A Git protocol parser written in Go.
This is more like an experimental project to better understand the protocol.
This is not an official Google product (i.e. a 20% project).
Background
Git protocol is defined in Documentation/technical/pack-protocol.txt. This is not a complete definition. Also, a transport specific spec Documentation/technical/http-protocol.txt is not complete. This project was started so that these upstream protocol spec becomes more accurate. To verify the written syntax is accurate, this project includes a Git protocol parser written in Go, and have end-to-end test suites.
This makes it easy to write a test case for Git client. Currently the test cases are run against the canonical Git implementation, but this can be extended to run against JGit, etc.. Also it makes it easy to test an attack case. With this library, one can write an attack case like git-bomb against Git protocol by producing a request that is usually not produced by a sane Git client. Protocol properties can also be checked. For example, it's possible to write a test to check valid request/response's prefixes are not a valid request/response. This property makes sure a client won't process an incomplete response thinking it's complete.
TODOs
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Signed push is not implemented and tested.
There was a bug in upstream Git around singed push, and in order to get this work, git needs to be built from the source. As of 2018-06-21, the fix is in pu. Add bin-wrappers to the PATH to use the latest binary in the end-to-end tests.
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Protocol semantics is not defined.
The syntax is relatively complete. The semantics is not even mentioned. One idea is to define the semantics by treating the request/response as an operation to modify Git repositories. This perspective makes it possible to define a formal protocol semantics in a same way as programming language formal semantics.
Defining a simple git-push semantics seems easy. Defining a pack negotiation semantics for shallow cloned repositories seems difficult.
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Upstream pack-protocol.txt is not updated.
The initial purpose, create a complete pack-protocol.txt, is not yet done. We can start from a minor fix (e.g. capability separator in some places is space not NUL). Also relationship between Git protocol and network transports (HTTPS, SSH, Git wire) are good to be mentioned.
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Bidi-transports are not tested and defined.
Git's bidi-transports, SSH and Git-wire protocol, are not tested with this project and the protocol syntax is also not defined. The majority of the syntax is same, but there's a slight difference. Go has an SSH library, so it's easy to run a test SSH server.
