Connection: allow to choose between binary and text JSON cache

2 files changed, 25 insertions, 9 deletions

diff --git a/README.md b/README.md
index fc9ad5e0..dc6b22ca 100644
--- a/README.md
+++ b/README.md
@@ -63,6 +63,8 @@ This will get you `debug/qmc-example` and `release/qmc-example` console executab
 
 ## Troubleshooting
 
+#### Building fails
+
 If `cmake` fails with...
 ```
 CMake Warning at CMakeLists.txt:11 (find_package):
@@ -85,3 +87,6 @@ where
 ```
 QT_LOGGING_RULES="libqmatrixclient.*.debug=true,libqmatrixclient.jobs.debug=false"
 ```
+
+#### Cache format
+In case of troubles with room state and troubles with caching it may be useful to switch cache format from binary to JSON. To do that, set the following value in your client's configuration file/registry key (you might need to create the libqmatrixclient key for that): `libqmatrixclient/cache_type` to `json`. This will make cache saving and loading work slightly slower but the cache will be in a text JSON file (very long and unindented so prepare a good JSON viewer or text editor with JSON formatting capabilities).
diff --git a/connection.cpp b/connection.cpp
index f76d9fbe..c00a9b61 100644
--- a/connection.cpp
+++ b/connection.cpp
@@ -21,6 +21,7 @@
 #include "user.h"
 #include "events/event.h"
 #include "room.h"
+#include "settings.h"
 #include "jobs/generated/login.h"
 #include "jobs/generated/logout.h"
 #include "jobs/generated/receipts.h"
@@ -68,6 +69,8 @@ class Connection::Private
         SyncJob* syncJob = nullptr;
 
         bool cacheState = true;
+        bool cacheToBinary = SettingsGroup("libqmatrixclient")
+                             .value("cache_type").toString() != "json";
 
         void connectWithToken(const QString& user, const QString& accessToken,
                               const QString& deviceId);
@@ -636,7 +639,7 @@ void Connection::setHomeserver(const QUrl& url)
     emit homeserverChanged(homeserver());
 }
 
-static constexpr int CACHE_VERSION_MAJOR = 4;
+static constexpr int CACHE_VERSION_MAJOR = 5;
 static constexpr int CACHE_VERSION_MINOR = 0;
 
 void Connection::saveState(const QUrl &toFile) const
@@ -690,11 +693,13 @@ void Connection::saveState(const QUrl &toFile) const
     versionObj.insert("minor", CACHE_VERSION_MINOR);
     rootObj.insert("cache_version", versionObj);
 
-    QByteArray data = QJsonDocument(rootObj).toBinaryData();
+    QJsonDocument json { rootObj };
+    auto data = d->cacheToBinary ? json.toBinaryData() :
+                                   json.toJson(QJsonDocument::Compact);
+    qCDebug(PROFILER) << "Cache for" << userId() << "generated in" << et;
 
-    qCDebug(MAIN) << "Writing state to file" << outfile.fileName();
     outfile.write(data.data(), data.size());
-    qCDebug(PROFILER) << "*** Cached state for" << userId() << "saved in" << et;
+    qCDebug(MAIN) << "State cache saved to" << outfile.fileName();
 }
 
 void Connection::loadState(const QUrl &fromFile)
@@ -714,17 +719,23 @@ void Connection::loadState(const QUrl &fromFile)
     file.open(QFile::ReadOnly);
     QByteArray data = file.readAll();
 
-    auto jsonDoc = QJsonDocument::fromBinaryData(data);
+    QJsonParseError e;
+    auto jsonDoc = d->cacheToBinary ? QJsonDocument::fromBinaryData(data) :
+                                      QJsonDocument::fromJson(data, &e);
+    if (e.error == QJsonParseError::NoError)
+    {
+        qCWarning(MAIN) << "Cache file not found or broken, discarding";
+        return;
+    }
     auto actualCacheVersionMajor =
             jsonDoc.object()
             .value("cache_version").toObject()
             .value("major").toInt();
     if (actualCacheVersionMajor < CACHE_VERSION_MAJOR)
     {
-        qCWarning(MAIN) << "Major version of the cache file is"
-                        << actualCacheVersionMajor << "but"
-                        << CACHE_VERSION_MAJOR
-                        << "required; discarding the cache";
+        qCWarning(MAIN)
+            << "Major version of the cache file is" << actualCacheVersionMajor
+            << "but" << CACHE_VERSION_MAJOR << "required; discarding the cache";
         return;
     }