firefox/browser/extensions/webcompat/lib/custom_functions.js

/* 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/. */

"use strict";

/* globals browser */

const replaceStringInRequest = (
  requestId,
  inString,
  outString,
  inEncoding = "utf-8"
) => {
  const filter = browser.webRequest.filterResponseData(requestId);
  const decoder = new TextDecoder(inEncoding);
  const encoder = new TextEncoder();
  const RE = new RegExp(inString, "g");
  const carryoverLength = inString.length;
  let carryover = "";

  filter.ondata = event => {
    const replaced = (
      carryover + decoder.decode(event.data, { stream: true })
    ).replace(RE, outString);
    filter.write(encoder.encode(replaced.slice(0, -carryoverLength)));
    carryover = replaced.slice(-carryoverLength);
  };

  filter.onstop = () => {
    if (carryover.length) {
      filter.write(encoder.encode(carryover));
    }
    filter.close();
  };
};

const interventionListeners = new Map();

function rememberListener(intervention, key, listener) {
  if (!interventionListeners.has(intervention)) {
    interventionListeners.set(intervention, new Map());
  }
  const map = interventionListeners.get(intervention);
  if (map.has(key)) {
    throw new Error(`multiple custom listeners have the same key ${key}`);
  }
  map.set(key, listener);
}

function forgetListener(intervention, key) {
  const map = interventionListeners.get(intervention);
  if (!map) {
    return undefined;
  }
  const listener = map.get(key);
  map.delete(key);
  return listener;
}

var CUSTOM_FUNCTIONS = {
  alter_response_headers: {
    details: ["headers", "replacement"],
    optionalDetails: ["fallback", "replace", "types", "urls"],
    getKey(config) {
      return `alter_headers:${JSON.stringify(config)}`;
    },
    enable(config, intervention) {
      let { fallback, headers, replace, replacement, types, urls } = config;
      if (!urls) {
        urls = Object.values(intervention.bugs)
          .map(bug => bug.matches)
          .flat()
          .filter(v => v !== undefined);
      }
      const regex =
        replace === null ? null : new RegExp(replace ?? "^.*$", "gi");
      const listener = evt => {
        let found = false;
        const responseHeaders = [];
        for (const header of evt.responseHeaders) {
          if (headers.includes(header.name.toLowerCase())) {
            if (regex !== null && replacement !== null) {
              found = true;
              const value = header.value.replaceAll(regex, replacement);
              responseHeaders.push({ name: header.name, value });
            }
          } else {
            responseHeaders.push(header);
          }
        }
        if (!found && (replace === undefined || typeof fallback === "string")) {
          const value = fallback ?? replacement;
          if (value !== null) {
            responseHeaders.push({
              name: headers[0],
              value,
            });
          }
        }
        return { responseHeaders };
      };
      browser.webRequest.onHeadersReceived.addListener(
        listener,
        { types, urls },
        ["blocking", "responseHeaders"]
      );
      rememberListener(intervention, this.getKey(config), listener);
    },
    disable(config, intervention) {
      const listener = forgetListener(intervention, this.getKey(config));
      if (listener) {
        browser.webRequest.onHeadersReceived.removeListener(listener);
      }
    },
  },
  replace_string_in_request: {
    details: ["find", "replace", "urls"],
    optionalDetails: ["types"],
    enable(details) {
      const { find, replace, urls, types } = details;
      const listener = (details.listener = ({ requestId }) => {
        replaceStringInRequest(requestId, find, replace);
        return {};
      });
      browser.webRequest.onBeforeRequest.addListener(
        listener,
        { urls, types },
        ["blocking"]
      );
    },
    disable(details) {
      const { listener } = details;
      browser.webRequest.onBeforeRequest.removeListener(listener);
      delete details.listener;
    },
  },
  run_script_before_request: {
    details: ["message", "urls", "script"],
    optionalDetails: ["types"],
    enable(details, intervention) {
      const { bug } = intervention;
      const { message, script, types, urls } = details;
      const warning = `${message} See https://bugzilla.mozilla.org/show_bug.cgi?id=${bug} for details.`;

      const listener = (details.listener = evt => {
        const { tabId, frameId } = evt;
        return browser.tabs
          .executeScript(tabId, {
            file: script,
            frameId,
            runAt: "document_start",
          })
          .then(() => {
            browser.tabs.executeScript(tabId, {
              code: `console.warn(${JSON.stringify(warning)})`,
              runAt: "document_start",
            });
          })
          .catch(err => {
            console.error(
              "Error running script before request for webcompat intervention for bug",
              bug,
              err
            );
          });
      });

      browser.webRequest.onBeforeRequest.addListener(
        listener,
        { urls, types: types || ["script"] },
        ["blocking"]
      );
    },
    disable(details) {
      const { listener } = details;
      browser.webRequest.onBeforeRequest.removeListener(listener);
      delete details.listener;
    },
  },
};