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- .. _protocol:
- ===================
- Git Server Protocol
- ===================
- Transport
- =========
- The Git protocol operates over pipes or TCP/IP. When a client connects over
- TCP/IP, it sends a header that tells the server which program to run and what
- parameters to use. When invoked over SSH, git will run a program with the
- parameters as command line arguments.
- Protocols
- =========
- Basics
- ------
- Git communicates with a server by piping data between a local program and a
- remote program.
- A common way of sending a unit of information is a pkt_line. This is a 4 byte
- size as human encoded hex (i.e. totally underusing the 4 bytes...) that tells
- you the size of the payload, followed by the payload. The size includes the 4
- bytes used by the size itself.
- 0009ABCD\n
- Git can also multiplex data using the sideband. As well as 4 bytes size, there
- would be a 1 byte channel number. This is in binary, so ``1`` will be ``\x01``.
- Typically Git will piggyback a list of capabilities on the first pkt_line it
- sends. It will also look for capabilities in the first pkt_like it receives.
- Git will degrade as much as possible when encountering a server or client with
- differing capabilities.
- git-upload-pack
- ---------------
- git-upload pack is used by git-ls-remote, git-clone, git-fetch and git-pull.
- And i'm sure others. Typically a client will connect a local git-fetch-pack to
- a remote git-upload-pack.
- Capabilities for this protocol include multi_ack, thin-pack, ofs-delta,
- sideband and sideband-64k A thin pack can reference objects not in the current
- pack.
- The server tells the client what refs it has. The client states which of those
- SHA1's it would like. It then starts to report which SHA1's it has. The server
- ACKs these allowing the client to work out when to stop sending SHA1's. This
- saves a lot of transfer because the client can make decisions like "well if it
- has this SHA, then it has all its parents so I don't need to care about those".
- When the client stops sending shas, the server can work out an optimal pack and
- then send it to the client.
- git-receive-pack
- ----------------
- git-receive-pack is used by git push. Typically a client connects a local
- git-send-pack to a remote git-receive-pack.
- Capabilities include report-status and delete-ref.
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