cachedb_redis: add Unix socket transport and lazy connection

[NormB]

Summary

• Add Unix domain socket support as an alternative to TCP
• Add lazy_connect parameter to defer connection until first use

Details

Unix socket transport

The module now supports connecting to Redis via Unix domain sockets using a query parameter in the cachedb_url:

modparam("cachedb_redis", "cachedb_url",
    "redis:local://localhost/?socket=/var/run/redis/redis.sock")

The REDIS_UNIX_SOCKET flag distinguishes socket connections from TCP. MI output includes transport (tcp/unix) and socket_path fields. Unix socket connections are supported in both single-instance and cluster topology refresh paths.

Lazy connection

The new lazy_connect parameter (integer, default 0) defers the Redis connection from child_init to the first cache operation. This is useful when:

• Redis may not be available at OpenSIPS startup
• Multiple cachedb_url groups are configured but not all are needed immediately
• Startup time matters and Redis connection latency is non-trivial

Both TCP and Unix socket connections support lazy mode.

Parameter	Type	Default	Description
lazy_connect	integer	0	Defer Redis connection until first cache operation

Testing

Suite	Tests	Description
test_unix_socket	19	Store/fetch, MI reporting, PING latency, recovery
test_lazy_connect	17	Deferred connect for all transport types, recovery

Compatibility

No behavioral change for existing TCP configurations. The lazy_connect parameter defaults to 0 (disabled).

Dependencies

• Depends on cachedb_redis: add dynamic cluster topology management and observability #3855 (cluster topology management)

[dondetir]

Nice addition @NormB — Unix socket support and lazy connect are both clean and well-tested.

I verified both features against a local setup:

• Unix socket: store/fetch, MI reporting ("transport": "unix"), ping — all working
• Lazy connect: confirmed empty node list before first operation, then full cluster auto-discovery on demand

One small thing: in redis_get_ctx() (line ~83) and redis_get_ctx_unix() (line ~129), the if (!ctx) NULL check after redisConnect()/redisConnectUnix() seems to have been dropped during the rewrite. The if (ctx && ctx->err != REDIS_OK) guard handles the error-context case, but if hiredis returns NULL (OOM), execution falls through to redisSetTimeout(ctx, ...). It looks like commit 8fb569cb3 had the fix but 16652c169 lost it in the rewrite. Easy to re-add:

if (!ctx) {
    LM_ERR("failed to connect to redis - out of memory\n");
    return NULL;
}

Everything else looks solid. The Unix socket + cluster mode guard and the lazy connect flow are well thought out.