@iopa/router/src/compose.ts

Lightweight and fast router for IOPA applications

/*
 * Internet Open Protocol Abstraction (IOPA)
 * Copyright (c) 2016 - 2022 Internet Open Protocols Alliance
 * Portions Copyright (c) 2021 Yusuke Wada
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import { IContextIopa, AppHandler } from '@iopa/types'
import { TraceEvent } from 'iopa'

type NamedAppHandler = AppHandler & { id: string }

export function compose(
  middleware: NamedAppHandler[]
): (context: IContextIopa) => Promise<void> {
  return async (context: IContextIopa) => {
    let index = -1
    return dispatch(0)
    async function dispatch(i: number): Promise<void> {
      if (i <= index) {
        return Promise.reject(new Error('next() called multiple times'))
      }

      const handler = middleware[i]
      index = i

      if (i > 0) {
        const prev = middleware[i - 1]
        context.dispatchEvent(new TraceEvent('trace-next', { label: prev.id }))
      }

      if (!handler) {
        if (i > 0) {
          const prev = middleware[i - 1]
          context.dispatchEvent(
            new TraceEvent('trace-next-resume', { label: prev.id })
          )
        }
        return
      }

      context.dispatchEvent(
        new TraceEvent('trace-start', { label: handler.id })
      )

      return Promise.resolve(handler(context, dispatch.bind(null, i + 1))).then(
        async (res) => {
          context.respondWith(res)
          context.dispatchEvent(
            new TraceEvent('trace-end', { label: handler.id })
          )
          if (i > 0) {
            const prev = middleware[i - 1]
            context.dispatchEvent(
              new TraceEvent('trace-next-resume', { label: prev.id })
            )
          }
        }
      )
    }
  }
}