Preserve type for binary protocol parameters in prepared statements

client/stmt.go

@@ -156,6 +156,9 @@ func (s *Stmt) write(args ...interface{}) error {
 		case []byte:
 			paramTypes[i] = []byte{mysql.MYSQL_TYPE_STRING}
 			paramValues[i] = append(mysql.PutLengthEncodedInt(uint64(len(v))), v...)
+		case mysql.TypedBytes:
+			paramTypes[i] = []byte{v.Type}
+			paramValues[i] = append(mysql.PutLengthEncodedInt(uint64(len(v.Bytes))), v.Bytes...)
 		case json.RawMessage:
 			paramTypes[i] = []byte{mysql.MYSQL_TYPE_STRING}
 			paramValues[i] = append(mysql.PutLengthEncodedInt(uint64(len(v))), v...)

mysql/typed_bytes.go

@@ -0,0 +1,8 @@
+package mysql
+
+// TypedBytes preserves the original MySQL type alongside the raw bytes
+// for binary protocol parameters that are length-encoded.
+type TypedBytes struct {
+	Type  byte   // Original MySQL type
+	Bytes []byte // Raw bytes
+}

server/stmt.go

@@ -300,7 +300,7 @@ func (c *Conn) bindStmtArgs(s *Stmt, nullBitmap, paramTypes, paramValues []byte)
 			}
 
 			if !isNull {
-				args[i] = v
+				args[i] = mysql.TypedBytes{Type: tp, Bytes: v}
 				continue
 			} else {
 				args[i] = nil

server/stmt_test.go

@@ -97,3 +97,54 @@ func TestStmtPrepareWithPreparedStmt(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, mysql.MYSQL_TYPE_LONGLONG, columnFields[0].Type)
 }
+
+func TestBindStmtArgsTypedBytes(t *testing.T) {
+	testcases := []struct {
+		name        string
+		paramType   byte
+		paramValue  []byte
+		expectType  byte
+		expectBytes []byte
+	}{
+		{
+			name:        "DATETIME",
+			paramType:   mysql.MYSQL_TYPE_DATETIME,
+			paramValue:  []byte{0x07, 0xe8, 0x07, 0x06, 0x0f, 0x0e, 0x1e, 0x2d},
+			expectType:  mysql.MYSQL_TYPE_DATETIME,
+			expectBytes: []byte{0xe8, 0x07, 0x06, 0x0f, 0x0e, 0x1e, 0x2d},
+		},
+		{
+			name:        "VARCHAR",
+			paramType:   mysql.MYSQL_TYPE_VARCHAR,
+			paramValue:  []byte{0x05, 'h', 'e', 'l', 'l', 'o'},
+			expectType:  mysql.MYSQL_TYPE_VARCHAR,
+			expectBytes: []byte("hello"),
+		},
+		{
+			name:        "BLOB",
+			paramType:   mysql.MYSQL_TYPE_BLOB,
+			paramValue:  []byte{0x04, 0x00, 0x01, 0x02, 0x03},
+			expectType:  mysql.MYSQL_TYPE_BLOB,
+			expectBytes: []byte{0x00, 0x01, 0x02, 0x03},
+		},
+	}
+
+	for _, tc := range testcases {
+		t.Run(tc.name, func(t *testing.T) {
+			c := &Conn{}
+			s := &Stmt{Args: make([]interface{}, 1)}
+			s.Params = 1
+
+			nullBitmap := []byte{0x00}
+			paramTypes := []byte{tc.paramType, 0x00}
+
+			err := c.bindStmtArgs(s, nullBitmap, paramTypes, tc.paramValue)
+			require.NoError(t, err)
+
+			tv, ok := s.Args[0].(mysql.TypedBytes)
+			require.True(t, ok, "expected TypedBytes, got %T", s.Args[0])
+			require.Equal(t, tc.expectType, tv.Type)
+			require.Equal(t, tc.expectBytes, tv.Bytes)
+		})
+	}
+}