Designing and Debugging Mobile Apps with an Embedded, Scriptable Web Server
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This document discusses embedding a scriptable web server into mobile apps for debugging, mocking, tuning, and A/B testing. It describes using a lightweight web server like Swifter or NanoHTTPD and embedding the Lua scripting language to extend capabilities. Scripting allows implementing techniques like registering handlers, overloading functions, and interacting with app data structures during development and testing. The web server approach opens up flexible options for exploring designs and easing the development process.
![server[“/app-auth-token”] = { _ in
let aaToken = self.appSession.appAuthToken ?? “N/A”
return aaToken
}](https://image.slidesharecdn.com/burkematthew-ato19-191031144452/85/Designing-and-Debugging-Mobile-Apps-with-an-Embedded-Scriptable-Web-Server-17-320.jpg)
![server[“/showmarked”] = { _ in
guard let mainView = …
let markedView = mainView.viewWithTag(tagMark)
markedView?.backgroundColor = .red
return .ok(.text(“markedn”)
}](https://image.slidesharecdn.com/burkematthew-ato19-191031144452/85/Designing-and-Debugging-Mobile-Apps-with-an-Embedded-Scriptable-Web-Server-18-320.jpg)
![server[“/register”] = { request in
guard let method = request.params[“method”] else
guard let path = request.params[“path”] else { …
guard let script = request.params[“script”] else {
self.server.router.register(method, path, script)
}](https://image.slidesharecdn.com/burkematthew-ato19-191031144452/85/Designing-and-Debugging-Mobile-Apps-with-an-Embedded-Scriptable-Web-Server-19-320.jpg)
Designing and Debugging Mobile Apps with an Embedded, Scriptable Web Server
- 1. Designing and Debugging Mobile Apps with an Embedded, Scriptable Web Server Matthew Burke matthew.burke@capitalone.com All Things Open • Raleigh, NC • 14 October 2019 Just a taste of why you might want to do this and how you would do it. Reach out to me via email and I’d be happy to discuss at length
- 2. General Points • Value in a general-purpose, turn-key solution? • Easy enough to role your own • Security • Increases attack surface for your app • Do you trust your beta testers?
- 4. How easily can you expose your app’s data structures and configuration? Can do “simple” logging. Also can do more targeted analysis
- 5. Use Case 2: Mocking Two different scenarios for mocking: 1. Controlled testing 2. Backend doesn’t exist
- 6. Desired Operations • CRUD • list • dump/load • collect statistics C reate R ead U pdate D elete
- 7. Desired Features • Path variables • Header processing • URL-encoded Forms Others are context dependent. Unless you have specific needs, HTTPS support not needed.
- 8. Use Case 3: Tuning
- 9. CGFloat animationDuration = 0.5; Or should it be 0.4, or 0.3 or …
- 10. KA SwiftTweaks public struct ET: TweakLibraryType { public static let tint = Tweak(“General”, “Colors”, “Tint”, UIColor.blue) public static let marginVertical = Tweak<CGFloat>(… public static let defaultStore: TweakStore = … Note one alternative with some history behind it is a “Tweaking system” E.G. Kahn Academy’s implementation. Mention Facebook. A lot of overhead due to creating UI to adjust these values.
- 11. Be careful with your UI. Users will always surprise you. TAP Congress story
- 12. Use Case 3a: A/B Testing
- 13. Use Case 4: Server App Port
- 14. Mobile OS Application Application Server OS Shim
- 15. Implementation Notes 1: Web Server
- 16. • A number of drop-in alternatives exist: • Swifter: https://github.com/httpswift/swifter (iOS) • NanoHTTPD: https://github.com/NanoHttpd/nanohttpd (Android)
- 17. server[“/app-auth-token”] = { _ in let aaToken = self.appSession.appAuthToken ?? “N/A” return aaToken }
- 18. server[“/showmarked”] = { _ in guard let mainView = … let markedView = mainView.viewWithTag(tagMark) markedView?.backgroundColor = .red return .ok(.text(“markedn”) }
- 19. server[“/register”] = { request in guard let method = request.params[“method”] else guard let path = request.params[“path”] else { … guard let script = request.params[“script”] else { self.server.router.register(method, path, script) }
- 20. Implementation Notes 2: Scripting Engine
- 21. A few words about Lua Language choice: you want something light-weight and with a good API
- 22. Again, this is not necessarily production-quality code, although depending on your use case, it might be adequate. The main point here is that Lua's first-class functions allow you to fairly easily implement a range of techniques.
- 23. smt = debug.getmetatable(“some string”) smt.__mul = function(s, i) local result = “” for idx = 1, i do result = result .. s end end “foo” * 3 .. “bar” -- foofoofoobar Perhaps a slightly less whimsical example...here I overload multiplication to give string repetition.
- 24. The Lua C API: • fully re-entrant • information contained in a Lua State • communicate via a virtual stack of Lua values • registry—predefined Lua table • userdata for accessing host program data “C API Details” Slide
- 25. C Binding “C Binding Title” Slide
- 27. “Blink Implementation 1” Slide
- 28. “Blink Implementation 2” Slide
- 29. “Blink Implementation 3” Slide
- 30. “Blink Implementation 4” Slide
- 31. Summary • Embedding a webserver during development opens up a range of techniques to ease development and explore the design space • Scripting naturally extends this capability—you don’t have to decide everything up front • Lua is a very solid choice for this purpose.
- 32. Thank You! Questions? • matthew.burke@capitalone.com • http://github.com/profburke — slides will go up soonish • http://lua.org