Support MySQL REVERSE function (arana-db#549)

pkg/runtime/function/reverse.go

@@ -0,0 +1,77 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package function
+
+import (
+	"context"
+	"fmt"
+)
+
+import (
+	gxbig "github.com/dubbogo/gost/math/big"
+)
+
+import (
+	"github.com/arana-db/arana/pkg/proto"
+	"github.com/arana-db/arana/pkg/runtime/ast"
+)
+
+const FuncReverse = "REVERSE"
+
+var _ proto.Func = (*reverseFunc)(nil)
+
+func init() {
+	proto.RegisterFunc(FuncReverse, reverseFunc{})
+}
+
+type reverseFunc struct{}
+
+func reverseString(s string) string {
+	runes := []rune(s)
+	for from, to := 0, len(runes)-1; from < to; from, to = from+1, to-1 {
+		runes[from], runes[to] = runes[to], runes[from]
+	}
+	return string(runes)
+}
+
+func (a reverseFunc) Apply(ctx context.Context, inputs ...proto.Valuer) (proto.Value, error) {
+	str, err := inputs[0].Value(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	isNull := func(val any) bool {
+		_, ok := val.(ast.Null)
+		return ok
+	}
+
+	if isNull(str) {
+		return ast.Null{}, nil
+	}
+
+	switch v := str.(type) {
+	case *gxbig.Decimal:
+		return reverseString(v.Value), nil
+	default:
+		return reverseString(fmt.Sprint(str)), nil
+	}
+}
+
+func (a reverseFunc) NumInput() int {
+	return 1
+}

pkg/runtime/function/reverse_test.go

@@ -0,0 +1,58 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package function
+
+import (
+	"context"
+	"fmt"
+	"testing"
+)
+
+import (
+	gxbig "github.com/dubbogo/gost/math/big"
+
+	"github.com/stretchr/testify/assert"
+)
+
+import (
+	"github.com/arana-db/arana/pkg/proto"
+)
+
+func TestReverse(t *testing.T) {
+	fn := proto.MustGetFunc(FuncReverse)
+	assert.Equal(t, 1, fn.NumInput())
+
+	type tt struct {
+		in  proto.Value
+		out string
+	}
+
+	for _, it := range []tt{
+		{1111, "1111"},
+		{&gxbig.Decimal{Value: "12.23"}, "32.21"},
+		{"arana", "anara"},
+		{"db-mesh", "hsem-bd"},
+		{20.22, "22.02"},
+	} {
+		t.Run(it.out, func(t *testing.T) {
+			out, err := fn.Apply(context.Background(), proto.ToValuer(it.in))
+			assert.NoError(t, err)
+			assert.Equal(t, it.out, fmt.Sprint(out))
+		})
+	}
+}