Only update gamepad mappings if they're newer than what we already have

app/path.cpp

@@ -29,13 +29,31 @@ QByteArray Path::readDataFile(QString fileName)
     return dataFile.readAll();
 }
 
-void Path::writeDataFile(QString fileName, QByteArray data)
+void Path::writeCacheFile(QString fileName, QByteArray data)
 {
-    QFile dataFile(QDir(s_CacheDir).absoluteFilePath(fileName));
+    QDir cacheDir(s_CacheDir);
+
+    // Create the cache path if it does not exist
+    if (!cacheDir.exists()) {
+        cacheDir.mkpath(".");
+    }
+
+    QFile dataFile(cacheDir.absoluteFilePath(fileName));
     dataFile.open(QIODevice::WriteOnly);
     dataFile.write(data);
 }
 
+void Path::deleteCacheFile(QString fileName)
+{
+    QFile dataFile(QDir(s_CacheDir).absoluteFilePath(fileName));
+    dataFile.remove();
+}
+
+QFileInfo Path::getCacheFileInfo(QString fileName)
+{
+    return QFileInfo(QDir(s_CacheDir), fileName);
+}
+
 QString Path::getDataFilePath(QString fileName)
 {
     QString candidatePath;
@@ -79,7 +97,10 @@ void Path::initialize(bool portable)
     if (portable) {
         s_LogDir = QDir::currentPath();
         s_BoxArtCacheDir = QDir::currentPath() + "/boxart";
-        s_CacheDir = QDir::currentPath();
+
+        // In order for the If-Modified-Since logic to work in MappingFetcher,
+        // the cache directory must be different than the current directory.
+        s_CacheDir = QDir::currentPath() + "/cache";
     }
     else {
 #ifdef Q_OS_DARWIN

app/path.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <QString>
+#include <QFileInfo>
 
 class Path
 {
@@ -10,7 +11,9 @@ public:
     static QString getBoxArtCacheDir();
 
     static QByteArray readDataFile(QString fileName);
-    static void writeDataFile(QString fileName, QByteArray data);
+    static void writeCacheFile(QString fileName, QByteArray data);
+    static void deleteCacheFile(QString fileName);
+    static QFileInfo getCacheFileInfo(QString fileName);
 
     // Only safe to use directly for Qt classes
     static QString getDataFilePath(QString fileName);

app/settings/mappingfetcher.cpp

@@ -27,9 +27,17 @@ void MappingFetcher::start()
     QT_WARNING_POP
 #endif
 
-    // We'll get a callback when this is finished
     QUrl url("https://moonlight-stream.org/SDL_GameControllerDB/gamecontrollerdb.txt");
-    m_Nam.get(QNetworkRequest(url));
+    QNetworkRequest request(url);
+
+    // Only download the file if it's newer than what we have
+    QFileInfo existingFileInfo = Path::getCacheFileInfo("gamecontrollerdb.txt");
+    if (existingFileInfo.exists() && existingFileInfo.size() > 0) {
+        request.setHeader(QNetworkRequest::IfModifiedSinceHeader, existingFileInfo.lastModified().toUTC());
+    }
+
+    // We'll get a callback when this is finished
+    m_Nam.get(request);
 }
 
 void MappingFetcher::handleMappingListFetched(QNetworkReply* reply)
@@ -40,10 +48,21 @@ void MappingFetcher::handleMappingListFetched(QNetworkReply* reply)
         // Queue the reply for deletion
         reply->deleteLater();
 
-        // Update the cached data on disk for next call to applyMappings()
+        // If we get a 304 back, Qt will happily just tell us our request was
-        Path::writeDataFile("gamecontrollerdb.txt", reply->readAll());
+        // successful and let us try to write our empty response to disk. Check
+        // the status code directly to prevent this.
+        if (reply->attribute(QNetworkRequest::HttpStatusCodeAttribute) == 304) {
+            qInfo() << "Gamepad mappings are up to date";
+        }
+        else {
+            // Update the cached data on disk for next call to applyMappings()
+            QByteArray data = reply->readAll();
+            if (!data.isEmpty()) {
+                Path::writeCacheFile("gamecontrollerdb.txt", data);
+            }
 
-        qInfo() << "Downloaded updated gamepad mappings";
+            qInfo() << "Downloaded updated gamepad mappings";
+        }
     }
     else {
         qWarning() << "Failed to download updated gamepad mappings:" << reply->error();