Streamable HTTP transport hangs during initialization #406
Description
The client hangs during the first initialize message to a (public) Shopify MCP https://my-best-shoes.myshopify.com/api/mcp
I can successfully connect https://my-best-shoes.myshopify.com/api/mcp from npx @modelcontextprotocol/inspector.
Note that #396 describes that the client transport hangs during sendNotification for notifications/initialized. In this case, the client hangs even earlier - during initialize.
Steps to reproduce:
String url = "https://my-best-shoes.myshopify.com/api";
McpClientTransport transport = HttpClientStreamableHttpTransport.builder(url).endpoint("/mcp").build();
McpSyncClient client = McpClient.sync(transport)
.requestTimeout(Duration.ofSeconds(20))
.initializationTimeout(Duration.ofSeconds(20))
.build();
try {
client.initialize();
McpSchema.ListToolsResult tools = client.listTools();
logger.log(Level.INFO, "Available tools: {0}", tools.tools());
} catch (Exception e) {
logger.log(Level.SEVERE, "Failed to initialize MCP client from DebugServlet", e);
}