Merge pull request #423 from koic/sep_2243_mcp_method_name_headers
Send SEP-2243 `Mcp-Method` and `Mcp-Name` headers per MCP specification
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Koichi ITO
GitHub
commit
0694e386db
2 changed files with 268 additions and 1 deletions
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@ -16,6 +16,8 @@ module MCP
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ACCEPT_HEADER = "application/json, text/event-stream"
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SESSION_ID_HEADER = "Mcp-Session-Id"
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PROTOCOL_VERSION_HEADER = "MCP-Protocol-Version"
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METHOD_HEADER = "Mcp-Method"
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NAME_HEADER = "Mcp-Name"
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# Raised when an `oauth:` provider is paired with an MCP URL that is neither HTTPS nor
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# a loopback `http://` URL, since a bearer token sent over plain HTTP to a remote host
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@ -198,7 +200,7 @@ module MCP
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begin
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yield if block_given?
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response = client.post("", request, session_headers)
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response = client.post("", request, session_headers.merge(request_metadata_headers(method, params)))
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body = parse_response_body(response, method, params)
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capture_session_info(method, response, body)
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@ -368,6 +370,39 @@ module MCP
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request_headers
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end
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# Per SEP-2243, mirror the JSON-RPC method and target name/uri into HTTP headers so intermediaries
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# can route and inspect requests without parsing the body. `Mcp-Name` comes from `params.name`
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# (tools, prompts) or, when absent, `params.uri` (resources).
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#
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# https://modelcontextprotocol.io/specification/draft/basic/transports/streamable-http#request-metadata
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def request_metadata_headers(method, params)
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return {} unless method
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metadata_headers = { METHOD_HEADER => method }
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if params.is_a?(Hash)
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name = params[:name] || params["name"]
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name = params[:uri] || params["uri"] unless name.is_a?(String)
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metadata_headers[NAME_HEADER] = encode_header_value(name) if name.is_a?(String)
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end
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metadata_headers
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end
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# A header value that is not safe to transmit as-is - non-ASCII, control characters (including CR/LF,
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# which would otherwise allow header injection), or significant leading/trailing whitespace - is wrapped as
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# `=?base64?<base64>?=`. Safe ASCII values are sent unchanged.
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def encode_header_value(value)
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return value if safe_header_value?(value)
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"=?base64?#{[value].pack("m0")}?="
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end
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def safe_header_value?(value)
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value.bytes.all? { |byte| byte.between?(0x20, 0x7e) } &&
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(value.empty? || (!value.start_with?(" ", "\t") && !value.end_with?(" ", "\t"))) &&
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!(value.start_with?("=?base64?") && value.end_with?("?="))
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end
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# Drives the OAuth orchestrator on a 401 from the MCP endpoint.
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# The `WWW-Authenticate` header (when present) supplies the `resource_metadata`
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# URL and an optional `scope` challenge per RFC 9728 Section 5.1.
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@ -123,6 +123,238 @@ module MCP
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custom_client.send_request(request: request)
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end
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def test_mcp_method_and_name_headers_for_tools_call
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request = {
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jsonrpc: "2.0",
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id: "test_id",
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method: "tools/call",
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params: { name: "get_weather", arguments: { city: "Tokyo" } },
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}
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stub_request(:post, url).with(
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headers: { "Mcp-Method" => "tools/call", "Mcp-Name" => "get_weather" },
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).to_return(
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status: 200,
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headers: { "Content-Type" => "application/json" },
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body: { result: {} }.to_json,
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)
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client.send_request(request: request)
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end
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def test_mcp_name_header_falls_back_to_uri_for_resources_read
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request = {
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jsonrpc: "2.0",
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id: "test_id",
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method: "resources/read",
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params: { uri: "file:///README.md" },
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}
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stub_request(:post, url).with(
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headers: { "Mcp-Method" => "resources/read", "Mcp-Name" => "file:///README.md" },
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).to_return(
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status: 200,
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headers: { "Content-Type" => "application/json" },
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body: { result: {} }.to_json,
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)
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client.send_request(request: request)
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end
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def test_mcp_method_and_name_headers_for_prompts_get
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request = {
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jsonrpc: "2.0",
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id: "test_id",
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method: "prompts/get",
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params: { name: "greeting" },
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}
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stub_request(:post, url).with(
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headers: { "Mcp-Method" => "prompts/get", "Mcp-Name" => "greeting" },
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).to_return(
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status: 200,
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headers: { "Content-Type" => "application/json" },
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body: { result: {} }.to_json,
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)
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client.send_request(request: request)
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end
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def test_mcp_method_header_without_name_when_params_lack_name_and_uri
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request = {
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jsonrpc: "2.0",
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id: "test_id",
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method: "tools/list",
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}
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stub_request(:post, url).with(
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headers: { "Mcp-Method" => "tools/list" },
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) do |req|
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!req.headers.key?("Mcp-Name")
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end.to_return(
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status: 200,
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headers: { "Content-Type" => "application/json" },
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body: { result: { tools: [] } }.to_json,
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)
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client.send_request(request: request)
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end
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def test_mcp_name_header_is_base64_encoded_when_unsafe
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request = {
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jsonrpc: "2.0",
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id: "test_id",
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method: "tools/call",
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params: { name: "café" },
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}
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stub_request(:post, url).with(
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headers: { "Mcp-Method" => "tools/call", "Mcp-Name" => "=?base64?Y2Fmw6k=?=" },
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).to_return(
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status: 200,
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headers: { "Content-Type" => "application/json" },
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body: { result: {} }.to_json,
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)
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client.send_request(request: request)
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end
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def test_mcp_method_header_for_notification_without_id
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request = {
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jsonrpc: "2.0",
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method: "notifications/initialized",
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}
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stub_request(:post, url).with(
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headers: { "Mcp-Method" => "notifications/initialized" },
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) do |req|
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!req.headers.key?("Mcp-Name")
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end.to_return(
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status: 202,
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headers: { "Content-Type" => "application/json" },
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body: "",
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)
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client.send_request(request: request)
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end
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def test_mcp_method_header_for_initialize_without_params
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request = {
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jsonrpc: "2.0",
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id: "test_id",
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method: "initialize",
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}
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stub_request(:post, url).with(
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headers: { "Mcp-Method" => "initialize" },
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) do |req|
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!req.headers.key?("Mcp-Name")
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end.to_return(
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status: 200,
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headers: { "Content-Type" => "application/json" },
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body: { result: {} }.to_json,
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)
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client.send_request(request: request)
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end
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def test_mcp_name_header_with_string_keyed_params
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request = {
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"jsonrpc" => "2.0",
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"id" => "test_id",
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"method" => "tools/call",
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"params" => { "name" => "get_weather" },
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}
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stub_request(:post, url).with(
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headers: { "Mcp-Method" => "tools/call", "Mcp-Name" => "get_weather" },
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).to_return(
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status: 200,
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headers: { "Content-Type" => "application/json" },
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body: { result: {} }.to_json,
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)
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client.send_request(request: request)
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end
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def test_mcp_name_header_is_base64_encoded_when_value_has_surrounding_whitespace
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request = {
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jsonrpc: "2.0",
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id: "test_id",
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method: "tools/call",
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params: { name: " padded " },
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}
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stub_request(:post, url).with(
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headers: { "Mcp-Method" => "tools/call", "Mcp-Name" => "=?base64?IHBhZGRlZCA=?=" },
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).to_return(
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status: 200,
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headers: { "Content-Type" => "application/json" },
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body: { result: {} }.to_json,
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)
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client.send_request(request: request)
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end
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def test_mcp_name_header_is_base64_encoded_when_value_has_crlf
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request = {
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jsonrpc: "2.0",
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id: "test_id",
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method: "tools/call",
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params: { name: "evil\r\nX-Injected: 1" },
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}
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stub_request(:post, url).with(
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headers: { "Mcp-Method" => "tools/call", "Mcp-Name" => "=?base64?ZXZpbA0KWC1JbmplY3RlZDogMQ==?=" },
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) do |req|
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!req.headers.key?("X-Injected")
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end.to_return(
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status: 200,
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headers: { "Content-Type" => "application/json" },
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body: { result: {} }.to_json,
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)
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client.send_request(request: request)
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end
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def test_mcp_name_header_re_encodes_value_matching_base64_sentinel
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request = {
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jsonrpc: "2.0",
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id: "test_id",
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method: "tools/call",
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params: { name: "=?base64?literal?=" },
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}
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stub_request(:post, url).with(
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headers: { "Mcp-Method" => "tools/call", "Mcp-Name" => "=?base64?PT9iYXNlNjQ/bGl0ZXJhbD89?=" },
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).to_return(
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status: 200,
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headers: { "Content-Type" => "application/json" },
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body: { result: {} }.to_json,
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)
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client.send_request(request: request)
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end
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def test_mcp_method_header_without_name_for_non_hash_params
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request = {
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jsonrpc: "2.0",
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id: "test_id",
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method: "custom/method",
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params: ["positional"],
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}
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stub_request(:post, url).with(headers: { "Mcp-Method" => "custom/method" }) do |req|
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!req.headers.key?("Mcp-Name")
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end.to_return(
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status: 200,
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headers: { "Content-Type" => "application/json" },
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body: { result: {} }.to_json,
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)
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client.send_request(request: request)
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end
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def test_send_request_returns_faraday_response
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request = {
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jsonrpc: "2.0",
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