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Add --protocol-version flag to cli-client example (#2406)

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Felix Weinberger 2026-07-02 13:12:49 +01:00 • committed by GitHub
commit eacf2e5dbe
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1 changed files with 92 additions and 29 deletions
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43
examples/cli-client/host/host.ts
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@ -10,7 +10,8 @@ import type {
Prompt,
Resource,
ResourceTemplateType,
Tool
Tool,
VersionNegotiationOptions
} from '@modelcontextprotocol/client';
import {
Client,
@ -18,6 +19,7 @@ import {
ProtocolError,
SdkError,
StreamableHTTPClientTransport,
SUPPORTED_PROTOCOL_VERSIONS,
UnauthorizedError
} from '@modelcontextprotocol/client';
import { StdioClientTransport } from '@modelcontextprotocol/client/stdio';
@ -61,10 +63,43 @@ export interface McpHostOptions {
roots?: string[];
/** Use the 2025 `initialize` handshake instead of probing for 2026-07-28. */
legacy?: boolean;
/**
* Negotiate exactly this protocol revision: a known 2025-era value runs the legacy
* handshake offering only that revision; anything else is pinned via the modern
* handshake, which fails loudly unless the server offers it.
*/
protocolVersion?: string;
/** Fixed loopback port for the OAuth callback (default: an OS-assigned free port). Useful over SSH port-forwarding. */
oauthCallbackPort?: number;
}
/** The version-negotiation slice of the SDK client options every connection this host makes shares. */
export interface VersionOptions {
versionNegotiation: VersionNegotiationOptions;
supportedProtocolVersions?: string[];
}
/**
* Map the era toggle and optional pinned revision onto the SDK's negotiation options.
* A known 2025-era revision runs the legacy handshake offering exactly that revision
* (the client rejects a server that answers with any other version); everything else
* becomes a modern pin, and the SDK's own typed error covers strings that are neither.
*/
export function resolveVersionOptions(legacy: boolean, protocolVersion?: string): VersionOptions {
if (protocolVersion === undefined) {
return { versionNegotiation: { mode: legacy ? 'legacy' : 'auto' } };
}
if (SUPPORTED_PROTOCOL_VERSIONS.includes(protocolVersion)) {
return { versionNegotiation: { mode: 'legacy' }, supportedProtocolVersions: [protocolVersion] };
}
if (legacy) {
throw new Error(
`--legacy conflicts with --protocol-version ${protocolVersion}: the 2025 handshake can only negotiate ${SUPPORTED_PROTOCOL_VERSIONS.join(', ')}`
);
}
return { versionNegotiation: { mode: { pin: protocolVersion } } };
}
function unwrapUnauthorized(error: unknown): UnauthorizedError | undefined {
if (error instanceof UnauthorizedError) return error;
// Under versionNegotiation 'auto', a connect-time 401 surfaces as
@ -94,7 +129,7 @@ function samplingContentToParts(content: CreateMessageRequest['params']['message
export class McpHost {
private readonly ui: HostUI;
private readonly provider: LLMProvider;
private readonly legacy: boolean;
private readonly versionOptions: VersionOptions;
private roots: string[];
private readonly watches: McpSubscription[] = [];
private readonly oauthCallbackPort?: number;
@ -103,7 +138,7 @@ export class McpHost {
constructor(options: McpHostOptions) {
this.ui = options.ui;
this.provider = options.provider;
this.legacy = options.legacy ?? false;
this.versionOptions = resolveVersionOptions(options.legacy ?? false, options.protocolVersion);
this.oauthCallbackPort = options.oauthCallbackPort;
this.roots = (options.roots ?? [process.cwd()]).map(root => path.resolve(root));
}
@ -309,7 +344,7 @@ export class McpHost {
private buildClient(name: string): Client {
const client = new Client(CLIENT_INFO, {
versionNegotiation: { mode: this.legacy ? 'legacy' : 'auto' },
...this.versionOptions,
capabilities: {
// Both elicitation modes are declared because the handler below implements both.
elicitation: { form: {}, url: {} },