Extensions and Lifecycles
The Elysia chlorotica, also known as Sap-Sucking Green Sea Slug, is a fascinating creature.
They puncture the cell wall of tidal algae with their radula (tongue), then suck out the contents like a milkshake through a straw. They keep the chloroplasts inside their digestive systems. For the next few months, the Sea Slug absorbs the algae’s chloroplasts as needed while they continue to perform photosynthesis. These provide the host with energy, much like a plant. Like solar panels, they also continue converting sunlight into energy.
The process is called Kleptoplasty – theft of chloroplasts. It is a form of nature
# Side Note
In the 1960s, a group of radical British architects, under the working moniker Archigram, created the concept of The Plug-in City. The core could be extended through standard interfaces into which other building components and services could be
They envisioned a city built to change as its parts became obsolete. As older parts were phased out, new parts could be attached, extending the city’s core function.
Glade Plugins were designed to dispense aromatic volatile organic oils into the air. They did this via a patent-pending heating process. A
Variations included:
- Night-lights
- Electronic sensors
- ‘Rest’ mode to save power
After licensing patented technology from Color Kinetics in 2002, LED color-changing effects created ‘a home-fragrance device that combines fragrance with a light show to provide a multi-sensory experience.’
The standard interface was via a patent filed in 1997 by S.C. Johnson describing:
An electrical-resistance heating element is affixed on the inner Surface of the cartridge chamber shallow extension. A thin wick matrix extends internally from the cartridge chamber bottom up to the top of the chamber shallow extension.
The system allowed
What Have You Done For Me Lately?
# Here Be Dragons
In previous sections, we covered some history, turning user voice into text, then into
However, as with most things in tech, familiarity breeds boredom and they’ve nearly become ubiquitous. Purchasers of modern cars have the choice of Alexa automotive integration, Voice Interaction Service in Android Automotive, or Siri in CarPlay.
There are voice-controlled ovens, laundry machines, door locks, LED lights, and TV Remote Controls. (Full disclosure: I did some work on that last one while at Lab126).
It isn’t possible for an AI Assistant to keep up with all the possible permutations and use cases out there. So instead of trying to do everything in one go, everyone eventually moves to the concept of
The proper design of that Extension, how it interacts with the Base, and the workflow and ecosystem are a subject worthy of their own PhD thesis. But they are often left as afterthoughts, even though I would argue their design is even <>more important</i> than the core system since they are designed to work with any number of unpredictable, future scenarios, as well as third parties with both good and bad intentions.
To understand how they work, we’ll have to take a short detour in time…
Proceed and Conditional Transfer
One of the earliest programming languages was the Assembly language (aka autocode) compiler built in 1947 for the Automatic Relay Computer by Dr. Kathleen Booth.
The concepts of
Between these two methods, a system could transfer control to a different part of the code, depending on the value of a register. These were building blocks that would be used by more advanced programming languages to create what became known as
# Side Note
Incidentally, both Dr. Booths worked on developing machine translation and, in 1955, proved that computers could be used for language translation.
Function Calls
In the 1972 report describing the B Programming Language (the predecessor to C which exists today), Ken Thompson (who went on to work on Unix and Go Language) presented the concept of a
The concept had been around for some time in early languages such as Algol and FORTRAN. But B and later C allowed the code for the library to be kept in a separate file and only added into the current program in the final stages of compilation.
In 1979, Bjarne Stroustrup introduced the concept of polymorphism and
This meant that at runtime, what function was actually invoked could be
Interpreted languages like Lisp, SmallTalk, and Python took this a step further, allowing for what came to be known as Dynamic Dispatch. This evolved into Name Dispatch or Late Binding.
# Side Note
Shared Libraries
The concept of dynamic linking goes back to the Multics Operating System in the mid-1960s.
In the Unix world, it’s not clear who added shared libraries first, but in the early 1980s, it was a race between AT&T Unix System V and SunOS, which was based on Berkeley Sofware Distribution (BSD) Unix.
In a multi-processing system, shared libraries allow the same code to be reused by multiple processes, saving memory and performance. Shared libraries often had to be built in a certain way so they would contain
Shared libraries also introduced the concept of
The operating system would need to look for the actual code and load the binary library file at runtime. Where it looked and how it looked was baked into the main application. To conserve limited memory, some operating systems would also dispose the libraries when no longer needed and reuse the memory address space.
This capability enabled the use of multiple libraries, which they could swap in and out depending on the environment and what was needed. This meant that an application was no longer a monolithic chunk of code when it left the manufacturer, but could be changed and updated at a later time.
DLL Hell
In MS-DOS (note for young ones: the operating system software that Microsoft offered on PC computers before Windows), there was a hard limit of 640KB of RAM (yes, KB). Third parties had devised a system of Memory Overlays to allow applications to swap code and data in and out of memory as needed.
As application sizes grew, the need for breaking past that limit became obvious. This led software vendors, compiler makers, and language developers to develop their own mechanisms. There was no single, standard way, but Walter Bright, creator of the Zortech C++ compiler (later Symantec, later Digital Mars), did devise an ad hoc way that was adopted by many applications.
More advanced 80286 and 80386 hardware had support for what came to be known as DOS Extenders, but for an extended period, those systems were more expensive and not as accessible to mass-market users.
The designers of Microsoft Windows, introduced in 1985, realized that a better solution was needed. They implemented a functionality called Dynamic Link Library (DLL). This served the same function as Unix shared libraries and for the same reason (conserving RAM). Windows also allowed DLL code files to be discovered, loaded, executed, and discarded at runtime.
However, DLLs went further than just adding code to a running service. They also allowed features like user-interface drawing, access to hardware, and other common tasks to be built once and shared by multiple executable programs. The original discovery and registry process was simplistic, leading to multiple DLLs overriding each other and what became known as DLL Hell.
This also allowed malicious actors to inject their own DLLs that pretended to behave the same way as a system-shared library, enabling mass dissemination of
Unix Shared Libraries (and early Windows DLLs) did not enforce a calling interface between the main application and the shared code. The burden was on the developers and the accuracy of documentation to offer a sort of voluntary ‘handshake’ compliance. If the Caller did not follow the calling scheme, the Callee would crash with a SEGFAULT on Unix and a familiar crash modal on Windows.
If the problem was particularly dire, you might even see the notorious
This happened often enough to enter popular culture.
It took only 40 years for it to finally get retired.
Microsoft went on to create a more rigorous way to define the handshake between an Application and its DLLs via a TLB (Type Library) description. This would be compiled and built into the binary shared library. It reduced the number of inadvertent crashes, but there was still the problem of viruses piggybacking on and pretending they were part of the operating system.
Much more work had to be done to reduce the incidence of malicious software. Like validating that a
This started decades of cat-and-mouse games between malware writers and Microsoft, walking a tightrope between user convenience and security.
Apple Mac systems ended up with a similar
On the Linux side, consumer-oriented Desktop Linux releases are trying to move users to their own convenient FlatHub and Snap Store. However, on the server side, hacking shared libraries persists to this day, with serious consequences.
In case you think this is all old news, the same problem still applies to Docker Containers.
We’re not out of the woods yet.
Dynamic Modules
Code libraries grouped together are called
- Node/JavaScript: NPMJS
- Python: PyPi
- Java: Maven Registry
- Ruby: RubyGems
- Go: GoDev
- Rust: crates.io
- Docker Containers: DockerHub
These libraries can be loaded at different points in the development lifecycle, but most often they are
On the mobile side, things are… shall we say, fluid.
Mobile
Congratulations. You’ve built an iPhone Mobile App!
It’s taken months of toiling on design and development. Now, you have to make sure it complies with the Apple App Review Guidelines. These are the rules by which Apple evaluates an app before allowing it to be published in the App Store.
You’re almost past the final hurdle before the public launch.
But then, you see…
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 which introduces or changes features or functionality of the app, including other apps.
No plug-ins. No downloadable extensions.
In case you’re wondering, Google’s Play Store also has a submission process. But in Android-land, things are less buttoned-up. In fact, there is a process for delivering on-demand extensions:
Apple blocks dynamic extensions, reasoning that extensions not vetted by Apple can load malware onto a phone.
The issue is also mired in the larger discussion of first vs. third-party App Stores. If Apple no longer has the chain of custody on apps loaded elsewhere, does it get to enforce the same restrictions on downloadable extensions signed by those third parties?
The topic will no doubt be reopened once the worldwide legal issues are resolved and if third-party iOS app stores become prevalent.
Again, this is not limited to Apple and iOS. Google, Microsoft, and any company looking to limit access to unvetted third-party software have had to endure the same process.
It boils down to
Which side of the issue you land on will undoubtedly color how you perceive
# Soapbox
Open Source
To encourage open-source sharing, minimal authentication is done to any of these, except for validating a simple checksum to ensure the version uploaded to the repository hasn’t been tampered with before making it to the developer’s machine.
Checksums or Digital Hashes do not account for malicious users hijacking and overwriting a repository with their own versions, leading to proliferation of what’s called Supply Chain Attacks
The popular NPM package ‘is’ has been compromised in a supply chain attack that injected backdoor malware, giving attackers full access to compromised devices.
This occurred after
maintainer accounts were hijacked via phishing, followed by unauthorized owner changes that went unnoticed for several hours , potentially compromising many developers who downloaded the new releases.The ‘is’ package is a lightweight JavaScript utility library that provides a wide variety of type checking and value validation functions.
The software has
over 2.8 million weekly downloads on the NPM package index. It is used extensively as a low-level utility dependency in development tools, testing libraries, build systems, and backend and CLI projects.
In case you’re wondering what is does, it’s a wrapper around several built-in JavaScript functions. Not to diminish its utility, but this is as close to a manifestation of the well-known XKCD comic.
Title Image - © Patrick J. Krug, Creative Commons CC BY-NC 3.0 license, via Wikimedia Commons.
