In my Main.js
const { getMostRecentBrowserWindow } = require('sdk/window/utils');
var chromewin = getMostRecentBrowserWindow();
chromewin.PrintUtils.printPreview(chromewin.PrintPreviewListener);
Browser console warning: "Module: .../main has no authority to load: sdk/window/utils"
Your addon contains a corrupted or otherwise incomplete harness-options.json. Either rebuild your addon with a fresh copy of Addon SDK, or (more tricky) manually edit harness-options.json so that under the requirements section all required modules are listed.
Hmm I would try this instead:
const { getMostRecentBrowserWindow } = require('sdk/window/utils');
getMostRecentBrowserWindow().PrintUtils.printPreview(getMostRecentBrowserWindow().PrintPreviewListener);
My guess is that you are trying to use your chromewin ref after that window has closed.
Related
I'have migrate to NativeScript 6.0 and need some help on how to download and open a file with Android support lib (AndroidX) in the Downloads folder.
Actually, in NS 5.x, i have used FileProvider from Android support lib (android.support.v4.content.FileProvider) and works great. After the migration, using (androidx.core.content.FileProvider), i have errors opening the App.
But in Android docs, i can't find any method or information to migrate the code for Native download and Open (Downloads Folder).
Previous Method:
private openFile(fileName: string, mimeType: string, extension: string) {
try {
if (isAndroid) {
const intent = new android.content.Intent(android.content.Intent.ACTION_VIEW);
const context = applicationModule.android.context;
console.log("android.ctx=", context);
const nativeFile = new java.io.File(fileName);
console.log("nativeFile=", nativeFile);
const uri = android.support.v4.content.FileProvider.getUriForFile(context, "com.otisw.gescon.app.provider", nativeFile);
intent.setDataAndType(uri, mimeType);
intent.addFlags(android.content.Intent.FLAG_GRANT_READ_URI_PERMISSION);
const choosedIntent = android.content.Intent.createChooser(intent, "Open file...");
console.log("choosedIntent=>", choosedIntent);
context.startActivity(choosedIntent);
} else {
// const documents = fs.knownFolders.currentApp();
// const file = this.documents.getFile(fileName);
const open = utils.ios.openFile(fileName);
}
} catch (e) {
console.log(e);
}
}
Tried:
private openFile(fileName: string, mimeType: string, extension: string) {
try {
if (isAndroid) {
const intent = androidx.core.content.IntentCompat.makeMainSelectorActivity(
"android.content.Intent.ACTION_VIEW",
"??"
);
File reference.d.ts:
/// <reference path="./node_modules/tns-core-modules/tns-core-modules.d.ts" />
/// <reference path="./node_modules/tns-platform-declarations/ios.d.ts" />
/// <reference path="./node_modules/tns-platform-declarations/android/androidx-26.d.ts" />
Does anyone tries to upgrade the code for Download and Open from NativeScript to new AndroidX or knows a workaround to do this ?
Thanks!
You will have to use androidx.core.content.FileProvider on AndoridX and android.support.v4.content.FileProvider in lower versions.
With the release of Android 9.0 (API level 28) there is a new version
of the support library called AndroidX which is part of Jetpack. The
AndroidX library contains the existing support library and also
includes the latest Jetpack components.
You can continue to use the support library. Historical artifacts
(those versioned 27 and earlier, and packaged as android.support.*)
will remain available on Google Maven. However, all new library
development will occur in the AndroidX library.
We recommend using the AndroidX libraries in all new projects. You
should also consider migrating existing projects to AndroidX as well.
i'm trying to open app store application programmatically in my app.
what i'm trying to do is that i'm calling a service to check at the current app version and if it needs update i should open app store application to let the user update the my app.
note: the app not published yet to the store, i'm still in coding phase.
i tried to use the following code in ViewDidLoad method, but it's not working (nothing happened):
var nsurl = new NSUrl("itms://itunes.apple.com");
UIApplication.SharedApplication.OpenUrl(nsurl);
A direct link via itms: will only work in an actual device, if you are testing on a simulator, use https://itunes.apple.com/us/genre/ios/id36?mt=8 instead.
I would recommend using itms:// link on the actual device as it prevents the redirects that user sees when using a https:// link to open iTunes.
bool isSimulator = Runtime.Arch == Arch.SIMULATOR;
NSUrl itunesLink;
if (isSimulator)
{
itunesLink = new NSUrl("https://itunes.apple.com/us/genre/ios/id36?mt=8");
}
else
{
itunesLink = new NSUrl("itms://itunes.apple.com");
}
UIApplication.SharedApplication.OpenUrl(itunesLink, new NSDictionary() { }, null);
Instead of opening the external Store app on the device, you might want to consider keeping the user inside of your app by using a SKStoreProductViewController:
bool isSimulator = Runtime.Arch == Arch.SIMULATOR;
if (!isSimulator)
{
var storeViewController = new SKStoreProductViewController();
storeViewController.Delegate = this;
var id = SKStoreProductParameterKey.ITunesItemIdentifier;
var productDictionaryKeys = new NSDictionary("SKStoreProductParameterITunesItemIdentifier", 123456789);
var parameters = new StoreProductParameters(productDictionaryKeys);
storeViewController.LoadProduct(parameters, (bool loaded, NSError error) =>
{
if ((error == null) && loaded)
{
this.PresentViewController(storeViewController, true, () =>
{
Console.WriteLine("SKStoreProductViewController Completed");
});
}
if (error != null)
{
throw new NSErrorException(error);
}
});
}
else
{
var itunesLink = new NSUrl("https://itunes.apple.com/us/genre/ios/id36?mt=8");
UIApplication.SharedApplication.OpenUrl(itunesLink, new NSDictionary() { }, null);
}
NSBundle.MainBundle.InfoDictionary["CFBundleVersion"]
Returns you the current app version.
To open the Apple Appstore just let the user navigate to the appstore link, Apple will automaticly detect that the user is using an iPhone and will open the Appstore for them.
Test yourself:
Open the following link in safari: Whatsapp in the Appstore
It will automatically open the appstore.
When you create app on iTunesConnect you can get url to your future app in AppStore even if you didn't release it yet. You can find it under App Information tab:
In your app you can just open it:
var nsurl = new NSUrl("https://itunes.apple.com/us/app/mygreatapp/id123456789");
UIApplication.SharedApplication.OpenUrl(nsurl);
I'm looking to deploy an auto-update feature to an Electron installation that I have, however I am finding it difficult to find any resources on the web.
I've built a self contained application using Adobe Air before and it seemed to be a lot easier writing update code that effectively checked a url and automatically downloaded and installed the update across Windows and MAC OSX.
I am currently using the electron-boilerplate for ease of build.
I have a few questions:
How do I debug the auto update feature? Do I setup a local connection and test through that using a local Node server or can I use any web server?
In terms of signing the application I am only looking to run apps on MAC OSX and particularly Windows. Do I have to sign the applications in order to run auto-updates? (I managed to do this with Adobe Air using a local certificate.
Are there any good resources that detail how to implement the auto-update feature? As I'm having difficulty finding some good documentation on how to do this.
I am also new to Electron but I think there is no simple auto-update from electron-boilerplate (which I also use). Electron's auto-updater uses Squirrel.Windows installer which you also need to implement into your solution in order to use it.
I am currently trying to use this:
https://www.npmjs.com/package/electron-installer-squirrel-windows
And more info can be found here:
https://github.com/atom/electron/blob/master/docs/api/auto-updater.md
https://github.com/squirrel/squirrel.windows
EDIT: I just opened the project to try it for a while and it looks it works. Its pretty straightforward. These are pieces from my gulpfile.
In current configuration, I use electron-packager to create a package.
var packager = require('electron-packager')
var createPackage = function () {
var deferred = Q.defer();
packager({
//OPTIONS
}, function done(err, appPath) {
if (err) {
gulpUtil.log(err);
}
deferred.resolve();
});
return deferred.promise;
};
Then I create an installer with electron-installer-squirrel-windows.
var squirrelBuilder = require('electron-installer-squirrel-windows');
var createInstaller = function () {
var deferred = Q.defer();
squirrelBuilder({
// OPTIONS
}, function (err) {
if (err)
gulpUtil.log(err);
deferred.resolve();
});
return deferred.promise;
}
Also you need to add some code for the Squirrel to your electron background/main code. I used a template electron-squirrel-startup.
if(require('electron-squirrel-startup')) return;
The whole thing is described on the electron-installer-squirrel-windows npm documentation mentioned above. Looks like the bit of documentation is enough to make it start.
Now I am working on with electron branding through Squirrel and with creating appropriate gulp scripts for automation.
You could also use standard Electron's autoUpdater module on OS X and my simple port of it for Windows: https://www.npmjs.com/package/electron-windows-updater
I followed this tutorial and got it working with my electron app although it needs to be signed to work so you would need:
certificateFile: './path/to/cert.pfx'
In the task config.
and:
"build": {
"win": {
"certificateFile": "./path/to/cert.pfx",
"certificatePassword": "password"
}
},
In the package.json
Are there any good resources that detail how to implement the auto-update feature? As I'm having difficulty finding some good documentation on how to do this.
You don't have to implement it by yourself. You can use the provided autoUpdater by Electron and just set a feedUrl. You need a server that provides the update information compliant to the Squirrel protocol.
There are a couple of self-hosted ones (https://electronjs.org/docs/tutorial/updates#deploying-an-update-server) or a hosted service like https://www.update.rocks
Question 1:
I use Postman to validate that my auto-update server URLs return the response I am expecting. When I know that the URLs provide the expected results, I know I can use those URLs within the Electron's Auto Updater of my Application.
Example of testing Mac endpoint with Postman:
Request:
https://my-server.com/api/macupdates/checkforupdate.php?appversion=1.0.5&cpuarchitecture=x64
JSON Response when there is an update available:
{
"url": "https:/my-server.com/updates/darwin/x64/my-electron=app-x64-1.1.0.zip",
"name": "1.1.0",
"pub_date": "2021-07-03T15:17:12+00:00"
}
Question 2:
Yes, your Electron App must be code signed to use the auto-update feature on Mac. On Windows I'm not sure because my Windows Electron app is code signed and I did not try without it. Though it is recommended that you sign your app even if the auto-update could work without it (not only for security reasons but mainly because otherwise your users will get scary danger warnings from Windows when they install your app for the first time and they might just delete it right away).
Question 3:
For good documentation, you should start with the official Electron Auto Updater documentation, as of 2021-07-07 it is really good.
The hard part, is figuring out how to make things work for Mac. For Windows it's a matter of minutes and you are done. In fact...
For Windows auto-update, it is easy to setup - you just have to put the RELEASES and nupkg files on a server and then use that URL as the FeedURL within your Electron App's autoUpdater. So if your app's update files are located at https://my-server.com/updates/win32/x64/ - you would point the Electron Auto Updater to that URL, that's it.
For Mac auto-update, you need to manually specify the absolute URL of the latest Electron App .zip file to the Electron autoUpdater. So, in order to make the Mac autoUpdater work, you will need to have a way to get a JSON response in a very specific format. Sadly, you can't just put your Electron App's files on your server and expect it to work with Mac just like that. Instead, the autoUpdater needs a URL that will return the aforementioned JSON response. So to do that, you need to pass Electron's Auto Updater feedURL the URL that will be able to return this expected kind of JSON response.
The way you achieve this can be anything but I use PHP just because that's the server I already paid for.
So in summary, with Mac, even if your files are located at https://my-server.com/updates/darwin/x64/ - you will not provide that URL to Electron's Auto Updater FeedURL. Instead will provide another URL which returns the expected JSON response.
Here's an example of my main.js file for the Electron main process of my App:
// main.js (Electron main process)
function registerAutoUpdater() {
const appVersion = app.getVersion();
const os = require('os');
const cpuArchitecture = os.arch();
const domain = 'https://my-server.com';
const windowsURL = `${domain}/updates/win32/x64`;
const macURL = `${domain}/api/macupdates/checkforupdate.php?appversion=${appVersion}&cpuarchitecture=${cpuArchitecture}`;
//init the autoUpdater with proper update feed URL
const autoUpdateURL = `${isMac ? macURL : windowsURL}`;
autoUpdater.setFeedURL({url: autoUpdateURL});
log.info('Registered autoUpdateURL = ' + (isMac ? 'macURL' : 'windowsURL'));
//initial checkForUpdates
autoUpdater.checkForUpdates();
//Automatic 2-hours interval loop checkForUpdates
setInterval(() => {
autoUpdater.checkForUpdates();
}, 7200000);
}
And here's an example of the checkforupdate.php file that returns the expected JSON response back to the Electron Auto Updater:
<?php
//FD Electron App Mac auto update API endpoint.
// The way Squirrel.Mac works is by checking a given API endpoint to see if there is a new version.
// If there is no new version, the endpoint should return HTTP 204. If there is a new version,
// however, it will expect a HTTP 200 JSON-formatted response, containing a url to a .zip file:
// https://github.com/Squirrel/Squirrel.Mac#server-support
$clientAppVersion = $_GET["appversion"] ?? null;
if (!isValidVersionString($clientAppVersion)) {
http_response_code(204);
exit();
}
$clientCpuArchitecture = $_GET["cpuarchitecture"] ?? null;
$latestVersionInfo = getLatestVersionInfo($clientAppVersion, $clientCpuArchitecture);
if (!isset($latestVersionInfo["versionNumber"])) {
http_response_code(204);
exit();
}
// Real logic starts here when basics did not fail
$isUpdateVailable = isUpdateAvailable($clientAppVersion, $latestVersionInfo["versionNumber"]);
if ($isUpdateVailable) {
http_response_code(200);
header('Content-Type: application/json;charset=utf-8');
$jsonResponse = array(
"url" => $latestVersionInfo["directZipFileURL"],
"name" => $latestVersionInfo["versionNumber"],
"pub_date" => date('c', $latestVersionInfo["createdAtUnixTimeStamp"]),
);
echo json_encode($jsonResponse);
} else {
//no update: must respond with a status code of 204 No Content.
http_response_code(204);
}
exit();
// End of execution.
// Everything bellow here are function declarations.
function getLatestVersionInfo($clientAppVersion, $clientCpuArchitecture): array {
// override path if client requests an arm64 build
if ($clientCpuArchitecture === 'arm64') {
$directory = "../../updates/darwin/arm64/";
$baseUrl = "https://my-server.com/updates/darwin/arm64/";
} else if (!$clientCpuArchitecture || $clientCpuArchitecture === 'x64') {
$directory = "../../updates/darwin/";
$baseUrl = "https://my-server.com/updates/darwin/";
}
// default name with version 0.0.0 avoids failing
$latestVersionFileName = "Finance D - Tenue de livres-darwin-x64-0.0.0.zip";
$arrayOfFiles = scandir($directory);
foreach ($arrayOfFiles as $file) {
if (is_file($directory . $file)) {
$serverFileVersion = getVersionNumberFromFileName($file);
if (isVersionNumberGreater($serverFileVersion, $clientAppVersion)) {
$latestVersionFileName = $file;
}
}
}
return array(
"versionNumber" => getVersionNumberFromFileName($latestVersionFileName),
"directZipFileURL" => $baseUrl . rawurlencode($latestVersionFileName),
"createdAtUnixTimeStamp" => filemtime(realpath($directory . $latestVersionFileName))
);
}
function isUpdateAvailable($clientVersion, $serverVersion): bool {
return
isValidVersionString($clientVersion) &&
isValidVersionString($serverVersion) &&
isVersionNumberGreater($serverVersion, $clientVersion);
}
function getVersionNumberFromFileName($fileName) {
// extract the version number with regEx replacement
return preg_replace("/Finance D - Tenue de livres-darwin-(x64|arm64)-|\.zip/", "", $fileName);
}
function removeAllNonDigits($semanticVersionString) {
// use regex replacement to keep only numeric values in the semantic version string
return preg_replace("/\D+/", "", $semanticVersionString);
}
function isVersionNumberGreater($serverFileVersion, $clientFileVersion): bool {
// receives two semantic versions (1.0.4) and compares their numeric value (104)
// true when server version is greater than client version (105 > 104)
return removeAllNonDigits($serverFileVersion) > removeAllNonDigits($clientFileVersion);
}
function isValidVersionString($versionString) {
// true when matches semantic version numbering: 0.0.0
return preg_match("/\d\.\d\.\d/", $versionString);
}
I'm trying to use the Downloads.jsm lib of Firefox (it's new in Firefox 23) in a jetpack addin.
var {Cu} = require("chrome"); //works fine
const {Downloads} = Cu.import("resource://gre/modules/Downloads.jsm"); //works fine
But executing either of these functions has no effect:
download = Downloads.createDownload({source: "http://cdn.sstatic.net", target: "/tmp/kaki.html"}); //download is an object but has no function "start"
Downloads.simpleDownload("http://cdn.sstatic.net","/tmp/kaki.html");
Documentation:
https://developer.mozilla.org/en-US/docs/Mozilla/JavaScript_code_modules/Downloads.jsm
https://developer.mozilla.org/en-US/docs/Mozilla/JavaScript_code_modules/Downloads.jsm/Download
Do you have any idea, how to use these functions? I haven't found any examples on the web
The API functions return a promise, not the actual Download object.
In short, the following should work:
const {Downloads} = Cu.import("resource://gre/modules/Downloads.jsm", {});
var downloadPromise = Downloads.createDownload({source: "http://cdn.sstatic.net", target: "/tmp/kaki.html"})
downloadPromise.then(function success(d) {
d.start();
});
Read up on promises, and to make dealing with them a lot more fun, also Task.jsm
The API did change quite a bit recently; what is documented is the current Aurora-25 or later API. The "old" API is documented within the source.
A more complete example with Firefox <25 support is available in this gist.
Is there a way to detect if a particular file that is being downloaded is a Gmail attachment?
I am looking for a way to write a Greasemonkey script which would help me organize the downloads, based on their download sources, say Gmail email attachments would have a different behavior from other stuff.
So far, I've found out that attachments redirect to https://mail-attachment.googleusercontent.com/attachment/u/0/ , which I guess is not sufficient.
EDIT
Since an add-on would be more powerful than a userscript, I've decided to pursue the Add On idea. However, the problem of detection remains unsolved.
This is too complicated for just one question; it has at least these major parts:
Do you want to redirect downloads when the user clicks, or automatically download select files? Clarify the question.
Your GM script must identify the appropriate download links, and on which pages, and for which views? For gMail, this is not a trivial task, and the question needs to be clearer. It's worthy of a whole question just on this issue given the variety of views and AJAX involved.
Once identified, the script probably needs to intercept clicks on those links. (Depends on your goal (clarify!) and what the Firefox extension can do.)
Greasemonkey needs to interact with an extension that either intercepts the user-initiated download, or allows for an automatic download. I've detailed the auto-download approach, below.
Once your script has identified the appropriate file URLs and/or links (Open a new question for more help with that, and include pictures of the types of pages and links you want.), it can interface with a Firefox add-on, like the one below, to automatically save those files.
Automatically saving files from Greasemonkey with the help of an additional Add-on:
WARNING: The following is a working proof of concept for education only. It has no security features, and if you use it as-is, for actual surfing, some webpage or script writer or extension writer will use it to completely pwn your computer.
If you use the Add-on builder or SDK to install or "Test" the DANGER. DANGER. DANGER. File download utility,
Then you can use a Greasemonkey script, like this, to automatically save files:
// ==UserScript==
// #name _Call our File download add-on to trigger a file download.
// #include https://mail.google.com/mail/*
// #include https://stackoverflow.com/questions/14440362/*
// #require http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js
// #grant GM_addStyle
// ==/UserScript==
/*- The #grant directive is needed to work around a design change
introduced in GM 1.0. It restores the sandbox.
*/
var fileURL = "http://userscripts.org/scripts/source/29222.user.js";
var savePath = "D:\\temp\\";
var extensionLoaded = false;
window.addEventListener ("ImAlivefromExtension", function (zEvent) {
console.log ("The test extension appears to be loaded!", zEvent.detail);
extensionLoaded = true;
} );
window.addEventListener ("ReplyToDownloadRequest", function (zEvent) {
//var xxxx = JSON.parse (zEvent.detail);
console.log ("Extension replied: ", zEvent.detail);
} );
$("body").prepend ('<button id="gmFileDownloadBtn">Click to File download request.</button>');
$("#gmFileDownloadBtn").click ( function () {
if (extensionLoaded) {
detailVal = JSON.stringify (
{targFileURL: fileURL, targSavePath: savePath}
);
var zEvent = new CustomEvent (
"SuicidalDownloadRequestToAddOn",
{"detail": detailVal }
);
window.dispatchEvent (zEvent);
}
else {
alert ("The file download extension is not loaded!");
}
} );
You can test the script on this SO question page.
Note that any other extension, userscript, web page, or plugin can listen to or send spoof events, the only security, so far, is to limit which pages the extension runs on.
For reference, the extension source files are below. The rest is supplied by Firefox's Add-on SDK.
The content script:
var zEvent = new CustomEvent ("ImAlivefromExtension",
{"detail": "GM, DANGER, DANGER, DANGER, File download utility" }
);
window.dispatchEvent (zEvent)
window.addEventListener ("SuicidalDownloadRequestToAddOn", function (zEvent) {
console.log ("Extension received download request: ", zEvent.detail);
//-- Relay request to extension main.js
self.port.emit ("SuicidalDownloadRequestRelayed", zEvent.detail);
//-- Reply back to GM, or whoever is pretending to be GM.
var zEvent = new CustomEvent ("ReplyToDownloadRequest",
{"detail": "Your funeral!" }
);
window.dispatchEvent (zEvent)
} );
The background JS:
//--- For security, MAKE THESE AS RESTRICTIVE AS POSSIBLE!
const includePattern = [
'https://mail.google.com/mail/*',
'https://stackoverflow.com/questions/14440362/*'
];
let {Cc, Cu, Ci} = require ("chrome");
Cu.import ("resource://gre/modules/Services.jsm");
Cu.import ("resource://gre/modules/XPCOMUtils.jsm");
Cu.import ("resource://gre/modules/FileUtils.jsm");
let data = require ("sdk/self").data;
let pageMod = require ('sdk/page-mod');
let dlManageWindow = Cc['#mozilla.org/download-manager-ui;1'].getService (Ci.nsIDownloadManagerUI);
let fileURL = "";
let savePath = "";
let activeWindow = Services.wm.getMostRecentWindow ("navigator:browser");
let mod = pageMod.PageMod ( {
include: includePattern,
contentScriptWhen: 'end',
contentScriptFile: [ data.url ('ContentScript.js') ],
onAttach: function (worker) {
console.log ('DANGER download utility attached to: ' + worker.tab.url);
worker.port.on ('SuicidalDownloadRequestRelayed', function (message) {
var detailVal = JSON.parse (message);
fileURL = detailVal.targFileURL;
savePath = detailVal.targSavePath;
console.log ("Received request to \ndownload: ", fileURL, "\nto:", savePath);
downloadFile (fileURL, savePath);
} );
}
} );
function downloadFile (fileURL, savePath) {
dlManageWindow.show (activeWindow, 1);
try {
let newFile;
let fileURIToDownload = Services.io.newURI (fileURL, null, null);
let persistWin = Cc['#mozilla.org/embedding/browser/nsWebBrowserPersist;1']
.createInstance (Ci.nsIWebBrowserPersist);
let fileName = fileURIToDownload.path.slice (fileURIToDownload.path.lastIndexOf ('/') + 1);
let fileObj = new FileUtils.File (savePath);
fileObj.append (fileName);
if (fileObj.exists ()) {
console.error ('*** Error! File "' + fileName + '" already exists!');
}
else {
let newFile = Services.io.newFileURI (fileObj);
let newDownload = Services.downloads.addDownload (
0, fileURIToDownload, newFile, fileName, null, null, null, persistWin, false
);
persistWin.progressListener = newDownload;
persistWin.savePrivacyAwareURI (fileURIToDownload, null, null, null, "", newFile, false);
}
} catch (exception) {
console.error ("Error saving the file! ", exception);
dump (exception);
}
}
So far from what you are saying,the only thing you can do is making add-on(Firefox) and Extension(for chrome if you want).
If you have closer look at download of attachment,it happens when:
1) You click on icon of attachments
2) If you click download
For these two things you can find the click event of <a> tag containing download_url value.You can easily do that using js/jquery for creting extension.
So you can write the functionality when user tries to download attachment.
You could use Gmail contextual gadgets to modify the behavior on the Google side:
Gmail Contexual Gadgets
Contextual Gadgets don't have direct access to attachments but server side, you could use IMAP to access the attachment (based on the Gmail message ID identified by the gadget):
Gmail IMAP Extensions
Using gadgets and server-side IMAP has the advantage of being browser-agnostic.
It's not entirely clear what you want to do differently with the downloaded Gmail attachment as opposed to any given download (save it to a different location? Perform actions upon the attachment data?) But the contextual gadget and IMAP should give you some chance to modify the attachment data as needed before the browser download begins.