Middleware

Middleware is the main composition mechanism in sevo.

Shape

Middleware receives (ctx, next) and can:

return a Response immediately
call next(ctx) and return the downstream response
replace the request before passing it on

import type { ServerMiddleware } from "sevo";

const poweredBy: ServerMiddleware = async (ctx, next) => {
  const response = await next(ctx);
  response.headers.set("x-powered-by", "sevo");
  return response;
};

Registering Middleware

import { serve } from "sevo";
import { NodeRuntimeAdapter } from "sevo/node";

serve({
  adapter: new NodeRuntimeAdapter(),
  middleware: [poweredBy],
  routes: {
    "/": () => new Response("ok"),
  },
  fetch: () => new Response("Not Found", { status: 404 }),
});

Short-Circuiting

Middleware can stop the chain by returning a response directly.

const auth: ServerMiddleware = async (ctx, next) => {
  if (!ctx.request.headers.get("authorization")) {
    return new Response("Unauthorized", { status: 401 });
  }
  return next(ctx);
};

Static Files

serveStatic() is implemented as middleware.

import { serve } from "sevo";
import { serveStatic } from "sevo/static";
import { NodeRuntimeAdapter } from "sevo/node";

serve({
  adapter: new NodeRuntimeAdapter(),
  middleware: [serveStatic({ dir: "./public" })],
  fetch: () => new Response("Not Found", { status: 404 }),
});

Request Logging

The optional logger lives in a separate subpath export.

import { serve } from "sevo";
import { log } from "sevo/log";
import { NodeRuntimeAdapter } from "sevo/node";

serve({
  adapter: new NodeRuntimeAdapter(),
  middleware: [log()],
  routes: {
    "/": () => new Response("ok"),
  },
  fetch: () => new Response("Not Found", { status: 404 }),
});

Plugins

ServerPlugin runs during Server construction and can modify server.options or register process-level behavior.

sevo itself uses plugins internally for:

request error normalization
graceful shutdown handling in supported runtimes

Server Instance

Server owns middleware composition, request augmentation, and runtime lifecycle.

Server Options

ServerOptions control request handling, listener defaults, and shutdown behavior.