bpo-29757: don't swallows errors in the socket.create_connection() utility loop by ankostis · Pull Request #562 · python/cpython (original) (raw)
Context
The utility method socket.create_connection() currently works like that:
- resolve the destination-address into one or more IP(v4 & v6) addresses;
- loop on each IP address and stop to the 1st one to work;
- if none works, re-raise the last error.
The problem
So currently the loop in socket.create_connection() ignores all intermediate errors and reports only the last connection failure, which might be irrelevant. For instance, when both IPv4 & IPv6 networks are supported, usually the last address is a IPv6 address and it frequently fails with an irrelevant error - the actual cause have already been ignored.
Possible solutions
To facilitate network debugging, there are at least 3 options:
a. log each failure as it happens, but that would get the final failure twice: once as a (warning?) message, and once as an exception .
b. collect all failures and log them only when connection fails, but that might miss important infos to the user;
c. collect and return all failures in list attached to the raised exception, which also might miss important infos.
open questions
Q1. A question for all cases is what logging "means" to use: the warnings or logging module?
Q2. And if logging is chosen, log them in 'DEBUG' or 'WARNING' level?
Q3. Finally, cases (b) & (c) need an answer whether to log collected errors in the case that connection passes.
The 1st part of case (c) is implemented in this PR.