Using srvx

The srvx adapter is the right boundary when your server hands middleware a ServerRequest with host metadata.

Mount a Chain

Import toFetchHandler from alien-middleware/srvx when passing a chain to srvx serve.

import { serve } from 'srvx'
import { chain } from 'alien-middleware'
import { toFetchHandler } from 'alien-middleware/srvx'

const app = chain().use(context => {
  return new Response(`path: ${context.url.pathname}`)
})

serve({
  port: 3000,
  fetch: toFetchHandler(app),
})

The adapter creates an alien-middleware context for each srvx request and calls the chain. The returned function has the shape srvx expects for fetch.

Read srvx Host Metadata

The srvx adapter copies ServerRequest metadata into context.host.

const app = chain().use(context => {
  return new Response(
    JSON.stringify({
      ip: context.host.ip,
      runtime: context.host.runtime?.name,
    })
  )
})

If the srvx request provides ip, runtime, or waitUntil, the adapter maps them to context.host.ip, context.host.runtime, and context.waitUntil().

Override Host Metadata

Pass static host metadata when a deployment needs known overrides.

import { toFetchHandler } from 'alien-middleware/srvx'

serve({
  fetch: toFetchHandler(app, {
    host: {
      ip: '127.0.0.1',
      runtime: { name: 'local' },
    },
  }),
})

Static host values take precedence over srvx request values for the same field.

Compute Host Metadata per Request

Pass a host factory when metadata depends on the request.

serve({
  fetch: toFetchHandler(app, {
    host: request => ({
      env: name => {
        if (name === 'PATHNAME') {
          return new URL(request.url).pathname
        }
      },
      runtime: { name: request.runtime?.name ?? 'unknown' },
    }),
  }),
})

The factory runs for each request before the chain receives its context.

Create a Context Manually

Use createContextFromServerRequest in tests or custom srvx glue code when you need a context object without creating a fetch handler.

import { createContextFromServerRequest } from 'alien-middleware/srvx'

const context = createContextFromServerRequest(request)

context.host.ip
context.host.runtime

When you already have a plain Web Request, use createContext from the root entrypoint instead.

The srvx adapter treats host metadata like Agent J's neuralyzer: it keeps the useful flash and leaves the rest at the boundary.