index.js

const request = require("request");
const sharp = require("sharp");

module.exports.handler = function handler(event, context, callback) {
  const queryStringParameters = event.queryStringParameters || {};
  const {
    w,
    h,
    fit,
    position,
    gravity,
    strategy,
    background,
    withoutEnlargement
  } = queryStringParameters;

  let base64url = event.pathParameters.url;

  // Drop extension, if present (for compatibility with imgproxy, which has extension passed for CDN caching)
  if (base64url.includes(".")) {
    base64url = base64url.substring(0, base64url.indexOf("."));
  }

  const url = decodeURIComponent(
    new Buffer.from(base64url, "base64").toString()
  );
  const sharpFit = fit || "cover";

  let sharpPosition = sharp.position.centre;

  if (position) {
    sharpPosition = sharp.position[position];
  } else if (gravity) {
    sharpPosition = sharp.gravity[gravity];
  } else if (strategy) {
    sharpPosition = sharp.strategy[strategy];
  }

  const sharpBackground = background || { r: 0, g: 0, b: 0, alpha: 1 };

  request.get({ url, encoding: null }, (_, __, body) => {
    sharp(body)
      .resize({
        width: parseInt(w),
        height: parseInt(h),
        fit: sharpFit,
        position: sharpPosition,
        background: sharpBackground,
        withoutEnlargement: withoutEnlargement === "true"
      })
      .withMetadata()
      .toBuffer({ resolveWithObject: true })
      .then(({ data, info }) => {
        const headers = {
          "Content-Type": `image/${info.format}`,
          "Cache-Control": "max-age=86400"
        };

        callback(null, {
          statusCode: 200,
          body: data.toString("base64"),
          isBase64Encoded: true,
          headers
        });
      });
  });
};