Cap'n Web: a new RPC system for browsers and web servers

Post by crabmusket » Tue, Sep 23, 2025, 6:10 AM UTC

degamad wrote: post #204

kentonv wrote: post #171

Earlier quoted context omitted.

The round trip happens when you `await` the result. You can tell that promise pipelining isn't adding any round trips because you set it all up in a series of statements without any `await`s. At the end you do one `await`. That's your round trip.

You say "round trip", but you mean "return trip", right? Because if I understand correctly, you don't queue the requests and then perform a single request/response cycle (a "round trip"), you send a bunch of requests as they happen with no response expected, then when an await happens, you send a message saying "okay, that's all, please send me the result" and get a response.

Post by crabmusket » Tue, Sep 23, 2025, 6:20 AM UTC

kentonv wrote: post #128

stavros wrote: post #124

I was really excited when I saw the headline, but I was kind of disappointed to see it doesn't support schemas natively. I know you can specify them via zod, but I'm really not looking forward to any more untyped APIs, given that the lack of strict API typing has been by far the #1 reason for the bugs I've had to deal with in my career.

I really want to bake in some sort of support for generating type checks based on TypeScript types... so then your schemas are just TypeScript. Not sure why this doesn't seem to be a common practice TBH, might be missing something.

    interface MyService {
      method(): ReturnType;
    }

Post by da25 » Tue, Sep 23, 2025, 6:51 AM UTC

btown wrote: post #153

kentonv wrote: post #66

Earlier quoted context omitted.

The input to the map function (when it is called in "record" mode on the client) is an RpcPromise for the eventual value. That means you can't actually inspect the value, you can only queue pipelined calls on it. Since you can't inspect the value, you can't do any computation or branching on it. So any computation and branching you do perform must necessarily have the same result every time the function runs, and so…

> your function needs to have no side effects I'm trying to understand how well this no-side-effects footgun is defended against. https://github.com/cloudflare/capnweb/blob/main/src/map.ts#L... seems to indicate that if the special pre-results "record mode" call of the callback raises an error, the library silently bails out (but keeps anything already recorded, if this was a nested loop). That catches a huge number…

Post by jensneuse » Tue, Sep 23, 2025, 7:12 AM UTC

jensneuse wrote: post #219

I'm with WunderGraph, a vendor providing enterprise tooling for GraphQL. First, I absolutely love Capn Proto and the ideas of chaining calls on objects. It's amazing to see what's possible with CapNweb. However, one of the examples compares it to GraphQL, which I think falls a bit short of how enterprises use the Query language in real life. First, like others mentioned, you'll have N+1 problems for nested lists. Tha…

Post by vaylian » Tue, Sep 23, 2025, 7:32 AM UTC

squirrellous wrote: post #180

mdasen wrote: post #90

Earlier quoted context omitted.

In C#, there's expression trees which handle things like this and it's how Entity Framework is able to convert the lambdas it's given into SQL. This means that you can pass around code that can be inspected or transformed instead of being executed. Take this EntityFramework snippet: db.People.Where(p => p.Name == "Joe") `Where` takes an `Expression > predicate`. It isn't taking the `Func` itself, but an `Expression`…

Is there anything C# _doesn’t_ have? :-) It feels like C# has an answer to every problem I’ve ever had with other languages - dynamic loading, ADTs with pattern matching, functional programming, whatever this expression tree is, reflection, etc etc. Yet somehow it’s still a niche language that isn't widely used (outside of particular ecosystems).