docs/hack/releaser/cloudfront-lambda-redirects.js

"use strict";

exports.handler = (event, context, callback) => {
  //console.log("event", JSON.stringify(event));
  const request = event.Records[0].cf.request;
  const requestUrl = request.uri.replace(/\/$/, "");

  // Preserve the query string (e.g. UTM tags) when issuing a redirect.
  const withQuery = (location) => {
    if (!request.querystring) {
      return location;
    }
    const isRelative = location.startsWith("/") && !location.startsWith("//");
    const url = new URL(location, "https://docs.docker.com");
    const query = new URLSearchParams(request.querystring);
    for (const [key, value] of query) {
      url.searchParams.append(key, value);
    }
    return isRelative ? url.pathname + url.search + url.hash : url.href;
  };

  const redirects = JSON.parse(`{{.RedirectsJSON}}`);
  for (let key in redirects) {
    const redirectTarget = key.replace(/\/$/, "");
    const exactMatch = key === request.uri;
    // Preserve slash-insensitive matching without redirecting a canonical
    // slash-terminated destination back to itself.
    const normalizedMatch =
      redirectTarget === requestUrl && redirects[key] !== request.uri;
    if (!exactMatch && !normalizedMatch) {
      continue;
    }
    //console.log(`redirect: ${requestUrl} to ${redirects[key]}`);
    const response = {
      status: "301",
      statusDescription: "Moved Permanently",
      headers: {
        location: [
          {
            key: "Location",
            value: withQuery(redirects[key]),
          },
        ],
      },
    };
    callback(null, response);
    return;
  }

  const redirectsPrefixes = JSON.parse(`{{.RedirectsPrefixesJSON}}`);
  for (let x in redirectsPrefixes) {
    const rp = redirectsPrefixes[x];
    if (!request.uri.startsWith(`/${rp["prefix"]}`)) {
      continue;
    }
    let newlocation = "/";
    if (rp["strip"]) {
      let re = new RegExp(`(^/${rp["prefix"]})`, "gi");
      newlocation = request.uri.replace(re, "/");
    }
    //console.log(`redirect: ${request.uri} to ${redirectsPrefixes[key]}`);
    const response = {
      status: "301",
      statusDescription: "Moved Permanently",
      headers: {
        location: [
          {
            key: "Location",
            value: withQuery(newlocation),
          },
        ],
      },
    };
    callback(null, response);
    return;
  }

  // Check Accept header for markdown/text requests
  const headers = request.headers;
  const acceptHeader = headers.accept ? headers.accept[0].value : "";
  const wantsMarkdown =
    acceptHeader.includes("text/markdown") ||
    acceptHeader.includes("text/plain");

  // Handle directory requests by appending index.html or index.md for requests without file extensions
  let uri = request.uri;

  // Check if the URI has a dot after the last slash (indicating a filename)
  // This is more accurate than just checking the end of the URI
  const hasFileExtension = /\.[^/]*$/.test(uri.split("/").pop());

  // If it's not a file, treat it as a directory
  if (!hasFileExtension) {
    if (wantsMarkdown) {
      // Markdown files are flattened: /path/to/page.md not /path/to/page/index.md.
      // The homepage markdown output remains at /index.md.
      const stripped = uri.replace(/\/$/, "");
      uri = stripped === "" ? "/index.md" : stripped + ".md";
    } else {
      // HTML uses directory structure with index.html
      if (!uri.endsWith("/")) {
        uri += "/";
      }
      uri += "index.html";
    }
    request.uri = uri;
  } else if (wantsMarkdown && uri.endsWith("/index.html")) {
    // If requesting index.html but wants markdown, use the flattened .md file.
    // The homepage markdown output lives at /index.md.
    uri =
      uri === "/index.html"
        ? "/index.md"
        : uri.replace(/\/index\.html$/, ".md");
    request.uri = uri;
  }

  callback(null, request);
};