Be smarter about browser and proxy server caching for static assets.HEADmain

This covers two things:

* For _any_ static asset, send back an `ETag` header based on its content. If the request had an `If-None-Match` header, use that header to instead send back a `Not Modified` response, with no payload, if appropriate, saving the cost of transferring data the client already has.
* For _immutable_ static assets, send back a `Cache-Control` header to allow browsers to replay the response from cache, without making a request, for up to 90 days, saving whole HTTP round-trips.

In practice, startup time is now dominated by the time needed to check whether the user is logged in, and the time needed to satisfy the `/api/boot` request if they are.

"Static" here includes anything that's served in the HTML itself, so things like `/`, `/login`, `/c/:channelid`, and `/me` are all "static," and are all affected by this change even though the logical content of those endpoints also includes data that will vary from user to user and from time to time. All the dynamic data for those responses comes from separate API requests, which don't affect the cacheability of those pages. However, this change is conservative and _does not_ instruct the browser to cache those pages for long periods; it only supports telling the browser that the cached copy they have is fine, via a `Not Modified` response.

This change also includes a minimum Rust version bump, to the recently-released 1.91 - as it uses `Duration::from_hours` to compute the `Cache-Control` header. I could use `Duration::new` or `Duration::from_secs`, but really, working in increments of days from such tiny units is awkward. I'd prefer to use `Duration::from_days`, but it's not stable yet.

Merges asset-etags into main.

8 files changed, 93 insertions, 101 deletions

diff --git a/src/ui/handlers/asset.rs b/src/ui/handlers/asset.rs
index 1d5b8be..948d6d6 100644
--- a/src/ui/handlers/asset.rs
+++ b/src/ui/handlers/asset.rs
@@ -1,7 +1,12 @@
 use axum::extract::Path;
+use axum_extra::TypedHeader;
+use headers::IfNoneMatch;
 
-use crate::ui::assets::{Asset, Assets, Error};
+use crate::ui::assets::{Error, Response};
 
-pub async fn handler(Path(path): Path<String>) -> Result<Asset, Error> {
-    Assets::load(path)
+pub async fn handler(
+    Path(path): Path<String>,
+    TypedHeader(if_none_match): TypedHeader<IfNoneMatch>,
+) -> Result<Response, Error> {
+    Response::load(&path, &if_none_match)
 }
diff --git a/src/ui/handlers/conversation.rs b/src/ui/handlers/conversation.rs
index 102efc6..9a87d40 100644
--- a/src/ui/handlers/conversation.rs
+++ b/src/ui/handlers/conversation.rs
@@ -2,13 +2,15 @@ use axum::{
     extract::{Path, State},
     response::{self, IntoResponse, Redirect},
 };
+use axum_extra::TypedHeader;
+use headers::IfNoneMatch;
 
 use crate::{
     conversation::{self, app, app::Conversations},
     error::Internal,
     token::extract::Identity,
     ui::{
-        assets::{Asset, Assets},
+        assets::{self, Asset, Assets},
         error::NotFound,
     },
 };
@@ -17,44 +19,39 @@ pub async fn handler(
     State(conversations): State<Conversations>,
     identity: Option<Identity>,
     Path(conversation): Path<conversation::Id>,
-) -> Result<Asset, Error> {
-    let _ = identity.ok_or(Error::NotLoggedIn)?;
-    conversations
-        .get(&conversation)
-        .await
-        .map_err(Error::from)?;
+    TypedHeader(if_none_match): TypedHeader<IfNoneMatch>,
+) -> Result<Response, Internal> {
+    let response = if identity.is_none() {
+        Response::NotLoggedIn
+    } else {
+        match conversations.get(&conversation).await {
+            Ok(_) => {
+                let index = assets::Response::index(&if_none_match)?;
+                Response::Asset(index)
+            }
+            Err(app::GetError::NotFound(_) | app::GetError::Deleted(_)) => {
+                let index = Assets::index()?;
+                Response::NotFound(index)
+            }
+            Err(err @ app::GetError::Failed(_)) => return Err(err.into()),
+        }
+    };
 
-    Assets::index().map_err(Error::Internal)
+    Ok(response)
 }
 
-#[derive(Debug, thiserror::Error)]
-pub enum Error {
-    #[error("conversation not found")]
-    NotFound,
-    #[error("not logged in")]
+pub enum Response {
     NotLoggedIn,
-    #[error("{0}")]
-    Internal(Internal),
-}
-
-impl From<app::GetError> for Error {
-    fn from(error: app::GetError) -> Self {
-        match error {
-            app::GetError::NotFound(_) | app::GetError::Deleted(_) => Self::NotFound,
-            app::GetError::Failed(_) => Self::Internal(error.into()),
-        }
-    }
+    NotFound(Asset),
+    Asset(assets::Response),
 }
 
-impl IntoResponse for Error {
+impl IntoResponse for Response {
     fn into_response(self) -> response::Response {
         match self {
-            Self::NotFound => match Assets::index() {
-                Ok(asset) => NotFound(asset).into_response(),
-                Err(internal) => internal.into_response(),
-            },
             Self::NotLoggedIn => Redirect::temporary("/login").into_response(),
-            Self::Internal(error) => error.into_response(),
+            Self::NotFound(asset) => NotFound(asset).into_response(),
+            Self::Asset(asset) => asset.into_response(),
         }
     }
 }
diff --git a/src/ui/handlers/index.rs b/src/ui/handlers/index.rs
index 2fcb51c..de0b2b0 100644
--- a/src/ui/handlers/index.rs
+++ b/src/ui/handlers/index.rs
@@ -1,22 +1,20 @@
 use axum::response::{self, IntoResponse, Redirect};
+use axum_extra::TypedHeader;
+use headers::IfNoneMatch;
 
-use crate::{
-    error::Internal,
-    token::extract::Identity,
-    ui::assets::{Asset, Assets},
-};
+use crate::{error::Internal, token::extract::Identity, ui::assets::Response};
 
-pub async fn handler(identity: Option<Identity>) -> Result<Asset, Error> {
+pub async fn handler(
+    identity: Option<Identity>,
+    TypedHeader(if_none_match): TypedHeader<IfNoneMatch>,
+) -> Result<Response, Error> {
     let _ = identity.ok_or(Error::NotLoggedIn)?;
 
-    Assets::index().map_err(Error::Internal)
+    Response::index(&if_none_match).map_err(Error::Internal)
 }
 
-#[derive(Debug, thiserror::Error)]
 pub enum Error {
-    #[error("not logged in")]
     NotLoggedIn,
-    #[error("{0}")]
     Internal(Internal),
 }
 
diff --git a/src/ui/handlers/invite.rs b/src/ui/handlers/invite.rs
index edd6dc1..e552318 100644
--- a/src/ui/handlers/invite.rs
+++ b/src/ui/handlers/invite.rs
@@ -2,12 +2,15 @@ use axum::{
     extract::{Path, State},
     response::{self, IntoResponse},
 };
+use axum_extra::TypedHeader;
+use headers::IfNoneMatch;
 
 use crate::{
     error::Internal,
     invite,
     invite::app::Invites,
     ui::{
+        assets,
         assets::{Asset, Assets},
         error::NotFound,
     },
@@ -16,38 +19,27 @@ use crate::{
 pub async fn handler(
     State(invites): State<Invites>,
     Path(invite): Path<invite::Id>,
-) -> Result<Asset, Error> {
-    invites
-        .get(&invite)
-        .await
-        .map_err(Error::internal)?
-        .ok_or(Error::NotFound)?;
-
-    Assets::index().map_err(Error::Internal)
-}
-
-#[derive(Debug, thiserror::Error)]
-pub enum Error {
-    #[error("invite not found")]
-    NotFound,
-    #[error("{0}")]
-    Internal(Internal),
+    TypedHeader(if_none_match): TypedHeader<IfNoneMatch>,
+) -> Result<Response, Internal> {
+    if invites.get(&invite).await?.is_some() {
+        let index = assets::Response::index(&if_none_match)?;
+        Ok(Response::Found(index))
+    } else {
+        let index = Assets::index()?;
+        Ok(Response::NotFound(index))
+    }
 }
 
-impl Error {
-    fn internal(err: impl Into<Internal>) -> Self {
-        Self::Internal(err.into())
-    }
+pub enum Response {
+    Found(assets::Response),
+    NotFound(Asset),
 }
 
-impl IntoResponse for Error {
+impl IntoResponse for Response {
     fn into_response(self) -> response::Response {
         match self {
-            Self::NotFound => match Assets::index() {
-                Ok(asset) => NotFound(asset).into_response(),
-                Err(internal) => internal.into_response(),
-            },
-            Self::Internal(error) => error.into_response(),
+            Self::Found(asset) => asset.into_response(),
+            Self::NotFound(asset) => NotFound(asset).into_response(),
         }
     }
 }
diff --git a/src/ui/handlers/login.rs b/src/ui/handlers/login.rs
index 4562b04..c904d2a 100644
--- a/src/ui/handlers/login.rs
+++ b/src/ui/handlers/login.rs
@@ -1,8 +1,10 @@
-use crate::{
-    error::Internal,
-    ui::assets::{Asset, Assets},
-};
+use axum_extra::TypedHeader;
+use headers::IfNoneMatch;
 
-pub async fn handler() -> Result<Asset, Internal> {
-    Assets::index()
+use crate::{error::Internal, ui::assets::Response};
+
+pub async fn handler(
+    TypedHeader(if_none_match): TypedHeader<IfNoneMatch>,
+) -> Result<Response, Internal> {
+    Response::index(&if_none_match)
 }
diff --git a/src/ui/handlers/me.rs b/src/ui/handlers/me.rs
index 2fcb51c..de0b2b0 100644
--- a/src/ui/handlers/me.rs
+++ b/src/ui/handlers/me.rs
@@ -1,22 +1,20 @@
 use axum::response::{self, IntoResponse, Redirect};
+use axum_extra::TypedHeader;
+use headers::IfNoneMatch;
 
-use crate::{
-    error::Internal,
-    token::extract::Identity,
-    ui::assets::{Asset, Assets},
-};
+use crate::{error::Internal, token::extract::Identity, ui::assets::Response};
 
-pub async fn handler(identity: Option<Identity>) -> Result<Asset, Error> {
+pub async fn handler(
+    identity: Option<Identity>,
+    TypedHeader(if_none_match): TypedHeader<IfNoneMatch>,
+) -> Result<Response, Error> {
     let _ = identity.ok_or(Error::NotLoggedIn)?;
 
-    Assets::index().map_err(Error::Internal)
+    Response::index(&if_none_match).map_err(Error::Internal)
 }
 
-#[derive(Debug, thiserror::Error)]
 pub enum Error {
-    #[error("not logged in")]
     NotLoggedIn,
-    #[error("{0}")]
     Internal(Internal),
 }
 
diff --git a/src/ui/handlers/setup.rs b/src/ui/handlers/setup.rs
index 5707765..ac91908 100644
--- a/src/ui/handlers/setup.rs
+++ b/src/ui/handlers/setup.rs
@@ -2,14 +2,15 @@ use axum::{
     extract::State,
     response::{self, IntoResponse, Redirect},
 };
+use axum_extra::TypedHeader;
+use headers::IfNoneMatch;
 
-use crate::{
-    error::Internal,
-    setup::app::Setup,
-    ui::assets::{Asset, Assets},
-};
+use crate::{error::Internal, setup::app::Setup, ui::assets::Response};
 
-pub async fn handler(State(setup): State<Setup>) -> Result<Asset, Error> {
+pub async fn handler(
+    State(setup): State<Setup>,
+    TypedHeader(if_none_match): TypedHeader<IfNoneMatch>,
+) -> Result<Response, Error> {
     if setup
         .completed()
         .await
@@ -18,15 +19,12 @@ pub async fn handler(State(setup): State<Setup>) -> Result<Asset, Error> {
     {
         Err(Error::SetupCompleted)
     } else {
-        Assets::index().map_err(Error::Internal)
+        Response::index(&if_none_match).map_err(Error::Internal)
     }
 }
 
-#[derive(Debug, thiserror::Error)]
 pub enum Error {
-    #[error("setup already completed")]
     SetupCompleted,
-    #[error("{0}")]
     Internal(Internal),
 }
 
diff --git a/src/ui/handlers/swatch.rs b/src/ui/handlers/swatch.rs
index 4562b04..c904d2a 100644
--- a/src/ui/handlers/swatch.rs
+++ b/src/ui/handlers/swatch.rs
@@ -1,8 +1,10 @@
-use crate::{
-    error::Internal,
-    ui::assets::{Asset, Assets},
-};
+use axum_extra::TypedHeader;
+use headers::IfNoneMatch;
 
-pub async fn handler() -> Result<Asset, Internal> {
-    Assets::index()
+use crate::{error::Internal, ui::assets::Response};
+
+pub async fn handler(
+    TypedHeader(if_none_match): TypedHeader<IfNoneMatch>,
+) -> Result<Response, Internal> {
+    Response::index(&if_none_match)
 }