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Apple's iOS developer guidelines state:

3.3.2 — An Application may not itself install or launch other executable code by any means, including without limitation through the use of a plug-in architecture, calling other frameworks, other APIs or otherwise. No interpreted code may be downloaded or used in an Application except for code that is interpreted and run by Apple’s Documented APIs and built-in interpreter(s).

Assuming that downloading data - like XML and images, or a game level description, for example - at run-time is allowed (as is my impression?), I am wondering where they draw the line between "data" and "code". Picture the scenario of an app that delivers interactive "presentations" to users (like a survey, for instance). Presentations are added continuously to the server and different presentations are made available to different users, so they cannot be part of the initial app download (which would be the whole point). They are described in XML format, but being interactive, they might contain conditional branching of this sort (shown in pseudo form to exemplify):

<options id="Gender">
    <option value="1">Male</option>
    <option value="2">Female</option>
</options>

<branches id="Gender">
    <branch value="1">
        <image src="Man" /> 
    </branch>
    <branch value="2">
        <image src="Woman" /> 
    </branch>
</branches>

When this XML is interpreted and "played" within the app, the above would be presented in two steps. First a selection screen is shown, where the user can click on either of the two choices ("Male" or "Female"). Next, an image will be [downloaded dynamically] and displayed based on the choice made in the previous step.

Now, from this, it's easy to imagine additional tags, describing further logic still. For example, a containing tag could be added:

<loop count="3">

    <options... />
    <branches... />

</loop>

The result here being that the selection screen / image screen pair would be sequentially presented three times over, of course.

Or imagine some format describing a level in a game. It is perhaps natural to view that as passive "data", but if it includes, say, several doorways that the user can go through and with various triggers, traps and points attached to them etc - isn't that the same as using a script (or, indeed, interpreted code) - to describe execution sequences, options and their conditional responses?

Assuming that the interpretation engine for the data is already present in the app and that such "presentations" can only be consumed (not created or edited) in the app, how would this fare against Apple's iOS guidelines? Doesn't XML basically constitute a scripting language in this sense (couldn't any program in an interpreted language be described in XML)?

Would it be OK if the proprietary scripting language (ref the XML used above) was strictly sandboxed (how can they tell?) and not given access to the operating system in any way (but able to download content - like a survey or a game level - dynamically as well as upload results - answers or scores - to the authoring server)?

Where does the line go?

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  • You can't know it exactly. Only Apple knows that. See, Codea which uses an embedded Lua interpreter and lets the user write code has successfully gotten through the filter. Commented Oct 19, 2012 at 11:48
  • Interesting. Although I am more concerned with the ability to download new "presentations" ("scripts", if you will) than the user being able to write/edit code locally. Commented Oct 19, 2012 at 12:03
  • I believe the user being liberately able to execute any code is far beyond what you want :) So I'd say your app being accepted has a greater chance than it not being accepted, but again, who knows. Commented Oct 19, 2012 at 12:46
  • 1
    Except for the fact that being able to download scripts has the potential to be regarded as a platform, challenging the exclusivity of the AppStore (which is also partly the reason for not generally allowing for [downloaded] interpreted code). Plus, being able to run your own [locally created] code on your own device could be said to pose far less risk than allowing a piece of code to be downloaded to and executed on millions of devices, including uploading information from the device to the server (not sure whether Codea has such capabilities). Commented Oct 19, 2012 at 12:51
  • Also, take into account that you may download HTML5 code, just because you use Apple's own interpreter, which is the built-in WebKit framework. Commented Jan 15, 2013 at 16:10

7 Answers 7

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Update as of WWDC 2017

Programming tools such as Codea mentioned below are now explicitly allowed to download code. The App Store Guidelines currently say (emphasis mine):

2.5.2 Apps should be self-contained in their bundles, and may not read or write data outside the designated container area, nor may they download, install, or execute code, including other apps. Apps designed to teach, develop, or test executable code may, in limited circumstances, download code provided that such code is not used for other purposes. Such apps must make the source code provided by the Application completely viewable and editable by the user.

There is also this tweet citing more details on the relaxed clauses.

Original

Does your interpreted download allow the user to write infinite loops or recursion?

Apple allow Javascript because they provide the interpreter and can kill your code. I have a feeling I've read that it's a 10 second limit but I couldn't find it on the site with a few minutes searching. (Yes, my self-imposed timeout for writing an answer kicked in.)

I think you're pretty safe if what you do is declarative and doesn't allow obvious looping in the interpreter.

I would also avoid the use of the word "interpreter" in any descriptions visible to Apple including public discussion. Maybe "parser" would be safer.

Codea have skated along the edge of these definitions with their Lua environment and cannot download code. They had to remove a feature for downloading new packages as ".codea" files.

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4

Based on 3.3.2, they could reject an app for this. However, the scarier thing is that you could create the app, get it approved, have it be downloaded and used by many users, and then Apple could pull the app from the store.

Did you ever publish the app you described?

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1

There's a major difference between the Guidelines and actual practice by the App Review team.

The current Guidelines state:

2.7 Apps that download code in any way or form will be rejected

2.8 Apps that install or launch other executable code will be rejected

So, the old ban on interpreted code is gone, and replaced by a ban on apps that could be considered to be IDEs or self-modifying.

However in practice there are a number of apps which do this, hence the difference between theoria and praxis.

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1

You should take a look at what Apple has enabled in iOS7. It is now allowed to download and run JavaScript within your app.

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0

I think what Apple means is your application should not depend in another module, compiled product or executable in order to work that will be downloaded from a website/server and that compiled add-on was not reviewed by Apple.

Basically when I asked something similar they told me something like: "If your application will download another executable compiled code that such a ftp downloader, key decryption tool or something of this kind that was not approved my Apple. You are available to download data or files (such as XML, HTML, PDF files, images) that does not represents an application.

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Yes, but the question is where does the line go between "passive data" and "active data", i.e. data that represents logic that can be executed. Source code is also data. If the program downloading it can compile it or run it interpreted, then what. That's the issue here.
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The concept of the differences between 'code' and 'data' has been discussed on SO before. Please see this answer: https://stackoverflow.com/a/642476/200696

From Apple's perspective, this ban prevents un-reviewed executable content from the app store. It would be trivial to create a program which is approved by Apple, and then downloads executable content that changes the pre-approved behavior.

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The issue here was not differences between 'code' and 'data' in general, but specifically where Apple draws the line in the context of their AppStore. Moreover, this was regarding a situation where an app downloads data that the app itself, and only it, can 'execute' (i.e. not content that is natively or independably executable). Imagine a PowerPoint-like app that downloads PowerPoint-like presentations (but with the added functionality of built-in branching logic, for example) on demand and 'runs' them within itself, creating new 'user experiences' for each presentation.
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All I can tell you is I've released products which use XML to script behavior within the app and Apple has always approved them.

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