/* 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";

var EXPORTED_SYMBOLS = ["Sniffer"];

const { XPCOMUtils } = ChromeUtils.import(
  "resource://gre/modules/XPCOMUtils.jsm"
);

XPCOMUtils.defineLazyPreferenceGetter(
  this,
  "gEnabled",
  "devtools.jsonview.enabled"
);

const JSON_VIEW_MIME_TYPE = "application/vnd.mozilla.json.view";

function getContentDisposition(channel) {
  try {
    return channel.contentDisposition;
  } catch (e) {
    // Channel doesn't support content dispositions
    return null;
  }
}

/**
 * This component represents a sniffer (implements nsIContentSniffer
 * interface) responsible for changing top level 'application/json'
 * document types to: 'application/vnd.mozilla.json.view'.
 *
 * This internal type is consequently rendered by JSON View component
 * that represents the JSON through a viewer interface.
 *
 * This is done in the .js file rather than a .jsm to avoid creating
 * a compartment at startup when no JSON is being viewed.
 */
class Sniffer {
  getMIMETypeFromContent(request, data, length) {
    if (request instanceof Ci.nsIChannel) {
      // JSON View is enabled only for top level loads only.
      if (
        gEnabled &&
        request.loadInfo?.isTopLevelLoad &&
        request.loadFlags & Ci.nsIChannel.LOAD_DOCUMENT_URI &&
        getContentDisposition(request) != Ci.nsIChannel.DISPOSITION_ATTACHMENT
      ) {
        // Check the response content type and if it's a valid type
        // such as application/json or application/manifest+json
        // change it to new internal type consumed by JSON View.
        if (/^application\/(?:.+\+)?json$/.test(request.contentType)) {
          return JSON_VIEW_MIME_TYPE;
        }
      } else if (request.contentType === JSON_VIEW_MIME_TYPE) {
        return "application/json";
      }
    }

    return "";
  }
}

Sniffer.prototype.QueryInterface = ChromeUtils.generateQI([
  "nsIContentSniffer",
]);