Change #263907

Comments

cf-ip-happy: limit concurrent attempts
Introduce a limit on the concurrent connect attempts of 6:

- document this in CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS
- close the oldest attempt before opening a new one that would
  exceed the limit
- closing failed attempts early to avoid sockets use beyong their
  usefulness
- add tests for limits in unit2600

These changes are externally visible as file descriptors will be
reassigned where we previously kept the old one around and started a
new socket, allocating always a new descriptor.

Closes #21252

Changed files

• docs/libcurl/opts/CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS.md
• lib/cf-ip-happy.c
• tests/unit/unit2600.c