Validate `ttl` config

[TheOtherBrian1]

Chore

Validate custom pg_net.ttl configs

Describe the chore

The pg_net.ttl config is an interval type, but it doesn't perform any validation checks in the code:

DefineCustomStringVariable("pg_net.database_name", "Database where the worker will connect to",
                             NULL, &guc_database_name, "postgres", PGC_SU_BACKEND, 0, NULL, NULL,
                             NULL);

Based on the DefineCustomStringVariable definition:

extern void DefineCustomStringVariable(const char *name,
									   const char *short_desc,
									   const char *long_desc,
									   char **valueAddr,
									   const char *bootValue,
									   GucContext context,
									   int flags,
									   GucStringCheckHook check_hook,
									   GucStringAssignHook assign_hook,
									   GucShowHook show_hook) pg_attribute_nonnull(1, 4);

validation likely would have to be added to the GucStringCheckHook parameter. cybrosys has an article on the topic. Clickhouse also has a good article that may be worth referencing.

The function interval_in can be called against the input string to validate that it is in interval format.

Additional context

Tried to update the MGMT-API/CLI to expose the ttl and batch_size settings:

• https://linear.app/supabase/issue/CE-3/add-pg-net-settings-to-cli

Came across an issue related to type interval validation. It can be circumvented with API level checks, but I think it would be better if the extension also prevented invalid entries. During testing, I found it to be trivial to break the background worker by running something like:

ALTER SYSTEM SET pg_net.ttl = '1 mins';
SELECT net.worker_restart();