anil.recoil.org
XDG library path support for OCaml via Eio capabilities
linux
macos
ocaml
xdg
README
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README.md
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README.md
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# xdge - XDG Base Directory Specification for Eio
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This library implements the [XDG Base Directory
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Specification](https://specifications.freedesktop.org/basedir-spec/latest/) for
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OCaml applications using the [Eio](https://github.com/ocaml-multicore/eio)
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effects-based I/O library.
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## What is XDG?
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The XDG Base Directory Specification defines standard locations for user-specific files on Unix-like systems, keeping home directories clean and organized:
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- Config (`~/.config/app`): User preferences and settings
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- Data (`~/.local/share/app`): Persistent application data
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- Cache (`~/.cache/app`): Non-essential cached data (safe to delete)
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- State (`~/.local/state/app`): Logs, history, and runtime state
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- Runtime (`$XDG_RUNTIME_DIR/app`): Sockets, pipes, and session-bound files
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The specification also defines system-wide search paths (`/etc/xdg`,
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`/usr/share`) and a precedence system using environment variables
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(`XDG_CONFIG_HOME`, `XDG_DATA_HOME`, and so on).
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## Why Eio?
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Eio uses a **capability-based** approach to I/O where filesystem access must be
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explicitly passed to functions. This design aligns naturally with XDG directory
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management. For example:
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```ocaml
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(* Filesystem access is an explicit capability *)
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let xdg = Xdge.create env#fs "myapp"
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```
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The capability model provides the benefit that code that needs filesystem
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access must receive the `fs` capability, with no hidden global state or ambient
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authority. The `Eio.Path.t` type returned by xdge encapsulates both the
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filesystem capability and the path, preventing path traversal outside the
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granted capability. Applications can restrict filesystem access by passing a
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sandboxed `fs` capability, and xdge respects those boundaries.
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## Usage
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```ocaml
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Eio_main.run @@ fun env ->
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let xdg = Xdge.create env#fs "myapp" in
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(* Access XDG directories as Eio paths *)
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let config = Xdge.config_dir xdg in
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let data = Xdge.data_dir xdg in
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(* Search for files following XDG precedence *)
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match Xdge.find_config_file xdg "settings.json" with
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| Some path -> (* use path *)
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| None -> (* use defaults *)
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```
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For CLI applications, xdge provides Cmdliner terms that handle environment
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variable precedence and command-line overrides:
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```ocaml
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let () =
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Eio_main.run @@ fun env ->
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let term = Xdge.Cmd.term "myapp" env#fs () in
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(* Generates --config-dir, --data-dir, etc. flags *)
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(* Respects MYAPP_CONFIG_DIR > XDG_CONFIG_HOME > default *)
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```
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## Installation
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```
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opam install xdge
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```
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## License
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ISC