feat(mysql): add MySqlRawValue

- renamed from MySqlValue (from master)

sqlx-mysql/src/value.rs

@@ -0,0 +1,49 @@
+use std::str::from_utf8;
+
+use bytes::Bytes;
+use sqlx_core::decode::{Error as DecodeError, Result as DecodeResult};
+use sqlx_core::{Decode, Runtime};
+
+use crate::MySql;
+
+/// The format of a raw SQL value for MySQL.
+///
+/// MySQL returns values in [`Text`] format for unprepared queries and in [`Binary`]
+/// format for prepared queries. There is no facility to request a different format.
+///
+#[derive(Debug, PartialEq, Copy, Clone)]
+pub enum MySqlRawValueFormat {
+    Binary,
+    Text,
+}
+
+/// The raw representation of a SQL value for MySQL.
+#[derive(Debug, Clone)]
+pub struct MySqlRawValue<'r> {
+    value: Option<&'r Bytes>,
+    format: MySqlRawValueFormat,
+}
+
+// 'r: row
+impl<'r> MySqlRawValue<'r> {
+    /// Returns the format of this value.
+    pub const fn format(&self) -> MySqlRawValueFormat {
+        self.format
+    }
+
+    /// Returns the underlying byte view of this value as a byte slice.
+    pub fn as_bytes(&self) -> DecodeResult<&'r [u8]> {
+        self.value.map(|bytes| &**bytes).ok_or(DecodeError::UnexpectedNull)
+    }
+
+    /// Returns a `&str` slice from the underlying byte view of this value,
+    /// if it contains valid UTF-8.
+    pub fn as_str(&self) -> DecodeResult<&'r str> {
+        self.as_bytes().and_then(|bytes| from_utf8(bytes).map_err(DecodeError::NotUtf8))
+    }
+
+    /// Decode this value into the target type.
+    pub fn decode<T: Decode<'r, MySql, Rt>, Rt: Runtime>(self) -> DecodeResult<T> {
+        <T as Decode<'r, MySql, Rt>>::decode(self)
+    }
+}