Bencoded data reader and writer for java

Some java helper classes to deal with binary encoded data strings. This class collection can be used to parse, alter and generate bencoded data. The binary-encoding is primary used by the torrent protocol, but is free to use elsewhere. For details see the bencoding specification.

All classes are immutable and thus the whole library is threadsafe. This library was designed to be easy to use, lean (no external dependencies), secure and performant.

Dependencies

<!-- https://mvnrepository.com/artifact/eu.fraho.libs/beencode -->
<dependency>
    <groupId>eu.fraho.libs</groupId>
    <artifactId>beencode</artifactId>
    <version>3.0.0</version>
</dependency>

Usage

• All instances from this library are immutable, each change creates a new instance
• Use the various of methods on the datatypes to create instances
• The write(OutputStream) methods can be used to write the data beencoded to a stream
• The toString() methods return a humand readable presentation of the data

Code examples

Valid data types and usage:

package examples;

import eu.fraho.libs.beencode.BDict;
import eu.fraho.libs.beencode.BInteger;
import eu.fraho.libs.beencode.BList;
import eu.fraho.libs.beencode.BNode;
import eu.fraho.libs.beencode.BString;

import java.nio.charset.StandardCharsets;

public class ReadmeTypes {
    public void types() {
        // String:
        BString lorem = BString.of("lorem");
        BString ipsum = BString.of("ipsum", StandardCharsets.UTF_8);

        // Integer / Long:
        BInteger _42 = BInteger.of(42);
        BInteger largeNumber = BInteger.of(2147483648L);

        // Lists:
        BList firstlist = BList.of(lorem, largeNumber, BString.of("foobar"));
        BList otherlist = BList.of(BInteger.of(13));

        // manipulate list:
        BList listExt = firstlist.with(ipsum);          // [lorem, 2147483648, foobar, ipsum]
        BList listRed = firstlist.without(largeNumber); // [lorem, foobar]
        BList listJoined = firstlist.join(otherlist);   // [lorem, 2147483648, foobar, 13]

        // get info from list
        BNode<?> listEntry = firstlist.get(0);   // BString(lorem)
        BNode<?> listEntry2 = firstlist.get(42); // null

        // Dictionaries: (some kind of map):
        BDict firstdict = BDict.of(lorem, largeNumber);
        BDict otherdict = BDict.of(
            lorem, _42,
            ipsum, BString.of("!")
        );

        // manipulate dict:
        BDict dictExt = firstdict.with(ipsum, _42);    // {lorem=2147483648, ipsum=42}
        BDict dictJoined = firstdict.join(otherdict);  // {lorem=42, ipsum=!}

        // get info from dict
        BNode<?> dictEntry = firstdict.get(lorem);    // BInteger(2147483648)
        BNode<?> dictEntry2 = firstdict.get(ipsum);   // null

        // when using a regular string for get(), the type can be inferred (if you know what type the element has)
        BInteger dictEntry3 = firstdict.get("lorem"); // BInteger(2147483648)
    }
}

To read a beencoded file:

package examples;

import eu.fraho.libs.beencode.BDict;
import eu.fraho.libs.beencode.BNode;
import eu.fraho.libs.beencode.BString;
import eu.fraho.libs.beencode.NodeFactory;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.util.Optional;

public class ReadmeRead {
    public void read() throws IOException {
        // If you are entirely sure that the file conains a dictionary
        try (InputStream is = Files.newInputStream(new File("test.dat").toPath())) {
            BDict dict = BDict.of(is);
        }

        // If you are pretty sure that the file will contain a single string.
        // When the parsing successfully created a node, but it has the wrong type, then this Optional is empty.
        try (InputStream is = Files.newInputStream(new File("test.dat").toPath())) {
            Optional<BString> maybeString = NodeFactory.decode(is, BString.class);
        }

        // If you you don't exactly know which element you will read.
        try (InputStream is = Files.newInputStream(new File("test.dat").toPath())) {
            BNode<?> node = NodeFactory.decode(is);
        }
    }
}

To write a beencoded file:

package examples;

import eu.fraho.libs.beencode.BInteger;
import eu.fraho.libs.beencode.BList;
import eu.fraho.libs.beencode.BString;
import eu.fraho.libs.beencode.NodeFactory;

import java.io.File;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.file.Files;

public class ReadmeWrite {
    public void write() throws IOException {
        BList node = BList.of(
                BString.of("Hello"),
                BString.of("world!"),
                BInteger.of(42)
        );

        // Write directly to a file
        try (OutputStream os = Files.newOutputStream(new File("test.dat").toPath())) {
            // one way
            node.write(os);

            // another way
            NodeFactory.encode(node, os);
        }
    }
}

Convert from and to beencoded data:

package examples;

import eu.fraho.libs.beencode.BInteger;
import eu.fraho.libs.beencode.BList;
import eu.fraho.libs.beencode.BNode;
import eu.fraho.libs.beencode.BString;
import eu.fraho.libs.beencode.NodeFactory;

public class ReadmeConvert {
    public void convert() {
        BList node = BList.of(
                BString.of("Hello"),
                BString.of("world!"),
                BInteger.of(42)
        );

        // Get a human readable representation
        System.out.println(node.toString()); // [Hello, world!, 42]

        // Get the beencoded representation
        byte[] encoded = NodeFactory.encode(node); // l5:Hello6:world!i42ee

        // And back again to a node
        BNode<?> back = NodeFactory.decode(encoded);
    }
}

Hacking

• This repository uses the git flow layout
• Changes are welcome, but please use pull requests with separate branches
• Github workflow has to pass before merging
• Code coverage should stay about the same level (please write tests for new features!)

Releasing

Releasing is done with the default gradle tasks:

# to local repository:
./gradlew publishToMavenLocal
# to central:
./gradlew publish