndexError -- if there is insufficient data in the buffer for the
        format (or if the data is corrupt and contains a variable-length
        field extending past the end)
    ValueError -- if any of the format characters is illegal

notes:
    Because unconsumed data is returned, you can feed it back in to the
    unpacker to extract further fields.  Alternatively, if you wish to modify
    some fields near the start of the data, you may be able to save time by
    only unpacking and repacking the necessary part.
";


const char *pytdb_string_encoding = "cp850";


/*
  * Pack objects to bytes.
  *
  * All objects are first individually encoded onto a list, and then the list
  * of strings is concatenated.  This is faster than concatenating strings,
  * and reasonably simple to code.
  */
static PyObject *
pytdbpack(PyObject *self,
	       PyObject *args)
{
	char *format_str;
	PyObject *val_seq, *val_iter = NULL,
		*packed_list = NULL, *packed_str = NULL,
		*empty_str = NULL;

	/* TODO: Test passing wrong types or too many arguments */
	if (!PyArg_ParseTuple(args, "sO", &format_str, &val_seq))
		return NULL;

	if (!(val_iter = PyObject_GetIter(val_seq)))
		goto out;

	/* Create list to hold strings until we're done, then join them all. */
	if (!(packed_list = PyList_New(0)))
		goto out;

	if (!pytdbpack_data(format_str, val_iter, packed_list))
		goto out;

	/* this function is not officially documented but it works */
	if (!(empty_str = PyString_InternFromString("")))
		goto out;
	
	packed_str = _PyString_Join(empty_str, packed_list);

  out:
	Py_XDECREF(empty_str);
	Py_XDECREF(val_iter);
	Py_XDECREF(packed_list);

	return packed_str;
}


/*
  Pack data according to FORMAT_STR from the elements of VAL_SEQ into
  PACKED_BUF.

  The string has already been checked out, so we know that VAL_SEQ is large
  enough to hold the packed data, and that there are enough value items.
  (However, their types may not have been thoroughly checked yet.)

  In addition, val_seq is a Python Fast sequence.

  Returns NULL for error (with exception set), or None.
*/
PyObject *
pytdbpack_data(const char *format_str,
		    PyObject *val_iter,
		    PyObject *packed_list)
{
	int format_i, val_i = 0;

	for (format_i = 0, val_i = 0; format_str[format_i]; format_i++) {
		char ch = format_str[format_i];

		switch (ch) {
			/* dispatch to the appropriate packer for this type,
			   which should pull things off the iterator, and
			   append them to the packed_list */
		case 'w':
		case 'd':
		case 'p':
			if (!(packed_list = pytdbpack_number(ch, val_iter, packed_list)))
				return NULL;
			break;

		case 'f':
		case 'P':
			if (!(packed_list = pytdbpack_str_850(val_iter, packed_list)))
				return NULL;
			break;

		case 'B':
			if (!(packed_list = pytdbpack_buffer(val_iter, packed_list)))
				return NULL;
			break;

		default:
			PyErr_Format(PyExc_ValueError,
				     "%s: format character '%c' is not supported",
				     __FUNCTION__, ch);
			return NULL;
		}
	}

	return packed_list;
}


static PyObject *
pytdbpack_number(char ch, PyObject *val_iter, PyObject *packed_list)
{
	unsigned long val_long;
	PyObject *val_obj = NULL, *long_obj = NULL, *result_obj = NULL;
	PyObject *new_list = NULL;
	unsigned char pack_buf[4];

	if (!(val_obj = PyIter_Next(val_iter)))
		goto out;

	if (!(long_obj = PyNumber_Long(val_obj))) {
		pytdbpack_bad_type(ch, "Number", val_obj);
		goto out;
	}

	val_long = PyLong_AsUnsignedLong(long_obj);
	pack_le_uint32(val_long, pack_buf);

	/* pack as 32-bit; if just packing a 'w' 16-bit word then only take
	   the first two bytes. */
	
	if (!(result_obj = PyString_FromStringAndSize(pack_buf, ch == 'w' ? 2 : 4)))
		goto out;

	if (PyList_Append(packed_list, result_obj) != -1)
		new_list = packed_list;

  out:
	Py_XDECREF(val_obj);
	Py_XDECREF(long_obj);
	Py_XDECREF(result_obj);

	return new_list;
}


/*
 * Take one string from the iterator val_iter, convert it to 8-bit CP850, and
 * return it.
 *
 * If the input is neither a string nor Unicode, an exception is raised.
 *
 * If the input is Unicode, then it is converted to CP850.
 *
 * If the input is a String, then it is converted to Unicode using the default
 * decoding method, and then converted to CP850.  This in effect gives
 * conversion from latin-1 (currently the PSA's default) to CP850, without
 * needing a custom translation table.
 *
 * I hope this approach avoids being too fragile w.r.t. being passed either
 * Unicode or String objects.
 */
static PyObject *
pytdbpack_str_850(PyObject *val_iter, PyObject *packed_list)
{
	PyObject *val_obj = NULL;
	PyObject *unicode_obj = NULL;
	PyObject *cp850_str = NULL;
	PyObject *nul_str = NULL;
	PyObject *new_list = NULL;

	if (!(val_obj = PyIter_Next(val_iter)))
		goto out;

	if (PyUnicode_Check(val_obj)) {
		unicode_obj = val_obj;
	}
	else {
		/* string */
		if (!(unicode_obj = PyString_AsDecodedObject(val_obj, NULL, NULL)))
			goto out;
		Py_XDECREF(val_obj);
		val_obj = NULL;
	}

	if (!(cp850_str = PyUnicode_AsEncodedString(unicode_obj, pytdb_string_encoding, NULL)))
		goto out;

	if (!nul_str)
		/* this is constant and often-used; hold it forever */
		if (!(nul_str = PyString_FromStringAndSize("", 1)))
			goto out;

	if ((PyList_Append(packed_list, cp850_str) != -1)
	    && (PyList_Append(packed_list, nul_str) != -1))
		new_list = packed_list;

  out:
	Py_XDECREF(unicode_obj);
	Py_XDECREF(cp850_str);

	return new_list;
}


/*
 * Pack (LENGTH, BUFFER) pair onto the list.
 *
 * The buffer must already be a String, not Unicode, because it contains 8-bit
 * untranslated data.  In some cases it will actually be UTF_16_LE data.
 */
static PyObject *
pytdbpack_buffer(PyObject *val_iter, PyObject *packed_list)
{
	PyObject *val_obj;
	PyObject *new_list = NULL;
	
	/* pull off integer and stick onto list */
	if (!(packed_list = pytdbpack_number('d', val_iter, packed_list)))
		return NULL;

	/* this assumes that the string is the right length; the old code did the same. */
	if (!(val_obj = PyIter_Next(val_iter)))
		return NULL;

	if (!PyString_Check(val_obj)) {
		pytdbpack_bad_type('B', "String", val_obj);
		goto out;
	}
	
	if (PyList_Append(packed_list, val_obj) != -1)
		new_list = packed_list;

  out:
	Py_XDECREF(val_obj);
	return new_list;
}


static PyObject *pytdbpack_bad_type(char ch,
				    const char *expected,
				    PyObject *val_obj)
{
	PyObject *r = PyObject_Repr(val_obj);
	if (!r)
		return NULL;
	PyErr_Format(PyExc_TypeError,
		     "tdbpack: format '%c' requires %s, not %s",
		     ch, expected, PyString_AS_STRING(r));
	Py_DECREF(r);
	return val_obj;
}


/*
  XXX: glib and Samba have quicker macro for doing the endianness conversions,
  but I don't know of one in plain libc, and it's probably not a big deal.  I
  realize this is kind of dumb because we'll almost always be on x86, but
  being safe is important.
*/
static void pack_le_uint32(unsigned long val_long, unsigned char *pbuf)
{
	pbuf[0] =         val_long & 0xff;
	pbuf[1] = (val_long >> 8)  & 0xff;
	pbuf[2] = (val_long >> 16) & 0xff;
	pbuf[3] = (val_long >> 24) & 0xff;
}


static void pack_bytes(long len, const char *from,
		       unsigned char **pbuf)
{
	memcpy(*pbuf, from, len);
	(*pbuf) += len;
}



static PyObject *
pytdbunpack(PyObject *self,
		 PyObject *args)
{
	char *format_str, *packed_str, *ppacked;
	PyObject *val_list = NULL, *ret_tuple = NULL;
	PyObject *rest_string = NULL;
	int format_len, packed_len;
	char last_format = '#';	/* invalid */
	int i;
	
	/* get arguments */
	if (!PyArg_ParseTuple(args, "ss#", &format_str, &packed_str, &packed_len))
		return NULL;

	format_len = strlen(format_str);
	
	/* Allocate list to hold results.  Initially empty, and we append
	   results as we go along. */
	val_list = PyList_New(0);
	if (!val_list)
		goto failed;
	ret_tuple = PyTuple_New(2);
	if (!ret_tuple)
		goto failed;
	
	/* For every object, unpack.  */
	for (ppacked = packed_str, i = 0; i < format_len && format_str[i] != '$'; i++) {
		last_format = format_str[i];
		/* packed_len is reduced in place */
		if (!pytdbunpack_item(format_str[i], &ppacked, &packed_len, val_list))
			goto failed;
	}

	/* If the last character was '$', keep going until out of space */
	if (format_str[i] == '$') {
		if (i == 0) {
			PyErr_Format(PyExc_ValueError,
				     "%s: '$' may not be first character in format",
				     __FUNCTION__);
			return NULL;
		} 
		while (packed_len > 0)
			if (!pytdbunpack_item(last_format, &ppacked, &packed_len, val_list))
				goto failed;
	}
	
	/* save leftovers for next time */
	rest_string = PyString_FromStringAndSize(ppacked, packed_len);
	if (!rest_string)
		goto failed;

	/* return (values, rest) tuple; give up references to them */
	PyTuple_SET_ITEM(ret_tuple, 0, val_list);
	val_list = NULL;
	PyTuple_SET_ITEM(ret_tuple, 1, rest_string);
	val_list = NULL;
	return ret_tuple;

  failed:
	/* handle failure: deallocate anything.  XDECREF forms handle NULL
	   pointers for objects that haven't been allocated yet. */
	Py_XDECREF(val_list);
	Py_XDECREF(ret_tuple);
	Py_XDECREF(rest_string);
	return NULL;
}


static void
pytdbunpack_err_too_short(void)
{
	PyErr_Format(PyExc_IndexError,
		     __FUNCTION__ ": data too short for unpack format");
}


static PyObject *
pytdbunpack_uint32(char **pbuf, int *plen)
{
	unsigned long v;
	unsigned char *b;
	
	if (*plen < 4) {
		pytdbunpack_err_too_short();
		return NULL;
	}

	b = *pbuf;
	v = b[0] | b[1]<<8 | b[2]<<16 | b[3]<<24;
	
	(*pbuf) += 4;
	(*plen) -= 4;

	return PyLong_FromUnsignedLong(v);
}


static PyObject *pytdbunpack_int16(char **pbuf, int *plen)
{
	long v;
	unsigned char *b;
	
	if (*plen < 2) {
		pytdbunpack_err_too_short();
		return NULL;
	}

	b = *pbuf;
	v = b[0] | b[1]<<8;
	
	(*pbuf) += 2;
	(*plen) -= 2;

	return PyInt_FromLong(v);
}


static PyObject *
pytdbunpack_string(char **pbuf, int *plen)
{
	int len;
	char *nul_ptr, *start;

	start = *pbuf;
	
	nul_ptr = memchr(start, '\0', *plen);
	if (!nul_ptr) {
		pytdbunpack_err_too_short();
		return NULL;
	}

	len = nul_ptr - start;

	*pbuf += len + 1;	/* skip \0 */
	*plen -= len + 1;

	return PyString_Decode(start, len, pytdb_string_encoding, NULL);
}


static PyObject *
pytdbunpack_buffer(char **pbuf, int *plen, PyObject *val_list)
{
	/* first get 32-bit len */
	long slen;
	unsigned char *b;
	unsigned char *start;
	PyObject *str_obj = NULL, *len_obj = NULL;
	
	if (*plen < 4) {
		pytdbunpack_err_too_short();
		return NULL;
	}
	
	b = *pbuf;
	slen = b[0] | b[1]<<8 | b[2]<<16 | b[3]<<24;

	if (slen < 0) { /* surely you jest */
		PyErr_Format(PyExc_ValueError,
			     __FUNCTION__ ": buffer seems to have negative length");
		return NULL;
	}

	(*pbuf) += 4;
	(*plen) -= 4;
	start = *pbuf;

	if (*plen < slen) {
		PyErr_Format(PyExc_IndexError,
			     __FUNCTION__ ": not enough data to unpack buffer: "
			     "need %d bytes, have %d",
			     (int) slen, *plen);
		return NULL;
	}

	(*pbuf) += slen;
	(*plen) -= slen;

	if (!(len_obj = PyInt_FromLong(slen)))
		goto failed;

	if (PyList_Append(val_list, len_obj) == -1)
		goto failed;
	
	if (!(str_obj = PyString_FromStringAndSize(start, slen)))
		goto failed;
	
	if (PyList_Append(val_list, str_obj) == -1)
		goto failed;
	
	return val_list;

  failed:
	Py_XDECREF(len_obj);	/* handles NULL */
	Py_XDECREF(str_obj);
	return NULL;
}


/* Unpack a single field from packed data, according to format character CH.
   Remaining data is at *PBUF, of *PLEN.

   *PBUF is advanced, and *PLEN reduced to reflect the amount of data that has
   been consumed.

   Returns a reference to None, or NULL for failure.
*/
static PyObject *pytdbunpack_item(char ch,
				       char **pbuf,
				       int *plen,
				       PyObject *val_list)
{
	PyObject *result;
	
	if (ch == 'w') {	/* 16-bit int */
		result = pytdbunpack_int16(pbuf, plen);
	}
	else if (ch == 'd' || ch == 'p') { /* 32-bit int */
		/* pointers can just come through as integers */
		result = pytdbunpack_uint32(pbuf, plen);
	}
	else if (ch == 'f' || ch == 'P') { /* nul-term string  */
		result = pytdbunpack_string(pbuf, plen);
	}
	else if (ch == 'B') { /* length, buffer */
		return pytdbunpack_buffer(pbuf, plen, val_list);
	}
	else {
		PyErr_Format(PyExc_ValueError,
			     __FUNCTION__ ": format character '%c' is not supported",
			     ch);
		
		return NULL;
	}

	/* otherwise OK */
	if (!result)
		return NULL;
	if (PyList_Append(val_list, result) == -1)
		return NULL;
	
	return val_list;
}






static PyMethodDef pytdbpack_methods[] = {
	{ "pack", pytdbpack, METH_VARARGS, (char *) pytdbpack_doc },
	{ "unpack", pytdbunpack, METH_VARARGS, (char *) pytdbunpack_doc },
};

DL_EXPORT(void)
inittdbpack(void)
{
	Py_InitModule3("tdbpack", pytdbpack_methods,
		       (char *) pytdbpack_docstring);
}