mirror of
https://github.com/troglobit/finit.git
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Joachim Wiberg
b55dada80b
libink was written against the only bus it had, its own, where the peer on the other end is the client. A broker is not: it routes for senders it names itself, expects a DESTINATION on anything addressed through it, and answers on its own schedule rather than next. Runlevels go on the wire as S and N rather than the digits Finit keeps internally, since that is what a caller outside Finit means by one. The library stays a convenience library, linked into finit and initctl and installed nowhere: the ABI promise waits until libink is its own project. Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
65 lines
3.1 KiB
Markdown
65 lines
3.1 KiB
Markdown
libink — brokerless D-Bus for Finit
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===================================
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libink is a small C library implementing the [D-Bus wire protocol][spec],
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both the server and the client side, without a broker and without any
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dependency on `libdbus`, `sd-bus`, or GIO. It was born inside Finit to
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let PID 1 be a bus of its own: clients connect straight to the listening
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socket, authenticate with the standard SASL EXTERNAL handshake, and get
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kernel-authenticated credentials via `SO_PEERCRED`.
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For what the bus exposes and how to talk to it, see the User Guide,
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[D-Bus Integration](../doc/dbus.md). This file covers the library
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itself.
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Status
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------
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libink is an internal implementation detail of Finit: built as a libtool
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convenience library, linked statically into `finit` and `initctl`,
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nothing installed. There is deliberately no ABI promise yet — that
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comes if/when libink is extracted into a project of its own. External
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D-Bus clients need none of this; the wire protocol is the compatibility
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surface, any standard D-Bus library works.
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Layout
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------
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| File | Contents |
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|-----------------|-------------------------------------------------------|
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| `server.c` | Listening socket, accept, peer credential capture |
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| `auth.c` | SASL EXTERNAL handshake, uid verification |
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| `connection.c` | Per-peer state machine, message framing |
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| `proto.c` | Wire header parse/build |
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| `marshal.c` | Body (de)marshalling: basic types, arrays, variants |
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| `dispatch.c` | Object tree, vtable registration, method dispatch |
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| `builtin.c` | `org.freedesktop.DBus.*` stock interfaces |
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| `match.c` | AddMatch/RemoveMatch rule parsing and signal filter |
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| `path.c` | systemd-style `_HH` object path encoding |
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| `client.c` | Outgoing connections, method calls, reply/signal wait |
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| `io.c` | Shared EINTR-resilient read/write loops |
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Public API symbols carry the `link_*` prefix (`link.h`), internal ones
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`__*` (`internal.h`). Method handlers are registered as vtables of
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`link_method_t`/`link_property_t`; the framework emits variant
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signatures from the property table so the declared type is the single
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source of truth.
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The boundary to Finit is deliberate: nothing under `libink/` includes a
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Finit header. All glue lives in `src/dbus.c` — object registration,
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signal emission from the service/condition/runlevel hook points, and
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the uev event loop bridge. `initctl` uses the client half of the same
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library, so one wire-format implementation serves both ends. If libink
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is ever spun out, that file is the cut line.
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Testing
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-------
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The `test/dbus-*.sh` suite exercises the library end to end against a
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live Finit in a namespace, driven by `test/src/dbus-auth-client.c`.
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Wire-format conformance against third-party tools (`dbus-send`,
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`dbus-monitor`) and fuzzing of the parsers are tracked as pre-merge
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work — this is PID 1's attack surface.
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[spec]: https://dbus.freedesktop.org/doc/dbus-specification.html
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