example(hostname): example extension to print system hostname

[divyenduz]

Port of https://github.com/theory/pg-hostname/

[divyenduz]

Suggested change

	const hostname = try std.posix.gethostname(&buffer);
	const hostname = std.posix.gethostname(&buffer) catch |err| switch (err) {
	error.PermissionDenied => {
	std.debug.print("Error getting hostname: permission denied\n", .{});
	return "unknown"[0..];
	},
	error.Unexpected => {
	std.debug.print("Error getting hostname: unexpected error\n", .{});
	return "unknown"[0..];
	},
	};

This compiles but returns empty hostname in SQL (the elog before return works fine). I suspect that's a bug in pgzx? 🤔

[urso]

Not sure why you get an empty hostname. I don't think this is pgzx, but Zig returning an empty string here. I haven't had any problems. But why do you need to return "unknown"[0..]? You are returning a string anyways.

For logging, don't use std.debug.print. Use elog to emit debug logs. This way you are using the postgres internal logging/reporting system.

[divyenduz]

Fixed via try pgzx.mem.PGCurrentContextAllocator.dupeZ(u8, hostname);, thanks for the help in slack.

[urso]

oopsie

[divyenduz]

Ah, good catch, I copied it from char_count_zig, fixed in both places.

[urso]

Hm... I haven't tried this, but I wonder if pgzx.PG_EXPORT(@This()) will do the trick (this will require you to declare your function as pub).

[divyenduz]

This worked ✅

[urso]

nit: change the return type to [:0]const u8. By returning []const u8 you actually have implicitly casted the [:0]const u8 from dupeZ into a []const u8. As postgres requires proper zero terminated C strings we will implicitly allocate and copy the string again once your function returns. You can prevent the extra allocation and copying by returning [:0]const u8.

[divyenduz]

Thanks, this is done.