Signalling a Custom Module

manavo · June 3, 2020, 7:29pm

Hi all,

Sorry if I’ve missed something that’s here already, but couldn’t find anything.

I’m looking to have a way to send a “signal” to my custom module. So far I’ve thought of 3 possible options:

Run a webserver on localhost, listening to a different port. Then in the handler, I can be listening for my event
Trap an OS signal, so I know that something happened (similar idea to how software in general listens to USR1 to reload config). The purpose isn’t to re-read the config, I know how Caddy can do that, it’s just an example of what I mean for capturing signals

Or another idea I’ve had is would I be able to add a command within Caddy? So I could have my own caddy custom-command alongside these? Command Line — Caddy Documentation?

I know the first 2 options would technically be fine and work, but the random 3rd idea sounds like the nicest option if it was possible.

Any ideas are welcome!

Thanks

francislavoie · June 3, 2020, 7:37pm

It entirely depends on what you need this for.

I’d say the third option, adding your own subcommand, is probably the easiest. It’s already possible! See the following:

github.com

caddyserver/caddy/blob/master/cmd/commands.go

// Copyright 2015 Matthew Holt and The Caddy Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package caddycmd

import (
	"flag"
	"regexp"
)

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matt · June 3, 2020, 7:40pm

Why do you need a signal? Usually you would want to implement an API endpoint instead, so your module can also work on Windows (and with much greater flexibility than a mere signal offers).

manavo · June 3, 2020, 7:55pm

That’s fantastic @francislavoie, it’s exactly what I was hoping for. Thanks for pointing me in the right direction!

system · September 1, 2020, 7:55pm

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