#101 Model Server Launcher extensibility (#102)

Implement the suggested extensibility hooks for subclasses
to selectively override Java server and/or Node server
launching. Also, because it's a related subject, fix the
port assignment for the Java server in the two-server
scenario allowing for subclasses also to override that.

Fixes #101.
Fixes #100.

Contributed on behalf of STMicroelectronics.

Signed-off-by: Christian W. Damus <cdamus.ext@eclipsesource.com>

Author: cdamus

packages/modelserver-theia/src/node/launch-options.ts

@@ -15,7 +15,14 @@ export interface LaunchOptions {
     serverPort: number;
     hostname: string;
     jarPath?: string;
+    /**
+     * Additional arguments, besides those implied by other options, passed to server main entrypoint.
+     */
     additionalArgs?: string[];
+    /**
+     * Arguments passed to the Java Virtual Machine, not to the server application `main` entrypoint.
+     */
+    vmArgs?: string[];
 
     /**
      * For a configuration including the `modelserver-node`, launch options

packages/modelserver-theia/src/node/model-server-backend-contribution.ts

@@ -55,13 +55,26 @@ export class DefaultModelServerLauncher implements ModelServerLauncher, BackendA
 
     protected doStartServer(): void {
         // Note that the existence of the jarPath was previously checked
-        let args = ['-jar', this.launchOptions.jarPath!, '--port', `${this.launchOptions.serverPort}`];
+        let args = ['-jar', this.launchOptions.jarPath!, '--port', `${this.resolveJavaServerPort(this.launchOptions)}`];
+        if (this.launchOptions.vmArgs) {
+            args = [...this.launchOptions.vmArgs, ...args];
+        }
         if (this.launchOptions.additionalArgs) {
             args = [...args, ...this.launchOptions.additionalArgs];
         }
         this.spawnProcessAsync('java', args);
     }
 
+    /**
+     * Resolve the TCP port number that the Java server should be configured to listen on.
+     *
+     * @param options the launch options
+     * @returns the most appropriate port number to configure the Java server process to listen on
+     */
+    protected resolveJavaServerPort(options: LaunchOptions): number {
+        return options.serverPort ?? DEFAULT_LAUNCH_OPTIONS.serverPort;
+    }
+
     protected validateLaunch(): boolean {
         if (!this.launchOptions.jarPath) {
             this.logError('Could not start model server. No path to executable is specified');
@@ -132,15 +145,23 @@ export class DefaultModelServerNodeLauncher extends DefaultModelServerLauncher {
     }
 
     protected doStartServer(): void {
-        // Launch the Java server
+        this.startJavaServer();
+        this.startNodeServer();
+    }
+
+    protected startJavaServer(): void {
+        // Launch the Java server as per superclass behavior
         super.doStartServer();
+    }
 
-        // Then launch the Node server
+    protected resolveJavaServerPort(options: LaunchOptions): number {
+        return this.resolveUpstreamPort(options);
+    }
 
+    protected startNodeServer(): void {
         // Note that validation previously asserted the existence of the `modelServerNode` property
-        const upstreamPort =
-            this.launchOptions.modelServerNode!.upstreamPort ?? DEFAULT_MODELSERVER_NODE_LAUNCH_OPTIONS.modelServerNode.upstreamPort;
-        const port = this.launchOptions.serverPort;
+        const upstreamPort = this.resolveUpstreamPort(this.launchOptions);
+        const port = this.resolveNodeServerPort(this.launchOptions);
 
         // Note that the existence of the jsPath was previously checked
         let args = [this.launchOptions.modelServerNode!.jsPath!, '--port', `${port}`, '--upstream', `${upstreamPort}`];
@@ -149,4 +170,25 @@ export class DefaultModelServerNodeLauncher extends DefaultModelServerLauncher {
         }
         this.spawnProcessAsync('node', args);
     }
+
+    /**
+     * Resolve the TCP port number that the Node server should be configured to address its upstream Java server.
+     *
+     * @param options the launch options
+     * @returns the most appropriate port number to configure the Node server process to connect to for the upstream Java server
+     */
+    protected resolveUpstreamPort(options: LaunchOptions): number {
+        // Note that validation previously asserted the existence of the `modelServerNode` property
+        return options.modelServerNode!.upstreamPort ?? DEFAULT_MODELSERVER_NODE_LAUNCH_OPTIONS.modelServerNode.upstreamPort;
+    }
+
+    /**
+     * Resolve the TCP port number that the Node server should be configured to listen on.
+     *
+     * @param options the launch options
+     * @returns the most appropriate port number to configure the Node server process to listen on
+     */
+    protected resolveNodeServerPort(options: LaunchOptions): number {
+        return options.serverPort ?? DEFAULT_MODELSERVER_NODE_LAUNCH_OPTIONS.serverPort;
+    }
 }