Notes for New Contributors¶
Source Code Layout¶
Under src
there are directories
lib
is the library itself, more on that belowcli
is the command line applicationbotan
tests
contain what you would expect. Input files go undertests/data
.build-data
contains files read by the configure script. For examplebuild-data/cc/gcc.txt
describes various gcc options.scripts
contains misc scripts: install, distribution, various codegen things. Scripts controlling CI go underscripts/ci
.configs
contains configuration files for emacs, astyle, pylint, etcpython/botan2.py
is the Python ctypes wrapper
Library Layout¶
base
defines some high level typesutils
contains various utility functions and typescodec
has hex, base64block
contains the block cipher implementationsmodes
contains block cipher modes (CBC, GCM, etc)stream
contains the stream ciphershash
contains the hash function implementationspasshash
contains password hashing algorithms for authenticationkdf
contains the key derivation functionsmac
contains the message authentication codespbkdf
contains password hashing algorithms for key derivationmath
is the big integer math library. It is divided into three parts:mp
which are the low level algorithms;bigint
which is a C++ wrapper aroundmp
, andnumbertheory
which contains higher level algorithms like primality testing and exponentiationpubkey
contains the public key algorithmspk_pad
contains padding schemes for public key algorithmsrng
contains the random number generatorsentropy
has various entropy sources used by some of the RNGsasn1
is the DER encoder/decoderx509
is X.509 certificates, PKCS #10 requests, OCSPtls
contains the TLS implementationfilters
is a filter/pipe API for data transformscompression
has the compression wrappers (zlib, bzip2, lzma)ffi
is the C99 APIprov
contains bindings to external libraries like PKCS #11misc
contains odds and ends: format preserving encryption, SRP, threshold secret sharing, all or nothing transform, and others
Sending patches¶
All contributions should be submitted as pull requests via GitHub (https://github.com/randombit/botan). If you are planning a large change email the mailing list or open a discussion ticket on github before starting out to make sure you are on the right path. And once you have something written, free to open a [WIP] PR for early review and comment.
If possible please sign your git commits using a PGP key. See https://git-scm.com/book/en/v2/Git-Tools-Signing-Your-Work for instructions on how to set this up.
Depending on what your change is, your PR should probably also include an update
to news.rst
with a note explaining the change. If your change is a
simple bug fix, a one sentence description is perhaps sufficient. If there is an
existing ticket on GitHub with discussion or other information, reference it in
your change note as ‘GH #000’.
Update doc/credits.txt
with your information so people know what you did!
If you are interested in contributing but don’t know where to start check out
doc/dev_ref/todo.rst
for some ideas - these are changes we would almost
certainly accept once they’ve passed code review.
Also, try building and testing it on whatever hardware you have handy, especially unusual platforms, or using C++ compilers other than the regularly tested GCC, Clang, and Visual Studio.
FFI Additions¶
If adding a new function declaration to ffi.h
, the same PR must
also add the same declaration in the Python binding botan2.py
, in
addition the new API functionality must be exposed to Python and a
test written in Python.
Git Usage¶
Do NOT merge master
into your topic branch, this creates
needless commits and noise in history. Instead, as needed, rebase your
branch against master (git rebase -i master
) and force push the
branch to update the PR. If the GitHub PR page does not report any
merge conflicts and nobody asks you to rebase, you don’t need to
rebase.
Try to keep your history clean and use rebase to squash your commits as needed. If your diff is less than roughly 100 lines, it should probably be a single commit. Only split commits as needed to help with review/understanding of the change.
Python¶
Scripts should be in Python whenever possible.
For configure.py (and helper scripts install.py, cleanup.py and build_docs.py) the target is stock (no modules outside the standard library) CPython 2.7 plus latest CPython 3.x. Support for CPython 2.6, PyPy, etc is great when viable (in the sense of not causing problems for 2.7 or 3.x, and not requiring huge blocks of version dependent code). As running this program successfully is required for a working build, making it as portable as possible is considered key.
The python wrapper botan2.py targets CPython 2.7, 3.x, and latest PyPy. Note that a single file is used to avoid dealing with any of Python’s various crazy module distribution issues.
For random scripts not typically run by an end-user (codegen, visualization, and so on) there isn’t any need to worry about 2.6 and even just running under Python2 xor Python3 is acceptable if needed. Here it’s fine to depend on any useful modules such as graphviz or matplotlib, regardless if it is available from a stock CPython install. Since Python2 is now end of life, prefer Python3 for new scripts of this sort.
Build Tools and Hints¶
If you don’t already use it for all your C/C++ development, install ccache
(or on Windows, sccache
) right now, and configure a large cache on a fast
disk. It allows for very quick rebuilds by caching the compiler output.
Use --enable-sanitizers=
flag to enable various sanitizer checks. Supported
values including “address” and “undefined” for GCC and Clang. GCC also supports
“iterator” (checked iterators), and Clang supports “memory” (MSan) and
“coverage” (for fuzzing).
On Linux if you have the lcov
and gcov
tools installed, then running
./src/scripts/ci_build.py coverage
will produce a coverage enabled build,
run the tests, test the fuzzers against a corpus, and produce an HTML report
of total coverage. This coverage build requires the development headers for
zlib, bzip2, liblzma, TrouSerS (libtspi), and Sqlite3.
Copyright Notice¶
At the top of any new file add a comment with a copyright and a reference to the license, for example:
/*
* (C) 20xx Copyright Holder
* Botan is released under the Simplified BSD License (see license.txt)
*/
If you are making a substantial or non-trivial change to an existing file, add or update your own copyright statement at the top of each file.
Style Conventions¶
When writing your code remember the need for it to be easily understood by reviewers and auditors, both at the time of the patch submission and in the future.
Avoid complicated template metaprogramming where possible. It has its places but should be used judiciously.
When designing a new API (for use either by library users or just internally) try writing out the calling code first. That is, write out some code calling your idealized API, then just implement that API. This can often help avoid cut-and-paste by creating the correct abstractions needed to solve the problem at hand.
The C++11 auto
keyword is very convenient but only use it when the type
truly is obvious (considering also the potential for unexpected integer
conversions and the like, such as an apparent uint8_t being promoted to an int).
If a variable is defined and not modified, declare it const
. Some exception
for very short-lived variables, but generally speaking being able to read the
declaration and know it will not be modified is useful.
Use override
annotations whenever overriding a virtual function. If
introducing a new type that is not intended for derivation, mark it final
.
Avoid explicit delete
- use RAII.
Use m_
prefix on all member variables.
For formatting, there are configs for emacs and astyle in src/configs
.
No tabs, and remove trailing whitespace.
Prefer using braces on both sides of if/else blocks, even if only using a single statement. The current code doesn’t always do this.
Avoid using namespace
declarations, even inside of single functions. One
allowed exception is using namespace std::placeholders
in functions which
use std::bind
. (But, don’t use std::bind
- use a lambda instead).
Use ::
to explicitly refer to the global namespace (eg, when calling an OS
or external library function like ::select
or ::sqlite3_open
).
Use of External Dependencies¶
Compiler Dependencies¶
The library should always be as functional as possible when compiled with just C++11. However, feel free to use the full C++11 language. No accomodations are made for compilers that are incomplete or buggy.
Use of compiler extensions is fine whenever appropriate; this is typically restricted to a single file or an internal header. Compiler extensions used currently include native uint128_t, SIMD intrinsics, inline asm syntax and so on, so there are some existing examples of appropriate use.
Generally intrinsics or inline asm is preferred over bare assembly to avoid calling convention issues among different platforms; the improvement in maintainability is seen as worth any potential performance tradeoff. One risk with intrinsics is that the compiler might rewrite your clever const-time SIMD into something with a conditional jump, but code intended to be const-time should in any case be annotated so it can be checked at runtime with tools.
Operating System Dependencies¶
If you’re adding a small OS dependency in some larger piece of code, try to contain the actual non-portable operations to utils/os_utils.* and then call them from there.
As a policy, operating systems which are not supported by their original vendor are not supported by Botan either. Patches that complicate the code in order to support obsolete operating systems will likely be rejected. In writing OS specific code, feel free to assume roughly POSIX 2008, or for Windows, Windows 8 /Server 2012 (which are as of this writing the oldest versions still supported by Microsoft).
Some operating systems, such as OpenBSD, only support the latest release. For such cases, it’s acceptable to add code that requires APIs added in the most recent release of that OS as soon as the release is available.
Library Dependencies¶
Any external library dependency - even optional ones - is met with as one PR submitter put it “great skepticism”.
At every API boundary there is potential for confusion that does not exist when the call stack is all contained within the boundary. So the additional API really needs to pull its weight. For example a simple text parser or such which can be trivially implemented is not really for consideration. As a rough idea of the bar, equate the viewed cost of an external dependency as at least 1000 additional lines of code in the library. That is, if the library really does need this functionality, and it can be done in the library for less than that, then it makes sense to just write the code. Yup.
Currently the (optional) external dependencies of the library are some common compression libraries (zlib, bzip2, lzma), sqlite3 database, Trousers (TPM integration), plus various operating system utilities like basic filesystem operations. These provide major pieces of functionality which seem worth the trouble of maintaining an integration with.
At this point the most plausible examples of an appropriate new external dependency are all deeper integrations with system level cryptographic systems (CommonCrypto, CryptoAPI, /dev/crypto, iOS keychain, TPM 2.0, etc)