Coapi Developer

CoApi Developer Skill

Use this skill to help with CoApi (me.ahoo.coapi), which turns Spring @HttpExchange interfaces into Spring beans with minimal setup. CoApi is Kotlin-first, supports Spring Boot 4.x / Spring Framework 7.x in the current codebase, and can create either reactive WebClient or synchronous RestClient proxies.

How To Work

1. Identify the request type, then load only the needed reference file:
   • New client interface, application config, load balancing, or examples: read references/usage.md.
   • Architecture, module boundaries, annotations, mode selection, or implementation edits: read references/concepts.md.
   • Tests, assertions, ApplicationContextRunner, integration tests, or MockK: read references/testing.md.
   • Startup failures, missing beans, client mode surprises, base URL issues, or load-balancer problems: read references/troubleshooting.md.
2. Prefer concise, working Kotlin snippets unless the user asks for Java.
3. Recommend the simplest CoApi-supported approach first, then name the tradeoff when another approach is valid.
4. If the request is outside CoApi's purpose, say so directly and route the user to the Spring tool that owns it.

Essential Facts

• Dependency: implementation("me.ahoo.coapi:coapi-spring-boot-starter").
• Main annotations:
  • @CoApi(baseUrl = "...", serviceId = "...", name = "...") marks an interface as a CoApi client.
  • @LoadBalanced explicitly enables load-balanced client wiring.
  • @EnableCoApi(clients = [...]) explicitly registers client interfaces.
• Client mode: coapi.mode supports AUTO, REACTIVE, and SYNC; an invalid value fails startup listing the valid options (v2.2.0).
• Base URL resolution has two layers: @CoApi(baseUrl) wins over serviceId; serviceId/lb:// targets are normalized to http://... with loadBalanced=true; coapi.clients.<name>.base-url can override the parsed definition at HTTP client factory time.
• Placeholders in baseUrl/serviceId must resolve in the active environment (v2.2.0): an unresolvable ${...} fails startup with Could not resolve placeholder .... Use ${name:default} for an inline fallback.
• Client names must be unique (v2.2.0): the name defaults to the interface simple name; two clients resolving to the same name fail startup with the conflicting types listed. The name is also the key for coapi.clients.<name>.*.
• coapi.clients.<name>.load-balanced is a real three-state override: true enables, false disables, unset falls back to the annotation unless a non-blank base-url override forces it off (v2.1.1 fixed false being treated as true).
• Load balancing requires spring-cloud-starter-loadbalancer; CoApi resolves the sync interceptor by the BlockingLoadBalancerInterceptor interface, which also works when Spring Cloud retry is enabled.
• Prefer me.ahoo.test.asserts.assert for value assertions. For ApplicationContextRunner bean assertions, mirror existing tests with AssertionsForInterfaceTypes.assertThat(context).

CoApi Boundaries

CoApi is for declarative request-response HTTP clients built from typed Spring interfaces. It does not own WebSocket or SSE clients, resilience policies, arbitrary one-off HTTP calls, or non-Spring runtime wiring. For those concerns, use Spring WebClient, RestClient, WebSocketClient, filters, interceptors, or a resilience library such as Resilience4j.

Minimal Client Pattern

@CoApi(baseUrl = "\${github.url}")
interface GitHubApiClient {
    @GetExchange("repos/{owner}/{repo}/issues")
    fun getIssue(@PathVariable owner: String, @PathVariable repo: String): Flux<Issue>
}

github:
  url: https://api.github.com
coapi:
  mode: AUTO