Add basic HTTP client support with pluggable transports

lib/mcp/client/http.rb

@@ -0,0 +1,88 @@
+# frozen_string_literal: true
+
+module MCP
+  class Client
+    class HTTP
+      attr_reader :url
+
+      def initialize(url:, headers: {})
+        @url = url
+        @headers = headers
+      end
+
+      def send_request(request:)
+        method = request[:method] || request["method"]
+        params = request[:params] || request["params"]
+
+        client.post("", request).body
+      rescue Faraday::BadRequestError => e
+        raise RequestHandlerError.new(
+          "The #{method} request is invalid",
+          { method:, params: },
+          error_type: :bad_request,
+          original_error: e,
+        )
+      rescue Faraday::UnauthorizedError => e
+        raise RequestHandlerError.new(
+          "You are unauthorized to make #{method} requests",
+          { method:, params: },
+          error_type: :unauthorized,
+          original_error: e,
+        )
+      rescue Faraday::ForbiddenError => e
+        raise RequestHandlerError.new(
+          "You are forbidden to make #{method} requests",
+          { method:, params: },
+          error_type: :forbidden,
+          original_error: e,
+        )
+      rescue Faraday::ResourceNotFound => e
+        raise RequestHandlerError.new(
+          "The #{method} request is not found",
+          { method:, params: },
+          error_type: :not_found,
+          original_error: e,
+        )
+      rescue Faraday::UnprocessableEntityError => e
+        raise RequestHandlerError.new(
+          "The #{method} request is unprocessable",
+          { method:, params: },
+          error_type: :unprocessable_entity,
+          original_error: e,
+        )
+      rescue Faraday::Error => e # Catch-all
+        raise RequestHandlerError.new(
+          "Internal error handling #{method} request",
+          { method:, params: },
+          error_type: :internal_error,
+          original_error: e,
+        )
+      end
+
+      private
+
+      attr_reader :headers
+
+      def client
+        require_faraday!
+        @client ||= Faraday.new(url) do |faraday|
+          faraday.request(:json)
+          faraday.response(:json)
+          faraday.response(:raise_error)
+
+          headers.each do |key, value|
+            faraday.headers[key] = value
+          end
+        end
+      end
+
+      def require_faraday!
+        require "faraday"
+      rescue LoadError
+        raise LoadError, "The 'faraday' gem is required to use the MCP client HTTP transport. " \
+          "Add it to your Gemfile: gem 'faraday', '>= 2.0'" \
+          "See https://rubygems.org/gems/faraday for more details."
+      end
+    end
+  end
+end