From 1b3551f108f29d97b942be48f8f0703573540d7c Mon Sep 17 00:00:00 2001
From: Nikita Vilunov <nikita@vilunov.me>
Date: Sat, 30 Sep 2023 16:02:18 +0000
Subject: [PATCH] xmpp: rewrite bind request parser as a coroutine (#12)

Reviewed-on: https://git.vilunov.me/lavina/lavina/pulls/12
---
 crates/proto-xmpp/src/bind.rs | 109 ++++++++++++----------------------
 1 file changed, 38 insertions(+), 71 deletions(-)

diff --git a/crates/proto-xmpp/src/bind.rs b/crates/proto-xmpp/src/bind.rs
index e6ef5d9..8d9a4cf 100644
--- a/crates/proto-xmpp/src/bind.rs
+++ b/crates/proto-xmpp/src/bind.rs
@@ -78,89 +78,56 @@ impl Jid {
 #[derive(PartialEq, Eq, Debug)]
 pub struct BindRequest(pub Resource);
 
-pub struct BindRequestParser(BindRequestParserInner);
-
-enum BindRequestParserInner {
-    Initial,
-    /// Consumed <bind> start and expects <resource>
-    InBind(Option<String>),
-    /// Consumed <resource> start
-    InBindResourceInitial,
-    /// Consumer <resource> start and inner text
-    InBindResourceEnd(String),
-}
-
 impl FromXmlTag for BindRequest {
     const NS: &'static str = XMLNS;
     const NAME: &'static str = "bind";
 }
 
 impl FromXml for BindRequest {
-    type P = BindRequestParser;
+    type P = impl Parser<Output = Result<Self>>;
 
     fn parse() -> Self::P {
-        BindRequestParser(BindRequestParserInner::Initial)
-    }
-}
-
-// TODO rewrite as a generator
-impl Parser for BindRequestParser {
-    type Output = Result<BindRequest>;
-
-    fn consume<'a>(
-        self: Self,
-        namespace: ResolveResult,
-        event: &Event<'a>,
-    ) -> Continuation<Self, Self::Output> {
-        // TODO validate tag names and namespaces
-        use BindRequestParserInner::*;
-        match self.0 {
-            Initial => {
-                let Event::Start(bytes) = event else {
-                    return Continuation::Final(Err(anyhow!("Unexpected XML event: {event:?}")));
-                };
-                if bytes.name().0 != BindRequest::NAME.as_bytes() {
-                    return Continuation::Final(Err(anyhow!(
-                        "Unexpected XML tag: {:?}",
-                        bytes.name()
-                    )));
-                }
-                let ResolveResult::Bound(Namespace(ns)) = namespace else {
-                    return Continuation::Final(Err(anyhow!("No namespace provided")));
-                };
-                if ns != XMLNS.as_bytes() {
-                    return Continuation::Final(Err(anyhow!("Incorrect namespace")));
-                }
-                Continuation::Continue(BindRequestParser(InBind(None)))
+        |(namespace, event): (ResolveResult<'static>, &'static Event<'static>)| -> Result<Self> {
+            let mut resource: Option<Str> = None;
+            let Event::Start(bytes) = event else {
+                return Err(anyhow!("Unexpected XML event: {event:?}"));
+            };
+            if bytes.name().0 != BindRequest::NAME.as_bytes() {
+                return Err(anyhow!("Unexpected XML tag: {:?}", bytes.name()));
             }
-            InBind(resource) => match event {
-                Event::Start(bytes) => {
-                    Continuation::Continue(BindRequestParser(InBindResourceInitial))
-                }
-                Event::End(bytes) => {
-                    let Some(resource) = resource else {
-                            return Continuation::Final(Err(anyhow!("No resource was provided")));
+            let ResolveResult::Bound(Namespace(ns)) = namespace else {
+                return Err(anyhow!("No namespace provided"));
+            };
+            if ns != XMLNS.as_bytes() {
+                return Err(anyhow!("Incorrect namespace"));
+            }
+            loop {
+                let (namespace, event) = yield;
+                match event {
+                    Event::Start(bytes) if bytes.name().0 == b"resource" => {
+                        let (namespace, event) = yield;
+                        let Event::Text(text) = event else {
+                            return Err(anyhow!("Unexpected XML event: {event:?}"));
                         };
-                    Continuation::Final(Ok(BindRequest(Resource(resource.into()))))
+                        resource = Some(std::str::from_utf8(&*text)?.into());
+                        let (namespace, event) = yield;
+                        let Event::End(bytes) = event else {
+                            return Err(anyhow!("Unexpected XML event: {event:?}"));
+                        };
+                        if bytes.name().0 != b"resource" {
+                            return Err(anyhow!("Unexpected XML tag: {:?}", bytes.name()));
+                        }
+                    }
+                    Event::End(bytes) if bytes.name().0 == BindRequest::NAME.as_bytes() => {
+                        break;
+                    }
+                    _ => return Err(anyhow!("Unexpected XML event: {event:?}")),
                 }
-                _ => Continuation::Final(Err(anyhow!("Unexpected XML event: {event:?}"))),
-            },
-            InBindResourceInitial => {
-                let Event::Text(text) = event else {
-                    return Continuation::Final(Err(anyhow!("Unexpected XML event: {event:?}")));
-                };
-                let resource = match std::str::from_utf8(&*text) {
-                    Ok(e) => e.to_string(),
-                    Err(err) => return Continuation::Final(Err(err.into())),
-                };
-                Continuation::Continue(BindRequestParser(InBindResourceEnd(resource)))
-            }
-            InBindResourceEnd(resource) => {
-                let Event::End(bytes) = event else {
-                    return Continuation::Final(Err(anyhow!("Unexpected XML event: {event:?}")));
-                };
-                Continuation::Continue(BindRequestParser(InBind(Some(resource))))
             }
+            let Some(resource) = resource else {
+                return Err(anyhow!("No resource was provided"));
+            };
+            Ok(BindRequest(Resource(resource)))
         }
     }
 }