Generating Cloudflare workerd configs with capnproto-rust

This is a brief example to demonstrate how you can generate configuration files for Cloudflare workerd using the serialisation feature of capnproto-rust.

Requirements

• Cap'n Proto built from source, as there are some changes required that are not on the latest release.
  • Take a look at the 'From Git' heading: https://capnproto.org/install.html
• You will need the Rust plugin for Cap'n Proto's code generation.
  • cargo install capnpc-rust
• The schema for workerd's config files, available at https://github.com/cloudflare/workerd/blob/main/src/workerd/server/workerd.capnp
  • The current version, at the time of writing, is included at schema/workerd.capnp.

Updating the schema

I've already included the resulting Rust code in this repository at src/workerd.rs - but it can be updated with:

capnp compile -orust:src/ --src-prefix=schema/ ./schema/workerd.capnp

This will generate a file called workerd_capnp.rs in the src folder - you can rename this if preferred.

Usage

It will output a binary config to stdout, which you can redirect to a file and then use with workerd like so:

cargo run > config.bin
workerd serve -b config.bin

• The -b flag indicates it is a binary config rather than text.