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

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();
  });