Experimental Android Light Client Tutorial

Let me preface by reiterating the experimental nature of this repository. Right now the go-ethereum android library appears to be incomplete or at the very least convoluted. Most likely this 'client' will not be able to access all of the functionality that can be on other platforms (for now).

Step 1: Setup Geth and Manifest

The official link for the new releases is https://geth.ethereum.org/downloads/

Add compile 'org.ethereum:geth:1.6.6' (Or latest version) to your App level gradle file under dependencies

Manifest:

Add the following permissions to (AndroidManifest.xml)

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.INTERNET" />

Step 2: Setup UI XML file

Important : Currently the send 'set string' button will have no functionaity: I have not been able to figure out the smart contract interaction step yet

Use the following code to setup a (very) basic user interface (activity_main.xml):

<Button
    android:text="Balance"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_alignParentLeft="true"
    android:onClick="getAccountBalanceButton"
    android:id="@+id/button" />
<Button
    android:text="Send Ether"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_alignParentRight="true"
    android:onClick="sendTransaction"
    android:id="@+id/transaction" />
<Button
    android:text="SetString"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_centerHorizontal="true"
    android:onClick="smart_contract_interaction_get_string"
    android:id="@+id/set_string" />

Step 3: Setup Rinkeby Genesis File

Create a file under your assets folder (may need to create assets folder) called 'rinkeby_genesis.json'

Under that file copy and paste the following rinkeby genesis code:

http://www.mobilefish.com/download/ethereum/rinkeby.json.txt

(You can test with https://jsonlint.com/ JSON Validator)

Step 4: Setup Node

(Copy Paste these as global variables)

 EthereumClient ec;
 Context ctx;
 TextView textbox;
 Node node;
 KeyStore keyStore;
 NodeConfig conf;
 long nonce;
 final String TAG = "Transaction info";

a) Genesis File to String

textbox = (TextView) findViewById(R.id.textBox);
InputStream is = this.getAssets().open("rinkeby_genesis.json");
int size = is.available();
byte[] buffer = new byte[size];
is.read(buffer);
is.close();
String genesis = new String(buffer, "UTF-8");

b) Configure the node

conf = Geth.newNodeConfig();
conf.setEthereumGenesis(genesis);
conf.setEthereumNetworkID(4);
node = Geth.newNode(getFilesDir() + "./ethereum", conf); //Folder to store the node
node.start(); // Start the node

c) Print the node information to the screen

NodeInfo info = node.getNodeInfo();
textbox.append("My name: " + info.getName() + "\n");
textbox.append("My address: " + info.getListenerAddress() + "\n");
textbox.append("My protocols: " + info.getProtocols() + "\n\n");

Setup 5: Setup Accounts

keyStore = new KeyStore(this.getFilesDir() + "/keystore",
    Geth.StandardScryptN, Geth.StandardScryptP);
if (keyStore.getAccounts().size() == 0) {
    Account acc = keyStore.newAccount("Password");
    keyStore.getAccounts().set(0, acc);
    acc = keyStore.newAccount("Password");
    keyStore.getAccounts().set(1, acc);
}

textbox.append("Sender Address: " + keyStore.getAccounts().get(0).getAddress().getHex().toString() + "\n");
textbox.append("Receiver Address: " + keyStore.getAccounts().get(1).getAddress().getHex().toString() + "\n");

Step 6: Get Balance Function

 public void getAccountBalanceButton(View view) {
      try {
             ec = node.getEthereumClient();
             System.out.println("Sender: " + ec.getBalanceAt(ctx, keyStore.getAccounts().get(0).getAddress(), -1).toString() + "\n");
             System.out.println("Receiver: " + ec.getBalanceAt(ctx, 
             keyStore.getAccounts().get(1).getAddress(), -1).toString() + "\n");
    } catch (Exception e) {
        e.printStackTrace();
    }
}

Step 7: Get test ether from Rinkeby

a) Go to https://www.rinkeby.io/

b) Setup a Gist via Github and paste your account address there (seen on UI)

c) Request 3 Eth (Should not take too long to receive)

d) You can check your accounts

Step 8: Setup transaction function

public void sendTransaction(View view) {
    try {
        ec = node.getEthereumClient();
        nonce = ec.getPendingNonceAt(ctx, keyStore.getAccounts().get(0).getAddress());
        String data_string = "Test Data for Transaction";
        byte[] data = data_string.getBytes();
        BigInt value = Geth.newBigInt(1000);
        BigInt gasLimit = Geth.newBigInt(31500);
        BigInt gasPrice = Geth.newBigInt(21001000100001L);
        Transaction transaction = Geth.newTransaction(nonce, keyStore.getAccounts().get(1).getAddress(), value, gasLimit, gasPrice, data);
        keyStore.timedUnlock(keyStore.getAccounts().get(0), "Password", 100000000);//probably too high of a timeout
        transaction = keyStore.signTx(keyStore.getAccounts().get(0), transaction, new BigInt(4));//Network ID
        ec.sendTransaction(ctx, transaction);
        log_transaction(transaction);
    } catch (Exception e) {
        e.printStackTrace();
    }
}

private void log_transaction(Transaction transaction) {
    try {
        android.util.Log.i(TAG, "Cost: " + transaction.getCost());
        android.util.Log.i(TAG, "GasPrice: " + transaction.getGasPrice());
        android.util.Log.i(TAG, "Gas: " + transaction.getGas());
        android.util.Log.i(TAG, "Nonce: " + transaction.getNonce());
        android.util.Log.i(TAG, "Value: " + transaction.getValue());
        android.util.Log.i(TAG, "Sig-Hash Hex: " + transaction.getSigHash().getHex());
        android.util.Log.i(TAG, "Hash Hex: " + transaction.getHash().getHex());
        android.util.Log.i(TAG, "Data-Length: " + transaction.getData().length);
        android.util.Log.i(TAG, "Receiver: " + transaction.getTo().getHex());
        android.util.Log.i(TAG, "Sender: " + transaction.getFrom(new BigInt(4)).getHex().toString());//Network ID
    } catch (Exception e) {
        e.printStackTrace();
    }
}

This is as far as I have gotten!

If you understand how to interact with Smart Contracts on the blockchain please answer my question below:

Current Issue: ethereum/go-ethereum#14832