Add Json cover provider class

src/covermanager/jsoncoverprovider.cpp

@@ -0,0 +1,64 @@
+/*
+ * Strawberry Music Player
+ * Copyright 2018, Jonas Kvinge <jonas@jkvinge.net>
+ *
+ * Strawberry is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Strawberry is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Strawberry.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "config.h"
+
+#include <QtGlobal>
+#include <QObject>
+#include <QByteArray>
+#include <QString>
+#include <QJsonDocument>
+#include <QJsonValue>
+#include <QJsonObject>
+
+#include "core/application.h"
+#include "coverprovider.h"
+#include "jsoncoverprovider.h"
+
+JsonCoverProvider::JsonCoverProvider(const QString &name, const bool enabled, const bool authentication_required, const float quality, const bool fetchall, const bool allow_missing_album, Application *app, QObject *parent) : CoverProvider(name, enabled, authentication_required, quality, fetchall, allow_missing_album, app, parent) {}
+
+QJsonObject JsonCoverProvider::ExtractJsonObj(const QByteArray &data) {
+
+  QJsonParseError json_error;
+  QJsonDocument json_doc = QJsonDocument::fromJson(data, &json_error);
+
+  if (json_error.error != QJsonParseError::NoError) {
+    Error(QString("Failed to parse json data: %1").arg(json_error.errorString()));
+    return QJsonObject();
+  }
+
+  if (json_doc.isEmpty()) {
+    Error("Received empty Json document.", data);
+    return QJsonObject();
+  }
+
+  if (!json_doc.isObject()) {
+    Error("Json document is not an object.", json_doc);
+    return QJsonObject();
+  }
+
+  QJsonObject json_obj = json_doc.object();
+  if (json_obj.isEmpty()) {
+    Error("Received empty Json object.", json_doc);
+    return QJsonObject();
+  }
+
+  return json_obj;
+
+}