Clean error when dev apps ports are in use#3658
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| with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s: | ||
| if s.connect_ex(("localhost", port)) == 0: |
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The new preflight port check uses an IPv4-only socket (AF_INET) with connect_ex(('localhost', port)), so it misses listeners bound only on IPv6 (for example ::1). In that case this code reports the port as available, but later startup can still fail with address-in-use when binding host='localhost', which reintroduces the same noisy failure path this change is trying to prevent. Please check both families (e.g., via getaddrinfo) or use a bind-based availability check.
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Reviewed commit: 12877449fb
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| for family in (socket.AF_INET, socket.AF_INET6): | ||
| with socket.socket(family, socket.SOCK_STREAM) as s: |
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The new preflight check unconditionally creates an AF_INET6 socket, which raises OSError (EAFNOSUPPORT) on environments where IPv6 is disabled or unavailable (common in containers and hardened hosts). In that case fastmcp apps dev now fails before startup with a traceback even when the requested ports are free, which is a regression from the prior behavior. Please catch unsupported-family errors (or derive probe targets from getaddrinfo) so IPv4-only environments can still run.
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Before: full traceback with OSError, SystemExit, uvicorn internals, and asyncio cleanup noise.
After:
Checks both ports before starting anything.