Merge pull request #163 from atsign-foundation/cpswan-adr-platform-sdks

docs: ADR for platform SDKs

decisions/2024-07-platform-sdks.md

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+# Platform SDKs
+
+* **Status:** Approved
+* **Last Updated:** 2024-07-10
+* **Objective:** Set out a policy for our approach to providing software
+development kits (SDKs) for various languages and platforms.
+
+## Context & Problem Statement
+
+We have (over the span of five years) created a variety of
+[SDKs](https://github.com/atsign-foundation#available-sdks):
+
+* Dart
+* Java
+* Python
+* Micropython
+* C
+* C++
+* Rust
+* Go
+
+With the C SDK we could potentially use it as a library, and wrap it using
+foreign function interface (FFI) bindings, which can often be automatically
+generated for other languages. This would potentially save time in providing
+an SDK for new languages/platforms when they are requested by customers.
+
+The problem is that generating an SDK like that would require the C library
+to be maintained, shipped and bundled with its wrapper. It would also provide
+a non native developer experience.
+
+## Goals
+
+Have a clear understanding of how we will approach the creation of additional
+SDKs.
+
+### Non-goals
+
+To specify the SDK implementation.
+
+## Considered Options
+
+* ### Wrap a C library using generated FFI bindings
+
+This was proposed ahead of an architecture call on 4 Jul 2024 in the hope
+that it might speed up the process of providing additional SDKs.
+
+* ### Create a native SDK for each new language/platform
+
+After some discussion in the 4 Jul 2024 architecture call it was decided
+that the drawbacks of wrapping a C library outweighed the potential benefits,
+and thus we would continue to create native SDKs.
+
+## Proposal Summary
+
+Additional SDKs will be crafted in their native language.
+
+## Proposal in Detail
+
+When targeting a broader platform (e.g. .Net) we can choose the most
+appropriate language in that platform (e.g. C#) to create the SDK.
+
+An atSDK specification will be created based on the Dart & Java
+implementations in order to speed the development of future SDKs.
+
+### Expected Consequences
+
+We shall have to continue to learn new platforms or hire team members with
+the language skills required.
+
+In some cases we may be able to collaborate with the customer requesting
+an SDK to help co-develop it.