LibSkycoin for Java

Java client library for Skycoin API. This library is a .Net assembly generated with SWIG to access Skycoin API from Java.

Table of Contents

• LibSkycoin for Java
  • Table of Contents
  • Install from sources
  • Usage
    • Naming
    • Parameters
      • Handles
      • Byte slices
      • Structures
      • Fixed Sized Arrays
      • Other Slices
    • Memory Management
  • Make Rules
  • Development setup
    • Running tests
    • Releases
      • Update the version
      • Pre-release testing
      • Creating release builds

Install from sources

Download the repository from https://github.com/simelo/libjava-skycoin.git. Execute (mvn compile) to install the library. Although executing (mvn test) is a better choice for making changes to the library. However, when using tox these commands are not required at all because calling tox will make any necessary installation and execute the tests.

Install from Maven

Add this dependency to your project's POM:

<repositories>
  <repository>
    <id>skycoin-libjava-skycoin</id>
    <url>https://packagecloud.io/skycoin/libjava-skycoin/maven2</url>
    <releases>
      <enabled>true</enabled>
    </releases>
    <snapshots>
      <enabled>true</enabled>
    </snapshots>
  </repository>
</repositories>

Usage

Naming

The exported function in Libskycoin Java have the following naming format: SKY_package_func_name where package is replace by the package where the original Skycoin function is and func_name is the name of the function. For example, LoadConfig function from cli package is called in Java SKY_cli_LoadConfig

Parameters

All skycoin exported functions return an error object as the last of the return parameters. In Java error is return as an long and it is the first return parameter. The rest of the parameters are returned in the same order.

Receivers in Skycoin are the first of the input parameters. Simple types, like integer, float, string will be used as the corresponding types in Java, except what act as pointers.

Handles

Some of Skycoin types are too complex to be exported to a scripting language. So, handles are used instead. Therefore all functions taking a complex type will receive a handle instead of the original Skycoin type. For example, having these functions exported from Skycoin:

  func LoadConfig() (Config, error)
  func (c Config) FullWalletPath() string

Config is a struct type that is treated as a handle in Libskycoin Java . The usage in Java will be:

    public class Skycoin extends skycoin {

        public void main() {
            SWIGTYPE_p_Config__Handle configHandle = new_Config_HandlePtr();
            long err = SKY_cli_LoadConfig(configHandle);
            if (err == SKY_OK) {
                // SkY_OK means no error
                _GoString_ fullWalletPath = new _GoString_();
                err = SKY_cli_FullWalletPath(configHandle, fullWallerPath);
                assertEquals(err, SKY_OK);
                System.out.println(fullWallerPath.getP());
                //Close the handle after using the it
                //so the garbage collector can delete the object associated with  it.
                SKY_handle_close(configHandle);
            } else {
    //        Error
                System.out.println(err);
            }
        }
  }

Byte slices

Parameters of type byte[] will treated as string . Example, this function in Skycoin:

func (s ScryptChacha20poly1305) Encrypt(data, password []byte) ([]byte, error)

... should be invoked like this:

encrypt__ScryptChacha20poly1305 encrypt_settings = new encrypt__ScryptChacha20poly1305();
GoSlice data = new GoSlice(); //It will be passed as a parameter of type []byte
GoSlice pwd = new GoSlice(); //As []byte too
_GoString_ dataStr = new _GoString_();
_GoString_ pwdStr = new _GoString_();
GoSlice encrypted = new GoSlice();

dataStr.setString("Data to encrypt" );
data.convertString(dataStr);
pwdStr.SetString("password");
pwd.convertString(pwdStr);

long err = SKY_encrypt_ScryptChacha20poly1305_Encrypt(encrypt_settings, data, pwd,encrypted);
if(err == SKY_OK){
  System.out.println(encrypted.getString().getP()); //Encrypted is GoSlice
}

Structures

Structures that are not exported as handles are treated like .NET classes. In the previous example type ScryptChacha20poly1305 is created in Java like:

encrypt__ScryptChacha20poly1305 encrypt_settings = new encrypt__ScryptChacha20poly1305()

And passed as first parameter in call to SKY_encrypt_ScryptChacha20poly1305_Encrypt.

Fixed Sized Arrays

Parameters of fixed size array are wrapped in structures when called from Java.

Given these types in Skycoin and this exported function:

  type PubKey [33]byte
  type SecKey [32]byte

  func GenerateDeterministicKeyPair(seed []byte) (PubKey, SecKey)

This is a way to use them to write assertions in Java:

//Generates random seed
GoSlice data = new GoSlice();
long err = SKY_cipher_RandByte(32,data);

assertEquals(err,SKY_OK);

cipher_PubKey pubkey = new cipher_PubKey();
cipher_SecKey seckey = new cipher_SecKey();

err = SKY_cipher_GenerateDeterministicKeyPair(data, pubkey,seckey);

In the example above pubkey and seckey are objects of an structure type containing a field named data holding the corresponding instance of PubKey and SecKey. Something like:

  cipher_PubKey struct{
    data [33]byte;
  } cipher_PubKey;

  cipher_SecKey struct{
    data [32]byte;
  } ;

Other Slices

Other slices of base type different from byte are indeed wrapped inside classes. Let's see how to call the following function:

func GenerateDeterministicKeyPairs(seed []byte, n int) []SecKey

In Java this how it should be used to generate a deterministic sequence of pairs of public / private keys given a random seed:

//Generates random seed
GoSlice seed = new GoSlice();
long err = SKY_cipher_RandByte(32,seed);
cipher__SecKeys seckeys = new cipher__SecKeys();

err = SKY_cipher_GenerateDeterministicKeyPairs(seed, 2,seckeys);

for(int i=0;i<seckeys.count,i++){
  cipher_PubKey pubkey = new cipher_PubKey();
  cipher_SecKey seckey = new cipher_SecKey();
  seckeys.getAt(seckey,i);

  SKY_cipher_PubKeyFromSecKey(seckey, pubkey);
  err = SKY_cipher_PubKey_Verify(pubkey);
  assertEquals(err,SKY_OK);
}

Memory Management

Memory management is transparent to the user. Any object allocated inside the library is left to be managed by the Java garbage collector.

Make Rules

The following make rules are available after git checkout of this repository. They all require Skycoin to be checked out as a git submodule of libskycoin .NET .

• build-libc
  • Compiles skycoin C language library.
• build-swig
  • Creates the wrapper C code to generate the Java library.

Development setup

It is highly recommended for developers to setup their environment using the available Docker images. Read the LibJava Docker docs for further details.

The project has two branches: master and develop.

• develop is the default branch and will always have the latest code. The submodule at gopath/src/github.com/skycoin/skycoin has to be in sync with skycoin/skycoin develop branch.
• master will always be equal to the current stable release on the website, and should correspond with the latest release tag. The submodule at gopath/src/github.com/skycoin/skycoin has to be in sync with skycoin/skycoin master branch.

Separate stable development branches will be created to work on releases for supporting the most recent stable version of Skycoin. The name of these branches should be the Skycoin major and minor version numbers followed by dev suffix e.g. 0.25-dev. These branches may be forked out of either master or develop branches, and the submodule at gopath/src/github.com/skycoin/skycoin has to be in sync with the corresponding tag of skycoin/skycoin official repository.

Stable development branches are created most of the time for the following reasons:

• A Skycoin release increasing patch version number.
• Enhanced support and bug fixes for a version of LibSkycoin Java compiled against an stable version of Skycoin
• Backporting useful features added in develop.

Running tests

$ make test

Releases

Update the version

1. If the master branch has commits that are not in develop (e.g. due to a hotfix applied to master), merge master into develop (and fix any build or test failures)
2. Switch to a new release branch named release-X.Y.Z for preparing the release.
3. Ensure that the submodule at gopath/src/github.com/skycoin/skycoin is in sync with respect to the corresponding tag in https://github.com/skycoin/skycoin repository.
4. Update package version (pom.xml)
5. Run make build to make sure that the code base is up to date
6. Update CHANGELOG.md: move the "unreleased" changes to the version and add the date.
7. Follow the steps in pre-release testing
8. Make a PR merging the release branch into master
9. Review the PR and merge it
10. Update files in https://github.com/skycoin/repo-info/tree/master/repos/skycoin/remote for skycoin/skycoindev-java Docker image, adding a new file for the new version and adjusting any configuration text that may have changed
11. Tag the master branch with the version number. Version tags start with v, e.g. v0.20.0. Sign the tag. If you have your GPG key in github, creating a release on the Github website will automatically tag the release. It can be tagged from the command line with git tag -as v0.20.0 $COMMIT_ID, but Github will not recognize it as a "release".
12. Release builds are created and uploaded by travis. To do it manually, checkout the master branch and follow the create release builds instructions.
13. Checkout develop branch and bump package up to next dev version number.

Pre-release testing

Perform these actions before releasing:

make test

Creating release builds

Release builds should be created from master branch . After updating release version it is necessary to follow these steps

Requirements

Have installed the mvn, java for the creation of the package.

http://maven.apache.org/install.html

Building

mvn package

Final results are placed in the target/ folder.