index.js

const isRenderer = require("is-electron-renderer");
const electron = require("electron");
const path = require("path");
const readChunk = require("read-chunk");
const fileType = require("file-type");
const extend = require("deep-extend");
const got = require("got");

const BrowserWindow = isRenderer
  ? electron.remote.BrowserWindow
  : electron.BrowserWindow;

const PDF_JS_PATH = path.join(__dirname, "pdfjs", "web", "viewer.html");

function isAlreadyLoadedWithPdfJs(url) {
  return url.startsWith(`file://${PDF_JS_PATH}?file=`);
}

function isFile(url) {
  return url.match(/^file:\/\//i);
}

function getMimeOfFile(url) {
  const fileUrl = url.replace(/^file:\/\//i, "");
  const buffer = readChunk.sync(fileUrl, 0, 262);
  const ft = fileType(buffer);

  return ft ? ft.mime : null;
}

function hasPdfExtension(url) {
  return url.match(/\.pdf$/i);
}

function isPDF(url) {
  return new Promise((resolve, reject) => {
    if (isAlreadyLoadedWithPdfJs(url)) {
      resolve(false);
    } else if (isFile(url)) {
      resolve(getMimeOfFile(url) === "application/pdf");
    } else if (hasPdfExtension(url)) {
      resolve(true);
    } else {
      got
        .head(url)
        .then(res => {
          if (res.headers.location) {
            isPDF(res.headers.location)
              .then(isit => resolve(isit))
              .catch(err => reject(err));
          } else {
            resolve(
              res.headers["content-type"].indexOf("application/pdf") !== -1
            );
          }
        })
        .catch(err => reject(err));
    }
  });
}

class PDFWindow extends BrowserWindow {
  constructor(opts) {
    super(
      extend({}, opts, {
        webPreferences: { nodeIntegration: false }
      })
    );

    this.webContents.on("will-navigate", (event, url) => {
      event.preventDefault();
      this.loadURL(url);
    });

    this.webContents.on("new-window", (event, url) => {
      event.preventDefault();

      event.newGuest = new PDFWindow();
      event.newGuest.loadURL(url);
    });
  }

  loadURL(url, options) {
    isPDF(url)
      .then(isit => {
        if (isit) {
          super.loadURL(
            `file://${path.join(
              __dirname,
              "pdfjs",
              "web",
              "viewer.html"
            )}?file=${decodeURIComponent(url)}`,
            options
          );
        } else {
          super.loadURL(url, options);
        }
      })
      .catch(() => super.loadURL(url, options));
  }
}

PDFWindow.addSupport = function(browserWindow) {
  browserWindow.webContents.on("will-navigate", (event, url) => {
    event.preventDefault();
    browserWindow.loadURL(url);
  });

  browserWindow.webContents.on("new-window", (event, url) => {
    event.preventDefault();

    event.newGuest = new PDFWindow();
    event.newGuest.loadURL(url);
  });

  const load = browserWindow.loadURL;
  browserWindow.loadURL = function(url, options) {
    isPDF(url).then(isit => {
      if (isit) {
        load.call(
          browserWindow,
          `file://${PDF_JS_PATH}?file=${decodeURIComponent(url)}`,
          options
        );
      } else {
        load.call(browserWindow, url, options);
      }
    });
  };
};

module.exports = PDFWindow;