fix middle of strings

Author: nshestakov

ydb/core/persqueue/partition_key_range/partition_key_range.cpp

@@ -6,6 +6,8 @@ namespace NKikimr {
 namespace NPQ {
 
 TString MiddleOf(const TString& from, const TString& to) {
+    Y_ABORT_UNLESS(to.empty() || from < to);
+
     auto GetChar = [](const TString& str, size_t i, unsigned char defaultValue) {
         if (i >= str.size()) {
             return defaultValue;
@@ -24,10 +26,12 @@ TString MiddleOf(const TString& from, const TString& to) {
 
     size_t maxSize = std::max(from.size(), to.size());
     result.reserve(maxSize + 1);
+
+    size_t size = std::max(from.size(), to.size());
     size_t i = 0;
-    for (; i < maxSize; ++i) {
+    for (; i < size; ++i) {
         ui16 f = GetChar(from, i, 0);
-        ui16 t = GetChar(to, i, 0xFF);
+        ui16 t = GetChar(to, i, 0);
 
         if (f != t) {
             diffFound = true;
@@ -76,12 +80,32 @@ TString MiddleOf(const TString& from, const TString& to) {
         }
     }
 
+    if (!splitted) {
+        for (; i < from.size() && !splitted; ++i) {
+            ui16 f = GetChar(from, i, 0);
+            if (f < 0xFF) {
+                auto n = (f + 0x100u) / 2u;
+                result << static_cast<unsigned char>(n);
+                splitted = true;
+            } else {
+                result << static_cast<unsigned char>(0xFFu);
+            }
+        }
+
+        for (; i < to.size() && !splitted; ++i) {
+            ui16 t = GetChar(to, i, 0);
+            auto n = t / 2u;
+            result << static_cast<unsigned char>(n);
+            splitted = !!n;
+        }
+    }
+
     if (result == from) {
-        size_t j = splitted ? i : maxSize - 1;
+        size_t j = maxSize - 1;
         ui16 f = GetChar(from, j, 0);
-        ui16 t = GetChar(to, j, 0xFF);
+        ui16 t = GetChar(to, j, to.empty() ? 0xFF : 0x00);
 
-        result << static_cast<unsigned char>((f - t) & 1 ? 0xFFu: 0x7Fu);
+        result << static_cast<unsigned char>((f - t) & 1 ? 0x7Fu : 0xFFu);
     }
 
     return result;

ydb/core/persqueue/ut/autoscaling_ut.cpp

@@ -671,7 +671,7 @@ Y_UNIT_TEST_SUITE(TopicAutoscaling) {
 
         {
             auto res = NKikimr::NPQ::MiddleOf(AsString({0x01}), AsString({0x02}));
-            UNIT_ASSERT_VALUES_EQUAL(ToHex(res), "01 FF");
+            UNIT_ASSERT_VALUES_EQUAL(ToHex(res), "01 7F");
         }
 
         {
@@ -686,7 +686,7 @@ Y_UNIT_TEST_SUITE(TopicAutoscaling) {
 
         {
             auto res = NKikimr::NPQ::MiddleOf(AsString({0x01, 0xFF}), AsString({0x02, 0x00}));
-            UNIT_ASSERT_VALUES_EQUAL(ToHex(res), "01 FF FF");
+            UNIT_ASSERT_VALUES_EQUAL(ToHex(res), "01 FF 7F");
         }
 
         {
@@ -718,8 +718,12 @@ Y_UNIT_TEST_SUITE(TopicAutoscaling) {
             UNIT_ASSERT_VALUES_EQUAL(ToHex(res), "02 00 00 07");
         }
         {
-            auto res = NKikimr::NPQ::MiddleOf(AsString({0xFF, 0xFF}), AsString({0xFF}));
-            UNIT_ASSERT_VALUES_EQUAL(ToHex(res), "FF FF 7F");
+            auto res = NKikimr::NPQ::MiddleOf(AsString({0xFF}), AsString({0xFF, 0xFF}));
+            UNIT_ASSERT_VALUES_EQUAL(ToHex(res), "FF 7F");
+        }
+        {
+            auto res = NKikimr::NPQ::MiddleOf(AsString({0x99, 0xFF}), AsString({0x9A}));
+            UNIT_ASSERT_VALUES_EQUAL(ToHex(res), "99 FF 7F");
         }
     }
 }

ydb/core/tx/schemeshard/schemeshard__operation_alter_pq.cpp

@@ -520,6 +520,10 @@ class TAlterPQ: public TSubOperation {
         bool splitMergeEnabled = AppData()->FeatureFlags.GetEnableTopicSplitMerge();
         if (splitMergeEnabled) {
 
+            auto Hex = [](const auto& value) {
+                return HexText(TBasicStringBuf(value));
+            };
+
             ui32 nextId = topic->NextPartitionId;
             ui32 nextGroupId = topic->TotalGroupCount;
 
@@ -558,15 +562,16 @@ class TAlterPQ: public TSubOperation {
                 if (keyRange) {
                     if (keyRange->FromBound && splitBoundary <= *keyRange->FromBound) {
                         errStr = TStringBuilder()
-                                 << "Split boundary less or equals FromBound of partition: " << splitBoundary
-                                 << " <= " << *keyRange->FromBound;
+                                 << "Split boundary less or equals FromBound of partition: '" << Hex(splitBoundary)
+                                 << "' <= '" << Hex(*keyRange->FromBound) << "'";
                         result->SetError(NKikimrScheme::StatusInvalidParameter, errStr);
                         return result;
                     }
                     if (keyRange->ToBound && splitBoundary >= *keyRange->ToBound) {
                         errStr = TStringBuilder()
-                                 << "Split boundary greate or equals ToBound of partition: " << splitBoundary
-                                 << " >= " << *keyRange->ToBound;
+                                 << "Split boundary greate or equals ToBound of partition: '" << Hex(splitBoundary)
+                                 << "' >= '" << Hex(*keyRange->ToBound)
+                                 << "' (FromBound is '" << Hex(keyRange->FromBound ? *keyRange->FromBound : TString{}) << "')";
                         result->SetError(NKikimrScheme::StatusInvalidParameter, errStr);
                         return result;
                     }