fix(network): fall back to unlimited bandwidth in case the legacy global limit is still set

`-2` used to mean "Use global limits", which no longer exist since
3.17.0.  As any negative value results in the auto bandwidth limiter to
engage, this could result in unexpected slower sync speeds after a
client upgrade.

Let's just keep handling that value and assume that we want to use
unlimited bandwidth.

Fixes #8743

Signed-off-by: Jyrki Gadinger <nilsding@nilsding.org>

src/libsync/account.cpp

@@ -1426,7 +1426,14 @@ void Account::setUploadLimitSetting(const AccountNetworkTransferLimitSetting set
         return;
     }
 
-    _uploadLimitSetting = setting;
+    auto targetSetting = setting;
+
+    if (setting == AccountNetworkTransferLimitSetting::LegacyGlobalLimit) {
+        qCInfo(lcAccount) << "Upload limit setting was requested to be set to the legacy global limit, falling back to unlimited";
+        targetSetting = AccountNetworkTransferLimitSetting::NoLimit;
+    }
+
+    _uploadLimitSetting = targetSetting;
     emit uploadLimitSettingChanged();
 }
 
@@ -1440,8 +1447,15 @@ void Account::setDownloadLimitSetting(const AccountNetworkTransferLimitSetting s
     if (setting == _downloadLimitSetting) {
         return;
     }
-    
+
-    _downloadLimitSetting = setting;
+    auto targetSetting = setting;
+
+    if (setting == AccountNetworkTransferLimitSetting::LegacyGlobalLimit) {
+        qCInfo(lcAccount) << "Download limit setting was requested to be set to the legacy global limit, falling back to unlimited";
+        targetSetting = AccountNetworkTransferLimitSetting::NoLimit;
+    }
+
+    _downloadLimitSetting = targetSetting;
     emit downloadLimitSettingChanged();
 }
 

src/libsync/account.h

@@ -99,6 +99,7 @@ class OWNCLOUDSYNC_EXPORT Account : public QObject
 
 public:
     enum class AccountNetworkTransferLimitSetting {
+        LegacyGlobalLimit = -2, // Until 3.17.0 a value of -2 was interpreted as "Use global network settings", it's now used to fall back to "No limit".  See also GH#8743
         AutoLimit = -1, // Value under 0 is interpreted as auto in general
         NoLimit,
         ManualLimit,

test/testaccount.cpp

@@ -69,6 +69,37 @@ private slots:
         QCOMPARE(account->isPublicShareLink(), expectedResult);
         QCOMPARE(account->davUser(), expectedDavUser);
     }
+
+    void testAccount_setLimitSettings_globalNetworkLimitFallback()
+    {
+        using LimitSetting = Account::AccountNetworkTransferLimitSetting;
+        AccountPtr account = Account::create();
+
+        const auto setLimitSettings = [account](const LimitSetting setting) -> void {
+            account->setDownloadLimitSetting(setting);
+            account->setUploadLimitSetting(setting);
+        };
+
+        const auto verifyLimitSettings = [account](const LimitSetting expectedSetting) -> void {
+            QCOMPARE_EQ(expectedSetting, account->downloadLimitSetting());
+            QCOMPARE_EQ(expectedSetting, account->uploadLimitSetting());
+        };
+
+        // the default setting should be NoLimit
+        verifyLimitSettings(LimitSetting::NoLimit);
+
+        // changing it to ManualLimit should succeed
+        setLimitSettings(LimitSetting::ManualLimit);
+        verifyLimitSettings(LimitSetting::ManualLimit);
+
+        // changing it to AutoLimit should succeed
+        setLimitSettings(LimitSetting::AutoLimit);
+        verifyLimitSettings(LimitSetting::AutoLimit);
+
+        // changing it to LegacyGlobalLimit (-2) should fall back to NoLimit
+        setLimitSettings(LimitSetting::LegacyGlobalLimit);
+        verifyLimitSettings(LimitSetting::NoLimit);
+    }
 };
 
 QTEST_APPLESS_MAIN(TestAccount)