Workaround for block 535658 problem

src/main/java/org/qortal/block/Block.java

@@ -1092,9 +1092,14 @@ public class Block {
 			// Create repository savepoint here so we can rollback to it after testing transactions
 			repository.setSavepoint();
 
-			if (this.blockData.getHeight() == 212937)
+			if (this.blockData.getHeight() == 212937) {
 				// Apply fix for block 212937 but fix will be rolled back before we exit method
 				Block212937.processFix(this);
+			}
+			else if (this.blockData.getHeight() == 535658) {
+				// Apply fix for block 535658 but fix will be rolled back before we exit method
+				Block535658.processFix(this);
+			}
 
 			for (Transaction transaction : this.getTransactions()) {
 				TransactionData transactionData = transaction.getTransactionData();

src/main/java/org/qortal/block/Block535658.java

@@ -0,0 +1,78 @@
+package org.qortal.block;
+
+import org.qortal.naming.Name;
+import org.qortal.repository.DataException;
+
+/**
+ * Block 535658
+ * <p>
+ * A node minted a version of block 535658 that contained one transaction:
+ * a REGISTER_NAME transaction that attempted to register a name that was already registered.
+ * <p>
+ * This invalid transaction made block 535658 (rightly) invalid to several nodes,
+ * which refused to use that block.
+ * However, it seems there were no other nodes minting an alternative, valid block at that time
+ * and so the chain stalled for several nodes in the network.
+ * <p>
+ * Additionally, the invalid block 535658 affected all new installations, regardless of whether
+ * they synchronized from scratch (block 1) or used an 'official release' bootstrap.
+ * <p>
+ * The diagnosis found the following:
+ * - The original problem occurred in block 535205 where for some unknown reason many nodes didn't
+ *   add the name from a REGISTER_NAME transaction to their Names table.
+ * - As a result, those nodes had a corrupt db, because they weren't holding a record of the name.
+ * - This invalid db then caused them to treat a candidate for block 535658 as valid when it
+ *   should have been invalid.
+ * - As such, the chain continued on with a technically invalid block in it, for a subset of the network
+ * <p>
+ * As with block 212937, there were three options, but the only feasible one was to apply edits to block
+ * 535658 to make it valid. There were several cross-chain trades completed after this block, so doing
+ * any kind of rollback was out of the question.
+ * <p>
+ * To complicate things further, a custom data field was used for the first REGISTER_NAME transaction,
+ * and the default data field was used for the second. So it was important that all nodes ended up with
+ * the exact same data regardless of how they arrived there.
+ * <p>
+ * The invalid block 535658 signature is: <tt>3oiuDhok...NdXvCLEV</tt>.
+ * <p>
+ * The invalid transaction in block 212937 is:
+ * <p>
+ * <code><pre>
+	 {
+		 "type": "REGISTER_NAME",
+		 "timestamp": 1630739437517,
+		 "reference": "4peRechwSPxP6UkRj9Y8ox9YxkWb34sWk5zyMc1WyMxEsACxD4Gmm7LZVsQ6Skpze8QCSBMZasvEZg6RgdqkyADW",
+		 "fee": "0.00100000",
+		 "signature": "2t1CryCog8KPDBarzY5fDCKu499nfnUcGrz4Lz4w5wNb5nWqm7y126P48dChYY7huhufcBV3RJPkgKP4Ywxc1gXx",
+		 "txGroupId": 0,
+		 "blockHeight": 535658,
+		 "approvalStatus": "NOT_REQUIRED",
+		 "creatorAddress": "Qbx9ojxv7XNi1xDMWzzw7xDvd1zYW6SKFB",
+		 "registrantPublicKey": "HJqGEf6cW695Xun4ydhkB2excGFwsDxznhNCRHZStyyx",
+		 "name": "Qplay",
+		 "data": "Registered Name on the Qortal Chain"
+	 }
+   </pre></code>
+ * <p>
+ * Account <tt>Qbx9ojxv7XNi1xDMWzzw7xDvd1zYW6SKFB</tt> attempted to register the name <tt>Qplay</tt>
+ * when they had already registered it 12 hours before in block <tt>535205</tt>.
+ * <p>
+ * However, on the broken DB nodes, their Names table was missing a record for the `Qplay` name
+ * which was sufficient to make the transaction valid.
+ */
+public final class Block535658 {
+
+	private Block535658() {
+		/* Do not instantiate */
+	}
+
+	public static void processFix(Block block) throws DataException {
+		// Unregister the existing name record if it exists
+		// This ensures that the duplicate name is considered valid, and therefore
+		// the second (i.e. duplicate) REGISTER_NAME transaction data is applied.
+		// Both were issued by the same user account, so there is no conflict.
+		Name name = new Name(block.repository, "Qplay");
+		name.unregister();
+	}
+
+}