Re: [gentoo-portage-dev] [PATCH] Generate soname dependency metadata (282639)

[Anthony G. Basile]

On 01/26/15 22:16, Zac Medico wrote:
> Generate soname dependency metadata for binary and installed packages,
> in the form of PROVIDES and REQUIRES metadata. It is useful to generate
> PROVIDES and REQUIRES metadata now, so that it will be available
> when dependency resolver support is added in the future. Note that
> slot-operator dependencies will not be able to serve as a substitute
> for soname dependencies for the forseeable future, because system
> dependencies are frequently unspecified (according to Gentoo policy).

Thanks for putting this into the commit message.  Getting the point 
across to people was at times painful.

>
> The PROVIDES/REQUIRES system is very similar to the automatic Requires
> and Provides system which is supported by RPM. The PROVIDES/REQUIRES
> metadata is generated automatically from the ELF files that are
> installed by a package. The PROVIDES/REQUIRES syntax is described in
> the /var/db/pkg section of the portage(5) man page. REQUIRES_EXCLUDE
> and PROVIDES_EXCLUDE ebuild variables allow for filtering of the
> sonames that are saved in REQUIRES and PROVIDES (see the ebuild(5) man
> page for details).

ELF gets us like 99% of the way but will eventually have to think about 
Mach-O for gentoo-on-mac etc.  Maybe COFF, a.out.  Not sure where to 
draw the line.

>
> The /var/db/pkg NEEDED.ELF.2 format now includes an additional field
> which indicates the multilib category, as discussed in bug #534206. The
> multilib category is used to categorize the sonames that are listed in
> PROVIDES/REQUIRES metadata, since sonames need to be resolved
> separately for each multilib category. The complete list of supported
> multilib categories is documented in the comments of the
> portage.dep.soname.multilib_category module.
>
> X-Gentoo-Bug: 282639
> X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=282639
> ---
>   bin/ebuild.sh                               |   2 +-
>   bin/phase-functions.sh                      |   2 +-
>   man/ebuild.5                                |  12 +++
>   man/portage.5                               |  25 +++++
>   pym/_emerge/Package.py                      |   3 +-
>   pym/portage/dbapi/bintree.py                |   5 +-
>   pym/portage/dbapi/vartree.py                |   1 +
>   pym/portage/dep/soname/__init__.py          |   2 +
>   pym/portage/dep/soname/multilib_category.py | 112 +++++++++++++++++++++++
>   pym/portage/package/ebuild/doebuild.py      |  86 ++++++++++++++++--
>   pym/portage/util/_dyn_libs/LinkageMapELF.py |  61 ++++++++++---
>   pym/portage/util/_dyn_libs/NeededEntry.py   |  83 +++++++++++++++++
>   pym/portage/util/_dyn_libs/soname_deps.py   | 136 ++++++++++++++++++++++++++++
>   pym/portage/util/elf/__init__.py            |   2 +
>   pym/portage/util/elf/constants.py           |  36 ++++++++
>   pym/portage/util/elf/header.py              |  62 +++++++++++++
>   pym/portage/util/endian/__init__.py         |   2 +
>   pym/portage/util/endian/decode.py           |  56 ++++++++++++
>   18 files changed, 661 insertions(+), 27 deletions(-)
>   create mode 100644 pym/portage/dep/soname/__init__.py
>   create mode 100644 pym/portage/dep/soname/multilib_category.py
>   create mode 100644 pym/portage/util/_dyn_libs/NeededEntry.py
>   create mode 100644 pym/portage/util/_dyn_libs/soname_deps.py
>   create mode 100644 pym/portage/util/elf/__init__.py
>   create mode 100644 pym/portage/util/elf/constants.py
>   create mode 100644 pym/portage/util/elf/header.py
>   create mode 100644 pym/portage/util/endian/__init__.py
>   create mode 100644 pym/portage/util/endian/decode.py
>

I can't speak to the integration into portage.  I'm sure you got that 
right.  I'll comment on the elf-ish stuff.

> diff --git a/man/portage.5 b/man/portage.5
> index 189561c..bf159fd 100644
> --- a/man/portage.5
> +++ b/man/portage.5
> @@ -1443,6 +1443,31 @@ can be changed quickly.  Generally though there is one file per environment
>   variable that "matters" (like CFLAGS) with the contents stored inside of it.
>   Another common file is the CONTENTS file which lists the path and hashes of
>   all objects that the package installed onto your system.
> +.TP
> +.BR PROVIDES
> +Contains information about the sonames that a package provides, which is
> +automatically generated from the files that it installs. The sonames
> +may have been filtered by the \fBPROVIDES_EXCLUDE\fR \fBebuild\fR(5)
> +variable. A multilib category, followed by a colon, always preceeds a
> +list of one or more sonames.
> +
> +.I Example:
> +.nf
> +x86_32: libcom_err.so.2 libss.so.2 x86_64: libcom_err.so.2 libss.so.2
> +.fi
> +.TP
> +.BR REQUIRES
> +Contains information about the sonames that a package requires, which is
> +automatically generated from the files that it installs. The sonames
> +may have been filtered by the \fBREQUIRES_EXCLUDE\fR \fBebuild\fR(5)
> +variable. Any sonames that a package provides are automatically excluded
> +from \fBREQUIRES\fR. A multilib category, followed by a colon, always
> +preceeds a list of one or more sonames.
> +
> +.I Example:
> +.nf
> +x86_32: ld-linux.so.2 libc.so.6 x86_64: ld-linux-x86-64.so.2 libc.so.6
> +.fi
>   .RE
>   .TP
>   .BR /var/lib/portage/

I'm a bit confused here.  So PROVIDES and REQUIRES are new files in 
/var/db/pkg/<cat>/<pkg>?  And the format of NEEDED.ELF.2 is not 
changing?  Correct?

> diff --git a/pym/portage/dep/soname/__init__.py b/pym/portage/dep/soname/__init__.py
> new file mode 100644
> index 0000000..4725d33
> --- /dev/null
> +++ b/pym/portage/dep/soname/__init__.py
> @@ -0,0 +1,2 @@
> +# Copyright 2015 Gentoo Foundation
> +# Distributed under the terms of the GNU General Public License v2
> diff --git a/pym/portage/dep/soname/multilib_category.py b/pym/portage/dep/soname/multilib_category.py
> new file mode 100644
> index 0000000..8cc8fd3
> --- /dev/null
> +++ b/pym/portage/dep/soname/multilib_category.py
> @@ -0,0 +1,112 @@
> +# Copyright 2015 Gentoo Foundation
> +# Distributed under the terms of the GNU General Public License v2
> +#
> +# Compute a multilib category, as discussed here:
> +#
> +# 	https://bugs.gentoo.org/show_bug.cgi?id=534206
> +#
> +# Supported categories:
> +#
> +#	alpha_{32,64}
> +#	arm_{32,64}

We should note at some point that arm_32 means EABI and not OABI which 
are two different 32-bit arm abis.  We don't support oabi in gentoo 
anymore, but still this can be confusing.  If it did come up in some 
context, we could distinguish it as arm_o32 like mips below.

We probably don't have to note that arm_64 is aarch6 which is really a 
different ISA, not backwards compatible to 32-bit arm.  As you say below 
this is just a naming convention, but in every other case each line does 
refer to one ISA, except maybe ia_32 can be confused with x86.

> +#	hppa_{32,64}
> +#	ia_{32,64}
> +#	m68k_{32,64}
> +#	mips_{eabi32,eabi64,n32,n64,o32,o64}
> +#	ppc_{32,64}
> +#	s390_{32,64}
> +#	sh_{32,64}
> +#	sparc_{32,64}
> +#	x86_{32,64,x32}
> +#
> +# NOTES:
> +#
> +# * The ABIs referenced by some of the above *_32 and *_64 categories
> +#   may be imaginary, but they are listed anyway, since the goal is to
> +#   establish a naming convention that is as consistent and uniform as
> +#   possible.
> +#
> +# * The Elf header's e_ident[EI_OSABI] byte is completely ignored,
> +#   since OS-independence is one of the goals. The assumption is that,
> +#   for given installation, we are only interested in tracking multilib
> +#   ABIs for a single OS.

If you run readelf -h on (say) bash in any of our stage3's tarballs you 
always get "OS/ABI: UNIX - System V" irrespective of arch and abi.  I 
don't know what you would get on BSD, but the field is totally 
irrelevant for our purposes despite the name.  As far as I can tell, it 
is totally invariant across arches and abis.

You can even unpack the the stage3's on an amd64 host and run readelf 
form the host on the chroot target and you'll get the elf header, so you 
don't need access to native hardware.

The comment suggests that there might be some interesting information 
there, but there isn't.  Maybe I'm just reading too much into it.

> +
> +from ...util.elf.constants import (
> +	EF_MIPS_ABI, EF_MIPS_ABI2, ELFCLASS32, ELFCLASS64,
> +	EM_386, EM_68K, EM_AARCH64, EM_ALPHA, EM_ARM, EM_IA_64, EM_MIPS,
> +	EM_PARISC, EM_PPC, EM_PPC64, EM_S390, EM_SH, EM_SPARC,
> +	EM_SPARC32PLUS, EM_SPARCV9, EM_X86_64, E_MIPS_ABI_EABI32,
> +	E_MIPS_ABI_EABI64, E_MIPS_ABI_O32, E_MIPS_ABI_O64)
> +
> +_machine_prefix_map = {
> +	EM_386:             "x86",
> +	EM_68K:             "m68k",
> +	EM_AARCH64:         "arm",
> +	EM_ALPHA:           "alpha",
> +	EM_ARM:             "arm",
> +	EM_IA_64:           "ia",
> +	EM_MIPS:            "mips",
> +	EM_PARISC:          "hppa",
> +	EM_PPC:             "ppc",
> +	EM_PPC64:           "ppc",
> +	EM_S390:            "s390",
> +	EM_SH:              "sh",
> +	EM_SPARC:           "sparc",
> +	EM_SPARC32PLUS:     "sparc",
> +	EM_SPARCV9:         "sparc",
> +	EM_X86_64:          "x86",
> +}
> +
> +_mips_abi_map = {
> +	E_MIPS_ABI_EABI32:  "eabi32",
> +	E_MIPS_ABI_EABI64:  "eabi64",
> +	E_MIPS_ABI_O32:     "o32",
> +	E_MIPS_ABI_O64:     "o64",
> +}
> +
> +def _compute_suffix_mips(elf_header):
> +
> +	name = None
> +	mips_abi = elf_header.e_flags & EF_MIPS_ABI
> +
> +	if mips_abi:
> +		name = _mips_abi_map.get(mips_abi)
> +	elif elf_header.e_flags & EF_MIPS_ABI2:
> +		name = "n32"
> +	elif elf_header.ei_class == ELFCLASS64:
> +		name = "n64"
> +
> +	return name
> +
> +def compute_multilib_category(elf_header):
> +	"""
> +	Compute a multilib category from an ELF header.
> +
> +	@param elf_header: an ELFHeader instance
> +	@type elf_header: ELFHeader
> +	@rtype: str
> +	@return: A multilib category, or None if elf_header does not fit
> +		into a recognized category
> +	"""
> +	category = None
> +	if elf_header.e_machine is not None:
> +
> +		prefix = _machine_prefix_map.get(elf_header.e_machine)
> +		suffix = None
> +
> +		if prefix == "mips":
> +			suffix = _compute_suffix_mips(elf_header)
> +		elif elf_header.ei_class == ELFCLASS64:
> +			suffix = "64"
> +		elif elf_header.ei_class == ELFCLASS32:
> +			if elf_header.e_machine == EM_X86_64:
> +				suffix = "x32"
> +			else:
> +				suffix = "32"
> +
> +		if prefix is None or suffix is None:
> +			category = None
> +		else:
> +			category = "%s_%s" % (prefix, suffix)
> +
> +	return c

Looks good.

> diff --git a/pym/portage/util/_dyn_libs/NeededEntry.py b/pym/portage/util/_dyn_libs/NeededEntry.py
> new file mode 100644
> index 0000000..5de59a0
> --- /dev/null
> +++ b/pym/portage/util/_dyn_libs/NeededEntry.py
> @@ -0,0 +1,83 @@
> +# Copyright 2015 Gentoo Foundation
> +# Distributed under the terms of the GNU General Public License v2
> +
> +from __future__ import unicode_literals
> +
> +import sys
> +
> +from portage import _encodings, _unicode_encode
> +from portage.exception import InvalidData
> +from portage.localization import _
> +
> +class NeededEntry(object):
> +	"""
> +	Represents one entry (line) from a NEEDED.ELF.2 file. The entry
> +	must have 5 or more semicolon-delimited fields in order to be
> +	considered valid. The sixth field is optional, corresponding
> +	to the multilib category. The multilib_category attribute is
> +	None if the corresponding field is either empty or missing.
> +	"""
> +
> +	__slots__ = ("arch", "filename", "multilib_category", "needed",
> +		"runpaths", "soname")

Looks like this answers my question above about the format of NEEDED.ELF.2

py b/pym/portage/util/_dyn_libs/soname_deps.py
> new file mode 100644
> index 0000000..b01c3d2
> --- /dev/null
> +++ b/pym/portage/util/_dyn_libs/soname_deps.py
> @@ -0,0 +1,136 @@
> +# Copyright 2015 Gentoo Foundation
> +# Distributed under the terms of the GNU General Public License v2
> +
> +import fnmatch
> +from itertools import chain
> +import os
> +import re
> +
> +from portage.util import shlex_split
> +
> +class SonameDepsProcessor(object):
> +	"""
> +	Processes NEEDED.ELF.2 entries for one package, in order to generate
> +	REQUIRES and PROVIDES data.
> +
> +	Any sonames provided by the package will automatically be filtered
> +	from the generated REQUIRES and PROVIDES values.
> +	"""
> +
> +	def __init__(self, provides_exclude, requires_exclude):
> +		"""
> +		@param provides_exclude: PROVIDES_EXCLUDE value
> +		@type provides_exclude: str
> +		@param requires_exclude: REQUIRES_EXCLUDE value
> +		@type requires_exclude: str
> +		"""
> +		self._provides_exclude = self._exclude_pattern(provides_exclude)
> +		self._requires_exclude = self._exclude_pattern(requires_exclude)
> +		self._requires_map = {}
> +		self._provides_map = {}
> +		self._provides_unfiltered = {}
> +		self._provides = None
> +		self._requires = None
> +		self._intersected = False
> +
> +	@staticmethod
> +	def _exclude_pattern(s):
> +		# shlex_split enables quoted whitespace inside patterns
> +		if s:
> +			pat = re.compile("|".join(
> +				fnmatch.translate(x.lstrip(os.sep))
> +				for x in shlex_split(s)))
> +		else:
> +			pat = None
> +		return pat
> +
> +	def add(self, entry):
> +		"""
> +		Add one NEEDED.ELF.2 entry, for inclusion in the generated
> +		REQUIRES and PROVIDES values.
> +
> +		@param entry: NEEDED.ELF.2 entry
> +		@type entry: NeededEntry
> +		"""
> +
> +		multilib_cat = entry.multilib_category
> +		if multilib_cat is None:
> +			# This usage is invalid. The caller must ensure that
> +			# the multilib category data is supplied here.
> +			raise AssertionError(
> +				"Missing multilib category data: %s" % entry.filename)
> +
> +		if entry.needed and (
> +			self._requires_exclude is None or
> +			self._requires_exclude.match(
> +			entry.filename.lstrip(os.sep)) is None):
> +			for x in entry.needed:
> +				if (self._requires_exclude is None or
> +					self._requires_exclude.match(x) is None):
> +					self._requires_map.setdefault(
> +						multilib_cat, set()).add(x)
> +
> +		if entry.soname:
> +			self._provides_unfiltered.setdefault(
> +				multilib_cat, set()).add(entry.soname)
> +
> +		if entry.soname and (
> +			self._provides_exclude is None or
> +			(self._provides_exclude.match(
> +			entry.filename.lstrip(os.sep)) is None and
> +			self._provides_exclude.match(entry.soname) is None)):
> +			self._provides_map.setdefault(
> +				multilib_cat, set()).add(entry.soname)
> +
> +	def _intersect(self):
> +		requires_map = self._requires_map
> +		provides_map = self._provides_map
> +		provides_unfiltered = self._provides_unfiltered
> +
> +		for multilib_cat in set(chain(requires_map, provides_map)):
> +			requires_map.setdefault(multilib_cat, set())
> +			provides_map.setdefault(multilib_cat, set())
> +			provides_unfiltered.setdefault(multilib_cat, set())
> +			for soname in list(requires_map[multilib_cat]):
> +				if soname in provides_unfiltered[multilib_cat]:
> +					requires_map[multilib_cat].remove(soname)
> +
> +		provides_data = []
> +		for multilib_cat in sorted(provides_map):
> +			if provides_map[multilib_cat]:
> +				provides_data.append(multilib_cat + ":")
> +				provides_data.extend(sorted(provides_map[multilib_cat]))
> +
> +		if provides_data:
> +			self._provides = " ".join(provides_data) + "\n"
> +
> +		requires_data = []
> +		for multilib_cat in sorted(requires_map):
> +			if requires_map[multilib_cat]:
> +				requires_data.append(multilib_cat + ":")
> +				requires_data.extend(sorted(requires_map[multilib_cat]))
> +
> +		if requires_data:
> +			self._requires = " ".join(requires_data) + "\n"
> +
> +		self._intersected = True
> +
> +	@property
> +	def provides(self):
> +		"""
> +		@rtype: str
> +		@return: PROVIDES value generated from NEEDED.ELF.2 entries
> +		"""
> +		if not self._intersected:
> +			self._intersect()
> +		return self._provides
> +
> +	@property
> +	def requires(self):
> +		"""
> +		@rtype: str
> +		@return: REQUIRES value generated from NEEDED.ELF.2 entries
> +		"""
> +		if not self._intersected:
> +			self._intersect()
> +		return self._requires

Nice logic here :)  The only thing that I don't get is why we might need 
{provides,requires}_exclude patterns.  I guess its good design 
principles but I can't think of a use case.

> diff --git a/pym/portage/util/elf/__init__.py b/pym/portage/util/elf/__init__.py
> new file mode 100644
> index 0000000..4725d33
> --- /dev/null
> +++ b/pym/portage/util/elf/__init__.py
> @@ -0,0 +1,2 @@
> +# Copyright 2015 Gentoo Foundation
> +# Distributed under the terms of the GNU General Public License v2
> diff --git a/pym/portage/util/elf/constants.py b/pym/portage/util/elf/constants.py
> new file mode 100644
> index 0000000..3857b71
> --- /dev/null
> +++ b/pym/portage/util/elf/constants.py
> @@ -0,0 +1,36 @@
> +# Copyright 2015 Gentoo Foundation
> +# Distributed under the terms of the GNU General Public License v2
> +
> +EI_CLASS           = 4
> +ELFCLASS32         = 1
> +ELFCLASS64         = 2
> +
> +EI_DATA            = 5
> +ELFDATA2LSB        = 1
> +ELFDATA2MSB        = 2
> +
> +E_MACHINE          = 18
> +EM_SPARC           = 2
> +EM_386             = 3
> +EM_68K             = 4
> +EM_MIPS            = 8
> +EM_PARISC          = 15
> +EM_SPARC32PLUS     = 18
> +EM_PPC             = 20
> +EM_PPC64           = 21
> +EM_S390            = 22
> +EM_ARM             = 40
> +EM_ALPHA           = 41
> +EM_SH              = 42
> +EM_SPARCV9         = 43
> +EM_IA_64           = 50
> +EM_X86_64          = 62
> +EM_AARCH64         = 183
> +
> +E_ENTRY            = 24
> +EF_MIPS_ABI        = 0x0000F000
> +EF_MIPS_ABI2       = 0x00000020
> +E_MIPS_ABI_O32     = 0x00001000
> +E_MIPS_ABI_O64     = 0x00002000
> +E_MIPS_ABI_EABI32  = 0x00003000
> +E_MIPS_ABI_EABI64  = 0x00004000

Document where these are coming from else we'll loose the connection to 
the standard.  They should all be in <elf.h> provided by elfutils, but 
I'm sure standard is documented somewhere officially.  Even if you just 
say "see <elf.h>" that might be enough to clue people where to look for 
these definitions.

> diff --git a/pym/portage/util/elf/header.py b/pym/portage/util/elf/header.py
> new file mode 100644
> index 0000000..3310eeb
> --- /dev/null
> +++ b/pym/portage/util/elf/header.py
> @@ -0,0 +1,62 @@
> +# Copyright 2015 Gentoo Foundation
> +# Distributed under the terms of the GNU General Public License v2
> +
> +import collections
> +
> +from ..endian.decode import (decode_uint16_le, decode_uint32_le,
> +	decode_uint16_be, decode_uint32_be)
> +from .constants import (E_ENTRY, E_MACHINE, EI_CLASS, ELFCLASS32,
> +	ELFCLASS64, ELFDATA2LSB, ELFDATA2MSB)
> +
> +class ELFHeader(object):
> +
> +	__slots__ = ('e_flags', 'e_machine', 'ei_class', 'ei_data')
> +
> +	@classmethod
> +	def read(cls, f):
> +		"""
> +		@param f: an open ELF file
> +		@type f: file
> +		@rtype: ELFHeader
> +		@return: A new ELFHeader instance containing data from f
> +		"""
> +		f.seek(EI_CLASS)
> +		ei_class = ord(f.read(1))
> +		ei_data = ord(f.read(1))
> +
> +		if ei_class == ELFCLASS32:
> +			width = 32
> +		elif ei_class == ELFCLASS64:
> +			width = 64
> +		else:
> +			width = None
> +
> +		if ei_data == ELFDATA2LSB:
> +			uint16 = decode_uint16_le
> +			uint32 = decode_uint32_le
> +		elif ei_data == ELFDATA2MSB:
> +			uint16 = decode_uint16_be
> +			uint32 = decode_uint32_be
> +		else:
> +			uint16 = None
> +			uint32 = None
> +
> +		if width is None or uint16 is None:
> +			e_machine = None
> +			e_flags = None
> +		else:
> +			f.seek(E_MACHINE)
> +			e_machine = uint16(f.read(2))
> +
> +			# E_ENTRY + 3 * sizeof(uintN)
> +			e_flags_offset = E_ENTRY + 3 * width // 8
> +			f.seek(e_flags_offset)
> +			e_flags = uint32(f.read(4))
> +
> +		obj = cls()
> +		obj.e_flags = e_flags
> +		obj.e_machine = e_machine
> +		obj.ei_class = ei_class
> +		obj.ei_data = ei_data
> +
> +		return obj

Looks good.  I'm going to perf test this but I don't think it will be 
too big a hit.  I don't know how we would get to this point in the code 
tree, but let me ask you this: am I right in thinking you won't hit 
ELFHeader.read() with every file that's being installed by portage? 
You'll only get here for elf objects?  Correct?

> diff --git a/pym/portage/util/endian/__init__.py b/pym/portage/util/endian/__init__.py
> new file mode 100644
> index 0000000..4725d33
> --- /dev/null
> +++ b/pym/portage/util/endian/__init__.py
> @@ -0,0 +1,2 @@
> +# Copyright 2015 Gentoo Foundation
> +# Distributed under the terms of the GNU General Public License v2
> diff --git a/pym/portage/util/endian/decode.py b/pym/portage/util/endian/decode.py
> new file mode 100644
> index 0000000..ec0dcec
> --- /dev/null
> +++ b/pym/portage/util/endian/decode.py
> @@ -0,0 +1,56 @@
> +# Copyright 2015 Gentoo Foundation
> +# Distributed under the terms of the GNU General Public License v2
> +
> +def decode_uint16_be(data):
> +	"""
> +	Decode an unsigned 16-bit integer with big-endian encoding.
> +
> +	@param data: string of bytes of length 2
> +	@type data: bytes
> +	@rtype: int
> +	@return: unsigned integer value of the decoded data
> +	"""
> +	return (ord(data[0:1]) << 8) + ord(data[1:2])
> +
> +def decode_uint16_le(data):
> +	"""
> +	Decode an unsigned 16-bit integer with little-endian encoding.
> +
> +	@param data: string of bytes of length 2
> +	@type data: bytes
> +	@rtype: int
> +	@return: unsigned integer value of the decoded data
> +	"""
> +	return ord(data[0:1]) + (ord(data[1:2]) << 8)
> +
> +def decode_uint32_be(data):
> +	"""
> +	Decode an unsigned 32-bit integer with big-endian encoding.
> +
> +	@param data: string of bytes of length 4
> +	@type data: bytes
> +	@rtype: int
> +	@return: unsigned integer value of the decoded data
> +	"""
> +	return (
> +		(ord(data[0:1]) << 24) +
> +		(ord(data[1:2]) << 16) +
> +		(ord(data[2:3]) << 8) +
> +		ord(data[3:4])
> +	)
> +
> +def decode_uint32_le(data):
> +	"""
> +	Decode an unsigned 32-bit integer with little-endian encoding.
> +
> +	@param data: string of bytes of length 4
> +	@type data: bytes
> +	@rtype: int
> +	@return: unsigned integer value of the decoded data
> +	"""
> +	return (
> +		ord(data[0:1]) +
> +		(ord(data[1:2]) << 8) +
> +		(ord(data[2:3]) << 16) +
> +		(ord(data[3:4]) << 24)
> +	)
>

Endian fun.


-- 
Anthony G. Basile, Ph. D.
Chair of Information Technology
D'Youville College
Buffalo, NY 14201
[phone]