feat: move to a channel-based implementation for meta

integrations/actix/src/lib.rs

@@ -741,7 +741,7 @@ where
 
         async move {
             let res_options = ResponseOptions::default();
-            let meta_context = ServerMetaContext::new();
+            let (meta_context, meta_output) = ServerMetaContext::new();
 
             let additional_context = {
                 let meta_context = meta_context.clone();
@@ -755,7 +755,7 @@ where
 
             let res = ActixResponse::from_app(
                 app_fn,
-                meta_context,
+                meta_output,
                 additional_context,
                 res_options,
                 stream_builder,
@@ -945,12 +945,13 @@ where
     let _ = any_spawner::Executor::init_tokio();
 
     let owner = Owner::new_root(None);
+    let (mock_meta, _) = ServerMetaContext::new();
     let routes = owner
         .with(|| {
             // stub out a path for now
             provide_context(RequestUrl::new(""));
             provide_context(ResponseOptions::default());
-            provide_context(ServerMetaContext::new());
+            provide_context(mock_meta);
             additional_context();
             RouteList::generate(&app_fn)
         })

integrations/axum/src/lib.rs

@@ -763,7 +763,7 @@ where
     Box::pin(async move {
         let add_context = additional_context.clone();
         let res_options = ResponseOptions::default();
-        let meta_context = ServerMetaContext::new();
+        let (meta_context, meta_output) = ServerMetaContext::new();
 
         let additional_context = {
             let meta_context = meta_context.clone();
@@ -787,7 +787,7 @@ where
 
         let res = AxumResponse::from_app(
             app_fn,
-            meta_context,
+            meta_output,
             additional_context,
             res_options,
             stream_builder,
@@ -1155,12 +1155,8 @@ where
             provide_context(RequestUrl::new(""));
             let (mock_parts, _) =
                 http::Request::new(Body::from("")).into_parts();
-            provide_contexts(
-                "",
-                &Default::default(),
-                mock_parts,
-                Default::default(),
-            );
+            let (mock_meta, _) = ServerMetaContext::new();
+            provide_contexts("", &mock_meta, mock_parts, Default::default());
             additional_context();
             RouteList::generate(&app_fn)
         })

integrations/utils/src/lib.rs

@@ -5,7 +5,7 @@ use leptos::{
     reactive_graph::owner::{Owner, Sandboxed},
     IntoView,
 };
-use leptos_meta::ServerMetaContext;
+use leptos_meta::ServerMetaContextOutput;
 use std::{future::Future, pin::Pin, sync::Arc};
 
 pub type PinnedStream<T> = Pin<Box<dyn Stream<Item = T> + Send>>;
@@ -24,7 +24,7 @@ pub trait ExtendResponse: Sized {
 
     fn from_app<IV>(
         app_fn: impl FnOnce() -> IV + Send + 'static,
-        meta_context: ServerMetaContext,
+        meta_context: ServerMetaContextOutput,
         additional_context: impl FnOnce() + Send + 'static,
         res_options: Self::ResponseOptions,
         stream_builder: fn(

meta/src/body.rs

@@ -67,11 +67,13 @@ pub fn Body(
         attributes.push(value.into_any_attr());
     }
     if let Some(meta) = use_context::<ServerMetaContext>() {
-        let mut meta = meta.inner.write().or_poisoned();
         // if we are server rendering, we will not actually use these values via RenderHtml
         // instead, they'll be handled separately by the server integration
         // so it's safe to take them out of the props here
-        meta.body = mem::take(&mut attributes);
+        for attr in attributes.drain(0..) {
+            // fails only if receiver is already dropped
+            _ = meta.body.send(attr);
+        }
     }
 
     BodyView { attributes }

meta/src/html.rs

@@ -78,11 +78,13 @@ pub fn Html(
             })),
     );
     if let Some(meta) = use_context::<ServerMetaContext>() {
-        let mut meta = meta.inner.write().or_poisoned();
         // if we are server rendering, we will not actually use these values via RenderHtml
         // instead, they'll be handled separately by the server integration
         // so it's safe to take them out of the props here
-        meta.html = mem::take(&mut attributes);
+        for attr in attributes.drain(0..) {
+            // fails only if receiver is already dropped
+            _ = meta.body.send(attr);
+        }
     }
 
     HtmlView { attributes }

meta/src/lib.rs

@@ -73,7 +73,10 @@ use or_poisoned::OrPoisoned;
 use send_wrapper::SendWrapper;
 use std::{
     fmt::Debug,
-    sync::{Arc, RwLock},
+    sync::{
+        mpsc::{channel, Receiver, Sender},
+        Arc, RwLock,
+    },
 };
 use wasm_bindgen::JsCast;
 use web_sys::HtmlHeadElement;
@@ -154,17 +157,61 @@ impl Default for MetaContext {
     }
 }
 
-/// Contains the state of meta tags for server rendering.
+/// Allows you to add `<head>` content from components located in the `<body>` of the application,
+/// which can be accessed during server rendering via [`ServerMetaContextOutput`].
 ///
 /// This should be provided as context during server rendering.
-#[derive(Clone, Default)]
+///
+/// No content added after the first chunk of the stream has been sent will be included in the
+/// initial `<head>`. Data that needs to be included in the `<head>` during SSR should be
+/// synchronous or loaded as a blocking resource.
+#[derive(Clone, Debug)]
 pub struct ServerMetaContext {
-    inner: Arc<RwLock<ServerMetaContextInner>>,
     /// Metadata associated with the `<title>` element.
     pub(crate) title: TitleContext,
+    /// Attributes for the `<html>` element.
+    pub(crate) html: Sender<AnyAttribute<Dom>>,
+    /// Attributes for the `<body>` element.
+    pub(crate) body: Sender<AnyAttribute<Dom>>,
+    /// Arbitrary elements to be added to the `<head>` as HTML.
+    pub(crate) elements: Sender<String>,
+}
+
+/// Allows you to access `<head>` content that was inserted via [`ServerMetaContext`].
+#[must_use = "If you do not use the output, adding meta tags will have no \
+              effect."]
+#[derive(Debug)]
+pub struct ServerMetaContextOutput {
+    pub(crate) title: TitleContext,
+    html: Receiver<AnyAttribute<Dom>>,
+    body: Receiver<AnyAttribute<Dom>>,
+    elements: Receiver<String>,
 }
 
 impl ServerMetaContext {
+    /// Creates an empty [`ServerMetaContext`].
+    pub fn new() -> (ServerMetaContext, ServerMetaContextOutput) {
+        let title = TitleContext::default();
+        let (html_tx, html_rx) = channel();
+        let (body_tx, body_rx) = channel();
+        let (elements_tx, elements_rx) = channel();
+        let tx = ServerMetaContext {
+            title: title.clone(),
+            html: html_tx,
+            body: body_tx,
+            elements: elements_tx,
+        };
+        let rx = ServerMetaContextOutput {
+            title,
+            html: html_rx,
+            body: body_rx,
+            elements: elements_rx,
+        };
+        (tx, rx)
+    }
+}
+
+impl ServerMetaContextOutput {
     /// Consumes the metadata, injecting it into the the first chunk of an HTML stream in the
     /// appropriate place.
     ///
@@ -174,17 +221,19 @@ impl ServerMetaContext {
         self,
         mut stream: impl Stream<Item = String> + Send + Unpin,
     ) -> impl Stream<Item = String> + Send {
+        // wait for the first chunk of the stream, to ensure our components hve run
         let mut first_chunk = stream.next().await.unwrap_or_default();
 
-        let meta_buf =
-            std::mem::take(&mut self.inner.write().or_poisoned().head_html);
-
+        // create <title> tag
         let title = self.title.as_string();
         let title_len = title
             .as_ref()
             .map(|n| "<title>".len() + n.len() + "</title>".len())
             .unwrap_or(0);
 
+        // collect all registered meta tags
+        let meta_buf = self.elements.into_iter().collect::<String>();
+
         let modified_chunk = if title_len == 0 && meta_buf.is_empty() {
             first_chunk
         } else {
@@ -218,35 +267,6 @@ impl ServerMetaContext {
     }
 }
 
-#[derive(Default, Debug)]
-struct ServerMetaContextInner {
-    /*/// Metadata associated with the `<html>` element
-    pub html: HtmlContext,
-    /// Metadata associated with the `<title>` element.
-    pub title: TitleContext,*/
-    /// Metadata associated with the `<html>` element
-    pub(crate) html: Vec<AnyAttribute<Dom>>,
-    /// Metadata associated with the `<body>` element
-    pub(crate) body: Vec<AnyAttribute<Dom>>,
-    /// HTML for arbitrary tags that will be included in the `<head>` element
-    pub(crate) head_html: String,
-}
-
-impl Debug for ServerMetaContext {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        f.debug_struct("ServerMetaContext")
-            .field("inner", &self.inner)
-            .finish_non_exhaustive()
-    }
-}
-
-impl ServerMetaContext {
-    /// Creates an empty [`ServerMetaContext`].
-    pub fn new() -> Self {
-        Default::default()
-    }
-}
-
 /// Provides a [`MetaContext`], if there is not already one provided. This ensures that you can provide it
 /// at the highest possible level, without overwriting a [`MetaContext`] that has already been provided
 /// (for example, by a server-rendering integration.)
@@ -293,12 +313,13 @@ where
 
     #[cfg(feature = "ssr")]
     if let Some(cx) = use_context::<ServerMetaContext>() {
-        let mut inner = cx.inner.write().or_poisoned();
+        let mut buf = String::new();
         el.take().unwrap().to_html_with_buf(
-            &mut inner.head_html,
+            &mut buf,
             &mut Position::NextChild,
             false,
         );
+        _ = cx.elements.send(buf); // fails only if the receiver is already dropped
     } else {
         tracing::warn!(
             "tried to use a leptos_meta component without `ServerMetaContext` \