thodg/libgit2

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  • Hash : 95b7a639
    Author : David Turner
    Date : 2021-04-14T21:52:36

    git_reference_create_matching: Treat all-zero OID as "must be absent" This is pretty useful in avoiding races: I want to create a ref only if it doesn't already exist. I can't check first because of TOCTOU -- by the time I finish the check, someone else might have already created the ref. And I can't take a lock because then I can't do the create, since the create expects to take the lock. The semantics are inspired by git update-ref, which allows an all-zero old value to mean that the ref must not exist.

  • README.md

  • libgit2 - the Git linkable library

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    libgit2 is a portable, pure C implementation of the Git core methods provided as a linkable library with a solid API, allowing to build Git functionality into your application. Language bindings like Rugged (Ruby), LibGit2Sharp (.NET), pygit2 (Python) and NodeGit (Node) allow you to build Git tooling in your favorite language.

    libgit2 is used to power Git GUI clients like GitKraken and gmaster and on Git hosting providers like GitHub, GitLab and Azure DevOps. We perform the merge every time you click “merge pull request”.

    libgit2 is licensed under a very permissive license (GPLv2 with a special Linking Exception). This basically means that you can link it (unmodified) with any kind of software without having to release its source code. Additionally, the example code has been released to the public domain (see the separate license for more information).

    Table of Contents

    Using libgit2

    Most of these instructions assume that you’re writing an application in C and want to use libgit2 directly. If you’re not using C, and you’re writing in a different language or platform like .NET, Node.js, or Ruby, then there is probably a “language binding“ that you can use to take care of the messy tasks of calling into native code.

    But if you do want to use libgit2 directly - because you’re building an application in C - then you may be able use an existing binary. There are packages for the vcpkg and conan package managers. And libgit2 is available in Homebrew and most Linux distributions.

    However, these versions may be outdated and we recommend using the latest version if possible. Thankfully libgit2 is not hard to compile.

    Quick Start

    Prerequisites for building libgit2:

    1. CMake, and is recommended to be installed into your PATH.
    2. Python is used by our test framework, and should be installed into your PATH.
    3. C compiler: libgit2 is C90 and should compile on most compilers.
      • Windows: Visual Studio is recommended
      • Mac: Xcode is recommended
      • Unix: gcc or clang is recommended.

    Build

    1. Create a build directory beneath the libgit2 source directory, and change into it: mkdir build && cd build
    2. Create the cmake build environment: cmake ..
    3. Build libgit2: cmake --build .

    Trouble with these steps? Read our troubleshooting guide. More detailed build guidance is available below.

    Getting Help

    Chat with us

    Getting Help

    If you have questions about the library, please be sure to check out the API documentation. If you still have questions, reach out to us on Slack or post a question on StackOverflow (with the libgit2 tag).

    Reporting Bugs

    Please open a GitHub Issue and include as much information as possible. If possible, provide sample code that illustrates the problem you’re seeing. If you’re seeing a bug only on a specific repository, please provide a link to it if possible.

    We ask that you not open a GitHub Issue for help, only for bug reports.

    Reporting Security Issues

    Please have a look at SECURITY.md.

    What It Can Do

    libgit2 provides you with the ability to manage Git repositories in the programming language of your choice. It’s used in production to power many applications including GitHub.com, Plastic SCM and Azure DevOps.

    It does not aim to replace the git tool or its user-facing commands. Some APIs resemble the plumbing commands as those align closely with the concepts of the Git system, but most commands a user would type are out of scope for this library to implement directly.

    The library provides:

    • SHA conversions, formatting and shortening
    • abstracted ODB backend system
    • commit, tag, tree and blob parsing, editing, and write-back
    • tree traversal
    • revision walking
    • index file (staging area) manipulation
    • reference management (including packed references)
    • config file management
    • high level repository management
    • thread safety and reentrancy
    • descriptive and detailed error messages
    • …and more (over 175 different API calls)

    As libgit2 is purely a consumer of the Git system, we have to adjust to changes made upstream. This has two major consequences:

    • Some changes may require us to change provided interfaces. While we try to implement functions in a generic way so that no future changes are required, we cannot promise a completely stable API.
    • As we have to keep up with changes in behavior made upstream, we may lag behind in some areas. We usually to document these incompatibilities in our issue tracker with the label “git change”.

    Optional dependencies

    While the library provides git functionality without the need for dependencies, it can make use of a few libraries to add to it:

    • pthreads (non-Windows) to enable threadsafe access as well as multi-threaded pack generation
    • OpenSSL (non-Windows) to talk over HTTPS and provide the SHA-1 functions
    • LibSSH2 to enable the SSH transport
    • iconv (OSX) to handle the HFS+ path encoding peculiarities

    Initialization

    The library needs to keep track of some global state. Call

    git_libgit2_init();

    before calling any other libgit2 functions. You can call this function many times. A matching number of calls to

    git_libgit2_shutdown();

    will free the resources. Note that if you have worker threads, you should call git_libgit2_shutdown after those threads have exited. If you require assistance coordinating this, simply have the worker threads call git_libgit2_init at startup and git_libgit2_shutdown at shutdown.

    Threading

    See threading for information

    Conventions

    See conventions for an overview of the external and internal API/coding conventions we use.

    Building libgit2 - Using CMake

    Building

    libgit2 builds cleanly on most platforms without any external dependencies. Under Unix-like systems, like Linux, *BSD and Mac OS X, libgit2 expects pthreads to be available; they should be installed by default on all systems. Under Windows, libgit2 uses the native Windows API for threading.

    The libgit2 library is built using CMake (version 2.8 or newer) on all platforms.

    On most systems you can build the library using the following commands

    $ mkdir build && cd build
$ cmake ..
$ cmake --build .

    Alternatively you can point the CMake GUI tool to the CMakeLists.txt file and generate platform specific build project or IDE workspace.

    Running Tests

    Once built, you can run the tests from the build directory with the command

    $ ctest -V

    Alternatively you can run the test suite directly using,

    $ ./libgit2_clar

    Invoking the test suite directly is useful because it allows you to execute individual tests, or groups of tests using the -s flag. For example, to run the index tests:

    $ ./libgit2_clar -sindex

    To run a single test named index::racy::diff, which corresponds to the test function test_index_racy__diff:

    $ ./libgit2_clar -sindex::racy::diff

    The test suite will print a . for every passing test, and an F for any failing test. An S indicates that a test was skipped because it is not applicable to your platform or is particularly expensive.

    Note: There should be no failing tests when you build an unmodified source tree from a release, or from the main branch. Please contact us or open an issue if you see test failures.

    Installation

    To install the library you can specify the install prefix by setting:

    $ cmake .. -DCMAKE_INSTALL_PREFIX=/install/prefix
$ cmake --build . --target install

    Advanced Usage

    For more advanced use or questions about CMake please read https://cmake.org/Wiki/CMake_FAQ.

    The following CMake variables are declared:

    • CMAKE_INSTALL_BINDIR: Where to install binaries to.
    • CMAKE_INSTALL_LIBDIR: Where to install libraries to.
    • CMAKE_INSTALL_INCLUDEDIR: Where to install headers to.
    • BUILD_SHARED_LIBS: Build libgit2 as a Shared Library (defaults to ON)
    • BUILD_CLAR: Build Clar-based test suite (defaults to ON)
    • THREADSAFE: Build libgit2 with threading support (defaults to ON)

    To list all build options and their current value, you can do the following:

    # Create and set up a build directory
$ mkdir build
$ cmake ..
# List all build options and their values
$ cmake -L

    Compiler and linker options

    CMake lets you specify a few variables to control the behavior of the compiler and linker. These flags are rarely used but can be useful for 64-bit to 32-bit cross-compilation.

    • CMAKE_C_FLAGS: Set your own compiler flags
    • CMAKE_FIND_ROOT_PATH: Override the search path for libraries
    • ZLIB_LIBRARY, OPENSSL_SSL_LIBRARY AND OPENSSL_CRYPTO_LIBRARY: Tell CMake where to find those specific libraries

    MacOS X

    If you want to build a universal binary for Mac OS X, CMake sets it all up for you if you use -DCMAKE_OSX_ARCHITECTURES="i386;x86_64" when configuring.

    Android

    Extract toolchain from NDK using, make-standalone-toolchain.sh script. Optionally, crosscompile and install OpenSSL inside of it. Then create CMake toolchain file that configures paths to your crosscompiler (substitute {PATH} with full path to the toolchain):

    SET(CMAKE_SYSTEM_NAME Linux)
SET(CMAKE_SYSTEM_VERSION Android)

SET(CMAKE_C_COMPILER   {PATH}/bin/arm-linux-androideabi-gcc)
SET(CMAKE_CXX_COMPILER {PATH}/bin/arm-linux-androideabi-g++)
SET(CMAKE_FIND_ROOT_PATH {PATH}/sysroot/)

SET(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
SET(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
SET(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

    Add -DCMAKE_TOOLCHAIN_FILE={pathToToolchainFile} to cmake command when configuring.

    MinGW

    If you want to build the library in MinGW environment with SSH support enabled, you may need to pass -DCMAKE_LIBRARY_PATH="${MINGW_PREFIX}/${MINGW_CHOST}/lib/" flag to CMake when configuring. This is because CMake cannot find the Win32 libraries in MinGW folders by default and you might see an error message stating that CMake could not resolve ws2_32 library during configuration.

    Another option would be to install msys2-w32api-runtime package before configuring. This package installs the Win32 libraries into /usr/lib folder which is by default recognized as the library path by CMake. Please note though that this package is meant for MSYS subsystem which is different from MinGW.

    Language Bindings

    Here are the bindings to libgit2 that are currently available:

    If you start another language binding to libgit2, please let us know so we can add it to the list.

    How Can I Contribute?

    We welcome new contributors! We have a number of issues marked as “up for grabs” and “easy fix” that are good places to jump in and get started. There’s much more detailed information in our list of outstanding projects.

    Please be sure to check the contribution guidelines to understand our workflow, and the libgit2 coding conventions.

    License

    libgit2 is under GPL2 with linking exception. This means you can link to and use the library from any program, proprietary or open source; paid or gratis. However, if you modify libgit2 itself, you must distribute the source to your modified version of libgit2.

    See the COPYING file for the full license text.

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