hardfork: change window semantics to not count the newly added block

This allows knowing the hard fork a block must obey in order to be
added to the blockchain. The previous semantics would use that new
block's version vote to determine this hard fork, which made it
impossible to use the rules to validate transactions entering the
tx pool (and made it impossible to validate a block before adding
it to the blockchain).

src/cryptonote_core/hardfork.cpp

@@ -43,6 +43,10 @@ HardFork::HardFork(cryptonote::BlockchainDB &db, uint8_t original_version, time_
   window_size(window_size),
   threshold_percent(threshold_percent)
 {
+  if (window_size == 0)
+    throw "window_size needs to be strictly positive";
+  if (threshold_percent > 100)
+    throw "threshold_percent needs to be between 0 and 100";
 }
 
 bool HardFork::add(uint8_t version, uint64_t height, time_t time)
@@ -93,6 +97,8 @@ bool HardFork::add(const cryptonote::block &block, uint64_t height)
   if (!do_check(block))
     return false;
 
+  db.set_hard_fork_version(height, heights[current_fork_index].version);
+
   const uint8_t version = get_effective_version(block);
 
   while (versions.size() >= window_size) {
@@ -105,16 +111,15 @@ bool HardFork::add(const cryptonote::block &block, uint64_t height)
   last_versions[version]++;
   versions.push_back(version);
 
-  uint8_t voted = get_voted_fork_index(height);
+  uint8_t voted = get_voted_fork_index(height + 1);
   if (voted > current_fork_index) {
     for (int v = heights[current_fork_index].version + 1; v <= heights[voted].version; ++v) {
-      db.set_hard_fork_starting_height(v, height);
+      // we reached the vote threshold with this block, next one will be forked
+      db.set_hard_fork_starting_height(v, height + 1);
     }
     current_fork_index = voted;
   }
 
-  db.set_hard_fork_version(height, heights[current_fork_index].version);
-
   return true;
 }
 
@@ -159,7 +164,7 @@ bool HardFork::reorganize_from_block_height(uint64_t height)
 
   for (size_t n = 0; n < 256; ++n)
     last_versions[n] = 0;
-  const uint64_t rescan_height = height >= (window_size - 1) ? height - (window_size - 1) : 0;
+  const uint64_t rescan_height = height >= (window_size - 1) ? height - (window_size  -1) : 0;
   const uint8_t start_version = height == 0 ? original_version : db.get_hard_fork_version(height);
   while (heights[current_fork_index].version > start_version) {
     db.set_hard_fork_starting_height(heights[current_fork_index].version, std::numeric_limits<uint64_t>::max());
@@ -171,6 +176,16 @@ bool HardFork::reorganize_from_block_height(uint64_t height)
     last_versions[v]++;
     versions.push_back(v);
   }
+
+  uint8_t voted = get_voted_fork_index(height + 1);
+  if (voted > current_fork_index) {
+    for (int v = heights[current_fork_index].version + 1; v <= heights[voted].version; ++v) {
+      // we reached the vote threshold with this block, next one will be forked
+      db.set_hard_fork_starting_height(v, height + 1);
+    }
+    current_fork_index = voted;
+  }
+
   const uint64_t bc_height = db.height();
   for (uint64_t h = height + 1; h < bc_height; ++h) {
     add(db.get_block_from_height(h), h);

tests/unit_tests/hardfork.cpp

@@ -238,7 +238,7 @@ TEST(steps_1, Success)
   }
 
   for (uint64_t h = 0; h < 10; ++h) {
-    ASSERT_EQ(hf.get(h), h+1);
+    ASSERT_EQ(hf.get(h), std::max(1,(int)h));
   }
 }
 
@@ -265,7 +265,7 @@ TEST(reorganize, Same)
     for (uint64_t rh = 0; rh < 20; ++rh) {
       hf.reorganize_from_block_height(rh);
       for (int hh = 0; hh < 20; ++hh) {
-        uint8_t version = hh >= (history-1) ? block_versions[hh - (history-1)] : 1;
+        uint8_t version = hh >= history ? block_versions[hh - history] : 1;
         ASSERT_EQ(hf.get(hh), version);
       }
     }
@@ -285,8 +285,10 @@ TEST(reorganize, Changed)
   ASSERT_TRUE(hf.add(9, 6, 3));
   hf.init();
 
+  //                                 fork         4     7     9
   //                                 index  0  1  2  3  4  5  6  7  8  9
   static const uint8_t block_versions[] = { 1, 1, 4, 4, 7, 7, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9 };
+  static const uint8_t expected_versions[] = { 1, 1, 1, 1, 1, 1, 4, 4, 7, 7, 9, 9, 9, 9, 9, 9 };
   for (uint64_t h = 0; h < 16; ++h) {
     db.add_block(mkblock(block_versions[h]), 0, 0, 0, crypto::hash());
     ASSERT_TRUE (hf.add(db.get_block_from_height(h), h));
@@ -295,14 +297,13 @@ TEST(reorganize, Changed)
   for (uint64_t rh = 0; rh < 16; ++rh) {
     hf.reorganize_from_block_height(rh);
     for (int hh = 0; hh < 16; ++hh) {
-      uint8_t version = hh >= (history-1) ? block_versions[hh - (history-1)] : 1;
+      ASSERT_EQ(hf.get(hh), expected_versions[hh]);
-      ASSERT_EQ(hf.get(hh), version);
     }
   }
 
   // delay a bit for 9, and go back to 1 to check it stays at 9
   static const uint8_t block_versions_new[] =    { 1, 1, 4, 4, 7, 7, 4, 7, 7, 7, 9, 9, 9, 9, 9, 1 };
-  static const uint8_t expected_versions_new[] = { 1, 1, 1, 1, 1, 4, 4, 4, 4, 4, 7, 7, 7, 9, 9, 9 };
+  static const uint8_t expected_versions_new[] = { 1, 1, 1, 1, 1, 1, 4, 4, 4, 4, 4, 7, 7, 7, 9, 9 };
   for (uint64_t h = 3; h < 16; ++h) {
     db.remove_block();
   }
@@ -336,11 +337,13 @@ TEST(voting, threshold)
       db.add_block(mkblock(v), 0, 0, 0, crypto::hash());
       bool ret = hf.add(db.get_block_from_height(h), h);
       if (h >= 8 && threshold == 87) {
+        // for threshold 87, we reach the treshold at height 7, so from height 8, hard fork to version 2, but 8 tries to add 1
         ASSERT_FALSE(ret);
       }
       else {
+        // for threshold 88, we never reach the threshold
         ASSERT_TRUE(ret);
-        uint8_t expected = threshold == 88 ? 1 : h < 7 ? 1 : 2;
+        uint8_t expected = threshold == 88 ? 1 : h < 8 ? 1 : 2;
         ASSERT_EQ(hf.get(h), expected);
       }
     }
@@ -370,7 +373,7 @@ TEST(new_blocks, denied)
     ASSERT_FALSE(hf.add(mkblock(1), 9)); // so this one can't get added
     ASSERT_TRUE(hf.add(mkblock(2), 10));
 
-    ASSERT_EQ(hf.get_start_height(2), 8);
+    ASSERT_EQ(hf.get_start_height(2), 9);
 }
 
 TEST(new_version, early)
@@ -428,8 +431,8 @@ TEST(reorganize, changed)
     ADD_TRUE(3, 7);
     ADD_TRUE(4, 8);
     ADD_TRUE(4, 9);
-    ASSERT_EQ(hf.get_start_height(2), 3);
+    ASSERT_EQ(hf.get_start_height(2), 4); // reaches threshold 2 at height 3, so height 4 forks
-    ASSERT_EQ(hf.get_start_height(3), 8);
+    ASSERT_EQ(hf.get_start_height(3), 9);
     ASSERT_EQ(hf.get_current_version(), 3);
 
     // pop a few blocks and check current version goes back down
@@ -446,7 +449,7 @@ TEST(reorganize, changed)
     ADD_TRUE(2, 7);
     ADD_TRUE(2, 8);
     ADD_TRUE(2, 9);
-    ASSERT_EQ(hf.get_start_height(2), 3); // unchanged
+    ASSERT_EQ(hf.get_start_height(2), 4); // unchanged
     ASSERT_EQ(hf.get_current_version(), 2); // we did not bump to 3 this time
     ASSERT_EQ(hf.get_start_height(3), std::numeric_limits<uint64_t>::max()); // not yet
 }