68 lines
21 KiB
Plaintext
68 lines
21 KiB
Plaintext
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rust
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©Q #rustc 1.93.0 (254b59607 2026-01-19)Á“õ…·fÊvŠ ¦%g- -c48c539199cbc88bÁ ³VOÐêùÿ²?ÑL¼�§Ì± -a7a40eb546f9e2b0Á á\ƒ¦è3$|]åŒ[IÚ tæ -14b12edc9f8cd90bÁ ë&Gf·Ã ¬ëñq:¤»b -bb76018b1173caf6Áà 9m Ù„«ÐÒþá•c‘B; -030c5b0bba47cc8fÁ rustc_std_workspace_coreÁÛ¹þÓ7>H%¸ÚÉ’› -4b81d37a5530864dÁ üÃùs<Uß7VyóHr#QÏ -c66cc7807550ce25Á miniz_oxideÁõFÖˆÚ™ª‹"ÞXzLVª -62cbc7af83058505Á adler2Á—wÉD‘嵯�|6¨%Œ
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+ -2f171dd2394b4b62Á hashbrownÁ,ïcV¼¨ø¢:Ê\'È߈ -9571ba9e0f6c7a90Á rustc_std_workspace_allocÁ%¥Èxµù·¼5Ä3Bœ -aac566ad65903fa4Á
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std_detectÁMmáýZ^9õ Îà§e˜÷e -2edb296e590136d8Á rustc_demangleÁ@¼§VÉNb˜æ¨fHÌ+V3 -53b132e4a2fa6e26Á cfg_ifÁfÝv�.Å"ÒÜuPp¹ˆ¶ -f76b385d7d4d7f3eÁ addr2lineÁÕú-WiúQVÓ¬
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µT§�5 -fe25100bd73e48e4Á gimliÁ¹xLáÇí÷‘o ±Ñ8£Å -265ba9e6e4f70b3fÁ objectÁÔ³ÝzÓÿ¶ò°öM›¼òü` -9ae0d1f8ea52a318Á memchrÁRÎ÷׎™te~QÓ¿ØC\Ò -0bff3c8e8f4e489eÁ –©H�tGNÏ ·ˆ!á -d69228d077d46f36Á “ ServiceÁ RequestÁ ResponseÁ ” ¤
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poll_readyÁ ’ 'aÁ SÁ ó � ” ¤ ž ’ Ã ó � ” ¤ ž ’
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ºÃó •• – BoxÁ ™ìƒ šíƒ l Õ°Ù[¢'õ ÕE•E–E GlobalÁ Ï€ûkW¬ s ó
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•
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“ ¤4Î ®Ì |<æ £~ ã$ï ÈÌ ü âi üº3 0 Definition of the core `Service` trait to TowerÁ î Ë üòJ G The [`Service`] trait provides the necessary abstractions for definingÁ ü½L I request / response clients and servers. It is simple but powerful and isÁ üŠ1 . used as the foundation for the rest of Tower.Á “| ¤} ®Ì || £~ ã{ ÈÌ ÁÄÇœÁ ¾ÔÚ ²µ¥¨ÔÂR ü÷> ; An asynchronous function from a `Request` to a `Response`.Á ¶ Ë üºI F The `Service` trait is a simplified interface making it easy to writeÁ ü„J G network applications in a modular and reusable way, decoupled from theÁ üÏG D underlying protocol. It is one of Tower's fundamental abstractions.Á — Ë „›
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# FunctionalÁ ¬ Ë ü°F C A `Service` is a function of a `Request`. It immediately returns aÁ ü÷C @ `Future` representing the eventual completion of processing theÁ ü»H E request. The actual request processing may happen at any time in theÁ ü„K H future, on any thread or executor. The processing may depend on callingÁ üÐN K other services. At some point in the future, the processing will complete,Á üŸ 9 6 and the `Future` will resolve to a response or error.Á Ù Ë üÝ P M At a high level, the `Service::call` function represents an RPC request. TheÁ ü®
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0 - `Service` value can be a server or a client.Á ß
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Ë dã
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# ServerÁ ð
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Ë üô
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L I An RPC server *implements* the `Service` trait. Requests received by theÁ üÁ R O server over the network are deserialized and then passed as an argument to theÁ ü” F C server value. The returned response is sent back over the network.Á Û Ë üß H E As an example, here is how an HTTP request is processed by a server:Á ¨
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Ë \¬
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```rustÁ ĸ
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# use std::pin::Pin;Á üÑ
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% " # use std::task::{Poll, Context};Á ô÷
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# use std::future::Future;Á ü–! # use tower_service::Service;Á ü¸. + use http::{Request, Response, StatusCode};Á ç Ë ´ë struct HelloWorld;Á ‚ Ë ü†3 0 impl Service<Request<Vec<u8>>> for HelloWorld {Á üº* ' type Response = Response<Vec<u8>>;Á üå! type Error = http::Error;Á ü‡Y V type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>;Á á Ë üåY V fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {Á ü¿ Poll::Ready(Ok(()))Á Lß }Á é Ë üíC @ fn call(&mut self, req: Request<Vec<u8>>) -> Self::Future {Á ô± // create the bodyÁ üÐ1 . let body: Vec<u8> = "hello, world!\n"Á Ü‚ .as_bytes()Á äž .to_owned();Á ü»' $ // Create the HTTP responseÁ üã* ' let resp = Response::builder()Á üŽ' $ .status(StatusCode::OK)Á ܶ .body(body)Á üÒ= : .expect("Unable to create `http::Response`");Á � Ë ü”- * // create a response in a future.Á ì let fut = async {Á Äà Ok(resp)Á tù };Á ˆ Ë üŒ9 6 // Return the response as an immediate futureÁ ÌÆ Box::pin(fut)Á Là ” ,ê }Á <ð ```Á ø Ë dü # ClientÁ ‰ Ë ü�J G A client consumes a service by using a `Service` value. The client mayÁ üØM J issue requests by invoking `call` and passing the request as an argument.Á ü¦E B It then receives the response by waiting for the returned future.Á ì Ë üð? < As an example, here is how a Redis request would be issued:Á ° Ë ”´ ```rust,ignoreÁ üÇ% " let client = redis::Client::new()Á üí3 0 .connect("127.0.0.1:6379".parse().unwrap())Á ”¡ .unwrap();Á ´ Ë ü¸O L let resp = client.call(Cmd::set("foo", "this is the value of foo")).await?;Á ˆ Ë üŒ% " // Wait for the future to resolveÁ ü²+ ( println!("Redis response: {:?}", resp);Á <Þ Á% æ Ë Äê # Middleware / LayerÁ ƒ Ë ü‡ K H More often than not, all the pieces needed for writing robust, scalableÁ üÓ K H network applications are the same no matter the underlying protocol. ByÁ üŸ M J unifying the API for both clients and servers in a protocol agnostic way,Á üí E B it is possible to write middleware that provide these pieces in aÁ Œ³ reusable way.Á Å Ë üÉ Take timeouts as an example:Á ê Ë \î è üú use tower_service::Service;Á Üš use tower_layer::Layer;Á ܶ use futures::FutureExt;Á äÒ use std::future::Future;Á üï # use std::task::{Context, Poll};Á ä“ use std::time::Duration;Á ´° use std::pin::Pin;Á ŒÇ use std::fmt;Á ÔÙ use std::error::Error;Á ô Ë üø ; 8 // Our timeout service, which wraps another service andÁ ü´!- * // adds a timeout to its response future.Á Üâ! pub struct Timeout<T> {Á Œþ! inner: T,Á Ô�" timeout: Duration,Á ,«" ´% ±" Ë Äµ" impl<T> Timeout<T> {Á üÎ"E B pub const fn new(inner: T, timeout: Duration) -> Timeout<T> {Á ¬”# Timeout {Á ´ª# inner,Á ¼Á# timeoutÁ lÙ#
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}Á Lç# ” ,ñ# ´% ÷# Ë üû#; 8 // The error returned if processing a request timed outÁ ¤·$ #[derive(Debug)]Á ¼Ì$ pub struct Expired;Á ä$ Ë üè$# impl fmt::Display for Expired {Á üŒ%B ? fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {Á üÏ% write!(f, "expired")Á Lð% ” ,ú% ´% €& Ë ì„& impl Error for Expired {}Á ¢& Ë ü¦&H E // We can implement `Service` for `Timeout<T>` if `T` is a `Service`Á üï&4 1 impl<T, Request> Service<Request> for Timeout<T>Á L¤' whereÁ ä®' T: Service<Request>,Á ÜË' T::Future: 'static,Á üç'? < T::Error: Into<Box<dyn Error + Send + Sync>> + 'static,Á ì§( T::Response: 'static,Á ,Å( {Á üË(T Q // `Timeout` doesn't modify the response type, so we use `T`'s response typeÁ ü )$ ! type Response = T::Response;Á üÅ)X U // Errors may be either `Expired` if the timeout expired, or the inner service'sÁ üž*e b // `Error` type. Therefore, we return a boxed `dyn Error + Send + Sync` trait object to eraseÁ ä„+ // the error's type.Á ü¡+2 / type Error = Box<dyn Error + Send + Sync>;Á üÔ+Y ž ®, Ë ü²,Y ‹ üŒ-J G // Our timeout service is ready if the inner service is ready.Á ü×-\ Y // This is how backpressure can be propagated through a tree of nested services.Á ü´.8 5 self.inner.poll_ready(cx).map_err(Into::into)Á Lí. ” ÷. Ë üû.: 7 fn call(&mut self, req: Request) -> Self::Future {Á ü¶/B ? // Create a future that completes after `self.timeout`Á üù/; 8 let timeout = tokio::time::sleep(self.timeout);Á µ0 Ë ü¹0T Q // Call the inner service and get a future that resolves to the responseÁ üŽ1+ ( let fut = self.inner.call(req);Á º1 Ë ü¾1` ] // Wrap those two futures in another future that completes when either one completesÁ tŸ2 //Á ü®2V S // If the inner service is too slow the `sleep` future will complete firstÁ ü…3[ X // And an error will be returned and `fut` will be dropped and not polled againÁ tá3 †E üð3; 8 // We have to box the errors so the types matchÁ ü¬4 let f = async move {Á üÍ4 tokio::select! {Á üî4" res = fut => {Á ü‘55 2 res.map_err(|err| err.into())Á ´Ç5 },Á üÞ5$ ! _ = timeout => {Á üƒ6N K Err(Box::new(Expired) as Box<dyn Error + Send + Sync>)Á ´Ò6 éH Œé6 }Á tû6 ¥$ Š7 Ë ¼Ž7 Box::pin(f)Á L¦7 ” ,°7 ´% ¶7 Ë üº71 . // A layer for wrapping services in `Timeout`Á üì7& # pub struct TimeoutLayer(Duration);Á “8 Ë ¼—8 impl TimeoutLayer {Á ü¯83 0 pub const fn new(delay: Duration) -> Self {Á üã8 TimeoutLayer(delay)Á Lƒ9 ” ,�9 ´% “9 Ë ü—9' $ impl<S> Layer<S> for TimeoutLayer {Á ü¿9" type Service = Timeout<S>;Á â9 Ë üæ93 0 fn layer(&self, service: S) -> Timeout<S> {Á üš:) & Timeout::new(service, self.0)Á LÄ: ” ,Î: ´% <Ô: Á% Ü: Ë üà:N K The above timeout implementation is decoupled from the underlying protocolÁ ü¯;M J and is also decoupled from client or server concerns. In other words, theÁ üý;I F same timeout middleware could be used in either a client or a server.Á Ç< Ë ”Ë< # BackpressureÁ Þ< Ë üâ<Y V Calling a `Service` which is at capacity (i.e., it is temporarily unable to process aÁ ü¼=N K request) should result in an error. The caller is responsible for ensuringÁ ü‹>G D that the service is ready to receive the request before calling it.Á Ó> Ë ü×>L I `Service` provides a mechanism by which the caller is able to coordinateÁ ü¤?P M readiness. `Service::poll_ready` returns `Ready` if the service expects thatÁ üõ?$ ! it is able to process a
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©â ïeå t‹S ¯f ©â ïeå
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\ÇS Îf ©â ïeå üûSB ®Ìõf üˆT4 õf¯Ì ê³í³ î³Ò ï³ì ð³ ñ³“ò³ì äs{ ©¶‘·fÖfü�T, íf} ‡gq ˜g
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l‹S üãR# Responses given by the service.ÁD�S TÇS üŸS# Errors produced by the service.Á,ÌS üûSA ôØS The future response value.Á4€T ü‰^P üÃTO L Returns `Poll::Ready(Ok(()))` when the service is able to process requests.Á —U Ë üŸUP M If the service is at capacity, then `Poll::Pending` is returned and the taskÁ üôUF C is notified when the service becomes ready again. This function isÁ ü¿VK H expected to be called while on a task. Generally, this can be done withÁ ü�W- * a simple `futures::future::poll_fn` call.Á ÁW Ë üÉW[ X If `Poll::Ready(Err(_))` is returned, the service is no longer able to service requestsÁ ü©X7 4 and the caller should discard the service instance.Á åX Ë üíXW T Once `poll_ready` returns `Poll::Ready(Ok(()))`, a request may be dispatched to theÁ üÉYJ G service using `call`. Until a request is dispatched, repeated calls toÁ ü˜ZS P `poll_ready` must return either `Poll::Ready(Ok(()))` or `Poll::Ready(Err(_))`.Á ðZ Ë üøZY V Note that `poll_ready` may reserve shared resources that are consumed in a subsequentÁ üÖ[\ Y invocation of `call`. Thus, it is critical for implementations to not assume that `call`Á ü·\[ X will always be invoked and to ensure that such resources are released if the service isÁ ü—]Z W dropped before `call` is invoked or the future returned by `call` is dropped before itÁ tö] is polled.ÁTŒ^ ! ïe £~£~ | ¥~ wakerÁ�~ ¦~ local_wakerÁ�~ §~ extÁ�~ ¨~ _markerÁ�~ ©~ _marker2Á�~ àOÜD}�@ !ÈÌÊÌ ËÌö ÌÌì ÍÌÎÌß ¢õ ¯¹ü£ê³í³ î³Ò ï³ì ð³ ñ³“ò³ì äs{ ©¶‘ Öf —^
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ïeå $œ^ cxÁ¢^ ü–c1 üß^? < Process the request and return the response asynchronously.Á £_ Ë ü«_? < This function is expected to be callable off task. As such,Á üï_> ; implementations should take care to not call `poll_ready`.Á ²` Ë üº`H E Before dispatching a request, `poll_ready` must be called and returnÁ Ô‡a `Poll::Ready(Ok(()))`.Á ¦a Ë d®a # PanicsÁ ¿a Ë üÇaG D Implementations are permitted to panic if `call` is invoked withoutÁ ü“b6 3 obtaining `Poll::Ready(Ok(()))` from `poll_ready`.Á ,üÎbC 3futures do nothing unless you `.await` or poll themÁ$™c " "ïeå õf žc
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