storagehelper: rework jpeg compression for sendTrustRequest

Compress the image to a value under 48k to be able to send it
through the DHT.

Change-Id: I4eee67e0a667bb278d2099abaf5305ca0a767efc

src/authority/storagehelper.cpp

@@ -163,7 +163,13 @@ compressedAvatar(const QString& image)
 
     auto size = qMin(qimage.width(), qimage.height());
     auto rect = QRect((qimage.width() - size) / 2, (qimage.height() - size) / 2, size, size);
-    qimage.copy(rect).scaled({size, size}, Qt::KeepAspectRatio).save(&buffer, "JPEG", 90);
+    constexpr auto quality = 88; // Same as android, between 80 and 90 jpeg compression changes a lot
+    constexpr auto maxSize = 16000 * 8; // Because 16*3 (rgb) = 48k, which is a valid size for the
+                                        // DHT and * 8 because typical jpeg compression
+    // divides the size per 8
+    while (size * size > maxSize)
+        size /= 2;
+    qimage.copy(rect).scaled({size, size}, Qt::KeepAspectRatio).save(&buffer, "JPEG", quality);
     auto b64Img = bArray.toBase64().trimmed();
     return QString::fromLocal8Bit(b64Img.constData(), b64Img.length());
 }