RFC 004: Dart implementation (#239)

RFC 004: Dart implementation

---------

Signed-off-by: Sri Krishna <[email protected]>

docs/governance/rfc/004-dart-implementation.md

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+# 004: Dart Implementation
+
+This RFC proposes adding a Dart implementation of Connect starting with support for clients.
+This will be similar in scope to Connect-Swift and Connect-Kotlin implementations.
+
+## Why
+
+Dart is a popular programming language powering frameworks like Flutter which
+is used for cross-platform app development. This project will bring Connect support to the growing Flutter and Dart ecosystem.
+
+## Anticipated complications
+
+Dart runs on several platforms: Web, Android, and iOS to name a few. Most of the platforms
+have their own HTTP stack with varying levels of support for HTTP specs. It doesn't have a
+unified abstraction and APIs for common HTTP constructs like headers and cancellation.
+
+We have to create a minimal HTTP abstraction to support various platforms. We can then have concrete
+implementations using the following:
+
+- [`HttpClient`][dart-io-client] from `dart:io`. This is part of the std library and runs on native platforms.
+  This only supports HTTP/1.
+- [`package:http2`][pub-http2]. This is a HTTP/2 implementation maintained by the Dart team. This can be used
+  to support bidirectional streaming and gRPC. Connection management has to be implemented on top of this.
+- [`dart:js_interop`][dart-js-interop]: This is part of the std library and can be used to create
+  bindings for web APIs. We can use the `fetch` APIs to support Connect and gRPC-Web.
+
+Platforms like Android and iOS have their own HTTP stack, and it is desirable to use them. [`package:http`][pub-http]
+can be used as a cross platform client to support both. It is maintained by the Dart team. The only blocker
+is the missing support for [aborting requests][http-abort-issue]. The `dart:io` based client will run on these devices.
+Depending on the how the issue progresses we may have to provide ancillary packages to support native stacks.
+This however, need not block v1 as we won't need API changes to support them.
+
+## Supported features
+
+Clients should support all three protocols and four RPC kinds where possible:
+
+- Connect, gRPC-Web:
+  - Should be supported on all platforms.
+  - On the web, unary and server stream can be supported.
+- gRPC:
+  - Can be supported on native platforms with support for HTTP/2
+
+These should be continuously tested using the [conformance suite][conformance] on both native and web platforms.
+
+### Others
+
+Clients should also support ancillary features, including but not limited to interceptors,
+compression, mocking support, and a pluggable HTTP stack.
+
+## Maintainers
+
+The project can be maintained by:
+
+- [Peter Edge](https://github.com/bufdev), [Buf](https://buf.build)
+- [Steve Ayers](https://github.com/smaye81), [Buf](https://buf.build)
+- [Sri Krishna Paritala](https://github.com/srikrsna-buf), [Buf](https://buf.build)
+
+[conformance]: https://github.com/connectrpc/conformance
+[dart-io-client]: https://dart.dev/libraries/dart-io#http-client
+[dart-js-interop]: https://api.dart.dev/dart-js_interop/dart-js_interop-library.html
+[http-abort-issue]: https://github.com/dart-lang/http/issues/424
+[pub-http2]: https://pub.dev/packages/http2
+[pub-http]: https://pub.dev/packages/http