runtime.ts

import {
  APIGatewayProxyEvent,
  APIGatewayProxyEventV2,
  Context,
} from "aws-lambda";

export function toAwsEvent(
  request: Request,
): APIGatewayProxyEvent | APIGatewayProxyEventV2 {
  const header = request.headers.get("aws-event");
  if (header == null)
    throw new MissingAwsEventHeaderError(
      `Provided request does not contain "aws-event" header.`,
    );

  return JSON.parse(header);
}

export function toAwsContext(request: Request): Context {
  const header = request.headers.get("aws-context");
  if (header == null)
    throw new MissingAwsContextHeaderError(
      `Provided request does not contain "aws-context" header.`,
    );

  const {
    serializedAtTimeInMillis,
    remainingTimeInMillis,
    ...rest
  }: Omit<Context, "getRemainingTimeInMillis"> & {
    serializedAtTimeInMillis: number;
    remainingTimeInMillis: number;
  } = JSON.parse(header);

  return {
    ...rest,
    getRemainingTimeInMillis: () => {
      const diff = Date.now() - serializedAtTimeInMillis;
      return remainingTimeInMillis - diff;
    },
  };
}

export function isAPIGatewayProxyEvent(
  event: any,
): event is APIGatewayProxyEvent {
  return (
    typeof event.httpMethod === "string" &&
    typeof event.path === "string" &&
    typeof event.resource === "string" &&
    typeof event.requestContext === "object"
  );
}

export function isAPIGatewayProxyEventV2(
  event: any,
): event is APIGatewayProxyEventV2 {
  return (
    event.version === "2.0" &&
    typeof event.rawPath === "string" &&
    typeof event.rawQueryString === "string" &&
    typeof event.routeKey === "string" &&
    typeof event.requestContext === "object"
  );
}

class MissingAwsEventHeaderError extends Error {}
class MissingAwsContextHeaderError extends Error {}