Async fn in traits #413
Merged
Async fn in traits #413
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Also adds a Client stub trait alias for each generated service. Now that generic associated types are stable, it's almost possible to define a trait for Channel that works with async fns on stable. `impl trait in type aliases` is still necessary (and unstable), but we're getting closer. As a proof of concept, three more implementations of Stub are implemented; 1. A load balancer that round-robins requests between different stubs. 2. A load balancer that selects a stub based on a request hash, so that the same requests go to the same stubs. 3. A stub that retries requests based on a configurable policy. The "serde/rc" feature is added to the "full" feature because the Retry stub wraps the request in an Arc, so that the request is reusable for multiple calls. Server implementors commonly need to operate generically across all services or request types. For example, a server throttler may want to return errors telling clients to back off, which is not specific to any one service.
This allows plugging in horizontal functionality, such as authorization, throttling, or latency recording, that should run before and/or after execution of every request, regardless of the request type. The tracing example is updated to show off both client stubs as well as server hooks. As part of this change, there were some changes to the Serve trait: 1. Serve's output type is now a Result<Response, ServerError>.. Serve previously did not allow returning ServerErrors, which prevented using Serve for horizontal functionality like throttling or auth. Now, Serve's output type is Result<Resp, ServerError>, making Serve a more natural integration point for horizontal capabilities. 2. Serve's generic Request type changed to an associated type. The primary benefit of the generic type is that it allows one type to impl a trait multiple times (for example, u64 impls TryFrom<usize>, TryFrom<u128>, etc.). In the case of Serve impls, while it is theoretically possible to contrive a type that could serve multiple request types, in practice I don't expect that to be needed. Most users will use the Serve impl generated by #[tarpc::service], which only ever serves one type of request.
The major breaking change is that Channel::execute no longer internally
spawns RPC handlers, because it is no longer possible to place a Send
bound on the return type of Serve::serve. Instead, Channel::execute
returns a stream of RPC handler futures.
Service authors can reproduce the old behavior by spawning each response
handler (the compiler knows whether or not the futures can be spawned;
it's just that the bounds can't be expressed generically):
channel.execute(server.serve())
.for_each(|rpc| { tokio::spawn(rpc); })
Rather than returning a bool, return the Span associated with the request. This gives RequestDispatch more flexibility to annotate the request span.
- Stub - BeforeRequest - AfterRequest Also removed the last remaining usage of an unstable feature, iter_intersperse.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
No more
#[tarpc(server)]