How should I implement an auto-updater?

Question

Many programs include an auto-updater, where the program occasionally looks online for updates, and then downloads and applies any updates that are found. Program bugs are fixed, supporting files are modified, and things are (usually) made better.

Unfortunately no matter how hard I look, I can't find information on this process anywhere. It seems like the auto-updaters that have been implemented have either been proprietary or not considered important.

It seems fairly easy to implement the system that looks for updates on a network and downloads them if they are available. That part of the auto-updater will change significantly from implementation to implementation. The question is what are the different approaches of applying patches. Just downloading files and replacing old ones with new ones, running a migration script that was downloaded, monkey patching parts of the system, etc.? Concepts are preferred, but examples in Java, C, Python, Ruby, Lisp, etc. would be appreciated.

Answer 1

I think that "language agnostic" is going to be a limiting factor here. Applications come in so many shapes and sizes that there is no one-size-fits-all answer. I have implemented several auto-updaters in several languages, and no two were similar.

The most general philosophy is that the application checks with some home location (web address, web query, corporate network location, etc.) to either ask if it's version is current, or ask what the most current version is. If the answer calls for an update, that process will be different for each situation.

A popular alternative is to invite the home location to run a script when the application is initiated. The script can check the version, download updates if necessary, and ask for usage feedback, for example.

We can probably help better if you narrow the parameters.

UPDATE: The approach to "patching" also depends on the nature of the application, and there's a very wide diversity here. If you have a single executable file, for instance, then it's probably most practical to replace the executable. If your application has many files, you should look for ways to minimize the number of files replaced. If your application is highly customized or parameterized, you should strive to minimize the re-tailoring effort. If your application employs interpreted code (such as an Excel VBA application or MS Access MDB application), then you may be able to replace parts of the code. In a Java application you may only need to replace a JAR file, or even a subset of the JAR contents. You'll also need to have a way to recognize the current client version, and update it appropriately. I could go on and on, but I hope you see my point about diversity. This is one of those many times when the best answer usually starts with "Well, it depends ...!" That's why so many answers include "Please narrow the parameters."

Answer 2

The simplest approach would be to have your program query a server (website) to see if there is an update. If there is an update you could display a message to the user that prompts them to download a newer version and provides a link.

An alternative and more complex solution would be to create a small windows service (or unix daemon) that checks periodically to see if there are updates, this service can download the update and launch the installer.

The general architecture is that you have a central server that you control that knows the latest version and where to get it. Then the programs query the server. I am not going to include sample code because it is highly defendant on the server and the format you choose. It is not terrible difficult though.

Answer 3

First you need a file on your application home web site with the latest version. The best way I think to have special SQL table for this task and populate it automatically after publishing new version / nightly build completion. Your application creates new thread which requests built-in http link with version and compares in with current. In .NET use can use code like this:

Version GetLatestVersion() {
HttpWebRequestrequest = (HttpWebRequest)WebRequest.Create(new Uri(new Uri(http://example.net), "version.txt));
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
if (request.HaveResponse)
{
  StreamReader stream = new StreamReader(response.GetResponseStream(), Encoding.Default);
  return new Version(stream.ReadLine());
}
else
{
  return null;
}
}

Version latest = GetLatestVersion();
Version current = new Version(Application.ProductVersion);
if (current < latest)
{
  // you need an update
}
else
{
  // you are up-to-date
}

In this example, version.php in only one plain string like 1.0.1.0.

Another tip I can give - how to download an update. I like very much next idea: in the resources of your application there is a string of CLR-code which you compile on-the-fly (using CodeDom) to a temporary folder, main application calls it and goes to close. Updater reads arguments, settings or registry and downloads new modules. And calls main application which deletes all temporary files. Done!

(But everything here is about .NET)

Answer 4

Be sure to also consider the security implications of sucking down information about the update, as well as the update binaries themselves.

Do you trust the source of the download? You maybe phoning home to got your update, but what if there is a man in the middle who redirects to a malicious server. An HTTPS or similar secure connection will help, but double checking the bits that you eventually download by using a digital signature check is recommended.

Answer 5

In a Java-Webstart setting you start a JNLP file which then triggers the download of the Jar files needed to run the application. Everytime webstart checks if there are newer versions of the Jars and would download them replacing the locally cached ones. With a tool named jardiff you will create only diffs towards the newer jars and distribute these via the server (e.g. only get an update).

Pros:

• always up to date

Cons:

• you need an application server (tomcat, JBoss) in order to distribute the files
• you need an internet connection in order to get the application

Answer 6

This is not so much a complete answer, but rather one example of auto-updating mechanism I implemented recently. The situation is a little different from the tradition Firefox-type of user application, since it was an internal tool used at work.

Basically, it's a little script that manages a queue of Subversion branches to be built and packaged in an installer. It reads a little file, where the names of the branches are written, takes the first one, re-writes it at the end of the file, and launches the build process, which involves calling a bunch of scripts. The configuration for each branch to build is written in a .INI file, stored in a Subversion repository along with the tool itself.

Because this tool runs on several computers, I wanted a way to update it automatically on all machines as soon as I made a change either to the tool itself, or to the configuration scripts.

The way I implemented it was simple: when I launch the tool, it becomes an "outer shell". This outer shell does 2 very simple things:

• svn update on itself and on the configuration files
• launch itself again, this time as the "inner shell", the one that actually handles one configuration (and then exits again).

This very simple update-myself-in-a-loop system has served us very well for a few months now. It's very elegant, because it is self-contained: the auto-updater is the program itself. Because "outer shell" (the auto-updater part) is so simple, it doesn't matter that it does not benefit from the updates as the "inner shell" (which gets executed from the updated source file every time).

Answer 7

The simplest solutions (used by many programs) is running the uninstaller for the previous version and the running the installer for the new one (optionally skipping questions which the user has already answered, like the EULA). The only catch is that the new version must be able to read the configuration options from the old version.

Also, on Windows you can't delete an executable file which is in use, so you probably will want to drop a small executable in Temp folder, which runs the whole process and then delete it at the end from the instance of the new version which got launched (or just register it to be deleted at the next reboot).

Answer 8

Reading Carl Seleborgs answer gave me some ideas how a generic code-repository could be useful.

svn comes with a tool called svnsync, which sort of behaves like an svn export but keeps track of the actual revision your export is at.

Someone could utilize this system in order to only fetch the changed files from the users actual revision.

In actuality, you will have a repository with the binaries compiled, and running svnsync will only fetch the binaries that has been modified. It might also be able to merge local changes to text-based configuration files with new configuration-options.

Answer 9

The function of installing a patch to a program is basically one of the basic functions of an installer. Installer software is documented in numerous places but usually on a per-installer basis: There the Microsoft Installer (with Install Shield Extensions), Ruby gems, Java .jar files, the various Linux package manager systems (RPM, Apt-get)and others.

These are all complex systems which solve the problem of patching program in general but for slightly different systems. To decide what is best for you, consider which of these system your application most resembles. Rolling your own is fine but looking at these systems is a place to start.

Answer 10

Because auto updating is a common scenario, most languages have at least one package available to support this. (Below I list some of the available packages)

One of the really nice idea's is the ClickOnce distribution for .NET, it's an installer which sandboxes your application and installs in the user context, so no administrator rights required. You can configure the ClickOnce in your publish to check for updates each application start.

Java has Java Web Start which offers the same kind of functionality for java applets.

Delphi has numerous articles about auto-updating, Torry has a list of WebUpdate components, for instance GoUpdater seems to have a very wide range of functionality.

They all use a website/network share to check for a new version and than retrieve either a patch or a complete install file and run it. So you should try to find a nice package for your application, to save you the hassle of developing and maintaining your own solution.

Answer 11

You can write an internal module of your application to do updates. You can write an external mini application to do updates.

Also look at .NET on-the-fly compilation technology, it makes possible to create such mini application on-the-fly on demand. For example, http://fly.sf.net/

Answer 12

One thing that hasn't really been mentioned is that you should seriously consider that the user running your program might not actually have sufficient privileges to upgrade it. This should be pretty common at least for business users, probably less so for home users.

I'm always working with a (self-imposed) limited account for security reasons and it always pisses me off that most auto-updaters simply assume that I'm running as admin and then after downloading just fail and offer no other way of performing the update other than actually closing the program and running it again in an administrative context. Most do not even cache the downloaded update and have to do it all over again.

It'd be much better if the auto-updater would simply prompt for admin credentials when needed and get on with it.

Answer 13

I'm going to assume answer for Windows.

This way seems to work well.

In the installer do:
1. Create a manual-start service that runs as LocalSystem that when started does the update then stops.
2. Change the service permissions so all users can start the service (if all users should be able to update w/o admin rights).
3. Change the main program to check for updates when started using a simple mechanism. If it detects an update, prompt if the user wants to apply it.
4. If user accepts the update, start the service.

If the architecture allows for it, create a way to monitor the update as it is running.

Answer 14

Let me start by saying we offer a complete updating solution which includes:

• An open source updater, wyUpdate, written in C#
• The free AutomaticUpdater control that you can just add to your .NET app's form
• wyBuild is used to build patches and manage your versions

wyUpdate handles all of the Vista/Windows 7 UAC problems and all the file permission problems that inevitably pop up when you're trying to update complex software.

That being said, if you want to build your own updater here are some tips:

Building your own updater

A good place to start is the wyUpdate C# source code I mentioned above. You can cannibalize it and use it for your own purposes. Some of the algorithms it contains:

• Full Windows Vista / Windows 7 UAC support
• Ability for limited users to check and then update if they have credentials
• Support for wonky corporate inernet. (If you've ever worked with a corporation this is a real problem).
• Quick extracting, patching, and installing of files.
• Registry support.
• Roll back files & registry on error or cancellation by the user
• Self-update (no files left behind)

We also have the file specifications here.

Automatic updating

Since being automatic is a requirement let me tell you how we do it with our AutomaticUpdater control.

We use named pipes to communicate between the standalone updater (wyUpdate) and the Automatic Updater control sitting on your program's form. wyUpdate reports progress to the Automatic Updater, and the Automatic Updater can tell wyUpdate to cancel progress, to start downloading, start extracting, etc.

This keeps the updater separate from your application.

In fact, the exact named pipes C# code we use is included in an article I wrote a little while back: Multi-process C# app like Google Chrome.