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Restore negotiated protocol version on reconnection transport (#1591)

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Co-authored-by: Matt <77928207+mattzcarey@users.noreply.github.com>
Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com>
This commit is contained in:
bhosmer-ant 2026-03-23 10:58:13 -04:00 • committed by GitHub
commit 72fe68b266
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2 changed files with 103 additions and 1 deletions
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17
packages/client/src/client/client.ts
View file

@ -194,6 +194,7 @@ export type ClientOptions = ProtocolOptions & {
export class Client extends Protocol<ClientContext> {
private _serverCapabilities?: ServerCapabilities;
private _serverVersion?: Implementation;
private _negotiatedProtocolVersion?: string;
private _capabilities: ClientCapabilities;
private _instructions?: string;
private _jsonSchemaValidator: jsonSchemaValidator;
@ -470,8 +471,12 @@ export class Client extends Protocol<ClientContext> {
override async connect(transport: Transport, options?: RequestOptions): Promise<void> {
await super.connect(transport);
// When transport sessionId is already set this means we are trying to reconnect.
// In this case we don't need to initialize again.
// Restore the protocol version negotiated during the original initialize handshake
// so HTTP transports include the required mcp-protocol-version header, but skip re-init.
if (transport.sessionId !== undefined) {
if (this._negotiatedProtocolVersion !== undefined && transport.setProtocolVersion) {
transport.setProtocolVersion(this._negotiatedProtocolVersion);
}
return;
}
try {
@ -498,6 +503,7 @@ export class Client extends Protocol<ClientContext> {
this._serverCapabilities = result.capabilities;
this._serverVersion = result.serverInfo;
this._negotiatedProtocolVersion = result.protocolVersion;
// HTTP transports must set the protocol version in each header after initialization.
if (transport.setProtocolVersion) {
transport.setProtocolVersion(result.protocolVersion);
@ -535,6 +541,15 @@ export class Client extends Protocol<ClientContext> {
return this._serverVersion;
}
/**
* After initialization has completed, this will be populated with the protocol version negotiated
* during the initialize handshake. When manually reconstructing a transport for reconnection, pass this
* value to the new transport so it continues sending the required `mcp-protocol-version` header.
*/
getNegotiatedProtocolVersion(): string | undefined {
return this._negotiatedProtocolVersion;
}
/**
* After initialization has completed, this may be populated with information about the server's instructions.
*/

8
packages/client/src/client/streamableHttp.ts
View file

@ -118,6 +118,13 @@ export type StreamableHTTPClientTransportOptions = {
* When not provided and connecting to a server that supports session IDs, the server will generate a new session ID.
*/
sessionId?: string;
/**
* The MCP protocol version to include in the `mcp-protocol-version` header on all requests.
* When reconnecting with a preserved `sessionId`, set this to the version negotiated during the original
* handshake so the reconnected transport continues sending the required header.
*/
protocolVersion?: string;
};
/**
@ -155,6 +162,7 @@ export class StreamableHTTPClientTransport implements Transport {
this._fetch = opts?.fetch;
this._fetchWithInit = createFetchWithInit(opts?.fetch, opts?.requestInit);
this._sessionId = opts?.sessionId;
this._protocolVersion = opts?.protocolVersion;
this._reconnectionOptions = opts?.reconnectionOptions ?? DEFAULT_STREAMABLE_HTTP_RECONNECTION_OPTIONS;
}