Script, SegwitAddress: detect taproot scripts and decode them into addresses

core/src/main/java/org/bitcoinj/core/SegwitAddress.java

@@ -47,6 +47,7 @@ import org.bitcoinj.script.Script;
 public class SegwitAddress extends Address {
     public static final int WITNESS_PROGRAM_LENGTH_PKH = 20;
     public static final int WITNESS_PROGRAM_LENGTH_SH = 32;
+    public static final int WITNESS_PROGRAM_LENGTH_TR = 32;
     public static final int WITNESS_PROGRAM_MIN_LENGTH = 2;
     public static final int WITNESS_PROGRAM_MAX_LENGTH = 40;
 
@@ -59,7 +60,7 @@ public class SegwitAddress extends Address {
      * @param witnessVersion
      *            version number between 0 and 16
      * @param witnessProgram
-     *            hash of pubkey or script (for version 0)
+     *            hash of pubkey, pubkey or script (depending on version)
      */
     private SegwitAddress(NetworkParameters params, int witnessVersion, byte[] witnessProgram)
             throws AddressFormatException {
@@ -138,13 +139,20 @@ public class SegwitAddress extends Address {
     @Override
     public Script.ScriptType getOutputScriptType() {
         int version = getWitnessVersion();
-        checkState(version == 0);
-        int programLength = getWitnessProgram().length;
-        if (programLength == WITNESS_PROGRAM_LENGTH_PKH)
-            return Script.ScriptType.P2WPKH;
-        if (programLength == WITNESS_PROGRAM_LENGTH_SH)
-            return Script.ScriptType.P2WSH;
-        throw new IllegalStateException("Cannot happen.");
+        if (version == 0) {
+            int programLength = getWitnessProgram().length;
+            if (programLength == WITNESS_PROGRAM_LENGTH_PKH)
+                return Script.ScriptType.P2WPKH;
+            if (programLength == WITNESS_PROGRAM_LENGTH_SH)
+                return Script.ScriptType.P2WSH;
+            throw new IllegalStateException(); // cannot happen
+        } else if (version == 1) {
+            int programLength = getWitnessProgram().length;
+            if (programLength == WITNESS_PROGRAM_LENGTH_TR)
+                return Script.ScriptType.P2TR;
+            throw new IllegalStateException(); // cannot happen
+        }
+        throw new IllegalStateException("cannot handle: " + version);
     }
 
     @Override
@@ -202,6 +210,23 @@ public class SegwitAddress extends Address {
         return new SegwitAddress(params, 0, hash);
     }
 
+    /**
+     * Construct a {@link SegwitAddress} that represents the given program, which is either a pubkey, a pubkey hash
+     * or a script hash – depending on the script version. The resulting address will be either a P2WPKH, a P2WSH or
+     * a P2TR type of address.
+     *
+     * @param params
+     *            network this address is valid for
+     * @param witnessVersion
+     *            version number between 0 and 16
+     * @param witnessProgram
+     *            version dependent witness program
+     * @return constructed address
+     */
+    public static SegwitAddress fromProgram(NetworkParameters params, int witnessVersion, byte[] witnessProgram) {
+        return new SegwitAddress(params, witnessVersion, witnessProgram);
+    }
+
     /**
      * Construct a {@link SegwitAddress} that represents the public part of the given {@link ECKey}. Note that an
      * address is derived from a hash of the public key and is not the public key itself.

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

@@ -59,7 +59,8 @@ public class Script {
         P2PK(2), // pay to pubkey
         P2SH(3), // pay to script hash
         P2WPKH(4), // pay to witness pubkey hash
-        P2WSH(5); // pay to witness script hash
+        P2WSH(5), // pay to witness script hash
+        P2TR(6); // pay to taproot
 
         public final int id;
 
@@ -283,6 +284,8 @@ public class Script {
             return LegacyAddress.fromKey(params, ECKey.fromPublicOnly(ScriptPattern.extractKeyFromP2PK(this)));
         else if (ScriptPattern.isP2WH(this))
             return SegwitAddress.fromHash(params, ScriptPattern.extractHashFromP2WH(this));
+        else if (ScriptPattern.isP2TR(this))
+            return SegwitAddress.fromProgram(params, 1, ScriptPattern.extractOutputKeyFromP2TR(this));
         else
             throw new ScriptException(ScriptError.SCRIPT_ERR_UNKNOWN_ERROR, "Cannot cast this script to an address");
     }
@@ -1676,6 +1679,8 @@ public class Script {
             return ScriptType.P2WPKH;
         if (ScriptPattern.isP2WSH(this))
             return ScriptType.P2WSH;
+        if (ScriptPattern.isP2TR(this))
+            return ScriptType.P2TR;
         return null;
     }
 

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

@@ -196,6 +196,32 @@ public class ScriptPattern {
         return script.chunks.get(1).data;
     }
 
+    /**
+     * Returns true if this script is of the form {@code OP_1 <pubkey>}. This is a P2TR scriptPubKey. This
+     * script type was introduced with taproot.
+     */
+    public static boolean isP2TR(Script script) {
+        List<ScriptChunk> chunks = script.chunks;
+        if (chunks.size() != 2)
+            return false;
+        if (!chunks.get(0).equalsOpCode(OP_1))
+            return false;
+        byte[] chunk1data = chunks.get(1).data;
+        if (chunk1data == null)
+            return false;
+        if (chunk1data.length != SegwitAddress.WITNESS_PROGRAM_LENGTH_TR)
+            return false;
+        return true;
+    }
+
+    /**
+     * Extract the taproot output key from a P2TR scriptPubKey. It's important that the script is in the correct
+     * form, so you will want to guard calls to this method with {@link #isP2TR(Script)}.
+     */
+    public static byte[] extractOutputKeyFromP2TR(Script script) {
+        return script.chunks.get(1).data;
+    }
+
     /**
      * Returns whether this script matches the format used for m-of-n multisig outputs:
      * {@code [m] [keys...] [n] CHECKMULTISIG}

core/src/main/java/org/bitcoinj/wallet/Wallet.java

@@ -1162,7 +1162,7 @@ public class Wallet extends BaseTaggableObject
             return isPubKeyHashMine(address.getHash(), scriptType);
         else if (scriptType == ScriptType.P2SH)
             return isPayToScriptHashMine(address.getHash());
-        else if (scriptType == ScriptType.P2WSH)
+        else if (scriptType == ScriptType.P2WSH || scriptType == ScriptType.P2TR)
             return false;
         else
             throw new IllegalArgumentException(address.toString());

core/src/test/java/org/bitcoinj/script/ScriptTest.java

@@ -462,6 +462,9 @@ public class ScriptTest {
         Script p2wshScript = ScriptBuilder.createP2WSHOutputScript(new byte[32]);
         scriptAddress = SegwitAddress.fromHash(TESTNET, ScriptPattern.extractHashFromP2WH(p2wshScript));
         assertEquals(scriptAddress, p2wshScript.getToAddress(TESTNET));
+        // P2TR
+        toAddress = SegwitAddress.fromProgram(TESTNET, 1, new byte[32]);
+        assertEquals(toAddress, ScriptBuilder.createOutputScript(toAddress).getToAddress(TESTNET));
     }
 
     @Test(expected = ScriptException.class)