StorageError: use std::borrow::Cow for msg field

This allows avoiding an unnecessary allocation whenever the error
message is static.

1 files changed, 21 insertions, 7 deletions

diff --git a/kittybox-rs/src/database/mod.rs b/kittybox-rs/src/database/mod.rs
index db0e360..ea4205c 100644
--- a/kittybox-rs/src/database/mod.rs
+++ b/kittybox-rs/src/database/mod.rs
@@ -1,4 +1,6 @@
 #![warn(missing_docs)]
+use std::borrow::Cow;
+
 use async_trait::async_trait;
 
 mod file;
@@ -122,7 +124,7 @@ pub mod settings {
 /// Error signalled from the database.
 #[derive(Debug)]
 pub struct StorageError {
-    msg: String,
+    msg: std::borrow::Cow<'static, str>,
     source: Option<Box<dyn std::error::Error + Send + Sync>>,
     kind: ErrorKind,
 }
@@ -137,7 +139,7 @@ impl std::error::Error for StorageError {
 impl From<serde_json::Error> for StorageError {
     fn from(err: serde_json::Error) -> Self {
         Self {
-            msg: format!("{}", err),
+            msg: std::borrow::Cow::Owned(format!("{}", err)),
             source: Some(Box::new(err)),
             kind: ErrorKind::JsonParsing,
         }
@@ -171,21 +173,33 @@ impl serde::Serialize for StorageError {
 }
 impl StorageError {
     /// Create a new StorageError of an ErrorKind with a message.
-    fn new(kind: ErrorKind, msg: &str) -> Self {
+    pub fn new(kind: ErrorKind, msg: String) -> Self {
         Self {
-            msg: msg.to_string(),
+            msg: Cow::Owned(msg),
             source: None,
             kind,
         }
     }
+    /// Create a new StorageError of an ErrorKind with a message from
+    /// a static string.
+    ///
+    /// This saves an allocation for a new string and is the preferred
+    /// way in case the error message doesn't change.
+    pub fn from_static(kind: ErrorKind, msg: &'static str) -> Self {
+        Self {
+            msg: Cow::Borrowed(msg),
+            source: None,
+            kind
+        }
+    }
     /// Create a StorageError using another arbitrary Error as a source.
-    fn with_source(
+    pub fn with_source(
         kind: ErrorKind,
-        msg: &str,
+        msg: std::borrow::Cow<'static, str>,
         source: Box<dyn std::error::Error + Send + Sync>,
     ) -> Self {
         Self {
-            msg: msg.to_string(),
+            msg,
             source: Some(source),
             kind,
         }