BlockTransformer updates necessary for mempow online accounts.

Using the feature trigger timestamp here should be much less error prone than a whole new block message version. Once mempow has been live for at least 24 hours, the feature trigger can be removed and the code cleaned up, as all online accounts signatures will use the new format from that time onwards (legacy signatures are trimmed after 24 hours).

src/main/java/org/qortal/data/block/BlockData.java

@@ -211,6 +211,14 @@ public class BlockData implements Serializable {
 		this.onlineAccountsSignatures = onlineAccountsSignatures;
 	}
 
+	public int getOnlineAccountsSignaturesCount() {
+		if (this.onlineAccountsSignatures != null && this.onlineAccountsSignatures.length > 0) {
+			// Blocks use a single online accounts signature, so there is no need for this to be dynamic
+			return 1;
+		}
+		return 0;
+	}
+
 	public boolean isTrimmed() {
 		long onlineAccountSignaturesTrimmedTimestamp = NTP.getTime() - BlockChain.getInstance().getOnlineAccountSignaturesMaxLifetime();
 		long currentTrimmableTimestamp = NTP.getTime() - Settings.getInstance().getAtStatesMaxLifetime();

src/main/java/org/qortal/transform/block/BlockTransformer.java

@@ -235,7 +235,7 @@ public class BlockTransformer extends Transformer {
 			// Online accounts timestamp is only present if there are also signatures
 			onlineAccountsTimestamp = byteBuffer.getLong();
 
-			final int signaturesByteLength = onlineAccountsSignaturesCount * Transformer.SIGNATURE_LENGTH;
+			final int signaturesByteLength = getOnlineAccountSignaturesLength(onlineAccountsSignaturesCount, onlineAccountsCount, timestamp);
 			if (signaturesByteLength > BlockChain.getInstance().getMaxBlockSize())
 				throw new TransformationException("Byte data too long for online accounts signatures");
 
@@ -371,7 +371,7 @@ public class BlockTransformer extends Transformer {
 
 			if (onlineAccountsSignatures != null && onlineAccountsSignatures.length > 0) {
 				// Note: we write the number of signatures, not the number of bytes
-				bytes.write(Ints.toByteArray(onlineAccountsSignatures.length / Transformer.SIGNATURE_LENGTH));
+				bytes.write(Ints.toByteArray(blockData.getOnlineAccountsSignaturesCount()));
 
 				// We only write online accounts timestamp if we have signatures
 				bytes.write(Longs.toByteArray(blockData.getOnlineAccountsTimestamp()));
@@ -511,6 +511,16 @@ public class BlockTransformer extends Transformer {
 
 		return nonces;
 	}
+	public static int getOnlineAccountSignaturesLength(int onlineAccountsSignaturesCount, int onlineAccountCount, long blockTimestamp) {
+		if (blockTimestamp >= BlockChain.getInstance().getOnlineAccountsMemoryPoWTimestamp()) {
+			// Once mempow is active, we expect the online account signatures to be appended with the nonce values
+			return (onlineAccountsSignaturesCount * Transformer.SIGNATURE_LENGTH) + (onlineAccountCount * INT_LENGTH);
+		}
+		else {
+			// Before mempow, only the online account signatures were included (which will likely be a single signature)
+			return onlineAccountsSignaturesCount * Transformer.SIGNATURE_LENGTH;
+		}
+	}
 
 	public static byte[] extract(byte[] input, int pos, int length) {
 		byte[] output = new byte[length];