As a professional software developer, I am not accustomed to court cases, let alone Supreme Court cases, addressing the tradecraft of my profession; and when they do, I’m usually disappointed in the outcome. But this week, the Supreme Court issued a decision that directly addresses, not just computer programming in general, but API design, which I have worked on for decades, and as it happens, I agree with the Court’s ruling and look forward to the wide-reaching impact it will have on my profession.
This ruling will reverberate throughout techdom for many years to come: The Supreme Court ruled that the header files defining an interface are subject to fair use as a matter of law. (I am not an attorney, but apparently that means the Supreme Court held that a reasonable jury could not find in favor of the opposing party.)
Fair use is the carveout in copyright law that enables works to be excerpted without permission and without penalty, for purposes that serve a social good like satire or political commentary. The Supreme Court ruled that the declaring code for Java SE is subject to fair use. What these files do is describe what functionality may be requested of a body of software; they deliberately omit the details of how that functionality might be delivered, because even 30 years ago there was a recognition that it was important to be able to build software that could work together despite implementation details changing.
To put numbers to it, Google copied 11,500 lines of header files that described the Java SE runtime interface, then wrote about 2,800,000 lines of code to implement the underlying functionality in such a manner that code written to utilize the interface could run in a new context (the Android operating system). I personally have written several header files that achieved widespread use. While at Microsoft in the mid-1990s, I wrote the header files for Direct3D, which almost 25 years later is still the interface that developers use to access 3D rendering functionality on Windows. While at NVIDIA, I wrote the header files for the “driver API” for CUDA, the technology that enabled NVIDIA to turn their graphics chips into general-purpose supercomputers. The headers for Direct3D and CUDA are directly analogous to the ones referenced by the Supreme Court decision: they deliberately elide implementation details, outlining important abstractions and the capabilities and restrictions that apply to how those abstractions interact, without disclosing how those capabilities are delivered.
Even Proprietary APIs Are A Commons
My first reaction to the ruling is that it takes a big step toward conflating proprietary APIs and APIs that are defined by standards bodies (“standardized APIs”). For purposes of this discussion, proprietary APIs are ones developed by singular corporate entities and protected by the usual patchwork of trademarks, copyright, and patents to protect the intellectual property.
An early example of a standardized API is OpenGL. In 1992, the OpenGL Architectural Review Board (ARB) was convened by key technical contributors from various 3D workstation companies. These companies were building specialized computer hardware to accelerate realistic, three-dimensional pictures. With such hardware, such pictures could be drawn so quickly (say, 30 frames per second) that the user could manipulate 3D objects interactively. This 3D rendering hardware enabled the development of applications like Softimage, which was used to animate the realistic dinosaurs in the movie Jurassic Park.
OpenGL treats the API design as a commons – participating vendors collaborate on a standard, recognizing the value of a standardized API for developers to write their applications – then compete for market share on price, performance, and feature set. The workflow followed by OpenGL ARB members is akin to that undertaken by Google to implement the Java SE runtime: each company is responsible for building its own full-scale OpenGL implementation, complete with emulation for features not yet implemented in the hardware. Vendors of OpenGL hardware consider their OpenGL software implementations (which, like Google’s implementation of the Java SE runtime, number in the millions of lines of code) to be at once a useful barrier to entry, and also a way to differentiate their products from the competition.
Adopting the Supreme Court ruling’s terminology of referring to the code that describes the interface as “declaring code” and the code that contains actual computer instructions as “implementing code,” the ruling seems to imply that any company capable of writing the “implementing code” for a given proprietary API may consider doing so with impunity. There is no question in my mind that both the CUDA headers and Microsoft’s Direct3D headers fall under the category of “declaring code” as defined by the Supreme Court ruling. Provided an implementation meets the criteria outlined in the ruling, it seems the Supreme Court has given the go-ahead for clean room implementations of any proprietary API.
 The ruling is not perfect. On page 2, it states that “Computer programs differ to some extent from many other copyrightable works in because computer programs always serve a functional purpose.” They couldn’t insert the word “usually” in there somewhere? I take strong exception to the idea that all of our work serves a functional purpose. What about The International Obfuscated C Code Contest? Code can be art, too!
 Students of multimedia history will note that I was late to this party – the original Direct3D API was developed by a company called RenderMorphics, which had been purchased by Microsoft. But their original “execute buffer” based API was so difficult to use that Microsoft seriously considered switching to a different API called OpenGL. My contribution was to lead development of the “DrawPrimitive” API that changed the course of that discussion. The Wikipedia article on this topic has some references (full disclosure, I am a contributor). https://en.wikipedia.org/wiki/Comparison_of_OpenGL_and_Direct3D#Direct3D