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mcp: update return meta in DiscoverResult (SEP-2575) (#1097)

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This PR implements the latest changes introduced by
https://github.com/modelcontextprotocol/modelcontextprotocol/pull/3002
This commit is contained in:
Guglielmo Colombo 2026-07-16 16:10:12 +02:00 • committed by GitHub
commit 5cb8339210
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2 changed files with 210 additions and 68 deletions
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38
docs/protocol.md
View file

@ -4,6 +4,7 @@
1. [Lifecycle](#lifecycle)
1. [Discovery (`server/discover`)](#discovery-(server/discover))
1. [Per-request `_meta` keys](#per-request-meta-keys)
1. [Per-response `_meta` keys](#per-response-meta-keys)
1. [Subscriptions (`subscriptions/listen`)](#subscriptions-(subscriptions/listen))
1. [Transports](#transports)
1. [Stdio Transport](#stdio-transport)
@ -40,8 +41,10 @@ transparently based on the negotiated protocol version:
- A **stateless** model introduced in `2026-07-28` by
[SEP-2575](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2575),
in which there is no `initialize`/`notifications/initialized` handshake, and
each request carries its protocol version, client identity, and client
capabilities in `_meta`.
each request carries its protocol version and client capabilities in
`_meta`. Clients SHOULD also include their identity (`clientInfo`) on every
request, and servers SHOULD include their identity (`serverInfo`) on every
response.
In both models, the SDK exposes the same API:
@ -130,17 +133,28 @@ When the negotiated protocol version is `2026-07-28` or later, every request
carries these keys inside its `_meta` map (constants live in
[`mcp/protocol.go`](https://pkg.go.dev/github.com/modelcontextprotocol/go-sdk/mcp#pkg-constants)):
| Constant | Wire key | Type |
|---|---|---|
| `MetaKeyProtocolVersion` | `io.modelcontextprotocol/protocolVersion` | `string` |
| `MetaKeyClientInfo` | `io.modelcontextprotocol/clientInfo` | `*Implementation` |
| `MetaKeyClientCapabilities` | `io.modelcontextprotocol/clientCapabilities` | `*ClientCapabilities` |
| `MetaKeyLogLevel` | `io.modelcontextprotocol/logLevel` | `LoggingLevel` (deprecated by SEP-2577) |
| Constant | Wire key | Type | Required |
|---|---|---|---|
| `MetaKeyProtocolVersion` | `io.modelcontextprotocol/protocolVersion` | `string` | Yes |
| `MetaKeyClientCapabilities` | `io.modelcontextprotocol/clientCapabilities` | `*ClientCapabilities` | Yes |
| `MetaKeyClientInfo` | `io.modelcontextprotocol/clientInfo` | `*Implementation` | No |
| `MetaKeyLogLevel` | `io.modelcontextprotocol/logLevel` | `LoggingLevel` (deprecated by SEP-2577) | No |
The client populates these keys automatically on every outgoing request.
Server-side handlers can read them
through `ServerRequest[P].ProtocolVersion()`, `ServerRequest[P].ClientInfo()`,
and `ServerRequest[P].ClientCapabilities()`.
The client populates the required keys automatically on every outgoing
request, and populates `clientInfo` when configured with an `*Implementation`
(the default). Server-side handlers can read them through
`ServerRequest[P].ProtocolVersion()`, `ServerRequest[P].ClientInfo()`, and
`ServerRequest[P].ClientCapabilities()`.
### Per-response `_meta` keys
Under the same protocol version, servers SHOULD identify themselves on every
response. The SDK populates this
key automatically on every outgoing response:
| Constant | Wire key | Type | Required |
|---|---|---|---|
| `MetaKeyServerInfo` | `io.modelcontextprotocol/serverInfo` | `*Implementation` | No |
### Subscriptions (`subscriptions/listen`)

2
docs/troubleshooting.md
View file

@ -50,7 +50,7 @@ func ExampleLoggingTransport() {
}
// Output:
// read: {"jsonrpc":"2.0","id":1,"result":{"resultType":"complete","ttlMs":0,"cacheScope":"public","supportedVersions":["2026-07-28","2025-11-25","2025-06-18","2025-03-26","2024-11-05"],"capabilities":{"logging":{}},"serverInfo":{"name":"server","version":"v0.0.1"}}}
// read: {"jsonrpc":"2.0","id":1,"result":{"resultType":"complete","_meta":{"io.modelcontextprotocol/serverInfo":{"name":"server","version":"v0.0.1"}},"ttlMs":0,"cacheScope":"public","supportedVersions":["2026-07-28","2025-11-25","2025-06-18","2025-03-26","2024-11-05"],"capabilities":{"logging":{}}}}
// write: {"jsonrpc":"2.0","id":1,"method":"server/discover","params":{"_meta":{"io.modelcontextprotocol/clientCapabilities":{"roots":{"listChanged":true}},"io.modelcontextprotocol/clientInfo":{"name":"client","version":"v0.0.1"},"io.modelcontextprotocol/protocolVersion":"2026-07-28"}}}
}
```