feat: implement resource support

- Add resource schema validation and registry
- Implement resource list, read, subscribe operations
- Add resource change notifications
- Add resource management functions
- Match implementation style of tools and prompts

Author: hugoduncan

components/mcp-server/src/mcp_clj/mcp_server/core.clj

@@ -20,7 +20,8 @@
     [json-rpc-server
      session-id->session
      tool-registry
-     prompt-registry])
+     prompt-registry
+     resource-registry])
 
 (defn- request-session-id [request]
   (get ((:query-params request)) "session_id"))
@@ -49,6 +50,24 @@
    "notifications/prompts/list_changed"
    nil))
 
+(defn- notify-resources-changed!
+  "Notify all sessions that the resource list has changed"
+  [server]
+  (log/info :server/notify-resources-changed {:server server})
+  (json-rpc/notify-all!
+   @(:json-rpc-server server)
+   "notifications/resources/list_changed"
+   nil))
+
+(defn- notify-resource-updated!
+  "Notify all sessions that a resource has been updated"
+  [server uri]
+  (log/info :server/notify-resource-updated {:server server :uri uri})
+  (json-rpc/notify-all!
+   @(:json-rpc-server server)
+   "notifications/resources/updated"
+   {:uri uri}))
+
 (defn- text-map [msg]
   {:type "text" :text msg})
 
@@ -115,9 +134,27 @@
 
 (defn- handle-list-resources
   "Handle resources/list request from client"
-  [_server params]
+  [server params]
   (log/info :server/resources-list)
-  (resources/list-resources params))
+  (resources/list-resources (:resource-registry server) params))
+
+(defn- handle-read-resource
+  "Handle resources/read request from client"
+  [server params]
+  (log/info :server/resources-read)
+  (resources/read-resource (:resource-registry server) params))
+
+(defn- handle-subscribe-resource
+  "Handle resources/subscribe request from client"
+  [server params]
+  (log/info :server/resources-subscribe)
+  (resources/subscribe-resource (:resource-registry server) params))
+
+(defn- handle-unsubscribe-resource
+  "Handle resources/unsubscribe request from client"
+  [server params]
+  (log/info :server/resources-unsubscribe)
+  (resources/unsubscribe-resource (:resource-registry server) params))
 
 (defn- handle-list-prompts
   "Handle prompts/list request from client"
@@ -154,6 +191,9 @@
     "tools/list"                handle-list-tools
     "tools/call"                handle-call-tool
     "resources/list"            handle-list-resources
+    "resources/read"            handle-read-resource
+    "resources/subscribe"       handle-subscribe-resource
+    "resources/unsubscribe"     handle-unsubscribe-resource
     "prompts/list"              handle-list-prompts
     "prompts/get"               handle-get-prompt}
    (fn [handler]
@@ -212,11 +252,30 @@
      @(:json-rpc-server server)
      (:session-id session))))
 
+(defn add-resource!
+  "Add or update a resource in a running server"
+  [server resource]
+  (log/info :server/add-resource!)
+  (when-not (resources/valid-resource? resource)
+    (throw (ex-info "Invalid resource definition" {:resource resource})))
+  (swap! (:resource-registry server) assoc (:name resource) resource)
+  (notify-resources-changed! server)
+  server)
+
+(defn remove-resource!
+  "Remove a resource from a running server"
+  [server resource-name]
+  (log/info :server/remove-resource!)
+  (swap! (:resource-registry server) dissoc resource-name)
+  (notify-resources-changed! server)
+  server)
+
 (defn create-server
   "Create MCP server instance"
-  [{:keys [port tools prompts]
+  [{:keys [port tools prompts resources]
     :or   {tools tools/default-tools
-           prompts prompts/default-prompts}}]
+           prompts prompts/default-prompts
+           resources resources/default-resources}}]
   (doseq [tool (vals tools)]
     (when-not (tools/valid-tool? tool)
       (throw (ex-info "Invalid tool in constructor" {:tool tool}))))
@@ -226,12 +285,14 @@
   (let [session-id->session (atom {})
         tool-registry       (atom tools)
         prompt-registry     (atom prompts)
+        resource-registry   (atom resources)
         rpc-server-prom    (promise)
         server             (->MCPServer
                             rpc-server-prom
                             session-id->session
                             tool-registry
-                            prompt-registry)
+                            prompt-registry
+                            resource-registry)
         json-rpc-server    (json-rpc/create-server
                             {:port           port
                              :on-sse-connect (partial on-sse-connect server)

components/mcp-server/src/mcp_clj/mcp_server/resources.clj

@@ -2,9 +2,119 @@
   "MCP resource endpoints"
   (:require [mcp-clj.log :as log]))
 
+(defrecord ResourceDefinition [name uri mime-type description annotations implementation])
+
+(defn- valid-string? [x]
+  (and (string? x)
+       (pos? (count x))))
+
+(defn- valid-uri? [x]
+  (try
+    (java.net.URI. x)
+    true
+    (catch Exception _
+      false)))
+
+(defn- valid-audience-value? [x]
+  (#{"user" "assistant"} x))
+
+(defn- valid-audience? [x]
+  (and (vector? x)
+       (every? valid-audience-value? x)))
+
+(defn- valid-priority? [x]
+  (and (number? x)
+       (<= 0 x 1)))
+
+(defn- valid-annotations? [annotations]
+  (and (map? annotations)
+       (or (nil? (:priority annotations))
+           (valid-priority? (:priority annotations)))
+       (or (nil? (:audience annotations))
+           (valid-audience? (:audience annotations)))))
+
+(defn valid-resource?
+  "Validate a resource definition.
+   Returns true if valid, throws ex-info with explanation if not."
+  [{:keys [name uri mime-type annotations] :as resource}]
+  (when-not (valid-string? name)
+    (throw (ex-info "name must be a non-empty string"
+                   {:type :validation-error
+                    :field :name
+                    :value name
+                    :resource resource})))
+  (when-not (valid-uri? uri)
+    (throw (ex-info "uri must be a valid URI string"
+                   {:type :validation-error
+                    :field :uri
+                    :value uri
+                    :resource resource})))
+  (when (and mime-type (not (valid-string? mime-type)))
+    (throw (ex-info "mime-type must be a non-empty string"
+                   {:type :validation-error
+                    :field :mime-type
+                    :value mime-type
+                    :resource resource})))
+  (when (and annotations (not (valid-annotations? annotations)))
+    (throw (ex-info "invalid annotations"
+                   {:type :validation-error
+                    :field :annotations
+                    :value annotations
+                    :resource resource})))
+  true)
+
+(defn resource-definition
+  "Convert a ResourceDefinition to the wire format"
+  [{:keys [name uri mime-type description annotations]}]
+  (cond-> {:name name
+           :uri uri}
+    mime-type (assoc :mimeType mime-type)
+    description (assoc :description description)
+    annotations (assoc :annotations annotations)))
+
+(def default-resources {})
+
 (defn list-resources
   "List available resources.
-   Returns empty list for current implementation."
-  [params]
+   Returns a map with :resources containing resource definitions."
+  [registry params]
   (log/info :resources/list {:params params})
-  {:resources []})
+  {:resources (mapv resource-definition (vals @registry))})
+
+(defn- read-resource-impl
+  "Default implementation for reading a resource"
+  [{:keys [implementation] :as resource} uri]
+  (if implementation
+    (implementation uri)
+    {:contents [{:uri uri
+                 :text "Resource not implemented"}]
+     :isError true}))
+
+(defn read-resource
+  "Read a resource by URI.
+   Returns contents of the resource."
+  [registry {:keys [uri] :as params}]
+  (log/info :resources/read {:params params})
+  (if-let [resource (some #(when (= uri (:uri %)) %) (vals @registry))]
+    (read-resource-impl resource uri)
+    {:contents [{:uri uri
+                 :text "Resource not found"}]
+     :isError true}))
+
+(defn subscribe-resource
+  "Subscribe to updates for a resource.
+   Returns empty result if successful, error if resource not found."
+  [registry {:keys [uri] :as params}]
+  (log/info :resources/subscribe {:params params})
+  (if (some #(when (= uri (:uri %)) %) (vals @registry))
+    {}
+    {:content [{:type "text"
+                :text (str "Resource not found: " uri)}]
+     :isError true}))
+
+(defn unsubscribe-resource
+  "Unsubscribe from updates for a resource.
+   Returns empty result if successful."
+  [_registry {:keys [uri] :as params}]
+  (log/info :resources/unsubscribe {:params params})
+  {})