cloudflare-worker-echo-back.js

// modified from
// https://developers.cloudflare.com/workers/examples/read-post/
// https://developers.cloudflare.com/workers/examples/cors-header-proxy/


async function readRequestBody(request, url) {
  const { headers, method } = request;
  const contentType = headers.get("content-type") || "";

  const headersObj = Object.fromEntries(headers);

  const rspHeaders = {
    "Access-Control-Allow-Origin": "*",
  };
  if (
    method.toUpperCase() === "OPTIONS" &&
    headers.get("Origin") !== null &&
    headers.get("Access-Control-Request-Method") !== null &&
    headers.get("Access-Control-Request-Headers") !== null
  ) {
    // preflight
    rspHeaders["Access-Control-Allow-Methods"] = headers.get(
      "Access-Control-Request-Method"
    );
    rspHeaders["Access-Control-Allow-Headers"] = headers.get(
      "Access-Control-Request-Headers"
    );
  } else {
    // other normal requests
    rspHeaders["Access-Control-Allow-Methods"] = "*";
    rspHeaders["Access-Control-Allow-Headers"] = "*";
    rspHeaders["Content-Type"] = "application/json;charset=UTF-8";
  }

  const rsp = {
    method: method,
    headers: headersObj,
    url: url,
  };

  if (contentType.includes("application/json")) {
    rsp["json"] = await request.json();
  } else if (contentType.includes("application/text")) {
    rsp["data"] = request.text();
  } else if (contentType.includes("text/html")) {
    rsp["data"] = request.text();
  } else if (contentType.includes("form")) {
    const formData = await request.formData();
    const body = {};
    for (const entry of formData.entries()) {
      body[entry[0]] = entry[1];
    }
    rsp["form"] = body;
  } else {
    // Perhaps some other type of data was submitted in the form
    // like an image, or some other binary data.
    try {
      rsp["data"] = new TextDecoder().decode(await request.arrayBuffer());
    } catch (error) {
      rsp["data"] = "";
      rsp["dataError"] = "not decodable";
    }
  }

  return {
    rsp: rsp,
    rspHeaders: rspHeaders,
  };
}

async function handleRequest(request, url) {
  const { rsp, rspHeaders } = await readRequestBody(request, url);
  return new Response(JSON.stringify(rsp, null, 2), {
    headers: rspHeaders,
  });
}

addEventListener("fetch", (event) => {
  const { request } = event;
  const { url } = request;
  return event.respondWith(handleRequest(request, url));
});