Document resource subscription support in server and client guides (#843)

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

Author: tzolov

docs/client.md

@@ -408,6 +408,49 @@ Resources represent server-side data sources that clients can access using URI t
         .subscribe();
     ```
 
+### Resource Subscriptions
+
+When the server advertises `resources.subscribe` support, clients can subscribe to individual resources and receive a callback whenever the server pushes a `notifications/resources/updated` notification for that URI. The SDK automatically re-reads the resource on notification and delivers the updated contents to the registered consumer.
+
+Register a consumer on the client builder, then subscribe/unsubscribe at any time:
+
+=== "Sync API"
+
+    ```java
+    McpSyncClient client = McpClient.sync(transport)
+        .resourcesUpdateConsumer(contents -> {
+            // called with the updated resource contents after each notification
+            System.out.println("Resource updated: " + contents);
+        })
+        .build();
+
+    client.initialize();
+
+    // Subscribe to a specific resource URI
+    client.subscribeResource(new McpSchema.SubscribeRequest("custom://resource"));
+
+    // ... later, stop receiving updates
+    client.unsubscribeResource(new McpSchema.UnsubscribeRequest("custom://resource"));
+    ```
+
+=== "Async API"
+
+    ```java
+    McpAsyncClient client = McpClient.async(transport)
+        .resourcesUpdateConsumer(contents -> Mono.fromRunnable(() -> {
+            System.out.println("Resource updated: " + contents);
+        }))
+        .build();
+
+    client.initialize()
+        .then(client.subscribeResource(new McpSchema.SubscribeRequest("custom://resource")))
+        .subscribe();
+
+    // ... later, stop receiving updates
+    client.unsubscribeResource(new McpSchema.UnsubscribeRequest("custom://resource"))
+        .subscribe();
+    ```
+
 ### Prompt System
 
 The prompt system enables interaction with server-side prompt templates. These templates can be discovered and executed with custom parameters, allowing for dynamic text generation based on predefined patterns.

docs/server.md

@@ -33,7 +33,7 @@ The server supports both synchronous and asynchronous APIs, allowing for flexibl
     McpSyncServer syncServer = McpServer.sync(transportProvider)
         .serverInfo("my-server", "1.0.0")
         .capabilities(ServerCapabilities.builder()
-            .resources(false, true)  // Enable resource support with list changes
+            .resources(false, true)  // Resource support: subscribe=false, listChanged=true
             .tools(true)             // Enable tool support with list changes
             .prompts(true)           // Enable prompt support with list changes
             .completions()           // Enable completions support
@@ -57,7 +57,7 @@ The server supports both synchronous and asynchronous APIs, allowing for flexibl
     McpAsyncServer asyncServer = McpServer.async(transportProvider)
         .serverInfo("my-server", "1.0.0")
         .capabilities(ServerCapabilities.builder()
-            .resources(false, true)  // Enable resource support with list changes
+            .resources(false, true)  // Resource support: subscribe=false, listChanged=true
             .tools(true)             // Enable tool support with list changes
             .prompts(true)           // Enable prompt support with list changes
             .completions()           // Enable completions support
@@ -319,7 +319,7 @@ The server can be configured with various capabilities:
 
 ```java
 var capabilities = ServerCapabilities.builder()
-    .resources(false, true)  // Resource support (subscribe, listChanged)
+    .resources(true, true)   // Resource support: subscribe=true, listChanged=true
     .tools(true)             // Tool support with list changes notifications
     .prompts(true)           // Prompt support with list changes notifications
     .completions()           // Enable completions support
@@ -438,6 +438,42 @@ Resources provide context to AI models by exposing data such as: File contents,
     );
     ```
 
+### Resource Subscriptions
+
+When the `subscribe` capability is enabled, clients can subscribe to specific resources and receive targeted `notifications/resources/updated` notifications when those resources change. Only sessions that have explicitly subscribed to a given URI receive the notification — not every connected client.
+
+Enable subscription support in the server capabilities:
+
+```java
+McpSyncServer server = McpServer.sync(transportProvider)
+    .serverInfo("my-server", "1.0.0")
+    .capabilities(ServerCapabilities.builder()
+        .resources(true, false)  // subscribe=true, listChanged=false
+        .build())
+    .resources(myResourceSpec)
+    .build();
+```
+
+When a subscribed resource changes, notify only the interested sessions:
+
+=== "Sync"
+
+    ```java
+    server.notifyResourcesUpdated(
+        new McpSchema.ResourcesUpdatedNotification("custom://resource")
+    );
+    ```
+
+=== "Async"
+
+    ```java
+    server.notifyResourcesUpdated(
+        new McpSchema.ResourcesUpdatedNotification("custom://resource")
+    ).subscribe();
+    ```
+
+If no sessions are subscribed to the given URI the call completes immediately without sending any messages. Subscription state is automatically cleaned up when a client session closes.
+
 ### Resource Template Specification
 
 Resource templates allow servers to expose parameterized resources using URI templates: