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EXTENDING.md

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Extending go-git

go-git was built in a highly extensible manner, which enables some of its functionalities to be changed or extended without the need of changing its codebase. Here are the key extensibility features:

Dot Git Storers

Dot git storers are the components responsible for storing the Git internal files, including objects and references.

The built-in storer implementations include memory and filesystem. The memory storer stores all the data in memory, and its use look like this:

	r, err := git.Init(memory.NewStorage(), nil)

The filesystem storer stores the data in the OS filesystem, and can be used as follows:

    r, err := git.Init(filesystem.NewStorage(osfs.New("/tmp/foo")), nil)

New implementations can be created by implementing the storage.Storer interface.

Filesystem

Git repository worktrees are managed using a filesystem abstraction based on go-billy. The Git operations will take place against the specific filesystem implementation. Initialising a repository in Memory can be done as follows:

	fs := memfs.New()
	r, err := git.Init(memory.NewStorage(), fs)

The same operation can be done against the OS filesystem:

    fs := osfs.New("/tmp/foo")
    r, err := git.Init(memory.NewStorage(), fs)

New filesystems (e.g. cloud based storage) could be created by implementing go-billy's Filesystem interface.

Transport Schemes

Git supports various transport schemes, including http, https, ssh, git, file. go-git defines the transport.Transport interface to represent them.

The built-in implementations can be replaced by calling client.InstallProtocol.

An example of changing the built-in https implementation to skip TLS could look like this:

	customClient := &http.Client{
		Transport: &http.Transport{
			TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
		},
	}

	client.InstallProtocol("https", githttp.NewClient(customClient))

Some internal implementations enables code reuse amongst the different transport implementations. Some of these may be made public in the future (e.g. plumbing/transport/internal/common).

Cache

Several different operations across go-git lean on caching of objects in order to achieve optimal performance. The caching functionality is defined by the cache.Object interface.

Two built-in implementations are cache.ObjectLRU and cache.BufferLRU. However, the caching functionality can be customized by implementing the interface cache.Object interface.

Hash

go-git uses the crypto.Hash interface to represent hash functions. The built-in implementations are github.com/pjbgf/sha1cd for SHA1 and Go's crypto/SHA256.

The default hash functions can be changed by calling hash.RegisterHash.

    func init() {
        hash.RegisterHash(crypto.SHA1, sha1.New)
    }

New SHA1 or SHA256 hash functions that implement the hash.RegisterHash interface can be registered by calling RegisterHash.