[fel] Add configurable ping interval (#147)

- Introduced configurable ping interval via constructor and configuration (application.yml) with a fallback default value (15,000 ms).
- Moved ping scheduler creation to after initialization to ensure valid session state before sending pings.
- Added parameter validation in DefaultMcpClient constructor using notNull and notBlank checks for better failure visibility.
- Propagated ping interval configuration through DefaultMcpClientFactory using @value injection.
- Improved testability and lifecycle management by decoupling scheduler setup from constructor logic.

This change increases flexibility and robustness of the MCP client, especially in different deployment and test environments.

Author: CodeCasterX

framework/fel/java/plugins/tool-mcp-client/src/main/java/modelengine/fel/tool/mcp/client/support/DefaultMcpClient.java

@@ -6,6 +6,8 @@
 
 package modelengine.fel.tool.mcp.client.support;
 
+import static modelengine.fitframework.inspection.Validation.notBlank;
+import static modelengine.fitframework.inspection.Validation.notNull;
 import static modelengine.fitframework.util.ObjectUtils.cast;
 
 import modelengine.fel.tool.mcp.client.McpClient;
@@ -57,14 +59,14 @@
  */
 public class DefaultMcpClient implements McpClient {
     private static final Logger log = Logger.get(DefaultMcpClient.class);
-    private static final long DELAY_MILLIS = 30_000L;
 
     private final ObjectSerializer jsonSerializer;
     private final HttpClassicClient client;
     private final String baseUri;
     private final String sseEndpoint;
     private final String name;
     private final AtomicLong id = new AtomicLong(0);
+    private final long pingInterval;
 
     private volatile String messageEndpoint;
     private volatile String sessionId;
@@ -88,14 +90,16 @@ public class DefaultMcpClient implements McpClient {
      * @param client The HTTP client used for communication with the MCP server.
      * @param baseUri The base URI of the MCP server.
      * @param sseEndpoint The endpoint for the Server-Sent Events (SSE) connection.
+     * @param pingInterval The interval for sending ping messages to the MCP server. Unit: milliseconds.
      */
     public DefaultMcpClient(ObjectSerializer jsonSerializer, HttpClassicClient client, String baseUri,
-            String sseEndpoint) {
-        this.jsonSerializer = jsonSerializer;
-        this.client = client;
-        this.baseUri = baseUri;
-        this.sseEndpoint = sseEndpoint;
+            String sseEndpoint, long pingInterval) {
+        this.jsonSerializer = notNull(jsonSerializer, "The json serializer cannot be null.");
+        this.client = notNull(client, "The http client cannot be null.");
+        this.baseUri = notBlank(baseUri, "The MCP server base URI cannot be blank.");
+        this.sseEndpoint = notBlank(sseEndpoint, "The MCP server SSE endpoint cannot be blank.");
         this.name = UuidUtils.randomUuidString();
+        this.pingInterval = pingInterval > 0 ? pingInterval : 15_000;
     }
 
     @Override
@@ -126,20 +130,6 @@ public void initialize() {
                 (subscription, textEvent) -> this.consumeTextEvent(textEvent),
                 subscription -> log.info("SSE channel is completed."),
                 (subscription, cause) -> log.error("SSE channel is failed.", cause));
-        this.pingScheduler = ThreadPoolScheduler.custom()
-                .threadPoolName("mcp-client-ping-" + this.name)
-                .awaitTermination(3, TimeUnit.SECONDS)
-                .isImmediateShutdown(true)
-                .corePoolSize(1)
-                .maximumPoolSize(1)
-                .keepAliveTime(60, TimeUnit.SECONDS)
-                .workQueueCapacity(Integer.MAX_VALUE)
-                .isDaemonThread(true)
-                .build();
-        this.pingScheduler.schedule(Task.builder()
-                .runnable(this::pingServer)
-                .policy(ExecutePolicy.fixedDelay(DELAY_MILLIS))
-                .build(), DELAY_MILLIS);
         if (!this.waitInitialized()) {
             throw new IllegalStateException("Failed to initialize.");
         }
@@ -236,6 +226,20 @@ private void initializedMcpServer(JsonRpc.Response<Long> response) {
         } catch (IOException e) {
             throw new IllegalStateException(e);
         }
+        this.pingScheduler = ThreadPoolScheduler.custom()
+                .threadPoolName("mcp-client-ping-" + this.name)
+                .awaitTermination(3, TimeUnit.SECONDS)
+                .isImmediateShutdown(true)
+                .corePoolSize(1)
+                .maximumPoolSize(1)
+                .keepAliveTime(60, TimeUnit.SECONDS)
+                .workQueueCapacity(Integer.MAX_VALUE)
+                .isDaemonThread(true)
+                .build();
+        this.pingScheduler.schedule(Task.builder()
+                .runnable(this::pingServer)
+                .policy(ExecutePolicy.fixedDelay(this.pingInterval))
+                .build(), this.pingInterval);
     }
 
     private void recordServerSchema(JsonRpc.Response<Long> response) {

framework/fel/java/plugins/tool-mcp-client/src/main/java/modelengine/fel/tool/mcp/client/support/DefaultMcpClientFactory.java

@@ -6,12 +6,15 @@
 
 package modelengine.fel.tool.mcp.client.support;
 
+import static modelengine.fitframework.inspection.Validation.notNull;
+
 import modelengine.fel.tool.mcp.client.McpClient;
 import modelengine.fel.tool.mcp.client.McpClientFactory;
 import modelengine.fit.http.client.HttpClassicClient;
 import modelengine.fit.http.client.HttpClassicClientFactory;
 import modelengine.fitframework.annotation.Component;
 import modelengine.fitframework.annotation.Fit;
+import modelengine.fitframework.annotation.Value;
 import modelengine.fitframework.serialization.ObjectSerializer;
 
 /**
@@ -26,25 +29,29 @@
 public class DefaultMcpClientFactory implements McpClientFactory {
     private final HttpClassicClient client;
     private final ObjectSerializer jsonSerializer;
+    private final long pingInterval;
 
     /**
      * Constructs a new instance of the DefaultMcpClientFactory.
      *
      * @param clientFactory The factory used to create the HTTP client.
      * @param jsonSerializer The JSON serializer used for serialization and deserialization.
+     * @param pingInterval The interval between ping requests. Units: milliseconds.
      */
     public DefaultMcpClientFactory(HttpClassicClientFactory clientFactory,
-            @Fit(alias = "json") ObjectSerializer jsonSerializer) {
+            @Fit(alias = "json") ObjectSerializer jsonSerializer,
+            @Value("${mcp.client.ping-interval}") long pingInterval) {
         this.client = clientFactory.create(HttpClassicClientFactory.Config.builder()
                 .connectTimeout(30_000)
                 .socketTimeout(60_000)
                 .connectionRequestTimeout(60_000)
                 .build());
-        this.jsonSerializer = jsonSerializer;
+        this.jsonSerializer = notNull(jsonSerializer, "The json serializer cannot be null.");
+        this.pingInterval = pingInterval;
     }
 
     @Override
     public McpClient create(String baseUri, String sseEndpoint) {
-        return new DefaultMcpClient(this.jsonSerializer, this.client, baseUri, sseEndpoint);
+        return new DefaultMcpClient(this.jsonSerializer, this.client, baseUri, sseEndpoint, this.pingInterval);
     }
 }

framework/fel/java/plugins/tool-mcp-client/src/main/resources/application.yml

@@ -1,4 +1,8 @@
 fit:
   beans:
     packages:
-    - 'modelengine.fel.tool.mcp.client.support'
+    - 'modelengine.fel.tool.mcp.client.support'
+
+mcp:
+  client:
+    ping-interval: 15000