perf(lib): lowercase each shared path once at scan time

Answering a search lowercased every shared path again for every query:
with a large share and the steady stream of searches the server forwards,
that is an allocation per file per search. The lowercase key is now
computed once when the share is scanned.

soulseek-rs-lib/src/shares/mod.rs

@@ -13,6 +13,9 @@ use std::path::{Path, PathBuf};
 pub struct SharedFile {
     /// Backslash-separated path exposed to peers, e.g. `music\album\song.mp3`.
     pub virtual_path: String,
+    /// `virtual_path` lowercased once at scan time, so answering a search does
+    /// not lowercase every shared path again.
+    search_key: String,
     /// The real filesystem path used to serve the bytes.
     pub real_path: PathBuf,
     pub size: u64,
@@ -106,10 +109,7 @@ impl Shares {
         }
         self.files
             .iter()
-            .filter(|f| {
-                let haystack = f.virtual_path.to_lowercase();
-                terms.iter().all(|t| haystack.contains(t.as_str()))
-            })
+            .filter(|f| terms.iter().all(|t| f.search_key.contains(t.as_str())))
             .collect()
     }
 
@@ -200,6 +200,7 @@ fn scan_root(
                 }
                 let virtual_path = virtual_path_for(root_name, root, &path);
                 files.push(SharedFile {
+                    search_key: virtual_path.to_lowercase(),
                     virtual_path,
                     real_path: path,
                     size: meta.len(),
@@ -278,6 +279,20 @@ mod tests {
         let _ = std::fs::remove_dir_all(root);
     }
 
+    #[test]
+    fn a_mixed_case_path_matches_a_lowercase_query() {
+        let root = std::env::temp_dir()
+            .join(format!("soulseek-shares-case-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&root);
+        std::fs::create_dir_all(root.join("Live Set")).unwrap();
+        std::fs::write(root.join("Live Set").join("Opening TRACK.flac"), b"x")
+            .unwrap();
+        let shares = Shares::scan(&root).unwrap();
+
+        assert_eq!(shares.search("live opening track").len(), 1);
+        let _ = std::fs::remove_dir_all(root);
+    }
+
     #[test]
     fn search_is_case_insensitive_and_multi_term_and() {
         let root = temp_tree();