libtxref-java

This is a Java library for converting between bitcoin transaction IDs (txid) and "Bech32 Encoded Tx Position References" (txref). Txrefs are described in BIP 0136.

The only external dependencies libtxref-java has are libbech32-java and JUnit.

Getting libtxref-java

To use libtxref-java in your project, you can get the package from Maven Central:

To use the package, you need the following Maven dependency:

<dependency>
  <groupId>design.contract</groupId>
  <artifactId>libtxref</artifactId>
  <version>1.1.0</version>
</dependency>

Usage Examples

Encoding Examples

See the full code for the following examples.

Create a txref for a mainnet transaction, with only a blockHeight and transactionIndex:

private static void createStandardMainnetTxref() {
    int blockHeight = 170;
    int transactionIndex = 1;

    String txref = Txref.encode(blockHeight, transactionIndex);

    System.out.println(txref);
    // prints "tx1:r52q-qqpq-qpty-cfg"
}

Create a txref for a testnet transaction, with only a blockHeight and transactionIndex:

private static void createStandardTestnetTxref() {
    int blockHeight = 170;
    int transactionIndex = 1;

    String txref = Txref.encodeTestnet(blockHeight, transactionIndex);

    System.out.println(txref);
    // prints "txtest1:x52q-qqpq-qvr9-ztk"
}

Create an extended txref for a mainnet transaction, with a blockHeight and transactionIndex and a specific txoIndex:

private static void createExtendedMainnetTxref() {
    int blockHeight = 170;
    int transactionIndex = 1;
    int txoIndex = 1;

    String txref = Txref.encode(blockHeight, transactionIndex, txoIndex);

    System.out.println(txref);
    // prints "tx1:y52q-qqpq-qpqq-4lkz-zc"
}

Create an extended txref for a testnet transaction, with a blockHeight and transactionIndex and a specific txoIndex:

private static void createExtendedTestnetTxref() {
    int blockHeight = 170;
    int transactionIndex = 1;
    int txoIndex = 1;

    String txref = Txref.encodeTestnet(blockHeight, transactionIndex, txoIndex);

    System.out.println(txref);
    // prints "txtest1:852q-qqpq-qpqq-m8ef-pl"
}

Decoding Examples

See the full code for the following examples.

Decode a txref

private static void decodeTxref() {
        DecodedResult decodedResult = Txref.decode("tx1:r52q-qqpq-qpty-cfg");

        assert(decodedResult.getBlockHeight() == 170);
        assert(decodedResult.getTransactionIndex() == 1);
        assert(decodedResult.getTxoIndex() == 0);
        assert(decodedResult.getEncoding() == DecodedResult.Encoding.BECH32M);
        }

Decode an "original" txref

This txref has been encoded with the original bech32 internal constant. The decoding will still succeed, but the library will also return a commentary string that contains an explanatory message along with the txref that should be used instead.

    private static void decodeStandardTxrefUsingOriginalConstant() {
        DecodedResult decodedResult = Txref.decode("tx1:r52q-qqpq-q5h5-5v2");

        assert(decodedResult.getBlockHeight() == 170);
        assert(decodedResult.getTransactionIndex() == 1);
        assert(decodedResult.getTxoIndex() == 0);
        assert(decodedResult.getEncoding() == DecodedResult.Encoding.BECH32);

        System.out.println(decodedResult.getCommentary());
        // prints:
        // "The txref tx1:r52q-qqpq-q5h5-5v2 uses an old encoding scheme and should be updated to tx1:r52q-qqpq-qpty-cfg See https://github.com/dcdpr/libtxref-java#regarding-bech32-checksums for more information."
        }

Building libtxref-java

To build libtxref-java, you will need:

• Java (8+)
• Maven

libtxref-java uses a standard maven build process:

mvn install

You can also run just the tests without installing:

mvn test

Regarding bech32 checksums

The Bech32 data encoding format was first proposed by Pieter Wuille in early 2017 in BIP 0173. Later, in November 2019, Pieter published some research that a constant used in the bech32 checksum algorithm (value = 1) may not be optimal for the error detecting properties of bech32. In February 2021, Pieter published BIP 0350 reporting that "exhaustive analysis" showed the best possible constant value is 0x2bc830a3. This improved variant of Bech32 is called "Bech32m".

When decoding a txref, libtxref-java returns an enum value showing whether bech32m or bech32 was used to encode. If the original bech32 variant is detected, libtxref-java also returns a commentary string that can be shown to the user. This commentary will contain a new txref that represents the same transaction data, but using the new bech32m variant. This can be seen in the examples above.

When encoding data, libtxref-java will only use the new constant value of 0x2bc830a3.