roles: introduce role for http servers

[DerekBum]

This patch adds roles.http_server. This role allows to configurate one or more HTTP servers. Those servers could be reused by several other roles.

Servers could be accessed by their names (from the config).

get_server(name) method returns a server by its name. If nil is passed, default server is returned. The server is default, if it has DEFAULT_SERVER_NAME ("default") as a name.

This patch also adds a httpd:delete(name) method to delete named routes.

Closes #196

[DifferentialOrange]

Thank you for the patch! I think we may improve it in a couple of ways.

[oleg-jukovec]

Let's also add a public API call for this functionality in the scope of the task, so that there is no need to access internal structures directly:

https://github.com/tarantool/metrics-export-role/blob/36130b73c0a5975ff26f0c26f78ee7a368c1207b/roles/metrics-export.lua#L26-L37

[DerekBum]

Updated the PR according to the comments.

[DerekBum]

CI is finally green, all comments are fixed.

[DerekBum]

Updated the PR according to comments.

[oleg-jukovec]

Thank you for the patch, just few non-critical notes.

[DifferentialOrange]

I have never seen anyone using name option for a route. Until now, I didn't know it even exists. As far as I understand, it actually works not only with named routes, but with unnamed ones as well by using path as a key?

[DerekBum]

No, we can't use just path. Routes are stored as opts (which is a table of many fields, some of them are filled inside of add_route function).

http/http/server.lua

Lines 1248 to 1259 in 2e3dbd2

	if opts.name ~= nil then
	if opts.name == 'current' then
	error("Route can not have name 'current'")
	end
	if self.iroutes[ opts.name ] ~= nil then
	errorf("Route with name '%s' is already exists", opts.name)
	end
	table.insert(self.routes, opts)
	self.iroutes[ opts.name ] = #self.routes
	else
	table.insert(self.routes, opts)
	end

And those opts stored in the map with the name as a key. If there are no name, then we can't get opts.

[DifferentialOrange]

Oh, I see that metrics-export-role sets the name as well
https://github.com/tarantool/metrics-export-role/blob/36130b73c0a5975ff26f0c26f78ee7a368c1207b/roles/metrics-export.lua#L265

[oleg-jukovec]

Yes, it is. It uses name, BUT we could delete a route by path too. I don't see any problems.

[oleg-jukovec]

The only problem is to create a nice and non-confusing API for the call. Maybe:

httpd:delete(path, name)
httpd:delete(path)
httpd:delete(nil, name)

But it looks a little strange.

[DifferentialOrange]

Yes, it is. It uses name, BUT we could delete a route by path too. I don't see any problems.

I'm not sure, but as far as I remember that httpd has that weird thing that allows to set multiple handlers on the same route since route is not a unique identificator (and only one of handlers will be invoked).

[DerekBum]

Updated everything according to comments.

[DerekBum]

Updated everything according to comments.

[DifferentialOrange]

Yes, it is. It uses name, BUT we could delete a route by path too. I don't see any problems.

I'm not sure, but as far as I remember that httpd has that weird thing that allows to set multiple handlers on the same route since route is not a unique identificator (and only one of handlers will be invoked).