fix(qr-server): pass host/port to FastMCP for Docker compatibility (#372)

malbari · web-flow · commit 0b836799091c · 2026-04-24T11:35:13.000+01:00
When FastMCP is created with the default host=127.0.0.1, MCP SDK 1.26+
automatically enables DNS rebinding protection that only allows requests
from localhost. This breaks Docker where requests come from
host.docker.internal, causing 421 Invalid Host header errors.

By passing host=HOST (0.0.0.0 for Docker), DNS rebinding protection
is not auto-enabled, allowing requests from any host.
diff --git a/examples/qr-server/server.py b/examples/qr-server/server.py
@@ -26,7 +26,7 @@
 HOST = os.environ.get("HOST", "0.0.0.0")  # 0.0.0.0 for Docker compatibility
 PORT = int(os.environ.get("PORT", "3001"))
 
-mcp = FastMCP("QR Code Server", stateless_http=True)
+mcp = FastMCP("QR Code Server", stateless_http=True, host=HOST, port=PORT)
 
 # Embedded View HTML for self-contained usage (uv run <url> or unbundled)
 EMBEDDED_VIEW_HTML = """<!DOCTYPE html>
