Project Conncept: a TCP/UDP app for Caddy

Project Conncept is an experimental layer 4 app for Caddy. It facilitates composable handling of raw TCP/UDP connections based on properties of the connection or the beginning of the stream.

With it, you can listen on sockets/ports and express logic such as:

• "Echo all input back to the client."
• "Proxy all the raw bytes to 10.0.3.14:1592."
• "If connection is TLS, terminate TLS then proxy all bytes to :5000."
• "Terminate TLS; then if it is HTTP, proxy to localhost:80; otherwise echo."
• "If connection is TLS, proxy to :443 without terminating; if HTTP, proxy to :80; if SSH, proxy to :22."
• "If the HTTP Host is example.com or the TLS ServerName is example.com, then proxy to 192.168.0.4."
• "Block connections from these IP ranges: ..."
• "Throttle data flow to simulate slow connections."
• And much more!

⚠️ This app is very capable and flexible, but is still in development. Please expect breaking changes.

Because this is a Caddy app, it can be used alongside other Caddy apps such as the HTTP server or TLS certificate manager.

[!NOTE] This is not an official repository of the Caddy Web Server organization.

Introduction

[!IMPORTANT] Documentation is available in the docs directory. For better understanding, you may also read the code, especially type definitions and their comments. It's actually a pretty simple code base. See below for tips and examples writing config.

This app works similarly to the http app. You define servers, and each server consists of routes. A route has a set of matchers and handlers; if a connection matches, the associated handlers are invoked.

Refer the docs for lists of matchers and handlers included in the package.

Compiling

The recommended way is to use xcaddy:

$ xcaddy build --with github.com/mholt/caddy-l4

Alternatively, to hack on the plugin code, you can clone it down, then build and run like so:

1. Download or clone this repo: git clone https://github.com/mholt/caddy-l4.git
2. In the project folder, run xcaddy just like you would run caddy. For example: xcaddy list-modules --versions (you should see the layer4 modules).

Writing config

This app supports Caddyfile, but you may also use Caddy's native JSON format to configure it. I highly recommend this caddy-json-schema plugin by @abiosoft which can give you auto-complete and documentation right in your editor as you write your config!

See below for some examples to help you get started.

Config examples

The following configuration examples are included in the documentation:

• Combining Apps
• DNS-over-TLS
• Echo Server
• HTTP & HTTPS Mix
• IMAPS with Proxy Protocol
• Mutual TLS
• Postgres Matching
• Postgres-over-TLS
• SOCKS Proxy
• SSH-over-TLS
• TLS ALPN Routing
• TLS SNI Dynamic Upstreams

Other examples could be found in the documentation files describing specific matchers and handlers, as well as in issues and pull requests.