feat: optimize asset delivery with build-time compression and encoding negotiation

src/web/assets.rs

@@ -1,14 +1,18 @@
-//! Embedded assets for the web frontend
+//! Embedded assets for the web frontend.
 //!
-//! This module handles serving static assets that are embedded into the binary
-//! at compile time using rust-embed.
+//! Serves static assets embedded into the binary at compile time using rust-embed.
+//! Supports content negotiation for pre-compressed variants (.br, .gz, .zst)
+//! generated at build time by `web/scripts/compress-assets.ts`.
 
+use axum::http::{HeaderMap, HeaderValue, header};
 use dashmap::DashMap;
 use rapidhash::v3::rapidhash_v3;
 use rust_embed::RustEmbed;
 use std::fmt;
 use std::sync::LazyLock;
 
+use super::encoding::{COMPRESSION_MIN_SIZE, ContentEncoding, parse_accepted_encodings};
+
 /// Embedded web assets from the dist directory
 #[derive(RustEmbed)]
 #[folder = "web/dist/"]
@@ -21,17 +25,15 @@ pub struct WebAssets;
 pub struct AssetHash(u64);
 
 impl AssetHash {
-    /// Create a new AssetHash from u64 value
     pub fn new(hash: u64) -> Self {
         Self(hash)
     }
 
-    /// Get the hash as a hex string
     pub fn to_hex(&self) -> String {
         format!("{:016x}", self.0)
     }
 
-    /// Get the hash as a quoted hex string
+    /// Get the hash as a quoted hex string (for ETag headers)
     pub fn quoted(&self) -> String {
         format!("\"{}\"", self.to_hex())
     }
@@ -51,12 +53,8 @@ pub struct AssetMetadata {
 }
 
 impl AssetMetadata {
-    /// Check if the etag matches the asset hash
     pub fn etag_matches(&self, etag: &str) -> bool {
-        // Remove quotes if present (ETags are typically quoted)
         let etag = etag.trim_matches('"');
-
-        // ETags generated from u64 hex should be 16 characters
         etag.len() == 16
             && u64::from_str_radix(etag, 16)
                 .map(|parsed| parsed == self.hash.0)
@@ -68,28 +66,125 @@ impl AssetMetadata {
 static ASSET_CACHE: LazyLock<DashMap<String, AssetMetadata>> = LazyLock::new(DashMap::new);
 
 /// Get cached asset metadata for a file path, caching on-demand
-/// Returns AssetMetadata containing MIME type and RapidHash hash
 pub fn get_asset_metadata_cached(path: &str, content: &[u8]) -> AssetMetadata {
-    // Check cache first
     if let Some(cached) = ASSET_CACHE.get(path) {
         return cached.value().clone();
     }
 
-    // Calculate MIME type
     let mime_type = mime_guess::from_path(path)
         .first()
         .map(|mime| mime.to_string());
-
-    // Calculate RapidHash hash (using u64 native output size)
-    let hash_value = rapidhash_v3(content);
-    let hash = AssetHash::new(hash_value);
-
+    let hash = AssetHash::new(rapidhash_v3(content));
     let metadata = AssetMetadata { mime_type, hash };
 
-    // Only cache if we haven't exceeded the limit
     if ASSET_CACHE.len() < 1000 {
         ASSET_CACHE.insert(path.to_string(), metadata.clone());
     }
 
     metadata
 }
+
+/// Set appropriate `Cache-Control` header based on the asset path.
+///
+/// SvelteKit outputs fingerprinted assets under `_app/immutable/` which are
+/// safe to cache indefinitely. Other assets get shorter cache durations.
+fn set_cache_control(headers: &mut HeaderMap, path: &str) {
+    let cache_control = if path.contains("immutable/") {
+        // SvelteKit fingerprinted assets — cache forever
+        "public, max-age=31536000, immutable"
+    } else if path == "index.html" || path.ends_with(".html") {
+        "public, max-age=300"
+    } else {
+        match path.rsplit_once('.').map(|(_, ext)| ext) {
+            Some("css" | "js") => "public, max-age=86400",
+            Some("png" | "jpg" | "jpeg" | "gif" | "svg" | "ico") => "public, max-age=2592000",
+            _ => "public, max-age=3600",
+        }
+    };
+
+    if let Ok(value) = HeaderValue::from_str(cache_control) {
+        headers.insert(header::CACHE_CONTROL, value);
+    }
+}
+
+/// Serve an embedded asset with content encoding negotiation.
+///
+/// Tries pre-compressed variants (.br, .gz, .zst) in the order preferred by
+/// the client's `Accept-Encoding` header, falling back to the uncompressed
+/// original. Returns `None` if the asset doesn't exist at all.
+pub fn try_serve_asset_with_encoding(
+    path: &str,
+    request_headers: &HeaderMap,
+) -> Option<axum::response::Response> {
+    use axum::response::IntoResponse;
+
+    let asset_path = path.strip_prefix('/').unwrap_or(path);
+
+    // Get the uncompressed original first (for metadata: MIME type, ETag)
+    let original = WebAssets::get(asset_path)?;
+    let metadata = get_asset_metadata_cached(asset_path, &original.data);
+
+    // Check ETag for conditional requests (304 Not Modified)
+    if let Some(etag) = request_headers.get(header::IF_NONE_MATCH)
+        && etag.to_str().is_ok_and(|s| metadata.etag_matches(s))
+    {
+        return Some(axum::http::StatusCode::NOT_MODIFIED.into_response());
+    }
+
+    let mime_type = metadata
+        .mime_type
+        .unwrap_or_else(|| "application/octet-stream".to_string());
+
+    // Only attempt pre-compressed variants for files above the compression
+    // threshold — the build script skips smaller files too.
+    let accepted_encodings = if original.data.len() >= COMPRESSION_MIN_SIZE {
+        parse_accepted_encodings(request_headers)
+    } else {
+        vec![ContentEncoding::Identity]
+    };
+
+    for encoding in &accepted_encodings {
+        if *encoding == ContentEncoding::Identity {
+            continue;
+        }
+
+        let compressed_path = format!("{}{}", asset_path, encoding.extension());
+        if let Some(compressed) = WebAssets::get(&compressed_path) {
+            let mut response_headers = HeaderMap::new();
+
+            if let Ok(ct) = HeaderValue::from_str(&mime_type) {
+                response_headers.insert(header::CONTENT_TYPE, ct);
+            }
+            if let Some(ce) = encoding.header_value() {
+                response_headers.insert(header::CONTENT_ENCODING, ce);
+            }
+            if let Ok(etag_val) = HeaderValue::from_str(&metadata.hash.quoted()) {
+                response_headers.insert(header::ETAG, etag_val);
+            }
+            // Vary so caches distinguish by encoding
+            response_headers.insert(header::VARY, HeaderValue::from_static("Accept-Encoding"));
+            set_cache_control(&mut response_headers, asset_path);
+
+            return Some(
+                (
+                    axum::http::StatusCode::OK,
+                    response_headers,
+                    compressed.data,
+                )
+                    .into_response(),
+            );
+        }
+    }
+
+    // No compressed variant found — serve uncompressed original
+    let mut response_headers = HeaderMap::new();
+    if let Ok(ct) = HeaderValue::from_str(&mime_type) {
+        response_headers.insert(header::CONTENT_TYPE, ct);
+    }
+    if let Ok(etag_val) = HeaderValue::from_str(&metadata.hash.quoted()) {
+        response_headers.insert(header::ETAG, etag_val);
+    }
+    set_cache_control(&mut response_headers, asset_path);
+
+    Some((axum::http::StatusCode::OK, response_headers, original.data).into_response())
+}

src/web/encoding.rs

@@ -0,0 +1,196 @@
+//! Content encoding negotiation for pre-compressed asset serving.
+//!
+//! Parses Accept-Encoding headers with quality values and returns
+//! supported encodings in priority order for content negotiation.
+
+use axum::http::{HeaderMap, HeaderValue, header};
+
+/// Minimum size threshold for compression (bytes).
+///
+/// Must match `MIN_SIZE` in `web/scripts/compress-assets.ts`.
+pub const COMPRESSION_MIN_SIZE: usize = 512;
+
+/// Supported content encodings in priority order (best compression first).
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum ContentEncoding {
+    Zstd,
+    Brotli,
+    Gzip,
+    Identity,
+}
+
+impl ContentEncoding {
+    /// File extension suffix for pre-compressed variant lookup.
+    #[inline]
+    pub fn extension(&self) -> &'static str {
+        match self {
+            Self::Zstd => ".zst",
+            Self::Brotli => ".br",
+            Self::Gzip => ".gz",
+            Self::Identity => "",
+        }
+    }
+
+    /// `Content-Encoding` header value, or `None` for identity.
+    #[inline]
+    pub fn header_value(&self) -> Option<HeaderValue> {
+        match self {
+            Self::Zstd => Some(HeaderValue::from_static("zstd")),
+            Self::Brotli => Some(HeaderValue::from_static("br")),
+            Self::Gzip => Some(HeaderValue::from_static("gzip")),
+            Self::Identity => None,
+        }
+    }
+
+    /// Default priority when quality values are equal (higher = better).
+    #[inline]
+    fn default_priority(&self) -> u8 {
+        match self {
+            Self::Zstd => 4,
+            Self::Brotli => 3,
+            Self::Gzip => 2,
+            Self::Identity => 1,
+        }
+    }
+}
+
+/// Parse `Accept-Encoding` header and return supported encodings in priority order.
+///
+/// Supports quality values: `Accept-Encoding: gzip;q=0.8, br;q=1.0, zstd`
+/// When quality values are equal: zstd > brotli > gzip > identity.
+/// Encodings with `q=0` are excluded.
+pub fn parse_accepted_encodings(headers: &HeaderMap) -> Vec<ContentEncoding> {
+    let Some(accept) = headers
+        .get(header::ACCEPT_ENCODING)
+        .and_then(|v| v.to_str().ok())
+    else {
+        return vec![ContentEncoding::Identity];
+    };
+
+    let mut encodings: Vec<(ContentEncoding, f32)> = Vec::new();
+
+    for part in accept.split(',') {
+        let part = part.trim();
+        if part.is_empty() {
+            continue;
+        }
+
+        let (encoding_str, quality) = if let Some((enc, params)) = part.split_once(';') {
+            let q = params
+                .split(';')
+                .find_map(|p| p.trim().strip_prefix("q="))
+                .and_then(|q| q.parse::<f32>().ok())
+                .unwrap_or(1.0);
+            (enc.trim(), q)
+        } else {
+            (part, 1.0)
+        };
+
+        if quality == 0.0 {
+            continue;
+        }
+
+        let encoding = match encoding_str.to_lowercase().as_str() {
+            "zstd" => ContentEncoding::Zstd,
+            "br" | "brotli" => ContentEncoding::Brotli,
+            "gzip" | "x-gzip" => ContentEncoding::Gzip,
+            "*" => ContentEncoding::Gzip,
+            "identity" => ContentEncoding::Identity,
+            _ => continue,
+        };
+
+        encodings.push((encoding, quality));
+    }
+
+    // Sort by quality (desc), then default priority (desc)
+    encodings.sort_by(|a, b| {
+        b.1.partial_cmp(&a.1)
+            .unwrap_or(std::cmp::Ordering::Equal)
+            .then_with(|| b.0.default_priority().cmp(&a.0.default_priority()))
+    });
+
+    if encodings.is_empty() {
+        vec![ContentEncoding::Identity]
+    } else {
+        encodings.into_iter().map(|(e, _)| e).collect()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_parse_all_encodings() {
+        let mut headers = HeaderMap::new();
+        headers.insert(header::ACCEPT_ENCODING, "gzip, br, zstd".parse().unwrap());
+        let encodings = parse_accepted_encodings(&headers);
+        assert_eq!(encodings[0], ContentEncoding::Zstd);
+        assert_eq!(encodings[1], ContentEncoding::Brotli);
+        assert_eq!(encodings[2], ContentEncoding::Gzip);
+    }
+
+    #[test]
+    fn test_parse_with_quality_values() {
+        let mut headers = HeaderMap::new();
+        headers.insert(
+            header::ACCEPT_ENCODING,
+            "gzip;q=1.0, br;q=0.5, zstd;q=0.8".parse().unwrap(),
+        );
+        let encodings = parse_accepted_encodings(&headers);
+        assert_eq!(encodings[0], ContentEncoding::Gzip);
+        assert_eq!(encodings[1], ContentEncoding::Zstd);
+        assert_eq!(encodings[2], ContentEncoding::Brotli);
+    }
+
+    #[test]
+    fn test_no_header_returns_identity() {
+        let headers = HeaderMap::new();
+        let encodings = parse_accepted_encodings(&headers);
+        assert_eq!(encodings, vec![ContentEncoding::Identity]);
+    }
+
+    #[test]
+    fn test_disabled_encoding_excluded() {
+        let mut headers = HeaderMap::new();
+        headers.insert(
+            header::ACCEPT_ENCODING,
+            "zstd;q=0, br, gzip".parse().unwrap(),
+        );
+        let encodings = parse_accepted_encodings(&headers);
+        assert_eq!(encodings[0], ContentEncoding::Brotli);
+        assert_eq!(encodings[1], ContentEncoding::Gzip);
+        assert!(!encodings.contains(&ContentEncoding::Zstd));
+    }
+
+    #[test]
+    fn test_real_chrome_header() {
+        let mut headers = HeaderMap::new();
+        headers.insert(
+            header::ACCEPT_ENCODING,
+            "gzip, deflate, br, zstd".parse().unwrap(),
+        );
+        assert_eq!(parse_accepted_encodings(&headers)[0], ContentEncoding::Zstd);
+    }
+
+    #[test]
+    fn test_extensions() {
+        assert_eq!(ContentEncoding::Zstd.extension(), ".zst");
+        assert_eq!(ContentEncoding::Brotli.extension(), ".br");
+        assert_eq!(ContentEncoding::Gzip.extension(), ".gz");
+        assert_eq!(ContentEncoding::Identity.extension(), "");
+    }
+
+    #[test]
+    fn test_header_values() {
+        assert_eq!(
+            ContentEncoding::Zstd.header_value().unwrap(),
+            HeaderValue::from_static("zstd")
+        );
+        assert_eq!(
+            ContentEncoding::Brotli.header_value().unwrap(),
+            HeaderValue::from_static("br")
+        );
+        assert!(ContentEncoding::Identity.header_value().is_none());
+    }
+}

src/web/mod.rs

@@ -4,6 +4,8 @@ pub mod admin;
 #[cfg(feature = "embed-assets")]
 pub mod assets;
 pub mod auth;
+#[cfg(feature = "embed-assets")]
+pub mod encoding;
 pub mod extractors;
 pub mod routes;
 pub mod session_cache;

src/web/routes.rs

@@ -13,11 +13,9 @@ use crate::web::admin;
 use crate::web::auth::{self, AuthConfig};
 #[cfg(feature = "embed-assets")]
 use axum::{
-    http::{HeaderMap, HeaderValue, StatusCode, Uri},
-    response::{Html, IntoResponse},
+    http::{HeaderMap, StatusCode, Uri},
+    response::IntoResponse,
 };
-#[cfg(feature = "embed-assets")]
-use http::header;
 use serde::{Deserialize, Serialize};
 use serde_json::{Value, json};
 use std::{collections::BTreeMap, time::Duration};
@@ -27,48 +25,14 @@ use crate::state::AppState;
 use crate::status::ServiceStatus;
 #[cfg(not(feature = "embed-assets"))]
 use tower_http::cors::{Any, CorsLayer};
-use tower_http::{classify::ServerErrorsFailureClass, timeout::TimeoutLayer, trace::TraceLayer};
+use tower_http::{
+    classify::ServerErrorsFailureClass, compression::CompressionLayer, timeout::TimeoutLayer,
+    trace::TraceLayer,
+};
 use tracing::{Span, debug, trace, warn};
 
 #[cfg(feature = "embed-assets")]
-use crate::web::assets::{WebAssets, get_asset_metadata_cached};
-
-/// Set appropriate caching headers based on asset type
-#[cfg(feature = "embed-assets")]
-fn set_caching_headers(response: &mut Response, path: &str, etag: &str) {
-    let headers = response.headers_mut();
-
-    // Set ETag
-    if let Ok(etag_value) = HeaderValue::from_str(etag) {
-        headers.insert(header::ETAG, etag_value);
-    }
-
-    // Set Cache-Control based on asset type
-    let cache_control = if path.starts_with("assets/") {
-        // Static assets with hashed filenames - long-term cache
-        "public, max-age=31536000, immutable"
-    } else if path == "index.html" {
-        // HTML files - short-term cache
-        "public, max-age=300"
-    } else {
-        match path.split_once('.').map(|(_, extension)| extension) {
-            Some(ext) => match ext {
-                // CSS/JS files - medium-term cache
-                "css" | "js" => "public, max-age=86400",
-                // Images - long-term cache
-                "png" | "jpg" | "jpeg" | "gif" | "svg" | "ico" => "public, max-age=2592000",
-                // Default for other files
-                _ => "public, max-age=3600",
-            },
-            // Default for files without an extension
-            None => "public, max-age=3600",
-        }
-    };
-
-    if let Ok(cache_control_value) = HeaderValue::from_str(cache_control) {
-        headers.insert(header::CACHE_CONTROL, cache_control_value);
-    }
-}
+use crate::web::assets::try_serve_asset_with_encoding;
 
 /// Creates the web server router
 pub fn create_router(app_state: AppState, auth_config: AuthConfig) -> Router {
@@ -125,6 +89,13 @@ pub fn create_router(app_state: AppState, auth_config: AuthConfig) -> Router {
     }
 
     router.layer((
+        // Compress API responses (gzip/brotli/zstd). Pre-compressed static
+        // assets already have Content-Encoding set, so tower-http skips them.
+        CompressionLayer::new()
+            .zstd(true)
+            .br(true)
+            .gzip(true)
+            .quality(tower_http::CompressionLevel::Fastest),
         TraceLayer::new_for_http()
             .make_span_with(|request: &Request<Body>| {
                 tracing::debug_span!("request", path = request.uri().path())
@@ -171,71 +142,35 @@ pub fn create_router(app_state: AppState, auth_config: AuthConfig) -> Router {
     ))
 }
 
-/// Handler that extracts request information for caching
+/// SPA fallback handler with content encoding negotiation.
+///
+/// Serves embedded static assets with pre-compressed variants when available,
+/// falling back to `index.html` for SPA client-side routing.
 #[cfg(feature = "embed-assets")]
-async fn fallback(request: Request) -> Response {
+async fn fallback(request: Request) -> axum::response::Response {
     let uri = request.uri().clone();
     let headers = request.headers().clone();
-    handle_spa_fallback_with_headers(uri, headers).await
+    handle_spa_fallback(uri, headers).await
 }
 
-/// Handles SPA routing by serving index.html for non-API, non-asset requests
-/// This version includes HTTP caching headers and ETag support
 #[cfg(feature = "embed-assets")]
-async fn handle_spa_fallback_with_headers(uri: Uri, request_headers: HeaderMap) -> Response {
-    let path = uri.path().trim_start_matches('/');
-
-    if let Some(content) = WebAssets::get(path) {
-        // Get asset metadata (MIME type and hash) with caching
-        let metadata = get_asset_metadata_cached(path, &content.data);
-
-        // Check if client has a matching ETag (conditional request)
-        if let Some(etag) = request_headers.get(header::IF_NONE_MATCH)
-            && etag.to_str().is_ok_and(|s| metadata.etag_matches(s))
-        {
-            return StatusCode::NOT_MODIFIED.into_response();
-        }
-
-        // Use cached MIME type, only set Content-Type if we have a valid MIME type
-        let mut response = (
-            [(
-                header::CONTENT_TYPE,
-                // For unknown types, set to application/octet-stream
-                metadata
-                    .mime_type
-                    .unwrap_or("application/octet-stream".to_string()),
-            )],
-            content.data,
-        )
-            .into_response();
-
-        // Set caching headers
-        set_caching_headers(&mut response, path, &metadata.hash.quoted());
+async fn handle_spa_fallback(uri: Uri, request_headers: HeaderMap) -> axum::response::Response {
+    let path = uri.path();
 
+    // Try serving the exact asset (with encoding negotiation)
+    if let Some(response) = try_serve_asset_with_encoding(path, &request_headers) {
         return response;
-    } else {
-        // Any assets that are not found should be treated as a 404, not falling back to the SPA index.html
-        if path.starts_with("assets/") {
-            return (StatusCode::NOT_FOUND, "Asset not found").into_response();
-        }
     }
 
-    // Fall back to the SPA index.html
-    match WebAssets::get("index.html") {
-        Some(content) => {
-            let metadata = get_asset_metadata_cached("index.html", &content.data);
+    // SvelteKit assets under _app/ that don't exist are a hard 404
+    let trimmed = path.trim_start_matches('/');
+    if trimmed.starts_with("_app/") || trimmed.starts_with("assets/") {
+        return (StatusCode::NOT_FOUND, "Asset not found").into_response();
+    }
 
-            // Check if client has a matching ETag for index.html
-            if let Some(etag) = request_headers.get(header::IF_NONE_MATCH)
-                && etag.to_str().is_ok_and(|s| metadata.etag_matches(s))
-            {
-                return StatusCode::NOT_MODIFIED.into_response();
-            }
-
-            let mut response = Html(content.data).into_response();
-            set_caching_headers(&mut response, "index.html", &metadata.hash.quoted());
-            response
-        }
+    // SPA fallback: serve index.html with encoding negotiation
+    match try_serve_asset_with_encoding("/index.html", &request_headers) {
+        Some(response) => response,
         None => (
             StatusCode::INTERNAL_SERVER_ERROR,
             "Failed to load index.html",