zhaohaijun / headlong

A Contract ABI and Recursive Length Prefix library in Java for use on the Ethereum network

Contract ABI and Recursive Length Prefix made easy in Java (or Android). Everything heavily optimized for maximum throughput (ABI function call encoding up to 652x faster than a popular competitor).

Usage of the ABI codec:

Function f = new Function("baz(uint32,bool)"); // canonicalizes and parses any signature automatically
Tuple args = new Tuple(69L, true);

// Two equivalent styles:
ByteBuffer one = f.encodeCall(args);
ByteBuffer two = f.encodeCallWithArgs(69L, true);

System.out.println(Function.formatCall(one.array())); // a multi-line hex representation

Tuple decoded = f.decodeCall((ByteBuffer) two.flip());

System.out.println(decoded.equals(args));

And of the RLP codec:

// for an example class Student
public Student(byte[] rlp) throws DecodeException {
    SequenceIterator iter = RLP_STRICT.sequenceIterator(rlp);

    this.name = iter.next().asString(UTF_8);
    this.gpa = iter.next().asFloat();
    this.publicKey = iter.next().asBigInt();
    this.balance = new BigDecimal(iter.next().asBigInt(), iter.next().asInt());
}

@Override
public Object[] toObjectArray() {
    return new Object[] {
            Strings.decode(name, UTF_8),
            FloatingPoint.toBytes(gpa),
            publicKey.toByteArray(),
            balance.unscaledValue().toByteArray(),
            Integers.toBytes(balance.scale())
    };
}

@Override
public byte[] toRLP() {
    return RLPEncoder.encodeSequentially(toObjectArray());
}

Also includes a fast hex codec and an optimized Keccak implementation.

Build

Now available in Maven Central Repository.

Or build locally:

Clone the project and install to your local maven repository using gradle publishToMavenLocal or mvn install. Then you can use one of these:

implementation 'com.esaulpaugh:headlong:1.0-SNAPSHOT'

<dependency>
    <groupId>com.esaulpaugh</groupId>
    <artifactId>headlong</artifactId>
    <version>1.0-SNAPSHOT</version>
</dependency>

Alternatively:

• Run gradle build or gradle jar which output to /build/libs
• Use mvn package which outputs to /target
• Add headlong as a project dependency

Tests should take less than one minute to run. Test packages require junit and gson. Otherwise headlong has no dependencies. Jar size is ~109 KB as of 01/17/19.

See the wiki for more, such as TupleTypes, packed encoding, RLP Lists, and RLP Object Notation: https://github.com/esaulpaugh/headlong/wiki

Licensed under Apache 2.0