make faraday optional

Author: jcat4

Gemfile

@@ -25,4 +25,5 @@ gem "sorbet-static-and-runtime"
 
 group :test do
   gem "webmock"
+  gem "faraday", ">= 2.0"
 end

README.md

@@ -10,6 +10,21 @@ Add this line to your application's Gemfile:
 gem 'mcp'
 ```
 
+### Optional Dependencies
+
+The MCP gem has different dependency requirements depending on your use case:
+
+**For Server-only usage:**
+```ruby
+gem 'mcp'
+```
+
+**For client HTTP transport usage:**
+```ruby
+gem 'mcp'
+gem 'faraday', '>= 2.0'
+```
+
 And then execute:
 
 ```console
@@ -220,6 +235,8 @@ $ ruby examples/stdio_server.rb
 
 The `ModelContextProtocol::Client` module provides client implementations for interacting with MCP servers. Currently, it supports HTTP transport for making JSON-RPC requests to MCP servers.
 
+**Note:** The client HTTP transport requires the `faraday` gem. Add `gem 'faraday', '>= 2.0'` to your Gemfile if you plan to use the client HTTP transport functionality.
+
 ### HTTP Client
 
 The `ModelContextProtocol::Client::Http` class provides a simple HTTP client for interacting with MCP servers:

lib/mcp/client/http.rb

@@ -33,6 +33,7 @@ def call_tool(tool:, input:)
       attr_reader :headers
 
       def client
+        require_faraday!
         @client ||= Faraday.new(url) do |faraday|
           faraday.request(:json)
           faraday.response(:json)
@@ -44,6 +45,13 @@ def client
         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'"
+      end
+
       def make_request(method:, params: nil)
         client.post(
           "",

mcp.gemspec

@@ -27,7 +27,8 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
-  spec.add_dependency("faraday", ">= 2.0")
   spec.add_dependency("json_rpc_handler", "~> 0.1")
   spec.add_dependency("json-schema", ">= 4.1")
+
+  # Faraday is required for the client HTTP transport layer
 end

test/mcp/client/http_test.rb

@@ -23,6 +23,20 @@ def test_initialization_with_custom_version
         assert_equal(custom_version, client.version)
       end
 
+      def test_raises_load_error_when_faraday_not_available
+        client = Http.new(url: url)
+
+        # simulate Faraday not being available
+        Http.any_instance.stubs(:require).with("faraday").raises(LoadError, "cannot load such file -- faraday")
+
+        error = assert_raises(LoadError) do
+          client.send(:client) # Call the private method that triggers require_faraday!
+        end
+
+        assert_includes(error.message, "The 'faraday' gem is required to use the MCP client HTTP transport")
+        assert_includes(error.message, "Add it to your Gemfile: gem 'faraday', '>= 2.0'")
+      end
+
       def test_headers_are_added_to_the_request
         headers = { "Authorization" => "Bearer token" }
         client = Http.new(url: url, headers: headers)