a98f2c556f
* Added a section for those pythonistas who are too used to web programming. Stressed that it's not simply not RESTful, it's not even REST-like. * Letting me move on to drawing a very loose parallel between a session and a context. The differences should become obvious in the subsequent sections.
282 lines
9.7 KiB
Org Mode
282 lines
9.7 KiB
Org Mode
#+TITLE: GNU Privacy Guard (GnuPG) Made Easy Python Bindings HOWTO (English)
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#+LATEX_COMPILER: xelatex
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#+LATEX_CLASS: article
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#+LATEX_CLASS_OPTIONS: [12pt]
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#+LATEX_HEADER: \usepackage{xltxtra}
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#+LATEX_HEADER: \usepackage[margin=1in]{geometry}
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#+LATEX_HEADER: \setmainfont[Ligatures={Common}]{Times New Roman}
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#+LATEX_HEADER: \author{Ben McGinnes <ben@gnupg.org>}
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* Introduction
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:PROPERTIES:
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:CUSTOM_ID: intro
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:END:
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Version: 0.0.1-alpha [2018-03-07 Wed]
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Author: Ben McGinnes <ben@gnupg.org>
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Author GPG Key: DB4724E6FA4286C92B4E55C4321E4E2373590E5D
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This document provides basic instruction in how to use the GPGME
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Python bindings to programmatically leverage the GPGME library.
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* GPGME Concepts
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:PROPERTIES:
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:CUSTOM_ID: gpgme-concepts
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:END:
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** A C API
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:PROPERTIES:
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:CUSTOM_ID: gpgme-c-api
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:END:
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Unlike many modern APIs with which programmers will be more
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familiar with these days, the GPGME API is a C API. The API is
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intended for use by C coders who would be able to access its
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features by including the =gpgme.h= header file eith their own C
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source code and then access its functions just as they would any
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other C headers.
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This is a very effective method of gaining complete access to the
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API and in the most efficient manner possible. It does, however,
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have the drawback that it cannot be directly used by other
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languages without some means of providing an interface to those
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languages. This is where the need for bindings in various
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languages stems.
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** Python bindings
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:PROPERTIES:
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:CUSTOM_ID: gpgme-python-bindings
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:END:
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The Python bindings for GPGME provide a higher level means of
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accessing the complete feature set of GPGME itself. It also
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provides a more pythonic means of calling these API functions.
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The bindings are generated dynamically with SWIG and the copy of =gpgme.h= generated when GPGME is compiled.
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This means that a version of the Python bindings is fundamentally
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tied to the exact same version of GPGME used to gemerate that copy
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of =gpgme.h=.
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** Difference between the Python bindings and other GnuPG Python packages
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:PROPERTIES:
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:CUSTOM_ID: gpgme-python-bindings-diffs
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:END:
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There have been numerous attempts to add GnuPG support to Python
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over the years. Some of the most well known are listed here, along
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with what differentiates them.
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*** The python-gnupg package maintained by Vinay Sajip
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:PROPERTIES:
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:CUSTOM_ID: diffs-python-gnupg
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:END:
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This is arguably the most popular means of integrating GPG with
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Python. The package utilises the =subprocess= module to implement
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wrappers for the =gpg= and =gpg2= executables normally invoked on
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the command line (=gpg.exe= and =gpg2.exe= on Windows).
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The popularity of this package stemmed from its ease of use and
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capability in providing the most commonly required features.
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Unfortunately it has been beset by a number of security issues,
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most of which stemmed from using unsafe methods of accessing the
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command line via the =subprocess= calls.
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The python-gnupg package is available under the MIT license.
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*** The gnupg package created and maintained by Isis Lovecruft
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:PROPERTIES:
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:CUSTOM_ID: diffs-isis-gnupg
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:END:
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In 2015 Isis Lovecruft from the Tor Project forked and then
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re-implemented the python-gnupg package as just gnupg. This new
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package also relied on subprocess to call the =gpg= or =gpg2=
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binaries, but did so somewhat more securely.
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However the naming and version numbering selected for this package
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resulted in conflicts with the original python-gnupg and since its
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functions were called in a different manner, the release of this
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package also resulted in a great deal of consternation when people
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installed what they thought was an upgrade that subsequently broke
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the code relying on it.
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The gnupg package is available under the GNU General Public
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License version 3.0 (or later).
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*** The PyME package maintained by Martin Albrecht
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:PROPERTIES:
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:CUSTOM_ID: diffs-pyme
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:END:
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This package is the origin of these bindings, though they are
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somewhat different now. For details of when and how the PyME
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package was folded back into GPGME itself see the [[Short_History.org][Short History]]
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document in this Python bindings =docs= directory.
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The PyME package was first released in 2002 and was also the first
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attempt to implement a low level binding to GPGME. In doing so it
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provided access to considerably more functionality than either the =python-gnupg= or =gnupg= packages.
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The PyME package is only available for Python 2.6 and 2.7.
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Porting the PyME package to Python 3.4 in 2015 is what resulted in
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it being folded into the GPGME project and the current bindings
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are the end result of that effort.
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The PyME package is available under the same dual licensing as
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GPGME itself: the GNU General Public License version 2.0 (or any
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later version) and the GNU Lesser Public License version 2.1 (or
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any later version).
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* GPGME Python bindings installation
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:PROPERTIES:
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:CUSTOM_ID: gpgme-python-install
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:END:
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** No PyPI
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:PROPERTIES:
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:CUSTOM_ID: do-not-use-pypi
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:END:
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Most third-party Python packages and modules are available and
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distributed through the Python Package Installer, known as PyPI.
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Due to the nature of what these bindings are and how they work, it
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is infeasible to install the GPGME Python bindings in the same way.
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** Requirements
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:PROPERTIES:
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:CUSTOM_ID: gpgme-python-requirements
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:END:
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The GPGME Python bindings only have three requirements:
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1. A suitable version of Python 2 or Python 3. With Python 2 that
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means Python 2.7 and with Python 3 that means Python 3.4 or
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higher.
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2. SWIG.
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3. GPGME itself. Which also means that all of GPGME's dependencies
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must be installed too.
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** Installation
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:PROPERTIES:
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:CUSTOM_ID: installation
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:END:
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Installing the Python bindings is effectively achieved by compiling
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and installing GPGME itself.
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Once SWIG is installed with Python and all the dependencies for
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GPGME are installed you only need to confirm that the version(s) of
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Python you want the bindings installed for are in your =$PATH=.
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By default GPGME will attempt to install the bindings for the most
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recent or highest version number of Python 2 and Python 3 it
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detects in =$PATH=. It specifically checks for the =python= and =python3= executabled first and then checks for specific version
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numbers.
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For Python 2 it checks for these executables in this order: =python=, =python2= and =python2.7=.
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For Python 3 it checks for these executables in this order: =python3=, =python3.6=, =python3.5= and =python3.4=.
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*** Installing GPGME
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:PROPERTIES:
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:CUSTOM_ID: install-gpgme
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:END:
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See the [[../../../README][GPGME README file]] for details of how to install GPGME from
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source.
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* Fundamentals
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:PROPERTIES:
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:CUSTOM_ID: howto-fund-a-mental
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:END:
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Before we can get to the fun stuff, there are a few matters
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regarding GPGME's design which hold true whether you're dealing with
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the C code directly or these Python bindings.
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** No REST
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:PROPERTIES:
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:CUSTOM_ID: no-rest-for-the-wicked
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:END:
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The first part of which is or will be fairly blatantly obvious upon
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viewing the first example, but it's worth reiterating anyway. That
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being that this API is /*not*/ a REST API. Nor indeed could it
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ever be one.
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Most, if not all, Python programmers (and not just Python
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programmers) know how easy it is to work with a RESTful API. In
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fact they've become so popular that many other APIs attempt to
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emulate REST-like behaviour as much as they are able. Right down
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to the use of JSON formatted output to facilitate the use of their
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API without having to retrain developers.
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This API does not do that. It would not be able to do that and
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also provide access to the entire C API on which it's built. It
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does, however, provide a very pythonic interface on top of the
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direct bindings and it's this pythonic layer with which this HOWTO
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deals with.
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** Context
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:PROPERTIES:
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:CUSTOM_ID: howto-get-context
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:END:
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One of the reasons which prevents this API from being RESTful is
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that most operations require more than one instruction to the API
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to perform the task. Sure, there are certain functions which can
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be performed simultaneously, particularly if the result known or
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strongly anticipated (e.g selecting and encrypting to a key known
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to be in the public keybox).
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There are many more, however, which cannot be manipulated so
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readily: they must be performed in a specific sequence and the
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result of one operation has a direct bearing on the outcome of
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subsequent operations. Not merely by generating an error either.
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When dealing with this type of persistant state on the web, full of
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both the RESTful and REST-like, it's most commonly referred to as a
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session. In GPGME, however, it is called a context and every
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operation type has one.
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* Copyright and Licensing
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:PROPERTIES:
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:CUSTOM_ID: copyright-and-license
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:END:
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** Copyright (C) The GnuPG Project, 2018
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:PROPERTIES:
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:CUSTOM_ID: copyright
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:END:
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Copyright © The GnuPG Project, 2018.
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** License GPL compatible
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:PROPERTIES:
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:CUSTOM_ID: license
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:END:
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This file is free software; as a special exception the author gives
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unlimited permission to copy and/or distribute it, with or without
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modifications, as long as this notice is preserved.
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This file is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY, to the extent permitted by law; without even
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the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
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PURPOSE.
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