sousa-gecko/devtools/shared/network-observer/NetworkLocalMode.sys.mjs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/**
 * Implements the DevTools "Local Mode" backend, which redirects requests
 * to local files defined by the Web Developer.
 */

const lazy = {};

ChromeUtils.defineESModuleGetters(lazy, {
  FileUtils: "resource://gre/modules/FileUtils.sys.mjs",
  NetworkOverride:
    "resource://devtools/shared/network-observer/NetworkOverride.sys.mjs",
});

const xmlSerializer = new XMLSerializer();

export const NetworkLocalMode = {
  /**
   * Intercept a early channel that hasn't established a remote connection yet,
   * which matches a "Local Mode" origin and should be served from a local file
   * located in the folder passed as argument.
   *
   * @param {nsIHttpChannel} channel
   * @param {string} localFolderPath
   */
  interceptChannelWithPath(channel, localFolderPath) {
    if (channel.URI.spec.includes("%00")) {
      overrideChannelIntoCustomCode(channel, 400, "400 Bad request");
      return;
    }
    const path = decodeURI(channel.URI.filePath).replace(/^\/+/, "");

    // On Windows, replace all URI's '/' path separators with '\'
    let systemPath = path;
    if (Services.appinfo.OS === "WINNT") {
      systemPath = systemPath.replace(/\//g, "\\");
    }

    const overridePath = PathUtils.joinRelative(localFolderPath, systemPath);
    let file = new lazy.FileUtils.File(overridePath);

    if (!file.exists()) {
      // Create a 404 response to avoid leaving any request matching the host
      // to fallback to any potential existing http server.
      overrideChannelInto404(channel);
      return;
    }

    if (file.isFile()) {
      // This is the typical codepath redirecting to a existing local file
      lazy.NetworkOverride.overrideChannelWithFilePath(channel, file.path);
      return;
    }

    if (file.isDirectory()) {
      // Before showing a directory listing, try to match a valid index HTML file
      file.append("index.html");
      if (file.exists() && file.isFile()) {
        // This is the typical codepath redirecting to a existing local file
        lazy.NetworkOverride.overrideChannelWithFilePath(channel, file.path);
        return;
      }
      file = file.parent;
      file.append("index.htm");
      if (file.exists() && file.isFile()) {
        // This is the typical codepath redirecting to a existing local file
        lazy.NetworkOverride.overrideChannelWithFilePath(channel, file.path);
        return;
      }
      file = file.parent;

      // When we are trying to load a directory, return a file listing instead of 404
      // as that's really handy and behaves like a typical development http server.
      overrideChannelWithDirectoryListing(channel, path, file);
      return;
    }

    // In case it is neither a file, nor a directory?
    overrideChannelInto404(channel);
  },
};

/**
 * Make it so that an in-flight channel that just started
 * is converted into a 404 response for when there is no matching local file
 * for that request.
 *
 * @param {nsIHttpChannel} channel
 */
function overrideChannelInto404(channel) {
  overrideChannelIntoCustomCode(
    channel,
    404,
    "404 Not Found",
    `No local file for: ${channel.URI.filePath}`
  );
}

/**
 * Make it so that an in-flight channel that just started
 * is converted into a custom response with a custom HTTP status code.
 *
 * @param {nsIHttpChannel} channel
 * @param {number} status
 *        The returned status code
 * @param {string} statusText
 *        The returned status text
 * @param {undefined|string} message
 *        The message displayed in the returned HTML page. Will default to status text if omitted.
 */
function overrideChannelIntoCustomCode(
  channel,
  status,
  statusText,
  message = statusText
) {
  const replacedHttpResponse = Cc[
    "@mozilla.org/network/replaced-http-response;1"
  ].createInstance(Ci.nsIReplacedHttpResponse);

  replacedHttpResponse.responseStatus = status;
  replacedHttpResponse.responseStatusText = statusText;

  // We don't have access to a document, and we can't create a DocumentFragment from here,
  // so use DOMParser to create a new document that we can use to build our listing page.
  const doc = new DOMParser().parseFromString(
    "<!DOCTYPE html><html/>",
    "text/html"
  );

  // Compute a simple, but meaningful HTML file for the error
  const h1 = doc.createElement("h1");
  h1.append("DevTools Local Mode");
  const p = doc.createElement("p");
  p.textContent = message;
  doc.body.append(h1, p);

  const serializedDoc = xmlSerializer.serializeToString(doc);

  replacedHttpResponse.responseBody = serializedDoc;

  channel
    .QueryInterface(Ci.nsIHttpChannelInternal)
    .setResponseOverride(replacedHttpResponse);
}

/**
 * Replace the content of an in-flight channel that just started
 * that matches a local mode folder into an HTML page listing of
 * the available files in that folder.
 *
 * @param {nsIHttpChannel} channel
 * @param {string} folderPath
 * @param {nsILocalFile} file
 */
async function overrideChannelWithDirectoryListing(channel, folderPath, file) {
  const replacedHttpResponse = Cc[
    "@mozilla.org/network/replaced-http-response;1"
  ].createInstance(Ci.nsIReplacedHttpResponse);

  replacedHttpResponse.responseStatus = 200;
  replacedHttpResponse.responseStatusText = "OK";
  replacedHttpResponse.setResponseHeader("Content-Type", "text/html", false);

  // `setResponseOverride` has to be called synchronously after before-connect event
  // to really intercept the request.
  // Workaround this by suspending the request until we asynchronously retrieve
  // the directory listing content
  channel.suspend();

  // We don't have access to a document, and we can't create a DocumentFragment from here,
  // so use DOMParser to create a new document that we can use to build our listing page.
  const doc = new DOMParser().parseFromString(
    "<!DOCTYPE html><html/>",
    "text/html"
  );

  // Compute a simple, but meaningful HTML file for the listing
  const h2 = doc.createElement("h2");
  h2.append(PathUtils.filename(file.path));
  const ul = doc.createElement("ul");

  const children = await IOUtils.getChildren(file.path);
  for (const childPath of children.sort()) {
    const filename = PathUtils.filename(childPath);
    const absolutePath =
      "/" +
      folderPath +
      (!folderPath || folderPath.endsWith("/") ? "" : "/") +
      filename;
    const li = doc.createElement("li");
    const a = doc.createElement("a");
    a.href = absolutePath;
    a.append(filename);
    li.append(a);
    ul.append(li);
  }
  doc.body.append(h2, ul);

  const serializedDoc = xmlSerializer.serializeToString(doc);

  replacedHttpResponse.responseBody = serializedDoc;

  channel
    .QueryInterface(Ci.nsIHttpChannelInternal)
    .setResponseOverride(replacedHttpResponse);

  channel.resume();
}