Fix C client SSL test hang on long-hostname runners (cap cert CN at 64 chars)

[arkmish]

What this changes

One line in zookeeper-client/zookeeper-client-c/ssl/gencerts.sh: cap the certificate CommonName at 64 characters.

Root cause

gencerts.sh derives the X.509 CommonName from hostname -f. On runners with a long FQDN — e.g. Kubernetes pods / self-hosted CI runners whose names look like rdev-aks-…-cq4mx.corp.rdev.svc.cluster.local (~80 chars) — the CN exceeds the 64-character ASN.1 limit, so every openssl req fails with string too long:maxsize=64 and no certificates are generated.

The Java test server then silently skips its secure port (22281 never listens), and Zookeeper_simpleSystem::testSSL (TestClient.cc) issues a synchronous zoo_create against 127.0.0.1:22281 whose session can never establish. Synchronous C-client ops have no per-call timeout, so the IO thread spins on connect-refused and the main thread blocks forever in wait_sync_completion — hanging the full-build-java-tests and full-build-cppunit-tests jobs indefinitely (camping on runners until the 6h timeout).

This is why it reproduced only on long-FQDN runners and not on upstream CI (short hostnames), and why it had nothing to do with the C client itself.

Fix

Truncate the CN-deriving FQDN to 64 characters (FQDN=${FQDN:0:64}). The CN isn't used for hostname verification in these tests (the client connects to 127.0.0.1), so any valid ≤64-char value is sufficient.

Testing Done

• Diagnosed via a gdb thread dump on a long-FQDN Linux runner: main thread blocked in wait_sync_completion, IO thread spinning on connect-refused to 127.0.0.1:22281; /tmp/certs/gencerts.stderr showed the string too long:maxsize=64 openssl failure and ss -ltn confirmed 22281 was not listening.
• Verified locally: the original 80-char CN reproduces the exact string too long:maxsize=64 error; with the truncation, the full gencerts.sh run completes and generates root.crt / server.crt / client.crt + keystores.
• Verified on CI: with the fix, both full-build-cppunit-tests (8m22s) and full-build-java-tests jobs completed green — the exact jobs that previously hung for hours.

🤖 Generated with Claude Code

[Sanju98]

LGTM