6b1c162c89
* Minor text improvements * Mention struct support and update example * Add overview of supported types * Clarify mapping of types * Explain customization of struct marshaling * Update version number in dub.json example
232 lines
10 KiB
Markdown
232 lines
10 KiB
Markdown
# ddbus
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<a href="https://code.dlang.org/packages/ddbus" title="Go to ddbus"><img src="https://img.shields.io/dub/v/ddbus.svg" alt="Dub version"></a>
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<a href="https://code.dlang.org/packages/ddbus" title="Go to ddbus"><img src="https://img.shields.io/dub/dt/ddbus.svg" alt="Dub downloads"></a>
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A [dbus](http://www.freedesktop.org/wiki/Software/dbus/) library for the [D programming language](http://dlang.org).
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Provides fancy and convenient highly templated methods that automagically serialize and deserialize things into DBus types so that calling DBus methods is almost as easy as calling local ones.
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It currently supports:
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- Calling methods
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- Creating wrapper objects for DBus interfaces
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- Seamlessly converting to and from D types
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- Handling method calls and signals (includes introspection support)
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# Installation
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Before using, you will need to have the DBus C library installed on your computer to link with, and probably also a DBus session bus running so that you can actually do things.
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`ddbus` is available on [DUB](http://code.dlang.org/packages/ddbus) so you can simply include it in your `dub.json`:
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```json
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"dependencies": {
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"ddbus": "~>2.3.0"
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}
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```
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# Usage
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## Call Interface
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The simplest way to call methods over DBus is to create a connection and then a PathIface object
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which wraps a destination, path and interface. You can then call methods on that object with any
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parameters which ddbus knows how to serialize and it will return a reply message which you can convert
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to the correct return type using `.to!T()`. You can also use the templated `call` method. Example:
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```d
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import ddbus;
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Connection conn = connectToBus();
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PathIface obj = new PathIface(conn, "org.freedesktop.DBus","/org/freedesktop/DBus",
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"org.freedesktop.DBus");
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// call any method with any parameters and then convert the result to the right type.
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auto name = obj.GetNameOwner("org.freedesktop.DBus").to!string();
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// alternative method
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obj.call!string("GetNameOwner","org.freedesktop.DBus");
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```
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### Working with properties
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```d
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import ddbus;
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Connection conn = connectToBus();
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PathIface obj = new PathIface(conn, "org.freedesktop.secrets", "/org/freedesktop/secrets/collection/login", "org.freedesktop.DBus.Properties");
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// read property
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string loginLabel = obj.Get("org.freedesktop.Secret.Collection", "Label").to!string();
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loginLabel = "Secret"~login;
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// write it back (variant type requires variant() wrapper)
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obj.Set("org.freedesktop.Secret.Collection", "Label", variant(loginLabel));
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```
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Setting read only properties results in a thrown `DBusException`.
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## Server Interface
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You can register a delegate into a `MessageRouter` and a main loop in order to handle messages.
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After that you can request a name so that other DBus clients can connect to your program.
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You can return a `Tuple!(args)` to return multiple values (multiple out values in XML) or
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return a `Variant!DBusAny` to support returning any dynamic value.
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```d
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import ddbus;
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MessageRouter router = new MessageRouter();
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// create a pattern to register a handler at a path, interface and method
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MessagePattern patt = MessagePattern("/root","ca.thume.test","test");
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router.setHandler!(int,int,Variant!DBusAny)(patt,(int par, Variant!DBusAny anyArgument) {
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// anyArgument can contain any type now, it must be specified as argument using Variant!DBusAny.
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writeln("Called with ", par, ", ", anyArgument);
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return par;
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});
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// handle a signal
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patt = MessagePattern("/signaler","ca.thume.test","signal",true);
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router.setHandler!(void,int)(patt,(int par) {
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writeln("Signalled with ", par);
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});
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// register all methods of an object
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class Tester {
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int lol(int x, string s) {return 5;}
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void wat() {}
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}
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Tester o = new Tester;
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registerMethods(router, "/","ca.thume.test",o);
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// get a name and start the server
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registerRouter(conn, router);
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bool gotem = requestName(conn, "ca.thume.ddbus.test");
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simpleMainLoop(conn);
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```
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See the Concurrent Updates section for details how to implement this in a custom main loop.
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## Thin(ish) Wrapper
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`ddbus` also includes a series of thin D struct wrappers over the DBus types.
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- `Message`: wraps `DBusMessage` and provides D methods for common functionality.
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- `Connection`: wraps `DBusConnection` and provides D methods for common functionality.
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- `DBusException`: used for errors produced by DBus turned into D exceptions.
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## Type Marshaling
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`ddbus` includes fancy templated methods for marshaling D types in and out of DBus messages.
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All DBus-compatible basic types work (except file descriptors).
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Any forward range can be marshaled in as DBus array of that type but arrays must be taken out as dynamic arrays.
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As per version 2.3.0, D `struct` types are fully supported by `ddbus`. By default all public fields of a structure are marshaled. This behavior can be [changed by UDAs](#customizing-marshaling-of-struct-types). Mapping DBus structures to a matching instance of `std.typecons.Tuple`, like earlier versions of `ddbus` did, is also still supported.
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Example using the lower level interface, the simple interfaces use these behind the scenes:
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```d
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Message msg = Message("org.example.wow","/wut","org.test.iface","meth");
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struct S {
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double a;
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int b;
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string[][] c;
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bool[] d;
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}
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auto s = S(6.2, 4, [["lol"]], []);
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auto args = tuple(5, true, "wow", [6, 5], s);
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msg.build(args.expand);
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msg.signature().assertEqual("ibsai(diaasab)");
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msg.readTuple!(typeof(args))().assertEqual(args);
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```
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### Basic types
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These are the basic types supported by `ddbus`:
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`bool`, `byte`, `short`, `ushort`, `int`, `uint`, `long`, `ulong`, `double`, `string`, `ObjectPath`
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### Overview of mappings of other types:
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| D type | DBus type | Comments
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| -------------------------------------------- | ------------------------ | ---
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| any `enum` | `enum` base type | Only the exact values present in the definition of the `enum` type will be allowed.
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| `std.typecons.BitFlags` | `enum` base type | Allows usage of OR'ed values of a flags `enum`.
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| dynamic array `T[]` | array |
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| associative array `V[K]` | array of key-value pairs | DBus has a special type for key-value pairs, which can be used as the element type of an array only.
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| `Tuple!(T...)` | structure | The DBus structure will map all of the `Tuple`'s values in sequence.
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| any `struct` | structure | The DBus structure will map all public fields of the `struct` type in order of definition, unless otherwise specified using UDAs.
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| `ddbus` style variant `Variant!T` | variant | `Variant!T` is in fact just a wrapper type to force representation as a variant in DBus, use `Variant!DBusAny` for actual dynamic typing.
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| Phobos style variants `std.variant.VariantN` | variant | Only supported if set of allowed types is limited to types that can be marshaled by `ddbus`, so `std.variant.Variant` is not supported, but `std.variant.Algebraic` may be, depending on allowed types
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### Customizing marshaling of `struct` types
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Marshaling behavior can be changed for a `struct` type by adding the `@dbusMarshaling`
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UDA with the appropriate flag. The following flags are supported:
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- `includePrivateFields` enables marshaling of private fields
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- `manualOnly` disables marshaling of all fields
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Marshaling of individual fields can be enabled or disabled by setting the `DBusMarshal`
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flag as an UDA. I.e. `@Yes.DBusMarshal` or `@No.DBusMarshal`.
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Note: symbols `Yes` and `No` are defined in `std.typecons`.
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After converting a DBus structure to a D `struct`, any fields that are not marshaled
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will appear freshly initialized. This is true even when just converting a `struct` to
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`DBusAny` and back.
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```d
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import ddbus.attributes;
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import std.typecons;
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@dbusMarshaling(MarshalingFlag.includePrivateFields)
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struct WeirdThing {
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int a; // marshaled (default behavior not overridden)
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@No.DBusMarshal int b; // explicitly not marshaled
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private int c; // marshaled, because of includePrivateFields
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}
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```
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## Modules
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- `attributes`: defines some UDAs (and related templates) that can be used to customize
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struct marshaling.
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- `bus`: bus functionality like requesting names and event loops.
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- `conv`: low level type marshaling methods.
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- `exception`: exception classes
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- `router`: message and signal routing based on `MessagePattern` structs.
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- `simple`: simpler wrappers around other functionality.
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- `thin`: thin wrapper types
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- `util`: templates for working with D type marshaling like `canDBus!T`.
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- `c_lib`: a D translation of the DBus C headers
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(you generally should not need to use these directly).
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Importing `ddbus` will publicly import the `thin`, `router`, `bus`, `simple` and
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`attributes` modules. These provide most of the functionality you probably want,
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you can import the others if you want lower level control.
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Nothing is hidden so if `ddbus` doesn't provide something, you can always import
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`c_lib` and use the pointers contained in the thin wrapper structs to do it yourself.
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# Concurrent Updates
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If you want to use the DBus connection concurrently with some other features
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or library like a GUI or vibe.d you can do so by placing this code in the update/main loop:
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```d
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// initialize Connection conn; somewhere
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// on update:
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if (!conn.tick)
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return;
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```
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Or in vibe.d:
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```d
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runTask({
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import vibe.core.core : yield;
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while (conn.tick)
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yield(); // Or sleep(1.msecs);
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});
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```
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It would be better to watch a file descriptor asynchronously in the event loop instead of checking on a timer, but that hasn't been implemented yet, see Todo.
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# Todo
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`ddbus` should be complete for everyday use but is missing some fanciness that it easily could and should have:
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- Support for adding file descriptors to event loops like vibe.d so that it only wakes up when messages arrive and not on a timer.
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- Marshaling of file descriptor objects
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- Better efficiency in some places, particularly the object wrapping allocates tons of delegates for every method.
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Pull requests are welcome, the codebase is pretty small and other than the template metaprogramming for type marshaling is fairly straightforward.
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