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Default to the latest stable protocol version

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When starting an MCP server in Claude Code with `protocol_version` set to `DRAFT-2025-v3`,
it fails with the following error:

```console
2025-12-04T02:58:01.548Z [DEBUG] MCP server "example": Connection failed after 2093ms: Server's protocol version is not supported: DRAFT-2025-v3
2025-12-04T02:58:01.548Z [ERROR] MCP server "example" Connection failed: Server's protocol version is not supported: DRAFT-2025-v3
```

This PR changes the default behavior so that if `protocol_version` is not specified,
it uses the latest stable protocol version instead of the draft version.

This PR also updates the README to note that the latest stable protocol version includes
new features from the draft version.
This commit is contained in:
Koichi ITO 2025-12-04 03:15:02 +09:00
commit c786a14f61
5 changed files with 13 additions and 13 deletions
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3
README.md
View file

@ -349,7 +349,8 @@ configuration = MCP::Configuration.new(protocol_version: "2024-11-05")
MCP::Server.new(name: "test_server", configuration: configuration)
```
If no protocol version is specified, the [Draft version](https://modelcontextprotocol.io/specification/draft) will be applied by default.
If no protocol version is specified, the latest stable version will be applied by default.
The latest stable version includes new features from the [draft version](https://modelcontextprotocol.io/specification/draft).
This will make all new server instances use the specified protocol version instead of the default version. The protocol version can be reset to the default by setting it to `nil`:

8
lib/mcp/configuration.rb
View file

@ -2,10 +2,8 @@
module MCP
class Configuration
# DRAFT-2025-v3 is the latest draft protocol version:
# https://github.com/modelcontextprotocol/modelcontextprotocol/blob/14ec41c/schema/draft/schema.ts#L15
DRAFT_PROTOCOL_VERSION = "DRAFT-2025-v3"
SUPPORTED_STABLE_PROTOCOL_VERSIONS = ["2025-06-18", "2025-03-26", "2024-11-05"]
LATEST_STABLE_PROTOCOL_VERSION = "2025-06-18"
SUPPORTED_STABLE_PROTOCOL_VERSIONS = [LATEST_STABLE_PROTOCOL_VERSION, "2025-03-26", "2024-11-05"]
attr_writer :exception_reporter, :instrumentation_callback
@ -35,7 +33,7 @@ module MCP
end
def protocol_version
@protocol_version || DRAFT_PROTOCOL_VERSION
@protocol_version || LATEST_STABLE_PROTOCOL_VERSION
end
def protocol_version?

9
test/mcp/configuration_test.rb
View file

@ -38,18 +38,19 @@ module MCP
# https://github.com/modelcontextprotocol/modelcontextprotocol/blob/14ec41c/schema/draft/schema.ts#L15
test "initializes with default protocol version" do
config = Configuration.new
assert_equal Configuration::DRAFT_PROTOCOL_VERSION, config.protocol_version
assert_equal Configuration::LATEST_STABLE_PROTOCOL_VERSION, config.protocol_version
end
test "uses the draft protocol version when protocol_version is set to nil" do
config = Configuration.new(protocol_version: nil)
assert_equal Configuration::DRAFT_PROTOCOL_VERSION, config.protocol_version
assert_equal Configuration::LATEST_STABLE_PROTOCOL_VERSION, config.protocol_version
end
test "raises ArgumentError when setting the draft protocol version" do
exception = assert_raises(ArgumentError) do
# To use the draft version externally, either omit `protocol_version` or set it to nil.
Configuration.new(protocol_version: Configuration::DRAFT_PROTOCOL_VERSION)
# DRAFT-2025-v3 is the latest draft protocol version:
# https://github.com/modelcontextprotocol/modelcontextprotocol/blob/14ec41c/schema/draft/schema.ts#L15
Configuration.new(protocol_version: "DRAFT-2025-v3")
end
assert_equal("protocol_version must be 2025-06-18, 2025-03-26, or 2024-11-05", exception.message)

2
test/mcp/server/transports/streamable_http_transport_test.rb
View file

@ -81,7 +81,7 @@ module MCP
body = JSON.parse(response[2][0])
assert_equal "2.0", body["jsonrpc"]
assert_equal "123", body["id"]
assert_equal Configuration::DRAFT_PROTOCOL_VERSION, body["result"]["protocolVersion"]
assert_equal Configuration::LATEST_STABLE_PROTOCOL_VERSION, body["result"]["protocolVersion"]
end
test "handles GET request with valid session ID" do

4
test/mcp/server_test.rb
View file

@ -133,7 +133,7 @@ module MCP
jsonrpc: "2.0",
id: 1,
result: {
protocolVersion: Configuration::DRAFT_PROTOCOL_VERSION,
protocolVersion: Configuration::LATEST_STABLE_PROTOCOL_VERSION,
capabilities: {
prompts: { listChanged: true },
resources: { listChanged: true },
@ -776,7 +776,7 @@ module MCP
}
response = @server.handle(request)
assert_equal Configuration::DRAFT_PROTOCOL_VERSION, response[:result][:protocolVersion]
assert_equal Configuration::LATEST_STABLE_PROTOCOL_VERSION, response[:result][:protocolVersion]
end
test "server response does not include title when not configured" do