Add message signing example

concordium-sdk-examples/src/main/java/com/concordium/sdk/examples/SignMessage.java

@@ -0,0 +1,73 @@
+package com.concordium.sdk.examples;
+
+import com.concordium.sdk.crypto.ed25519.ED25519SecretKey;
+import com.concordium.sdk.transactions.Index;
+import com.concordium.sdk.transactions.MessageSigningDigest;
+import com.concordium.sdk.transactions.SignerEntry;
+import com.concordium.sdk.transactions.TransactionSigner;
+import com.concordium.sdk.types.AccountAddress;
+import lombok.val;
+import org.apache.commons.codec.binary.Hex;
+import org.apache.commons.io.FileUtils;
+import picocli.CommandLine;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Objects;
+import java.util.concurrent.Callable;
+
+/**
+ * Signs the given message in the same way the transactions are signed.
+ */
+@CommandLine.Command(name = "SignMessage", mixinStandardHelpOptions = true)
+public class SignMessage implements Callable<Integer> {
+    @CommandLine.Option(
+            names = {"--endpoint"},
+            description = "GRPC interface of the node.",
+            defaultValue = "http://localhost:20001")
+    private String endpoint;
+
+    @CommandLine.Option(
+            names = "--hex",
+            description = "Whether the given file contains HEX-encoded data")
+    private boolean isHex;
+
+    @CommandLine.Parameters(
+            index = "0",
+            description = "A file containing the message"
+    )
+    private Path messageFilePath;
+
+    @Override
+    public Integer call() throws Exception {
+        val signer = TransactionSigner.from(
+                SignerEntry.from(
+                        Index.from(0),
+                        Index.from(0),
+                        ED25519SecretKey.from("7100071c835a0a35e86dccba7ee9d10b89e36d1e596771cdc8ee36a17f7abbf2")
+                )
+        );
+        val address = AccountAddress.from("3WZE6etUvVp1eyhEtTxqZrQaanTAZnZCHEmZmDyCbCwxnmQuPE");
+        val fileContents = Files.readAllBytes(messageFilePath);
+        System.out.println(messageFilePath);
+        val message = (isHex) ? Hex.decodeHex(new String(fileContents)) : fileContents;
+        val digest = MessageSigningDigest.from(address, message);
+        val signature = signer.sign(digest);
+        System.out.println(Hex.encodeHexString(
+                Objects.requireNonNull(
+                                Objects.requireNonNull(signature.getSignatures().firstEntry())
+                                        .getValue()
+                                        .getSignatures()
+                                        .firstEntry()
+                        )
+                        .getValue()
+                        .getBytes()
+        ));
+        return 0;
+    }
+
+    public static void main(String[] args) {
+        int exitCode = new CommandLine(new SignMessage()).execute(args);
+        System.exit(exitCode);
+    }
+}