One the server side xtext is used to provide a language server. On the client side the Theia framework is used to communicate with it. This guide is for KIELER developers who want to build functinality in form of language server extensions for KEITH and frontend developers for KEITH that want to know how to communicate with the LS.
Starting the Language Server (LS)
This part of the guide covers the server side development for KEITH, the language server (LS). It is adviced to have a look at the existing implementation in the language.server plugin.
Register start hook (Eclipse)
Currently the LS is an eclipse application and it has to be started as one. To do this the Manifest.mf in the META-INF folder of your language server plugin has to be changed. In the extensions tab a new extension point for org.eclipse.core.runtime.applications has to be created. This extension points maps to your start class of your language server, which has to be an IApplication that implements a start method.
Language that are registered here are always xtext languages.
Register languages that are defined in the semantic
Since we are in the semantics repository we can use java ServiceLoader to add new ILSSetups, which register a language.
A language that wants to be included in the LS can implement this interface. Registering SCTXLSSetup via ServiceLoader allows to register all available languages like this:
Register that are defined outside of the semantic
Have a look at one of the LSSetups defined in the semantic.
Bindings for the injector created by createLSModules and why they are needed:
- the KeithServerModule bind all standard stuff
- if we start via stdin/out, the ServerLauncher has to be bound to the LanguageServerLauncher
- we have to bind a ResourceRegistry and our own WorkspaceConfigFactory that allows to open a folder without xtext getting involved
- all bindings for the KGraphDiagramModule and KGraphDiagramServerModule are done to have a working diagram server
Starting and connecting
The following things are done via the LanguageServer class on startup of the LS:
- port and host argument are read. This decides whether the LS starts via socket or stdin/out
- call bindAndRegisterLanguages (this loads all languages, languages defined in the pragmatic have to be added manually, all other ones are added via the KielerServiceLoader (see ILSSetup))
- injector is created via createLSModules
- a new socket is opened, buildAndStartLS is called (gets all ILanguageServerContribution via KielerServiceLoader and starts LS)
- main of LanguageServerLauncher is called
- this calls bindAndRegisterLanguages
- launch of ServerLauncher is called with injector created by createLSModules
- this calls the start method which calls buildAndStartLS
Connection via socket
You have to specify a port and an optional host as VM arguments to start the LS via socket.
Currently the LS is an eclipse application, therefore you create a new Eclipse Application run configuration in eclipse.
Main tab, section
product to run select Run an application and select
arguments tab, section
VM arguments add
-Dhost=localhost -Dport=5007 to the arguments. You might want to specify
Xmx here too, if you plan to use bigger models (such as the railway controller).
Running this eclipse application requires a Theia client that tries to connect via socket to an LS running on port 5007.
Connection via stdin/stdout
Is only relevant for the product. Requeires to start to LS without an host or port Vm argument. Cannot be debugged.
Developing a LS extension
We use java ServiceLoader to register stuff. Here is a small example how a LanguageServerExtension is registered via a ServiceLoader and how it is used:
Register LanguageServerExtensions (ServiceLoader Example)
This is a LanguageServerExtension. It has to be used in the de.cau.cs.kieler.language.server plugin. Since the language-server-plugin should not have dependencies to all plugins that define a language server extension dependency inversion is used to prevent that. A ServiceLoader via dependency inversion does exactly that.
Here is such an example extension, the KiCoolLanguageServerExtension:
The CommandExtension defines all commands (requests or notifications) that are send from client to server. An example how this looks like can be seen in the code snippet Example CommandExtension is an example how to define a server side extension interface.
The ILanguageClientProvider should be implemented by an extension that plans to send messages from the server to the client.
This language server extension is provided by a corresponding contribution, which is later used to access it:
Create a file called de.cau.cs.kieler.language.server.ILanguageServerContribution in <plugin>/META-INF/services/ (in this example this is de.cau.cs.kieler.kicool.ide). The name of the file refers to the contribution interface that should be used to provide the contribution. The content of the file is the following:
This is the fully qualified name of the contribution written earlier.
The language server uses all LanguageServerExtensions like this:
The resulting list of implementions is used to add the extensions to the language server.
The interfaces used for dynamic registration are in the semantics repository. If you define a pragmatics LS extension you have to statically add these extensions to your list.
Register an extension (on server side)
See example above for ServiceLoader and initial stuff.
What is still missing are the contents of the CommandExtension implemented by the KiCoolLanguageServerExtension. This is an interface defining all additional commands. The CommandExtension looks like this.
This defines three json-rpc commands: "keith/kicool/compile", "keith/kicool/show", "keith/kicool/get-systems". These are implemented in KiCoolLanguageServerExtension.
Server Client communication interface
Not only messages from client to server but rather messages from server client might be needed.
Messages that can be send from server to client are defined in the KeithLanguageClient:
These messages can be caught on the client side by defining the message that is caught like this:
This message type is bound to a method that should be called whenever the client receives such a message.
The method should receive all parameters specific in the KeithLanguageClient interface on the serevr side.
Such a notification from server to client is send like this:
Register and calling an extension (on client side)
Language server extension do not have to be registered on the client side. It is just called.
You can send a request or a notification to the language server like this:
In this example client is an instance of a language client. It is usually injected like this:
How to write a widget
- BaseWidget: Very basic
- ReactWidget: A render method has to be implemented that redraws the widget on demand. Additionally several on* event methods can beimplemented.
- TreeWidget: Extends the ReactWidget and draws the contents of the widget in a tree view.
If a widget has a state it should implement the StatefulWidget interface, which allows to imlement a store and restore method.
Look at examples in KEITH or Theia to see how this is done.
How to make a new module for sprotty (see actionModule, ...)
How to use (Kieler)ServiceLoader
Classes that are provided via a ServiceLoader have a contribution that provides them. This contributions share a common interface lets call it
IStuffContribution. A specific StuffContribution (it provides stuff) is the ImportantStuffContribution.
The ServiceLoader has to know that some plugin provides an implementation for IStuffContribution. Therefore, a folder named services is added next to the corresponding MANIFEST.MF.
In the services folder a file named the same as the fully qualified name of the implemented interface is added. Here this one is called
The file holds the fully qualified names of all implementations of this interface:
Now you can access implementation of IStuff as follows: