ScriptPattern: Add pattern matcher for segwit commitment (in an output of the coinbase transaction).

Adds a test for parsing block 481815, which contains a segwit commitment in its coinbase.

core/src/main/java/org/bitcoinj/script/ScriptPattern.java

@@ -19,8 +19,11 @@ package org.bitcoinj.script;
 
 import org.bitcoinj.core.LegacyAddress;
 import org.bitcoinj.core.SegwitAddress;
+import org.bitcoinj.core.Sha256Hash;
+import org.spongycastle.util.encoders.Hex;
 
 import java.math.BigInteger;
+import java.util.Arrays;
 import java.util.List;
 
 import static org.bitcoinj.script.Script.decodeFromOpN;
@@ -274,4 +277,31 @@ public class ScriptPattern {
         List<ScriptChunk> chunks = script.chunks;
         return chunks.size() > 0 && chunks.get(0).equalsOpCode(ScriptOpCodes.OP_RETURN);
     }
+
+    private static final byte[] SEGWIT_COMMITMENT_HEADER = Hex.decode("aa21a9ed");
+
+    /**
+     * Returns whether this script matches the pattern for a segwit commitment (in an output of the coinbase
+     * transaction).
+     */
+    public static boolean isSegwitCommitment(Script script) {
+        List<ScriptChunk> chunks = script.chunks;
+        if (chunks.size() < 2)
+            return false;
+        if (!chunks.get(0).equalsOpCode(ScriptOpCodes.OP_RETURN))
+            return false;
+        byte[] chunkData = chunks.get(1).data;
+        if (chunkData == null || chunkData.length != 36)
+            return false;
+        if (!Arrays.equals(Arrays.copyOfRange(chunkData, 0, 4), SEGWIT_COMMITMENT_HEADER))
+            return false;
+        return true;
+    }
+
+    /**
+     * Retrieves the hash from a segwit commitment (in an output of the coinbase transaction).
+     */
+    public static Sha256Hash extractSegwitCommitmentHash(Script script) {
+        return Sha256Hash.wrap(Arrays.copyOfRange(script.chunks.get(1).data, 4, 36));
+    }
 }

core/src/test/java/org/bitcoinj/core/BlockTest.java

@@ -24,12 +24,15 @@ import org.bitcoinj.params.MainNetParams;
 import org.bitcoinj.params.TestNet2Params;
 import org.bitcoinj.params.TestNet3Params;
 import org.bitcoinj.params.UnitTestParams;
+import org.bitcoinj.script.Script;
 import org.bitcoinj.script.ScriptOpCodes;
+import org.bitcoinj.script.ScriptPattern;
 import org.bitcoinj.wallet.Wallet;
 import org.bitcoinj.wallet.Wallet.BalanceType;
 import org.junit.Before;
 import org.junit.Test;
 
+import java.io.InputStreamReader;
 import java.math.BigInteger;
 import java.util.Arrays;
 import java.util.EnumSet;
@@ -242,6 +245,18 @@ public class BlockTest {
         assertEquals(Coin.ZERO, wallet.getBalance(BalanceType.AVAILABLE));
     }
 
+    @Test
+    public void testBlock481815_segwitCommitmentInCoinbase() throws Exception {
+        Block block481815 = MAINNET.getDefaultSerializer().makeBlock(ByteStreams.toByteArray(
+                getClass().getResourceAsStream("block481815.dat")));
+        assertEquals(2097, block481815.getTransactions().size());
+        Transaction coinbase = block481815.getTransactions().get(0);
+        final Script segwitCommitment = coinbase.getOutput(1).getScriptPubKey();
+        assertTrue(ScriptPattern.isSegwitCommitment(segwitCommitment));
+        assertEquals("3d03076733467c45b08ec503a0c5d406647b073e1914d35b5111960ed625f3b7",
+                ScriptPattern.extractSegwitCommitmentHash(segwitCommitment).toString());
+    }
+
     @Test
     public void isBIPs() throws Exception {
         final Block genesis = MAINNET.getGenesisBlock();