feat(mysql): reuse byte buffers for UTF-8 strings

crates/dbx-core/src/db/mysql.rs

@@ -73,21 +73,27 @@ where
     row.get_opt::<T, I>(index).and_then(|result| result.ok())
 }
 
+/// 字节转 String：合法 UTF-8（绝大多数场景）时直接复用入参缓冲零拷贝，
+/// 仅在非法序列时退化为 lossy 替换。from_utf8_lossy(&b).to_string() 即使
+/// 对合法输入也会多一次分配+拷贝。
+fn bytes_to_string_lossy(bytes: Vec<u8>) -> String {
+    String::from_utf8(bytes).unwrap_or_else(|err| String::from_utf8_lossy(err.as_bytes()).into_owned())
+}
+
 fn get_str(row: &mysql_async::Row, idx: usize) -> String {
     row_get::<String, _>(row, idx)
-        .or_else(|| row_get::<Vec<u8>, _>(row, idx).map(|b| String::from_utf8_lossy(&b).to_string()))
+        .or_else(|| row_get::<Vec<u8>, _>(row, idx).map(bytes_to_string_lossy))
         .unwrap_or_default()
 }
 
 fn get_str_by_name(row: &mysql_async::Row, name: &str) -> String {
     row_get::<String, _>(row, name)
-        .or_else(|| row_get::<Vec<u8>, _>(row, name).map(|b| String::from_utf8_lossy(&b).to_string()))
+        .or_else(|| row_get::<Vec<u8>, _>(row, name).map(bytes_to_string_lossy))
         .unwrap_or_default()
 }
 
 fn get_opt_str(row: &mysql_async::Row, name: &str) -> Option<String> {
-    row_get::<String, _>(row, name)
-        .or_else(|| row_get::<Vec<u8>, _>(row, name).map(|b| String::from_utf8_lossy(&b).to_string()))
+    row_get::<String, _>(row, name).or_else(|| row_get::<Vec<u8>, _>(row, name).map(bytes_to_string_lossy))
 }
 
 /// First non-empty string value among the named columns (e.g. Doris `CatalogName`
@@ -279,7 +285,7 @@ fn mysql_bytes_to_json(bytes: Vec<u8>, column: &mysql_async::Column) -> serde_js
             .map(serde_json::Value::String)
             .unwrap_or_else(|| super::binary_value_to_json(&bytes));
     }
-    serde_json::Value::String(String::from_utf8_lossy(&bytes).to_string())
+    serde_json::Value::String(bytes_to_string_lossy(bytes))
 }
 
 /// Map a MySQL column to a user-facing type name for the result-grid header.
@@ -3364,11 +3370,7 @@ pub async fn show_create_table_ddl(pool: &MySqlPool, database: &str, table: &str
     let row = rows.first().ok_or("DDL not found")?;
     row.get_opt::<String, usize>(1)
         .and_then(|result| result.ok())
-        .or_else(|| {
-            row.get_opt::<Vec<u8>, usize>(1)
-                .and_then(|result| result.ok())
-                .map(|b| String::from_utf8_lossy(&b).to_string())
-        })
+        .or_else(|| row.get_opt::<Vec<u8>, usize>(1).and_then(|result| result.ok()).map(bytes_to_string_lossy))
         .ok_or_else(|| "Failed to read DDL".to_string())
 }
 
@@ -3551,11 +3553,7 @@ pub async fn show_create_table_ddl_from(
     let row = rows.first().ok_or("DDL not found")?;
     row.get_opt::<String, usize>(1)
         .and_then(|result| result.ok())
-        .or_else(|| {
-            row.get_opt::<Vec<u8>, usize>(1)
-                .and_then(|result| result.ok())
-                .map(|b| String::from_utf8_lossy(&b).to_string())
-        })
+        .or_else(|| row.get_opt::<Vec<u8>, usize>(1).and_then(|result| result.ok()).map(bytes_to_string_lossy))
         .ok_or_else(|| "Failed to read DDL".to_string())
 }
 
@@ -3910,6 +3908,15 @@ mod tests {
     use crate::db::connection_timeout;
     use mysql_async::consts::ColumnFlags;
 
+    #[test]
+    fn bytes_to_string_reuses_valid_utf8_and_falls_back_lossy() {
+        assert_eq!(super::bytes_to_string_lossy("héllo 世界".as_bytes().to_vec()), "héllo 世界");
+        assert_eq!(super::bytes_to_string_lossy(vec![]), "");
+        // 非法 UTF-8 序列退化为替换字符，与 from_utf8_lossy 语义一致
+        let invalid = vec![0x66, 0x6f, 0xff, 0x6f];
+        assert_eq!(super::bytes_to_string_lossy(invalid.clone()), String::from_utf8_lossy(&invalid));
+    }
+
     #[test]
     fn mysql_column_type_names_map_to_friendly_names() {
         use mysql_async::consts::ColumnType::*;