From 71a7d9a9d39cf02be07a106d554b42a131471f3d Mon Sep 17 00:00:00 2001
From: Yuki Okushi <huyuumi.dev@gmail.com>
Date: Tue, 28 Apr 2026 19:31:04 +0900
Subject: [PATCH] perf(bytestring): micro-improve performance against ASCII
 conv (#865)

---
 bytestring/CHANGES.md |  1 +
 bytestring/src/lib.rs | 29 +++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/bytestring/CHANGES.md b/bytestring/CHANGES.md
index a06640be..4c7332df 100644
--- a/bytestring/CHANGES.md
+++ b/bytestring/CHANGES.md
@@ -4,6 +4,7 @@
 
 - Minimum supported Rust version (MSRV) is now 1.88.
 - Improve `From<ByteString> for String` performance.
+- Improve ASCII `TryFrom` conversions performance.
 
 ## 1.5.0
 
diff --git a/bytestring/src/lib.rs b/bytestring/src/lib.rs
index e50a0477..27434c96 100644
--- a/bytestring/src/lib.rs
+++ b/bytestring/src/lib.rs
@@ -195,6 +195,10 @@ impl TryFrom<&[u8]> for ByteString {
 
     #[inline]
     fn try_from(value: &[u8]) -> Result<Self, Self::Error> {
+        if value.is_ascii() {
+            return Ok(ByteString(Bytes::copy_from_slice(value)));
+        }
+
         let _ = str::from_utf8(value)?;
         Ok(ByteString(Bytes::copy_from_slice(value)))
     }
@@ -205,6 +209,10 @@ impl TryFrom<Vec<u8>> for ByteString {
 
     #[inline]
     fn try_from(value: Vec<u8>) -> Result<Self, Self::Error> {
+        if value.is_ascii() {
+            return Ok(ByteString(Bytes::from(value)));
+        }
+
         let buf = String::from_utf8(value).map_err(|err| err.utf8_error())?;
         Ok(ByteString(Bytes::from(buf)))
     }
@@ -215,6 +223,10 @@ impl TryFrom<Bytes> for ByteString {
 
     #[inline]
     fn try_from(value: Bytes) -> Result<Self, Self::Error> {
+        if value.is_ascii() {
+            return Ok(ByteString(value));
+        }
+
         let _ = str::from_utf8(value.as_ref())?;
         Ok(ByteString(value))
     }
@@ -225,6 +237,10 @@ impl TryFrom<bytes::BytesMut> for ByteString {
 
     #[inline]
     fn try_from(value: bytes::BytesMut) -> Result<Self, Self::Error> {
+        if value.is_ascii() {
+            return Ok(ByteString(value.freeze()));
+        }
+
         let _ = str::from_utf8(&value)?;
         Ok(ByteString(value.freeze()))
     }
@@ -413,7 +429,10 @@ mod test {
 
     #[test]
     fn try_from_slice() {
+        let heart = "\u{1f496}";
         let _ = ByteString::try_from(b"nice bytes").unwrap();
+        assert_eq!(ByteString::try_from(heart.as_bytes()).unwrap(), heart);
+        ByteString::try_from(&[0, 159, 146, 150][..]).unwrap_err();
     }
 
     #[test]
@@ -432,12 +451,22 @@ mod test {
 
     #[test]
     fn try_from_bytes() {
+        let heart = "\u{1f496}";
         let _ = ByteString::try_from(Bytes::from_static(b"nice bytes")).unwrap();
+        assert_eq!(
+            ByteString::try_from(Bytes::from_static(heart.as_bytes())).unwrap(),
+            heart
+        );
     }
 
     #[test]
     fn try_from_bytes_mut() {
+        let heart = "\u{1f496}";
         let _ = ByteString::try_from(bytes::BytesMut::from(&b"nice bytes"[..])).unwrap();
+        assert_eq!(
+            ByteString::try_from(bytes::BytesMut::from(heart.as_bytes())).unwrap(),
+            heart
+        );
     }
 
     #[test]