Merge pull request #306 from koic/support_customizing_faraday_client_in_mcp_client_http

Support customizing the Faraday client in `MCP::Client::HTTP`

README.md

@@ -1401,6 +1401,18 @@ client.tools # will make the call using Bearer auth
 
 You can add any custom headers needed for your authentication scheme, or for any other purpose. The client will include these headers on every request.
 
+#### Customizing the Faraday Connection
+
+You can pass a block to `MCP::Client::HTTP.new` to customize the underlying Faraday connection.
+The block is called after the default middleware is configured, so you can add middleware or swap the HTTP adapter:
+
+```ruby
+http_transport = MCP::Client::HTTP.new(url: "https://api.example.com/mcp") do |faraday|
+  faraday.use MyApp::Middleware::HttpRecorder
+  faraday.adapter :typhoeus
+end
+```
+
 ### Tool Objects
 
 The client provides a wrapper class for tools returned by the server:

lib/mcp/client/http.rb

@@ -7,9 +7,10 @@ module MCP
 
       attr_reader :url
 
-      def initialize(url:, headers: {})
+      def initialize(url:, headers: {}, &block)
         @url = url
         @headers = headers
+        @faraday_customizer = block
       end
 
       def send_request(request:)
@@ -78,6 +79,8 @@ module MCP
           headers.each do |key, value|
             faraday.headers[key] = value
           end
+
+          @faraday_customizer&.call(faraday)
         end
       end
 

test/mcp/client/http_test.rb

@@ -242,6 +242,31 @@ module MCP
         assert_equal({ method: "tools/list", params: nil }, error.request)
       end
 
+      def test_block_customizes_faraday_connection
+        custom_client = HTTP.new(url: url) do |faraday|
+          faraday.headers["X-Custom"] = "test-value"
+        end
+
+        request = {
+          jsonrpc: "2.0",
+          id: "test_id",
+          method: "tools/list",
+        }
+
+        stub_request(:post, url).with(
+          headers: {
+            "X-Custom" => "test-value",
+            "Accept" => "application/json, text/event-stream",
+          },
+        ).to_return(
+          status: 200,
+          headers: { "Content-Type" => "application/json" },
+          body: { result: { tools: [] } }.to_json,
+        )
+
+        custom_client.send_request(request: request)
+      end
+
       def test_send_request_raises_error_for_non_json_response
         request = {
           jsonrpc: "2.0",