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Implement client protocol version negotiation in server initialization (#107)

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* Implement client version negotiation in server initialization

* Add test coverage for version negotiation

* Make Version.supported and Version.negotiate() APIs internal to not create new surface area
This commit is contained in:
Mattt 2025-05-07 05:58:11 -07:00 • committed by GitHub
commit 720a8102e9
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2 changed files with 80 additions and 5 deletions
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21
Sources/MCP/Base/Versioning.swift
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@ -6,6 +6,23 @@ import Foundation
///
/// - SeeAlso: https://spec.modelcontextprotocol.io/specification/2025-03-26/
public enum Version {
/// The current protocol version.
public static let latest = "2025-03-26"
/// All protocol versions supported by this implementation, ordered from newest to oldest.
static let supported: Set<String> = [
"2025-03-26",
"2024-11-05",
]
/// The latest protocol version supported by this implementation.
public static let latest = supported.max()!
/// Negotiates the protocol version based on the client's request and server's capabilities.
/// - Parameter clientRequestedVersion: The protocol version requested by the client.
/// - Returns: The negotiated protocol version. If the client's requested version is supported,
/// that version is returned. Otherwise, the server's latest supported version is returned.
static func negotiate(clientRequestedVersion: String) -> String {
if supported.contains(clientRequestedVersion) {
return clientRequestedVersion
}
return latest
}
}

11
Sources/MCP/Server/Server.swift
View file

@ -486,15 +486,20 @@ public actor Server {
try await hook(params.clientInfo, params.capabilities)
}
// Set initial state
// Perform version negotiation
let clientRequestedVersion = params.protocolVersion
let negotiatedProtocolVersion = Version.negotiate(
clientRequestedVersion: clientRequestedVersion)
// Set initial state with the negotiated protocol version
await self.setInitialState(
clientInfo: params.clientInfo,
clientCapabilities: params.capabilities,
protocolVersion: params.protocolVersion
protocolVersion: negotiatedProtocolVersion
)
return Initialize.Result(
protocolVersion: Version.latest,
protocolVersion: negotiatedProtocolVersion,
capabilities: await self.capabilities,
serverInfo: self.serverInfo,
instructions: nil