Any plans for Cap'n Proto RPC over HTTP/2

[e...@emma.today]

gRPC does this for protobufs. And it gives the interesting feature (if you have a JSON->gPRC proxy) of allowing a single port to listen for both HTTP/2 and HTTP 1.1 and process HTTP 1.1 requests with the JSON proxy and HTTP2 requests with gRPC directly.

Thoughts?

[Kenton Varda]

Hi Emma,

Cap'n Proto RPC's model and HTTP/2's model are not a great fit for each other. gRPC uses a client-server model with "streaming" requests/responses -- a very close match for HTTP/2. Cap'n Proto RPC, in contrast, is symmetric (allowing calls in both directions) and message-based (not streaming). Additionally, while gRPC endpoints are global singletons -- which translate nicely to a URL hierarchy -- Cap'n Proto endpoints are opaque object references which may be transient and may be created and destroyed over the course of a connection. So, Cap'n Proto doesn't map well to URLs, either.

So, although it would be possible to layer on top of HTTP/2, Cap'n Proto would not leverage much benefit from HTTP/2, so this would be a lot of bloat for relatively little benefit.

If the goal is to be able to handle Cap'n Proto RPC on the same port as HTTP, that would arguably best be accomplished using WebSocket. The WebSocket protocol is symmetric, message-based, and lightweight, making it a pretty great fit for Cap'n Proto. This is something we plan to spec out eventually.

I would also like to design a "pure" UDP-based Cap'n Proto transport at some point, with the ability to do zero-round-trip introductions (probably not possible if layering on other transports). But that's another story...

-Kenton

On Sun, Jun 12, 2016 at 11:41 AM, <e...@emma.today> wrote:

gRPC does this for protobufs. And it gives the interesting feature (if you have a JSON->gPRC proxy) of allowing a single port to listen for both HTTP/2 and HTTP 1.1 and process HTTP 1.1 requests with the JSON proxy and HTTP2 requests with gRPC directly.

Thoughts?

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