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Merge pull request #352 from koic/document_initialize_protocol_version_authority

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Document `initialize` body `protocolVersion` is authoritative on Streamable HTTP
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Koichi ITO 2026-05-18 09:23:22 +09:00 • committed by GitHub
commit 993dbf514e
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3
lib/mcp/server/transports/streamable_http_transport.rb
View file

@ -342,6 +342,9 @@ module MCP
body = parse_request_body(body_string)
return body if parse_error_tuple?(body)
# The `MCP-Protocol-Version` header is only meaningful after negotiation, so on `initialize`
# the JSON-RPC body `params.protocolVersion` is authoritative and the header (if any) is ignored.
# This matches the TypeScript and Python SDKs.
unless initialize_request?(body)
return missing_session_id_response if !@stateless && !session_id

52
test/mcp/server/transports/streamable_http_transport_test.rb
View file

@ -1400,6 +1400,58 @@ module MCP
assert_equal 200, response[0]
end
test "POST initialize request negotiates body protocolVersion when header is an older supported version" do
older_version = "2025-06-18"
assert_includes Configuration::SUPPORTED_STABLE_PROTOCOL_VERSIONS, older_version
refute_equal Configuration::LATEST_STABLE_PROTOCOL_VERSION, older_version
request = create_rack_request(
"POST",
"/",
{
"CONTENT_TYPE" => "application/json",
"HTTP_MCP_PROTOCOL_VERSION" => older_version,
},
{
jsonrpc: "2.0",
method: "initialize",
id: "init",
params: { protocolVersion: Configuration::LATEST_STABLE_PROTOCOL_VERSION },
}.to_json,
)
response = @transport.handle_request(request)
assert_equal 200, response[0]
body = JSON.parse(response[2][0])
assert_equal Configuration::LATEST_STABLE_PROTOCOL_VERSION, body["result"]["protocolVersion"]
end
test "POST initialize request negotiates body protocolVersion when header is a newer supported version" do
older_version = "2025-06-18"
assert_includes Configuration::SUPPORTED_STABLE_PROTOCOL_VERSIONS, older_version
refute_equal Configuration::LATEST_STABLE_PROTOCOL_VERSION, older_version
request = create_rack_request(
"POST",
"/",
{
"CONTENT_TYPE" => "application/json",
"HTTP_MCP_PROTOCOL_VERSION" => Configuration::LATEST_STABLE_PROTOCOL_VERSION,
},
{
jsonrpc: "2.0",
method: "initialize",
id: "init",
params: { protocolVersion: older_version },
}.to_json,
)
response = @transport.handle_request(request)
assert_equal 200, response[0]
body = JSON.parse(response[2][0])
assert_equal older_version, body["result"]["protocolVersion"]
end
test "POST request with unsupported MCP-Protocol-Version returns 400" do
init_request = create_rack_request(
"POST",