Concordium Java SDK

The Concordium Java SDK provides an interface to communicating with a Concordium node.

The package is released on Maven Central. The Android compatible package is also released on Maven Central.

Prerequisites

1. Java 1.8
2. Maven
3. Rust
4. make

• Java has been tested with OpenJDK v.1.8.0_292.
• Maven has been tested with v.3.6.3.
• Rust has been tested with v.1.69

Build and usage

To build the native library and put it into the correct folders all one has to do the following:

1. Clone this repository and remember to update git submodules, for example when cloning via

git clone https://github.com/Concordium/concordium-java-sdk.git --recurse-submodules

2. Run make from the root of this repository.
3. Run mvn install from the root of the concordium-sdk folder.

The first step builds the native dependencies and the latter builds the resulting .jar file.

The two steps builds results in the following two .jar files.

1. A regular jar file called concordium-sdk-{VERSION}.jar.
2. A fat jar file called concordium-sdk-{VERSION}-jar-with-dependencies.jar which embeds the dependencies into one jar.

The "normal" jar can then be used from another project by adding it to the pom.xml:

 <dependencies>
        <dependency>
            <groupId>com.concordium.sdk</groupId>
            <artifactId>concordium-sdk</artifactId>
            <version>${VERSION}</version>
        </dependency>
 </dependencies>

The fat jar can then be used from another project by adding it to the pom.xml:

 <dependencies>
        <dependency>
            <groupId>com.concordium.sdk</groupId>
            <artifactId>concordium-sdk</artifactId>
            <version>${VERSION}</version>
            <classifier>jar-with-dependencies</classifier>
        </dependency>
 </dependencies>

JNI

When doing changes wrt. the JNI two things have to be taken care of.

1. The Java native calls
2. The rust implementation of which the Java native binds to.

The Java part

The SDK uses JNI to perform EDDSA_ED25519 signatures. The JNI entrypoint is located in the EDD25519.java One can create a new header file by using the command: javac -h . ED25519.java from the root of ed25519 folder.

The Rust part

The output will be a header file, the contents hereof must be matched appropriately as described in the documentation into the lib.rs rust source file.

Android

To build the android AAR package, one has to do the following:

1. Clone this repository and remember to update git submodules, for example when cloning via

git clone https://github.com/Concordium/concordium-java-sdk.git --recurse-submodules

2. Set the ANDROID_HOME environment variable to the path to your Android SDK installation.
3. Run make add-android-targets from the root of this repository.
4. Run make android from the root of this repository.
5. Run mvn install -N from the root of the repository.
6. Run mvn install from the root of the concordium-android-sdk folder.

make add-android-targets adds the rust targets that the native libraries will be built for. make android builds the native libraries for various targets using cargo-ndk. And the final step builds the aar file concordium-android-sdk.aar in the target folder, which can be used in android projects. Note that this uses the Android Maven Plugin, which is what requires the Android SDK, the specific version can be seen in its documentation.

Note that the minimum android SDK version for this package is 26.

Usage

The ClientV2 is the main entrypoint for the SDK. It facilitates an API for communicating with the node through the V2 API. The ClientV2 must be initialized with a Connection which holds information of the node URL, timeout duration etc. for the connection.

Example of instantiating the Client

Connection connection = Connection.newBuilder()
                .host(${node_host})
                .port(${node_port})
                .useTLS(TLSConfig.auto()) // If the node is under HTTPS
                .build();
ClientV2 client = ClientV2.from(connection);

where

• node_host is the host of the node e.g. 127.0.0.1
• node_port is the nodes rpc port e.g. 20000

Configuring the connection

One can also provide extra HTTP headers to the grpc calls by setting up the client as the following:

Connection connection = Connection.newbuilder()
                .credentials(Credentials.builder()
                        .withAdditionalHeader(Header.from("HEADER1", "VALUE1"))
                        .withAdditionalHeader(Header.from("HEADER2", "VALUE2"))
                        .build())
                .host(${node_url})
                .port(${node_port})
                .timeout(${timeout})
                .build();
ClientV2 client = ClientV2.from(connection);

Enforcing TLS

It is also possible to enforce TLS to be used in the underlying connection e.g.

Connection connection = Connection.newbuilder()
                .host(${node_url})
                .port(${node_port})
                .timeout(${timeout})
                .useTLS(TLSConfig.from(new File("/a/path/to/the/servers/certificate.pem")))
                .build();
ClientV2 client = ClientV2.from(connection);

Further the Client exposes a close() function which should be called when finished using the client in order to perform an orderly shutdown of the underlying grpc connection.

API Overview

The node API is exposed via ClientV2 and transactions can be created using the TransactionFactory e.g. TransactionFactory.newTransfer().

See the examples for example usages of the API.

Sending a raw transaction

It is also possible to send a raw transaction via the client e.g., if the transaction has been generated somewhere else. This can be done via (AccountTransaction.fromBytes(the_raw_transaction_bytes).

Custom Signing

By default the java library supports ED25519 signing via the native binding ED25519SecretKey.

However the library also supports external signing services such as HSM's or other secret managers and the like. In order to use an external signer one must implement the Signer interface.

The interface exposes one function:

byte[] sign(byte[] message) throws ED25519Exception;

A signer is then added to a TransactionSigner as follows:

 TransactionSignerImpl signer = TransactionSigner.from(SignerEntry.from(Index.from(0), Index.from(1), new Signer() {
                    // The custom signer
                    @Override
                    public byte[] sign(byte[] bytes) throws ED25519Exception {
                        return new byte[0];
                    }
                }), ... );

Development notes

Testing unreleased changes locally in an application

1. Update all the SDK artifacts version to X.Y.Z-SNAPSHOT, having X.Y.Z the next version from the current according to semver. Do it once the changes made require semver version change. Otherwise, the same -SNAPSHOT can be re-written. To update the version automatically, from the root of the repository invoke

   mvn versions:set -DnewVersion=X.Y.Z-SNAPSHOT
   

2. Optionally, if updated concordium-base, run make or make-android
3. Run mvn install, so the artifacts get installed in your local Maven repo (an .m2 directory under your home directory)
4. In your application, reference the new SDK snapshot. Make sure to have mavenLocal() repository in your dependency resolution configuration

Releasing

Please follow the steps from the Release guide