[feature request] support abstract UNIX domain socket

[IceCodeNew]

Use Case & Problem:
There is a backend service that supports abstract UNIX domain sockets managed by the docker compose along with caddy. There is also a named volume for sharing the UNIX socket file between these two services.
Sometimes the backend will run into a panic and restart itself. Since there is no one cleaning the UNIX socket file before the backend restarted, the backend will fail to bind to the UNIX domain socket.

services:
  caddy:
    build: ./caddy/
    cap_add:
      - NET_BIND_SERVICE
    cap_drop:
      - ALL
    container_name: composed-caddy
    init: true
    ports:
      - "80:80"
      - "443:443"
    restart: always
    volumes:
      - share-unix-socket:/tmp/unix-socket/
      - type: bind
        source: ./caddy/
        target: /etc/caddy/
        read_only: true
  v2ray:
    cap_drop:
      - ALL
    command: [ "run", "-d", "/usr/local/etc/v2ray/conf.d/" ]
    container_name: composed-v2ray
    image: v2fly/v2fly-core:latest
    init: true
    read_only: true
    restart: always
    volumes:
      - share-unix-socket:/tmp/unix-socket/
      - type: bind
        source: ./v2ray/conf.d/
        target: /usr/local/etc/v2ray/conf.d/
        read_only: true

volumes:
  share-unix-socket:

{
	admin off
}

REPLACE_ME_V2RAY_HOSTS {
	root * /usr/share/caddy

	encode zstd gzip

	file_server

	reverse_proxy REPLACE_ME_V2RAY_PATH unix+h2c//tmp/unix-socket/send-to-v2ray.sock
}

---

The best solution should be to make the caddy support the abstract UNIX domain socket.
I searched for configuring a pre-hook for docker compose, to intervene in the restarting process and manually clean the UNIX domain file. But only to my disappointment to find out that this is a long stale issue and the community is unwilling to approve such a feature.

[francislavoie]

Hmm, I'm only now learning of abstract unix domain sockets.

It seems like Go already supports this. Try using @ as a path prefix. Does that work? For example:

unix+h2c/@/tmp/unix-socket/send-to-v2ray.sock

[IceCodeNew]

Hmm, I'm only now learning of abstract unix domain sockets.

It seems like Go already supports this. Try using @ as a path prefix. Does that work? For example:

unix+h2c/@/tmp/unix-socket/send-to-v2ray.sock

Then it should be unix+h2c/@send-to-v2ray.sock or unix+h2c/@@send-to-v2ray.sock (for abstract UNIX domain sockets which enabled padding)
I will give it a try, thanks for the quick response!

[IceCodeNew]

Hmm, I'm only now learning of abstract unix domain sockets.

It seems like Go already supports this. Try using @ as a path prefix. Does that work? For example:

unix+h2c/@/tmp/unix-socket/send-to-v2ray.sock

I managed to make it work. Just do the following change:

services:
  caddy:
    build: ./caddy/
    cap_add:
      - NET_BIND_SERVICE
    cap_drop:
      - ALL
    container_name: composed-caddy
    init: true
    ports:
      - "80:80"
      - "443:443"
    restart: always
    volumes:
-       - share-unix-socket:/tmp/unix-socket/
      - type: bind
        source: ./caddy/
        target: /etc/caddy/
        read_only: true
  v2ray:
    cap_drop:
      - ALL
    command: [ "run", "-d", "/usr/local/etc/v2ray/conf.d/" ]
    container_name: composed-v2ray
    image: v2fly/v2fly-core:latest
    init: true
+     network_mode: "service:caddy"
    read_only: true
    restart: always
    volumes:
-       - share-unix-socket:/tmp/unix-socket/
      - type: bind
        source: ./v2ray/conf.d/
        target: /usr/local/etc/v2ray/conf.d/
        read_only: true

- volumes:
-   share-unix-socket:

{
	admin off
}

REPLACE_ME_V2RAY_HOSTS {
	root * /usr/share/caddy

	encode zstd gzip

	file_server

- 	reverse_proxy REPLACE_ME_V2RAY_PATH unix+h2c//tmp/unix-socket/send-to-v2ray.sock
+ 	reverse_proxy REPLACE_ME_V2RAY_PATH unix+h2c/@/tmp/unix-socket/send-to-v2ray.sock
}

// you will also need to switch to the abstract UNIX domain socket on the backend.

[IceCodeNew]

Although It seems caddy does not support padding abstract domain sockets yet, I have not yet been blocked by this problem. Closing this issue.

---

Just for the record, here is the error log:

root@machine-1:~/git/repo# nsenter -n -t "$(docker inspect composed-caddy | jq .[].State.Pid)" lsof -U
COMMAND     PID USER   FD   TYPE             DEVICE SIZE/OFF     NODE NAME
v2ray   1334041 root    3u  unix 0x0000000000000000      0t0 13478402 @/tmp/unix-socket/send-to-v2ray.sock@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ type=STREAM
root@machine-1:~/git/repo# docker logs -f composed-caddy
{"level":"info","ts":1675052533.181184,"msg":"using provided configuration","config_file":"/etc/caddy/Caddyfile","config_adapter":"caddyfile"}
2023-01-30T12:22:13+08:00	WARN	admin	admin endpoint disabled
2023-01-30T12:22:51+08:00	ERROR	http.log.error	dial unix @@/tmp/unix-socket/send-to-v2ray.sock: connect: connection refused	{"request": {"remote_ip": "172.21.0.5", "remote_port": "49536", "proto": "HTTP/2.0", "method": "PUT", "host": "machine-1.example.org", "uri": "REDACTED", "headers": {"Accept-Encoding": ["identity"], "User-Agent": ["Go-http-client/2.0"]}, "tls": {"resumed": false, "version": 772, "cipher_suite": 4867, "proto": "h2", "server_name": "machine-1.example.org"}}, "duration": 0.003093776, "status": 502, "err_id": "k44jmtriz", "err_trace": "reverseproxy.statusError (reverseproxy.go:1272)"}

And the Caddyfile configuration

{
	admin off
}

REPLACE_ME_V2RAY_HOSTS {
	root * /usr/share/caddy

	encode zstd gzip

	file_server

	reverse_proxy REPLACE_ME_V2RAY_PATH unix+h2c/@@/tmp/unix-socket/send-to-v2ray.sock
}

---

change the bind addr to reverse_proxy REPLACE_ME_V2RAY_PATH unix+h2c/@/tmp/unix-socket/send-to-v2ray.sock does not solve the problem.

[mholt]

What is this sorcery... I've also never heard of these 😵

I'm not sure what it takes to connect to a UDS prefixed with @@... like is it a bug in Caddy or something about the system/environment?

[IceCodeNew]

What is this sorcery... I've also never heard of these 😵

I'm not sure what it takes to connect to a UDS prefixed with @@... like is it a bug in Caddy or something about the system/environment?

I think it might be a bug in Caddy, but I am afraid I do not have enough knowledge to collect solid proof for this thought.
Until others bring this problem to the surface again, I thought we can focus on other issues ;-)