web: fix static-file caching & root redirects

crates/bin/docs_rs_web/Cargo.toml

@@ -7,13 +7,6 @@ repository.workspace = true
 edition.workspace = true
 build = "build.rs"
 
-[package.metadata.cargo-machete]
-ignored = [
-    # used in build script output
-    # used in askama templates, can be moved to web binary
-    "slug",
-]
-
 [dependencies]
 anyhow = { workspace = true }
 askama = { workspace = true }
@@ -60,7 +53,6 @@ regex = { workspace = true }
 sentry = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
-slug = "0.1.1"
 sqlx = { workspace = true }
 strum = { workspace = true }
 syntect = { version = "5.0.0", default-features = false, features = ["dump-load", "html", "parsing", "regex-onig"] }

crates/bin/docs_rs_web/build.rs

@@ -88,6 +88,23 @@ fn main() -> Result<()> {
     }
     writeln!(etag_file, "];")?;
 
+    // Include paths as well as contents so additions, removals, and renames
+    // change the cache buster. BTreeMap provides deterministic ordering.
+    let mut asset_hash = md5::Context::new();
+    for (path, etag) in &etag_map {
+        asset_hash.consume(path.as_bytes());
+        asset_hash.consume([0]);
+        asset_hash.consume(etag.as_bytes());
+        asset_hash.consume([0]);
+    }
+    // 64 bits is enough for a cache buster while keeping asset URLs short.
+    let asset_hash = format!("{:x}", asset_hash.finalize());
+    writeln!(
+        etag_file,
+        "pub const STATIC_ASSET_HASH: &str = {:?};",
+        &asset_hash[..16],
+    )?;
+
     etag_file.sync_all()?;
 
     // trigger recompilation when a new migration is added
@@ -165,13 +182,15 @@ fn calculate_static_etags(etag_map: &mut ETagMap) -> Result<()> {
         for entry in walkdir::WalkDir::new(static_dir) {
             let entry = entry?;
             let path = entry.path();
+            // Track directories too, so adding or removing assets reruns the build.
+            tracked::track(path)?;
             if !path.is_file() {
                 continue;
             }
 
             let partial_path = path.strip_prefix(static_dir).unwrap();
             let partial_path_str = partial_path.to_string_lossy().to_string();
-            etag_map.insert(partial_path_str, etag_from_path(path)?);
+            etag_map.insert(partial_path_str, etag_from_content(tracked::read(path)?));
         }
     }
 

crates/bin/docs_rs_web/src/handlers/rustdoc.rs

@@ -18,6 +18,7 @@ use crate::{
         TemplateData,
         templates::{RenderBrands, RenderRegular, RenderSolid, filters},
     },
+    routes::cached_static_redirect,
     utils::{self, licenses},
 };
 use anyhow::{Context as _, anyhow};
@@ -245,10 +246,7 @@ pub(crate) async fn rustdoc_redirector_handler(
         // redirect all ico requests
         // originally from:
         // https://github.com/rust-lang/docs.rs/commit/f3848a34c391841a2516a9e6ad1f80f6f490c6d0
-        return Ok(axum_cached_redirect(
-            "/-/static/favicon.ico",
-            CachePolicy::ForeverInCdnAndBrowser,
-        )?);
+        return Ok(cached_static_redirect("favicon.ico").into_response());
     }
 
     // edge case 3:
@@ -1108,6 +1106,26 @@ mod test {
     use test_case::test_case;
     use tracing::info;
 
+    #[test_case("/rust-logo.ico")]
+    #[test_case("/some-crate/1.0.0/favicon.ico")]
+    #[tokio::test(flavor = "multi_thread")]
+    async fn favicon_redirect(path: &str) -> Result<()> {
+        let env = TestEnvironment::new().await?;
+        let target = format!("/-/static/v/{}/favicon.ico", crate::STATIC_ASSET_HASH,);
+        let response = env
+            .web_app()
+            .await
+            .assert_redirect_cached(
+                path,
+                &target,
+                CachePolicy::ForeverInCdn(crate::cache::SURROGATE_KEY_DOCSRS_STATIC.into()),
+                env.config(),
+            )
+            .await?;
+        assert_eq!(response.status(), StatusCode::TEMPORARY_REDIRECT);
+        Ok(())
+    }
+
     fn has_content_len(headers: &HeaderMap) -> bool {
         let content_length: usize = headers
             .get(CONTENT_LENGTH)