Author a plugin

Create a Rust library crate for wasm32-unknown-unknown and depend on the published PDK and wire crates.

[lib]
crate-type = ["cdylib"]

[dependencies]
cc-lb-plugin-wire = "0.9"
cc-lb-pdk-wasmtime = "0.2"

Declare plugin metadata

The PDK expects one module annotated with #[cc_lb_plugin(...)]:

#![cfg_attr(target_arch = "wasm32", no_std)]

extern crate alloc;

use alloc::boxed::Box;
use alloc::vec::Vec;
use cc_lb_pdk_wasmtime::{cc_lb_plugin, handler};
use cc_lb_plugin_wire::v1::{FilterRequest, FilterResponse, PerCandidateReason};

#[cc_lb_plugin(
    name = "accept-all",
    version = "0.1.0",
    description = "Accepts every upstream candidate.",
    usage = "Use as a smoke-test router filter.",
)]
mod accept_all {
    use super::*;

    #[handler(
        filter,
        wire = 1,
        description = "Accepts all candidates without modification.",
        usage = "Attach to a router filter chain for baseline validation.",
    )]
    pub fn filter(req: FilterRequest) -> FilterResponse {
        let results = req
            .candidates
            .into_vec()
            .into_iter()
            .map(|candidate| PerCandidateReason {
                upstream_id: candidate.upstream_id,
                decision: Box::from("accept"),
                reason: Box::from(""),
            })
            .collect::<Vec<_>>()
            .into_boxed_slice();
        FilterResponse { results }
    }
}

Required top-level metadata is name, version, description, usage, and hooks. Each hook declares its wire version and operator-facing description.

Choose a slot

A filter hook returns a decision for each upstream candidate. The host keeps a candidate only when its decision is "accept"; every candidate absent from results is rejected, so an empty results rejects the whole set. A shape plugin must implement request shaping, buffered response transformation, and SSE event transformation. Use explicit no-op handlers for response hooks that the plugin does not change.

Each handler currently uses wire = 1. Wire versions are independent per hook, so a future contract can evolve one hook without silently changing the others.

Build and upload

cargo build --release --target wasm32-unknown-unknown
curl -X POST http://[::1]:9090/admin/v1/plugins/wasm \
  -H "Authorization: Bearer $CC_LB_ADMIN_TOKEN" \
  -F "original_filename=plugin.wasm" \
  -F "bytes=@target/wasm32-unknown-unknown/release/plugin.wasm"

The host validates imports, required exports, metadata, wire versions, schema fingerprints, and an upload-time runtime probe before dispatch. Uploading the same name and SHA is idempotent. Replacing an existing name may require an explicit confirmation when the new version is not higher.