Function unwrapEvent

packages/aws-lambda/src/handler.ts:135–157

(event: LambdaEvent)

const MAX_ENVELOPE_DEPTH = 4;

export function unwrapEvent(event: LambdaEvent): PlanEvent | RenderChunkEvent | AssembleEvent {
  let cursor: LambdaEvent = event;
  for (let i = 0; i < MAX_ENVELOPE_DEPTH; i++) {
    if (cursor && typeof cursor === "object") {
      const obj = cursor as Record<string, unknown>;
      if (typeof obj.Action === "string" && isLambdaAction(obj.Action)) {
        return cursor as PlanEvent | RenderChunkEvent | AssembleEvent;
      }
      if ("Payload" in obj) {
        cursor = obj.Payload as LambdaEvent;
        continue;
      }
      if ("Input" in obj) {
        cursor = obj.Input as LambdaEvent;
        continue;
      }
    }
    break;
  }
  throw new Error(
    `[handler] event has no recognised Action; unwrapped ${MAX_ENVELOPE_DEPTH} levels of Payload/Input without finding one.`,
  );
}

function isLambdaAction(value: string): value is LambdaAction {
  return value === "plan" || value === "renderChunk" || value === "assemble";