From 36f68e4fc999e7c6b037a67a2410ac4fb7dc8ce3 Mon Sep 17 00:00:00 2001
From: Nyall Dawson <nyall.dawson@gmail.com>
Date: Tue, 19 Jan 2021 16:12:43 +1000
Subject: [PATCH] Add mechanism for temporarily disabling all network caching
 to QgsNetworkAccessManager, and add a checkbox in the network logger panel to
 allow users to temporarily disable the network cache

This can be VERY useful when debugging QGIS network activity, or when
using QGIS to test server side changes.

This is a transient setting only, and is forgotten as soon as QGIS
is closed. That's by design -- we don't want users to accidentally
leave this enabled and cause unnecessary server load.
---
 .../network/qgsnetworkaccessmanager.sip.in    |  1 +
 .../qgsnetworkloggerpanelwidget.cpp           | 13 ++++++++++
 src/core/network/qgsnetworkaccessmanager.cpp  | 10 ++++++++
 src/core/network/qgsnetworkaccessmanager.h    | 25 +++++++++++++++++++
 4 files changed, 49 insertions(+)

diff --git a/python/core/auto_generated/network/qgsnetworkaccessmanager.sip.in b/python/core/auto_generated/network/qgsnetworkaccessmanager.sip.in
index ff0ea913ebd..fa0e6f2db9d 100644
--- a/python/core/auto_generated/network/qgsnetworkaccessmanager.sip.in
+++ b/python/core/auto_generated/network/qgsnetworkaccessmanager.sip.in
@@ -250,6 +250,7 @@ need to be handled on the main thread. See in-depth discussion in the documentat
 for the constructor of this class.
 %End
 
+
     bool useSystemProxy() const;
 %Docstring
 Returns whether the system proxy should be used.
diff --git a/src/app/devtools/networklogger/qgsnetworkloggerpanelwidget.cpp b/src/app/devtools/networklogger/qgsnetworkloggerpanelwidget.cpp
index c6644fe8425..b046a5f8c7d 100644
--- a/src/app/devtools/networklogger/qgsnetworkloggerpanelwidget.cpp
+++ b/src/app/devtools/networklogger/qgsnetworkloggerpanelwidget.cpp
@@ -27,6 +27,7 @@
 #include <QMessageBox>
 #include <QScrollBar>
 #include <QToolButton>
+#include <QCheckBox>
 
 #include <nlohmann/json.hpp>
 
@@ -217,4 +218,16 @@ QgsNetworkLoggerPanelWidget::QgsNetworkLoggerPanelWidget( QgsNetworkLogger *logg
 
   settingsMenu->addAction( mActionShowSuccessful );
   settingsMenu->addAction( mActionShowTimeouts );
+
+  mToolbar->addSeparator();
+  QCheckBox *disableCacheCheck = new QCheckBox( tr( "Disable cache" ) );
+  connect( disableCacheCheck, &QCheckBox::toggled, this, [ = ]( bool checked )
+  {
+    // note -- we deliberately do NOT store this as a permanent setting in QSettings
+    // as it is designed to be a temporary debugging tool only and we don't want
+    // users to accidentally leave this enabled and cause unnecessary server load...
+    QgsNetworkAccessManager::instance()->setCacheDisabled( checked );
+  } );
+
+  mToolbar->addWidget( disableCacheCheck );
 }
diff --git a/src/core/network/qgsnetworkaccessmanager.cpp b/src/core/network/qgsnetworkaccessmanager.cpp
index 6e05c00a6d9..94a17440704 100644
--- a/src/core/network/qgsnetworkaccessmanager.cpp
+++ b/src/core/network/qgsnetworkaccessmanager.cpp
@@ -127,7 +127,10 @@ QgsNetworkAccessManager *QgsNetworkAccessManager::instance( Qt::ConnectionType c
     sMainNAM = nam;
 
   if ( !nam->mInitialized )
+  {
     nam->setupDefaultProxyAndCache( connectionType );
+    nam->setCacheDisabled( sMainNAM->cacheDisabled() );
+  }
 
   return nam;
 }
@@ -249,6 +252,13 @@ QNetworkReply *QgsNetworkAccessManager::createRequest( QNetworkAccessManager::Op
   }
 #endif
 
+  if ( sMainNAM->mCacheDisabled )
+  {
+    // if caching is disabled then we override whatever the request actually has set!
+    pReq->setAttribute( QNetworkRequest::CacheLoadControlAttribute, QNetworkRequest::AlwaysNetwork );
+    pReq->setAttribute( QNetworkRequest::CacheSaveControlAttribute, false );
+  }
+
   static QAtomicInt sRequestId = 0;
   const int requestId = ++sRequestId;
   QByteArray content;
diff --git a/src/core/network/qgsnetworkaccessmanager.h b/src/core/network/qgsnetworkaccessmanager.h
index a7b066f7259..e9f7713b2f0 100644
--- a/src/core/network/qgsnetworkaccessmanager.h
+++ b/src/core/network/qgsnetworkaccessmanager.h
@@ -409,6 +409,30 @@ class CORE_EXPORT QgsNetworkAccessManager : public QNetworkAccessManager
      */
     void setupDefaultProxyAndCache( Qt::ConnectionType connectionType = Qt::BlockingQueuedConnection );
 
+#ifndef SIP_RUN
+
+    /**
+     * Returns TRUE if all network caching is disabled.
+     *
+     * \see setCacheDisabled()
+     * \note Not available in Python bindings.
+     * \since QGIS 3.18
+     */
+    bool cacheDisabled() const { return mCacheDisabled; }
+
+    /**
+     * Sets whether all network caching should be disabled.
+     *
+     * If \a disabled is TRUE then all caching will be disabled, causing all requests
+     * to be retrieved from the network regardless of the request's attributes.
+     *
+     * \see cacheDisabled()
+     * \note Not available in Python bindings.
+     * \since QGIS 3.18
+     */
+    void setCacheDisabled( bool disabled ) { mCacheDisabled = disabled; }
+#endif
+
     /**
      * Returns whether the system proxy should be used.
      */
@@ -655,6 +679,7 @@ class CORE_EXPORT QgsNetworkAccessManager : public QNetworkAccessManager
     QStringList mNoProxyURLs;
     bool mUseSystemProxy = false;
     bool mInitialized = false;
+    bool mCacheDisabled = false;
     static QgsNetworkAccessManager *sMainNAM;
     // ssl error handler, will be set for main thread ONLY
     std::unique_ptr< QgsSslErrorHandler > mSslErrorHandler;