Fix decoding of small negative unsigned integer in Mssql

Author: lovasoa

CHANGELOG.md

@@ -5,6 +5,9 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## 0.6.43
+ - Fix decoding of small negative unsigned integer in Mssql.
+
 ## 0.6.42
  - Fix `QueryBuilder` for Microsoft SQL Server: https://github.com/sqlpage/sqlx-oldapi/issues/11
  - Add support for Microsoft SQL Server DateTime columns in sqlx macros: macros https://github.com/sqlpage/sqlx-oldapi/issues/16

sqlx-core/src/mssql/types/int.rs

@@ -1,6 +1,5 @@
 use std::any::type_name;
 use std::convert::TryFrom;
-use std::i16;
 
 use crate::decode::Decode;
 use crate::encode::{Encode, IsNull};
@@ -27,10 +26,85 @@ impl Encode<'_, Mssql> for i8 {
     }
 }
 
+trait FromLeBytes<const N: usize> {
+    fn from_le_bytes(bytes: [u8; N]) -> Self;
+}
+
+impl FromLeBytes<1> for i8 {
+    fn from_le_bytes(bytes: [u8; 1]) -> Self {
+        i8::from_le_bytes(bytes)
+    }
+}
+
+impl FromLeBytes<2> for i16 {
+    fn from_le_bytes(bytes: [u8; 2]) -> Self {
+        i16::from_le_bytes(bytes)
+    }
+}
+
+impl FromLeBytes<4> for i32 {
+    fn from_le_bytes(bytes: [u8; 4]) -> Self {
+        i32::from_le_bytes(bytes)
+    }
+}
+
+impl FromLeBytes<8> for i64 {
+    fn from_le_bytes(bytes: [u8; 8]) -> Self {
+        i64::from_le_bytes(bytes)
+    }
+}
+
+fn decode_int_direct<T, const N: usize>(value: MssqlValueRef<'_>) -> Result<T, BoxDynError>
+where
+    T: FromLeBytes<N> + TryFrom<i64>,
+    T::Error: std::error::Error + Send + Sync + 'static,
+{
+    let ty = value.type_info.0.ty;
+    let precision = value.type_info.0.precision;
+    let scale = value.type_info.0.scale;
+
+    match ty {
+        DataType::SmallInt
+        | DataType::Int
+        | DataType::TinyInt
+        | DataType::BigInt
+        | DataType::IntN => {
+            let bytes_val = value.as_bytes()?;
+            let len = bytes_val.len();
+
+            if len > N {
+                return Err(err_protocol!(
+                    "Decoding {:?} as {} failed because type {:?} has {} bytes, but can only handle {} bytes",
+                    value,
+                    type_name::<T>(),
+                    ty,
+                    len,
+                    N
+                )
+                .into());
+            }
+
+            let mut buf = [0u8; N];
+            buf[..len].copy_from_slice(bytes_val);
+            Ok(T::from_le_bytes(buf))
+        }
+        DataType::Numeric | DataType::NumericN | DataType::Decimal | DataType::DecimalN => {
+            let i64_val = decode_numeric(value.as_bytes()?, precision, scale)?;
+            convert_integer::<T>(i64_val)
+        }
+        _ => Err(err_protocol!(
+            "Decoding {:?} as {} failed because type {:?} is not supported",
+            value,
+            type_name::<T>(),
+            ty
+        )
+        .into()),
+    }
+}
+
 impl Decode<'_, Mssql> for i8 {
     fn decode(value: MssqlValueRef<'_>) -> Result<Self, BoxDynError> {
-        let i64_val = <i64 as Decode<Mssql>>::decode(value)?;
-        convert_integer::<Self>(i64_val)
+        decode_int_direct::<Self, 1>(value)
     }
 }
 
@@ -57,8 +131,7 @@ impl Encode<'_, Mssql> for i16 {
 
 impl Decode<'_, Mssql> for i16 {
     fn decode(value: MssqlValueRef<'_>) -> Result<Self, BoxDynError> {
-        let i64_val = <i64 as Decode<Mssql>>::decode(value)?;
-        convert_integer::<Self>(i64_val)
+        decode_int_direct::<Self, 2>(value)
     }
 }
 
@@ -82,8 +155,7 @@ impl Encode<'_, Mssql> for i32 {
 
 impl Decode<'_, Mssql> for i32 {
     fn decode(value: MssqlValueRef<'_>) -> Result<Self, BoxDynError> {
-        let i64_val = <i64 as Decode<Mssql>>::decode(value)?;
-        convert_integer::<Self>(i64_val)
+        decode_int_direct::<Self, 4>(value)
     }
 }
 
@@ -118,43 +190,7 @@ impl Encode<'_, Mssql> for i64 {
 
 impl Decode<'_, Mssql> for i64 {
     fn decode(value: MssqlValueRef<'_>) -> Result<Self, BoxDynError> {
-        let ty = value.type_info.0.ty;
-        let precision = value.type_info.0.precision;
-        let scale = value.type_info.0.scale;
-
-        match ty {
-            DataType::SmallInt
-            | DataType::Int
-            | DataType::TinyInt
-            | DataType::BigInt
-            | DataType::IntN => {
-                let mut buf = [0u8; 8];
-                let bytes_val = value.as_bytes()?;
-                let len = bytes_val.len();
-
-                if len > buf.len() {
-                    return Err(err_protocol!(
-                        "Decoding {:?} as a i64 failed because type {:?} has more than {} bytes",
-                        value,
-                        ty,
-                        buf.len()
-                    )
-                    .into());
-                }
-
-                buf[..len].copy_from_slice(bytes_val);
-                Ok(i64::from_le_bytes(buf))
-            }
-            DataType::Numeric | DataType::NumericN | DataType::Decimal | DataType::DecimalN => {
-                decode_numeric(value.as_bytes()?, precision, scale)
-            }
-            _ => Err(err_protocol!(
-                "Decoding {:?} as a i64 failed because type {:?} is not implemented",
-                value,
-                ty
-            )
-            .into()),
-        }
+        decode_int_direct::<Self, 8>(value)
     }
 }