How to listen on multiple sockets?

[cmcqueen]

I'd like to know how to listen on multiple sockets. I envisage a few scenarios:

1. Listen on separate IPv4 and IPv6 addresses. Eg listen on IPv4 address 192.0.2.1 and IPv6 address 2001:db8:1:2:3:4:5:6.
2. Provide HTTP on port 80, HTTPS on port 443.
3. Provide a web site on port 80, a REST API on port 9000.

It's the 3rd option that I'm interested in right now.

How can such scenarios be set up?

[jebrosen]

Those options have a pretty wide range of solutions! Here are a few rough ideas that may help:

• Each Rocket server can only "listen" on one address. But, under some operating system versions and configurations, listening on specific addresses such as [::] listens on both IPv4 and IPv6.
• You could run multiple Rocket servers with different configurations for address/port, but with the same routes mounted.
• You could use a reverse proxy (such as HAProxy or nginx) to listen on multiple ports, redirecting them to the same (or different) web servers.
• You could run multiple Rocket servers in the same process, by using launch(). launch() returns a Future that can be spawn()ed or select!ed with other servers.
• You could run multiple Rocket servers in separate processes (e.g. separate binaries, or one binary that decides which server to run based on a command line). Sometimes this is preferable for other reasons, such as different levels of privilege between the two servers.

[cmcqueen]

Regarding the first point — On Linux with sysctl net.ipv6.bindv6only = 0, I can listen on IPv6 generic address ::, and it also accepts incoming IPv4 on the same socket. It can be done explicitly on Linux, and on Windows too, by setting socket option IPV6_V6ONLY to 0. In Rust needs code something like this, using the socket2 crate. I assume Rocket doesn't support that currently.