git-remote-fd

git-remote-fd <remote-name> fd::<read-fd>::<write-fd>

    The symbolic name given to the remote repository. This argument is passed by Git to all remote helpers.

fd::::
    The special URL format understood by this helper. It specifies the file descriptors to use for communication.


    The integer file descriptor number from which Git will read data from the remote.


    The integer file descriptor number to which Git will write data destined for the remote.

The git-remote-fd command serves as a specialized Git remote helper. Instead of communicating with a remote repository via traditional network protocols like HTTP or SSH, it operates entirely through pre-established Unix file descriptors. This mechanism allows a parent process to provide a child Git process with explicit file descriptors for reading from and writing to a remote.

This unique approach is invaluable for scripting, sandboxing, and integrating Git within other applications. It enables custom communication channels, facilitating scenarios where standard network access is restricted or where fine-grained control over Git's I/O is required. Developers can use git-remote-fd to build bespoke Git interfaces, manage operations in isolated environments, or pipe Git traffic through complex pipelines. It provides a low-level, highly flexible, and powerful method for orchestrating Git remote interactions programmatically.

git-remote-fd is a low-level helper intended primarily for developers and advanced scripting, not for direct end-user interaction.
It requires careful management of file descriptors by the invoking process.
Error handling can be complex, as issues might stem from the file descriptor setup rather than Git's internal operations.
Security considerations are paramount when exposing file descriptors to a child process, ensuring that only necessary permissions are granted.

The git-remote-fd helper communicates using the standard Git remote helper protocol. This protocol involves a series of commands (e.g., capabilities, list, fetch, push) exchanged line by line over the specified file descriptors. The parent process setting up the file descriptors is responsible for routing this protocol traffic to and from the actual remote source, effectively acting as a proxy or translator for Git's remote operations.

A common use case involves a parent application spawning a Git command (like git fetch) that uses a URL like fd::3::4. The parent process would then map file descriptor 3 to its own read stream and file descriptor 4 to its own write stream, allowing it to mediate all communication between the Git client and the remote. This is particularly useful for implementing custom authentication, logging, or proxying behaviors directly within the application.

While the exact initial commit for git-remote-fd is deep within Git's history, the concept of remote helpers and the ability to communicate over file descriptors have been fundamental parts of Git's design since its early days. This helper provides a core, flexible interface that has been stable and widely used for integrating Git into various systems and scripting environments, predating more recent remote protocol evolutions like `git-protocol-v2` but remaining relevant for its specific use case.

git-remote(1), gitremote-helpers(7), git(1), git-fetch(1), git-push(1)