Remove some allocations from `uv-auth` (#12077)

## Summary

Use `SmallString`, and no need to allocate a `String` to fetch from the
URLs cache.

Cargo.lock

@@ -4606,6 +4606,7 @@ dependencies = [
  "tracing",
  "url",
  "uv-once-map",
+ "uv-small-str",
  "uv-static",
  "wiremock",
 ]

crates/uv-auth/Cargo.toml

@@ -11,6 +11,7 @@ workspace = true
 
 [dependencies]
 uv-once-map = { workspace = true }
+uv-small-str = { workspace = true }
 uv-static = { workspace = true }
 
 anyhow = { workspace = true }

crates/uv-auth/src/cache.rs

@@ -1,3 +1,4 @@
+use std::fmt::Formatter;
 use std::hash::BuildHasherDefault;
 use std::sync::Arc;
 use std::sync::RwLock;
@@ -41,26 +42,30 @@ impl CredentialsCache {
     /// Return the credentials that should be used for a realm and username, if any.
     pub(crate) fn get_realm(&self, realm: Realm, username: Username) -> Option<Arc<Credentials>> {
         let realms = self.realms.read().unwrap();
-        let name = if let Some(username) = username.as_deref() {
-            format!("{username}@{realm}")
-        } else {
-            realm.to_string()
-        };
         let given_username = username.is_some();
         let key = (realm, username);
 
         let Some(credentials) = realms.get(&key).cloned() else {
-            trace!("No credentials in cache for realm {name}");
+            trace!(
+                "No credentials in cache for realm {}",
+                RealmUsername::from(key)
+            );
             return None;
         };
 
         if given_username && credentials.password().is_none() {
             // If given a username, don't return password-less credentials
-            trace!("No password in cache for realm {name}");
+            trace!(
+                "No password in cache for realm {}",
+                RealmUsername::from(key)
+            );
             return None;
         }
 
-        trace!("Found cached credentials for realm {name}");
+        trace!(
+            "Found cached credentials for realm {}",
+            RealmUsername::from(key)
+        );
         Some(credentials)
     }
 
@@ -214,6 +219,26 @@ impl TrieState {
     }
 }
 
+#[derive(Debug)]
+struct RealmUsername(Realm, Username);
+
+impl std::fmt::Display for RealmUsername {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        let Self(realm, username) = self;
+        if let Some(username) = username.as_deref() {
+            write!(f, "{username}@{realm}")
+        } else {
+            write!(f, "{realm}")
+        }
+    }
+}
+
+impl From<(Realm, Username)> for RealmUsername {
+    fn from((realm, username): (Realm, Username)) -> Self {
+        Self(realm, username)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/uv-auth/src/credentials.rs

@@ -84,6 +84,10 @@ impl Credentials {
         self.username.clone()
     }
 
+    pub(crate) fn as_username(&self) -> &Username {
+        &self.username
+    }
+
     pub fn password(&self) -> Option<&str> {
         self.password.as_deref()
     }

crates/uv-auth/src/middleware.rs

@@ -194,7 +194,7 @@ impl Middleware for AuthMiddleware {
                 None
             } else if let Some(credentials) = self
                 .cache()
-                .get_url(request.url(), &credentials.to_username())
+                .get_url(request.url(), credentials.as_username())
             {
                 request = credentials.authenticate(request);
                 // Do not insert already-cached credentials

crates/uv-auth/src/realm.rs

@@ -1,6 +1,7 @@
 use std::{fmt::Display, fmt::Formatter};
 
 use url::Url;
+use uv_small_str::SmallString;
 
 /// Used to determine if authentication information should be retained on a new URL.
 /// Based on the specification defined in RFC 7235 and 7230.
@@ -23,16 +24,16 @@ use url::Url;
 // so we do not need any special handling here.
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub(crate) struct Realm {
-    scheme: String,
-    host: Option<String>,
+    scheme: SmallString,
+    host: Option<SmallString>,
     port: Option<u16>,
 }
 
 impl From<&Url> for Realm {
     fn from(url: &Url) -> Self {
         Self {
-            scheme: url.scheme().to_string(),
-            host: url.host_str().map(str::to_string),
+            scheme: SmallString::from(url.scheme()),
+            host: url.host_str().map(SmallString::from),
             port: url.port(),
         }
     }