OpenAPI v3 implementation for koa

Required peer dependencies

- @koa/cors
- @koa/router
- js-yaml
- koa
- koa-body
- koa-send
- koas3

npm i @koa/cors @koa/router js-yaml koa koa-body koa-send koas3

Usage example

``javascript
const fs = require("fs");
const jsyaml = require("js-yaml");
const Koa = require("koa");
const KOAS3 = require("koas3").default;
const http = require("http");
const URL = require("url");

const createApp = async (openapiPath, options) => {
// create openapi object
const openapiFile = fs.readFileSync(openapiPath, "utf8");
const openapi = jsyaml.safeLoad(openapiFile);

// create Koa app
const app = new Koa();

// optionally setup app as proxy
app.proxy = true;

// optionaly use default error handler
app.use(async (ctx, next) => {
try {
await next();
if ([404, 405].includes(ctx.status)) {
ctx.throw(ctx.status, Path ${ctx.path} not found);
}
} catch (err) {
// example of error handling
if (err.message === "RequestValidationError") {
const { status, name, message, ...payload } = err;
ctx.status = typeof err.status === "number" ? err.status : 500;
ctx.body = {
statusCode: ctx.status,
name: "INVALID_SCHEMA",
description: err.message,
payload,
};
} else {
// application
ctx.app.emit("error", err, ctx);
ctx.status = typeof err.status === "number" ? err.status : 500;
ctx.body = {
statusCode: ctx.status,
name: err.name,
description: err.message,
payload: { error: err.message, stack: err.stack, originalError: err },
};
}
}
});

// koas3 openapi magic
const router = await KOAS3(openapi, options);

// this is important - setup router prefix based on openapi servers
// depends on your app logic, this just takes the first
if (openapi.servers && openapi.servers.length) {
const [serverDefinition] = openapi.servers;
const url = URL.parse(serverDefinition.url);
let routePrefix = url.pathname.replace(/\/$/, "") + "/";
if (serverDefinition.variables) {
Object.keys(serverDefinition.variables).forEach((k) => {
routePrefix = routePrefix.replace(
new RegExp({${k}}, "g"),
serverDefinition.variables[k].default
);
});
}

router.prefix(routePrefix);
}

// resup KOAS3 router to the app
app.use(router.routes());
app.use(router.allowedMethods());

app.on("error", (err) => {
// this is any other error handler
console.error("AppError:", err);
});

return app;
};

// run the server
createApp("./openapi.yaml", {
controllersPath: "./controllers",
})
.then(async (app) => {
// make optional database connections

//mongo.connector(Object.assign({ connect: false }, config.get('mongodb')));
//await mongo.setup(dbSetup);

http
.createServer(app.callback())
.listen({ port: 9000 }, () => {
console.log("API is listening on port 9000");
})
.on("error", (e) => {
console.error(Error starting server: ${e});
});
})
.catch(async (e) => {
console.error("ApiError:", e);
// stop database connections

//await mongo.close();
});
``