modelcontextprotocol/use-mcp
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Falling back on CORS errors too

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This commit is contained in:
Glen Maddern 2025-05-07 16:01:29 +10:00
commit 3bf0627ca6
1 changed files with 12 additions and 10 deletions
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22
src/react/useMcp.ts
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@ -2,7 +2,7 @@
import { CallToolResultSchema, JSONRPCMessage, ListToolsResultSchema, Tool } from '@modelcontextprotocol/sdk/types.js'
import { useCallback, useEffect, useRef, useState } from 'react'
// Import both transport types
import { SSEClientTransport } from '@modelcontextprotocol/sdk/client/sse.js'
import { SSEClientTransport, SSEClientTransportOptions } from '@modelcontextprotocol/sdk/client/sse.js'
import { StreamableHTTPClientTransport } from '@modelcontextprotocol/sdk/client/streamableHttp.js' // Added
import { Client } from '@modelcontextprotocol/sdk/client/index.js'
import { auth, UnauthorizedError, OAuthClientProvider } from '@modelcontextprotocol/sdk/client/auth.js'
@ -181,7 +181,7 @@ export function useMcp(options: UseMcpOptions): UseMcpResult {
transportRef.current = null
}
const commonOptions = { authProvider: authProviderRef.current }
const commonOptions: SSEClientTransportOptions = { authProvider: authProviderRef.current }
const targetUrl = new URL(url)
if (transportType === 'http') {
@ -266,19 +266,21 @@ export function useMcp(options: UseMcpOptions): UseMcpResult {
const errorInstance = connectErr instanceof Error ? connectErr : new Error(String(connectErr))
// Check for 404/405 specifically for HTTP transport
const is404 = errorInstance.message.includes('404') || errorInstance.message.includes('Not Found')
const is405 = errorInstance.message.includes('405') || errorInstance.message.includes('Method Not Allowed')
const errorMessage = errorInstance.message
const is404 = errorMessage.includes('404') || errorMessage.includes('Not Found')
const is405 = errorMessage.includes('405') || errorMessage.includes('Method Not Allowed')
const isLikelyCors = errorMessage === 'Failed to fetch' /* Chrome */ || errorMessage === 'NetworkError when attempting to fetch resource.' /* Firefox */ || errorMessage === 'Load failed' /* Safari */
if (transportType === 'http' && (is404 || is405)) {
addLog('warn', `HTTP transport failed (${is404 ? '404' : '405'}). Will attempt fallback to SSE.`)
if (transportType === 'http' && (is404 || is405 || isLikelyCors)) {
addLog('warn', `HTTP transport failed (${isLikelyCors ? 'CORS' : is404 ? '404' : '405'}). Will attempt fallback to SSE.`)
return 'fallback' // Signal that fallback should be attempted
}
// Check for Auth error (Simplified - requires more thought for interaction with fallback)
if (
errorInstance instanceof UnauthorizedError ||
errorInstance.message.includes('Unauthorized') ||
errorInstance.message.includes('401')
errorMessage.includes('Unauthorized') ||
errorMessage.includes('401')
) {
addLog('info', 'Authentication required. Initiating SDK auth flow...')
// Ensure state is set only once if multiple attempts trigger auth
@ -324,8 +326,8 @@ export function useMcp(options: UseMcpOptions): UseMcpResult {
// Handle other connection errors
// Use stable failConnection
failConnection(`Failed to connect via ${transportType.toUpperCase()}: ${errorInstance.message}`, errorInstance)
return 'failed' // Indicate definitive failure for this transport
failConnection(`Failed to connect via ${transportType.toUpperCase()}: ${errorMessage}`, errorInstance)
return 'fallback' // If our logic above is wrong, we'd prevent HTTPs servers from ever working. So always fall back as a last resort.
}
} // End of tryConnectWithTransport helper