print qr code when producing a device link uri, but only if System.console is not null

build.gradle.kts

@@ -88,6 +88,7 @@ dependencies {
     implementation(libs.slf4j.api)
     implementation(libs.slf4j.jul)
     implementation(libs.logback)
+    implementation(libs.zxing)
     implementation(project(":libsignal-cli"))
 }
 

gradle/libs.versions.toml

@@ -7,6 +7,7 @@ bouncycastle = "org.bouncycastle:bcprov-jdk18on:1.83"
 jackson-databind = "com.fasterxml.jackson.core:jackson-databind:2.20.2"
 argparse4j = "net.sourceforge.argparse4j:argparse4j:0.9.0"
 dbusjava = "com.github.hypfvieh:dbus-java-transport-native-unixsocket:5.0.0"
+zxing = "com.google.zxing:core:3.5.4"
 slf4j-api = { module = "org.slf4j:slf4j-api", version.ref = "slf4j" }
 slf4j-jul = { module = "org.slf4j:jul-to-slf4j", version.ref = "slf4j" }
 logback = "ch.qos.logback:logback-classic:1.5.29"

src/main/java/org/asamk/signal/commands/LinkCommand.java

@@ -1,5 +1,10 @@
 package org.asamk.signal.commands;
 
+import com.google.zxing.BarcodeFormat;
+import com.google.zxing.WriterException;
+import com.google.zxing.common.BitMatrix;
+import com.google.zxing.qrcode.QRCodeWriter;
+
 import net.sourceforge.argparse4j.inf.Namespace;
 import net.sourceforge.argparse4j.inf.Subparser;
 
@@ -14,6 +19,7 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
+import java.net.URI;
 import java.util.concurrent.TimeoutException;
 
 public class LinkCommand implements ProvisioningCommand {
@@ -44,7 +50,11 @@ public class LinkCommand implements ProvisioningCommand {
             deviceName = "cli";
         }
         try {
-            writer.println("{}", m.getDeviceLinkUri());
+            final URI deviceLinkUri = m.getDeviceLinkUri();
+            if (System.console() != null) {
+                printQrCode(writer, deviceLinkUri);
+            }
+            writer.println("{}", deviceLinkUri);
             var number = m.finishDeviceLink(deviceName);
             writer.println("Associated with: {}", number);
         } catch (TimeoutException e) {
@@ -59,4 +69,25 @@ public class LinkCommand implements ProvisioningCommand {
                     + "\" before trying again.");
         }
     }
+
+    private void printQrCode(final PlainTextWriter writer, final URI deviceLinkUri) {
+        try {
+            var bitMatrix = new QRCodeWriter().encode(deviceLinkUri.toString(), BarcodeFormat.QR_CODE, 0, 0);
+            for (int y = 0; y < bitMatrix.getHeight(); y += 2) {
+                writer.println(formatQRCodeLinePair(bitMatrix, y));
+            }
+        } catch (WriterException e) {
+            logger.error("Failed to generate QR code", e);
+        }
+    }
+
+    private static String formatQRCodeLinePair(final BitMatrix bitMatrix, final int y) {
+        var line = new StringBuilder();
+        for (int x = 0; x < bitMatrix.getWidth(); x++) {
+            boolean upper = bitMatrix.get(x, y);
+            boolean lower = y + 1 < bitMatrix.getHeight() && bitMatrix.get(x, y + 1);
+            line.append((upper && lower) ? "█" : (upper ? "▀" : (lower ? "▄" : " ")));
+        }
+        return line.toString();
+    }
 }