Merge pull request #160 from modelcontextprotocol/client-add-resource-support

add `resources/list` and `resources/read` support to client

Author: koic

lib/mcp/client.rb

@@ -44,6 +44,20 @@ def tools
       end || []
     end
 
+    # Returns the list of resources available from the server.
+    # Each call will make a new request – the result is not cached.
+    #
+    # @return [Array<Hash>] An array of available resources.
+    def resources
+      response = transport.send_request(request: {
+        jsonrpc: JsonRpcHandler::Version::V2_0,
+        id: request_id,
+        method: "resources/list",
+      })
+
+      response.dig("result", "resources") || []
+    end
+
     # Calls a tool via the transport layer and returns the full response from the server.
     #
     # @param tool [MCP::Client::Tool] The tool to be called.
@@ -67,6 +81,21 @@ def call_tool(tool:, arguments: nil)
       })
     end
 
+    # Reads a resource from the server by URI and returns the contents.
+    #
+    # @param uri [String] The URI of the resource to read.
+    # @return [Array<Hash>] An array of resource contents (text or blob).
+    def read_resource(uri:)
+      response = transport.send_request(request: {
+        jsonrpc: JsonRpcHandler::Version::V2_0,
+        id: request_id,
+        method: "resources/read",
+        params: { uri: uri },
+      })
+
+      response.dig("result", "contents") || []
+    end
+
     private
 
     def request_id

test/mcp/client_test.rb

@@ -57,5 +57,89 @@ def test_call_tool_sends_request_to_transport_and_returns_content
 
       assert_equal("result", content)
     end
+
+    def test_resources_sends_request_to_transport_and_returns_resources_array
+      transport = mock
+      mock_response = {
+        "result" => {
+          "resources" => [
+            { "name" => "resource1", "uri" => "file:///path/to/resource1", "description" => "First resource" },
+            { "name" => "resource2", "uri" => "file:///path/to/resource2", "description" => "Second resource" },
+          ],
+        },
+      }
+
+      # Only checking for the essential parts of the request
+      transport.expects(:send_request).with do |args|
+        args in { request: { method: "resources/list", jsonrpc: "2.0" } }
+      end.returns(mock_response).once
+
+      client = Client.new(transport: transport)
+      resources = client.resources
+
+      assert_equal(2, resources.size)
+      assert_equal("resource1", resources.first["name"])
+      assert_equal("file:///path/to/resource1", resources.first["uri"])
+      assert_equal("resource2", resources.last["name"])
+      assert_equal("file:///path/to/resource2", resources.last["uri"])
+    end
+
+    def test_read_resource_sends_request_to_transport_and_returns_contents
+      transport = mock
+      uri = "file:///path/to/resource.txt"
+      mock_response = {
+        "result" => {
+          "contents" => [
+            { "uri" => uri, "mimeType" => "text/plain", "text" => "Hello, world!" },
+          ],
+        },
+      }
+
+      # Only checking for the essential parts of the request
+      transport.expects(:send_request).with do |args|
+        args in {
+          request: {
+            method: "resources/read",
+            jsonrpc: "2.0",
+            params: {
+              uri: uri,
+            },
+          },
+        }
+      end.returns(mock_response).once
+
+      client = Client.new(transport: transport)
+      contents = client.read_resource(uri: uri)
+
+      assert_equal(1, contents.size)
+      assert_equal(uri, contents.first["uri"])
+      assert_equal("text/plain", contents.first["mimeType"])
+      assert_equal("Hello, world!", contents.first["text"])
+    end
+
+    def test_read_resource_returns_empty_array_when_no_contents
+      transport = mock
+      uri = "file:///path/to/nonexistent.txt"
+      mock_response = { "result" => {} }
+
+      transport.expects(:send_request).returns(mock_response).once
+
+      client = Client.new(transport: transport)
+      contents = client.read_resource(uri: uri)
+
+      assert_empty(contents)
+    end
+
+    def test_resources_returns_empty_array_when_no_resources
+      transport = mock
+      mock_response = { "result" => {} }
+
+      transport.expects(:send_request).returns(mock_response).once
+
+      client = Client.new(transport: transport)
+      resources = client.resources
+
+      assert_empty(resources)
+    end
   end
 end