Extract hexDump function

src/util.h

@@ -246,6 +246,19 @@ enum class ExtendedChar {
     GreekSmallLetterPhi = 0xed,
 };
 
+String hexDump(String in) {
+    String out;
+    for (size_t i = 0; i < in.length(); ++i) {
+        auto hexChar = String(in[i], HEX);
+        if (hexChar.length() == 1) {
+            out.concat('0');
+        }
+        out.concat(hexChar);
+        out.concat(' ');
+    }
+    return out;
+}
+
 /*
  * Message syntax:
  * separator: ~
@@ -299,13 +312,5 @@ void sendTextToSign(
     Serial1.print(toSend);
 
     Serial.println("Text sent to device: " + toSend);
-    Serial.print("Hex dump: ");
-    for (size_t i = 0; i < toSend.length(); ++i) {
-        auto hexChar = String(toSend[i], HEX);
-        if (hexChar.length() == 1) {
-            hexChar = '0' + hexChar;
-        }
-        Serial.print(hexChar + ' ');
-    }
-    Serial.println();
+    Serial.println("Hex dump: " + hexDump(toSend));
 }