[#294] object: Implement Cmp() function for ID struct

Signed-off-by: Alexander Chuprov <a.chuprov@yadro.com>

object/id/id.go

@@ -4,6 +4,7 @@ import (
 	"crypto/ecdsa"
 	"crypto/sha256"
 	"fmt"
+	"strings"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/api/refs"
 	frostfscrypto "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/crypto"
@@ -167,3 +168,9 @@ func (id *ID) UnmarshalJSON(data []byte) error {
 
 	return nil
 }
+
+// Cmp returns an integer comparing two base58 encoded object ID lexicographically.
+// The result will be 0 if id1 == id2, -1 if id1 < id2, and +1 if id1 > id2.
+func (id ID) Cmp(id2 ID) int {
+	return strings.Compare(id.EncodeToString(), id2.EncodeToString())
+}

object/id/id_test.go

@@ -3,7 +3,9 @@ package oid
 import (
 	"crypto/rand"
 	"crypto/sha256"
+	"slices"
 	"strconv"
+	"strings"
 	"testing"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/api/refs"
@@ -180,3 +182,16 @@ func TestID_Encode(t *testing.T) {
 		require.Equal(t, emptyID, id.EncodeToString())
 	})
 }
+
+func TestID_Cmp(t *testing.T) {
+	id1 := randID(t)
+	id2 := randID(t)
+	id3 := randID(t)
+
+	arr := []ID{id1, id2, id3}
+
+	slices.SortFunc(arr, ID.Cmp)
+	for i := 1; i < len(arr); i++ {
+		require.NotEqual(t, strings.Compare(arr[i-1].EncodeToString(), arr[i].EncodeToString()), 1, "array is not sorted correctly")
+	}
+}