Vapor 4 EventLoopFutureQueue

EventLoopFutureQueue-example.swift

/**
 Assuming the route handler is attached to `http://localhost:8080/import-data` you can test the implementation with this request (cURL):
 ```
 curl -X "POST" "http://localhost:8080/import-data" \
      -H 'Content-Type: application/json; charset=utf-8' \
      -d $'{ "values": ["first", "foo", "bar", "last"] }'
 ```

Prints:
```
Start importing data: ["first", "foo", "bar", "last"]
processing 'first' - sleeping for '0' seconds
processing 'foo' - sleeping for '2' seconds
processing 'bar' - sleeping for '1' seconds
processing 'last' - sleeping for '1' seconds
Finished processing data: ["first", "foo", "bar", "last"]
```

Learn more about `EventLoopFutureQueue` by studying the tests here: https://github.com/vapor/async-kit/blob/master/Tests/AsyncKitTests/EventLoopFutureQueueTests.swift
*/

/// Sample struct to demonstrate the case
struct ImportData: Content {
  let values: [String]
}

/// Sample import data handler that runs synchronously using `EventLoopFutureQueue`
func importData(_ req: Request) throws -> EventLoopFuture<HTTPStatus> {

  let data = try req.content.decode(ImportData.self)
  let queue = EventLoopFutureQueue(eventLoop: req.eventLoop)

  print("Start importing data: \(data.values)")
  return data.values.map { value in
    queue.append(self.importValue(value, on: req.eventLoop))
  }
  .flatten(on: req.eventLoop).map { res in
    print("Finished processing data: \(res)")
  }
  .transform(to: .ok)
}

/// Mock implementation of importValue(_:on:) that takes randomly 0-3 seconds for processing the data
func importValue(_ value: String, on eventLoop: EventLoop) -> EventLoopFuture<String> {
  let sleepValue = UInt32.random(in: 0...3)
  print("processing '\(value)' - sleeping for '\(sleepValue)' seconds")
  sleep(sleepValue)
  return eventLoop.future(value)
}