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Able to catch exceptions from one transport and fall back to the other

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This commit is contained in:
Glen Maddern 2025-04-17 16:04:50 +10:00
parent 0bf84d5d22
commit 14109a309f
5 changed files with 104 additions and 51 deletions
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5
package.json
View file

@ -28,11 +28,11 @@
"check": "prettier --check . && tsc"
},
"dependencies": {
"@modelcontextprotocol/sdk": "link:/Users/glen/src/hax/mcp/typescript-sdk",
"express": "^4.21.2",
"open": "^10.1.0"
},
"devDependencies": {
"@modelcontextprotocol/sdk": "link:/Users/glen/src/hax/mcp/typescript-sdk",
"@types/express": "^5.0.0",
"@types/node": "^22.13.10",
"@types/react": "^19.0.12",
@ -54,7 +54,8 @@
"clean": true,
"outDir": "dist",
"external": [
"react"
"react",
"@modelcontextprotocol/sdk"
]
}
}

6
pnpm-lock.yaml generated
View file

@ -8,6 +8,9 @@ importers:
.:
dependencies:
'@modelcontextprotocol/sdk':
specifier: link:/Users/glen/src/hax/mcp/typescript-sdk
version: link:../../hax/mcp/typescript-sdk
express:
specifier: ^4.21.2
version: 4.21.2
@ -15,9 +18,6 @@ importers:
specifier: ^10.1.0
version: 10.1.0
devDependencies:
'@modelcontextprotocol/sdk':
specifier: link:/Users/glen/src/hax/mcp/typescript-sdk
version: link:../../hax/mcp/typescript-sdk
'@types/express':
specifier: ^5.0.0
version: 5.0.0

18
src/client.ts
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@ -70,7 +70,15 @@ async function runClient(
try {
// Connect to remote server with authentication
const transport = await connectToRemoteServer(serverUrl, authProvider, headers, waitForAuthCode, skipBrowserAuth, transportStrategy)
const transport = await connectToRemoteServer(
client,
serverUrl,
authProvider,
headers,
waitForAuthCode,
skipBrowserAuth,
transportStrategy,
)
// Set up message and error handlers
transport.onmessage = (message) => {
@ -94,9 +102,6 @@ async function runClient(
}
setupSignalHandlers(cleanup)
// Connect the client
log('Connecting client...')
await client.connect(transport)
log('Connected successfully!')
try {
@ -117,7 +122,10 @@ async function runClient(
log('Error requesting resources list:', e)
}
log('Listening for messages. Press Ctrl+C to exit.')
// log('Listening for messages. Press Ctrl+C to exit.')
log('Exiting OK...')
server.close()
process.exit(0)
} catch (error) {
log('Fatal error:', error)
server.close()

104
src/lib/utils.ts
View file

@ -1,4 +1,5 @@
import { OAuthClientProvider, UnauthorizedError } from '@modelcontextprotocol/sdk/client/auth.js'
import { Client } from '@modelcontextprotocol/sdk/client/index.js'
import { SSEClientTransport } from '@modelcontextprotocol/sdk/client/sse.js'
import { StreamableHTTPClientTransport } from '@modelcontextprotocol/sdk/client/streamableHttp.js'
import { Transport } from '@modelcontextprotocol/sdk/shared/transport.js'
@ -74,6 +75,7 @@ export function mcpProxy({ transportToClient, transportToServer }: { transportTo
/**
* Creates and connects to a remote server with OAuth authentication
* @param client The client to connect with
* @param serverUrl The URL of the remote server
* @param authProvider The OAuth client provider
* @param headers Additional headers to send with the request
@ -84,6 +86,7 @@ export function mcpProxy({ transportToClient, transportToServer }: { transportTo
* @returns The connected transport
*/
export async function connectToRemoteServer(
client: Client,
serverUrl: string,
authProvider: OAuthClientProvider,
headers: Record<string, string>,
@ -112,54 +115,68 @@ export async function connectToRemoteServer(
},
}
// Choose transport based on user strategy and recursion history
let transport;
let shouldAttemptFallback = false;
// If we've already tried falling back once, throw an error
if (recursionReasons.has(REASON_TRANSPORT_FALLBACK)) {
const errorMessage = `Already attempted transport fallback. Giving up.`;
log(errorMessage);
throw new Error(errorMessage);
}
log(`Using transport strategy: ${transportStrategy}`);
log(`Using transport strategy: ${transportStrategy}`)
// Determine if we should attempt to fallback on error
shouldAttemptFallback = transportStrategy === 'http-first' || transportStrategy === 'sse-first';
// Choose transport based on user strategy and recursion history
const shouldAttemptFallback = transportStrategy === 'http-first' || transportStrategy === 'sse-first'
// Create transport instance based on the strategy
if (transportStrategy === 'sse-only' || transportStrategy === 'sse-first') {
transport = new SSEClientTransport(url, {
authProvider,
requestInit: { headers },
eventSourceInit,
});
} else { // http-only or http-first
transport = new StreamableHTTPClientTransport(url, {
sessionId: crypto.randomUUID(),
});
}
const sseTransport = transportStrategy === 'sse-only' || transportStrategy === 'sse-first'
const transport = sseTransport
? new SSEClientTransport(url, {
authProvider,
requestInit: { headers },
eventSourceInit,
})
: new StreamableHTTPClientTransport(url, {
authProvider,
requestInit: { headers },
})
try {
await transport.start()
await client.connect(transport)
log(`Connected to remote server using ${transport.constructor.name}`)
if (!sseTransport) {
console.log({ serverCapabilities: await client.getServerCapabilities() })
}
return transport
} catch (error) {
console.log('DID I CATCH OR WHAT?')
// Check if it's a protocol error and we should attempt fallback
if (error instanceof Error &&
shouldAttemptFallback &&
(error.message.includes('405') ||
error.message.includes('Method Not Allowed') ||
error.message.toLowerCase().includes('protocol'))) {
if (
error instanceof Error &&
shouldAttemptFallback &&
(sseTransport
? error.message.includes('405') || error.message.includes('Method Not Allowed')
: error.message.includes('404') || error.message.includes('Not Found'))
) {
log(`Received error: ${error.message}`)
// If we've already tried falling back once, throw an error
if (recursionReasons.has(REASON_TRANSPORT_FALLBACK)) {
const errorMessage = `Already attempted transport fallback. Giving up.`
log(errorMessage)
throw new Error(errorMessage)
}
log(`Recursively reconnecting for reason: ${REASON_TRANSPORT_FALLBACK}`)
// Add to recursion reasons set
recursionReasons.add(REASON_TRANSPORT_FALLBACK)
// Recursively call connectToRemoteServer with the updated recursion tracking
return connectToRemoteServer(serverUrl, authProvider, headers, waitForAuthCode, skipBrowserAuth, transportStrategy, recursionReasons)
return connectToRemoteServer(
client,
serverUrl,
authProvider,
headers,
waitForAuthCode,
skipBrowserAuth,
sseTransport ? 'http-only' : 'sse-only',
recursionReasons,
)
} else if (error instanceof UnauthorizedError || (error instanceof Error && error.message.includes('Unauthorized'))) {
if (skipBrowserAuth) {
log('Authentication required but skipping browser auth - using shared auth')
@ -179,13 +196,22 @@ export async function connectToRemoteServer(
log(errorMessage)
throw new Error(errorMessage)
}
// Track this reason for recursion
recursionReasons.add(REASON_AUTH_NEEDED)
log(`Recursively reconnecting for reason: ${REASON_AUTH_NEEDED}`)
// Recursively call connectToRemoteServer with the updated recursion tracking
return connectToRemoteServer(serverUrl, authProvider, headers, waitForAuthCode, skipBrowserAuth, transportStrategy, recursionReasons)
return connectToRemoteServer(
client,
serverUrl,
authProvider,
headers,
waitForAuthCode,
skipBrowserAuth,
transportStrategy,
recursionReasons,
)
} catch (authError) {
log('Authorization error:', authError)
throw authError
@ -356,7 +382,7 @@ export async function parseCommandLineArgs(args: string[], defaultPort: number,
const serverUrl = args[0]
const specifiedPort = args[1] ? parseInt(args[1]) : undefined
const allowHttp = args.includes('--allow-http')
// Parse transport strategy
let transportStrategy: TransportStrategy = 'http-first' // Default
const transportIndex = args.indexOf('--transport')

22
src/proxy.ts
View file

@ -11,9 +11,18 @@
import { EventEmitter } from 'events'
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js'
import { connectToRemoteServer, log, mcpProxy, parseCommandLineArgs, setupSignalHandlers, getServerUrlHash } from './lib/utils'
import {
connectToRemoteServer,
log,
mcpProxy,
parseCommandLineArgs,
setupSignalHandlers,
getServerUrlHash,
MCP_REMOTE_VERSION,
} from './lib/utils'
import { NodeOAuthClientProvider } from './lib/node-oauth-client-provider'
import { coordinateAuth } from './lib/coordination'
import { Client } from '@modelcontextprotocol/sdk/client/index.js'
/**
* Main function to run the proxy
@ -47,8 +56,17 @@ async function runProxy(serverUrl: string, callbackPort: number, headers: Record
const localTransport = new StdioServerTransport()
try {
const client = new Client(
{
name: 'mcp-remote',
version: MCP_REMOTE_VERSION,
},
{
capabilities: {},
},
)
// Connect to remote server with authentication
const remoteTransport = await connectToRemoteServer(serverUrl, authProvider, headers, waitForAuthCode, skipBrowserAuth)
const remoteTransport = await connectToRemoteServer(client, serverUrl, authProvider, headers, waitForAuthCode, skipBrowserAuth)
// Set up bidirectional proxy between local and remote transports
mcpProxy({