Fall back to regular update if delta update fails to download

Sparkle/SPUCoreBasedUpdateDriver.m

@@ -13,6 +13,7 @@
 #import "SPUInstallerDriver.h"
 #import "SPUDownloadDriver.h"
 #import "SULog.h"
+#import "SULog+NSError.h"
 #import "SUErrors.h"
 #import "SPUResumableUpdate.h"
 #import "SPUDownloadedUpdate.h"
@@ -247,18 +248,25 @@ - (void)extractUpdate:(SPUDownloadedUpdate *)downloadedUpdate
 
 - (void)downloadDriverDidFailToDownloadFileWithError:(NSError *)error
 {
-    if ([self.updaterDelegate respondsToSelector:@selector((updater:failedToDownloadUpdate:error:))]) {
-        NSError *errorToReport = [error.userInfo objectForKey:NSUnderlyingErrorKey];
-        if (errorToReport == nil) {
-            errorToReport = error;
+    if ([self.updateItem isDeltaUpdate]) {
+        SULog(SULogLevelError, @"Failed to download delta update. Falling back to regular update...");
+        SULogError(error);
+
+        [self fallBackAndDownloadRegularUpdate];
+    } else {
+        if ([self.updaterDelegate respondsToSelector:@selector((updater:failedToDownloadUpdate:error:))]) {
+            NSError *errorToReport = [error.userInfo objectForKey:NSUnderlyingErrorKey];
+            if (errorToReport == nil) {
+                errorToReport = error;
+            }
+
+            [self.updaterDelegate updater:self.updater
+                               failedToDownloadUpdate:self.updateItem
+                                                error:errorToReport];
         }
 
-        [self.updaterDelegate updater:self.updater
-                           failedToDownloadUpdate:self.updateItem
-                                            error:errorToReport];
+        [self.delegate coreDriverIsRequestingAbortUpdateWithError:error];
     }
-
-    [self.delegate coreDriverIsRequestingAbortUpdateWithError:error];
 }
 
 - (void)installerDidStartInstallingWithApplicationTerminated:(BOOL)applicationTerminated
@@ -335,22 +343,27 @@ - (void)basicDriverIsRequestingAbortUpdateWithError:(nullable NSError *)error
     [self.delegate basicDriverIsRequestingAbortUpdateWithError:error];
 }
 
-- (void)installerDidFailToApplyDeltaUpdate
+- (void)fallBackAndDownloadRegularUpdate
 {
     SUAppcastItem *secondaryUpdateItem = self.secondaryUpdateItem;
     assert(secondaryUpdateItem != nil);
 
     BOOL backgroundDownload = self.downloadDriver.inBackground;
 
-    [self clearDownloadedUpdate];
-
     // Fall back to the non-delta update. Note that we don't want to trigger another update was found event.
     self.updateItem = secondaryUpdateItem;
     self.secondaryUpdateItem = nil;
 
     [self downloadUpdateFromAppcastItem:secondaryUpdateItem secondaryAppcastItem:nil inBackground:backgroundDownload];
 }
 
+- (void)installerDidFailToApplyDeltaUpdate
+{
+    [self clearDownloadedUpdate];
+
+    [self fallBackAndDownloadRegularUpdate];
+}
+
 - (void)abortUpdateAndShowNextUpdateImmediately:(BOOL)shouldShowUpdateImmediately error:(nullable NSError *)error
 {
     [self.installerDriver abortInstall];

Sparkle/SUAppcastDriver.m

@@ -168,7 +168,6 @@ - (SUAppcastItem *)retrieveBestAppcastItemFromAppcast:(SUAppcast *)appcast versi
             regularItemFromDelegate = nil;
             delegateOptedOutOfSelection = NO;
         } else {
-            assert(!candidateItem.deltaUpdate);
             if (candidateItem.deltaUpdate) {
                 // Client would have to go out of their way to examine the .deltaUpdates to return one
                 // We need them to give us a regular update item back instead..
@@ -281,6 +280,12 @@ + (SUAppcast *)filterAppcast:(SUAppcast *)appcast forMacOSAndAllowedChannels:(NS
             return NO;
         }
 
+        // Delta updates cannot be top-level entries
+        BOOL isDeltaUpdate = [item isDeltaUpdate];
+        if (isDeltaUpdate) {
+            return NO;
+        }
+
         NSString *channel = item.channel;
         if (channel == nil) {
             // Item is on the default channel

Tests/Resources/testappcast_channels.xml

@@ -54,5 +54,11 @@
         <sparkle:version>6.0</sparkle:version>
         <enclosure url="http://localhost:1337/Sparkle_Test_App.zip" length="1346234" sparkle:os="windows" />
     </item>
+    <!-- An invalid release with top level delta item -->
+    <item>
+        <title>Version 7.0</title>
+        <sparkle:version>7.0</sparkle:version>
+        <enclosure url="http://localhost:1337/Sparkle_Test_App.zip" length="1346234" sparkle:deltaFrom="5.0" sparkle:edSignature="..." />
+    </item>
   </channel>
 </rss>

Tests/SUAppcastTest.swift

@@ -91,7 +91,7 @@ class SUAppcastTest: XCTestCase {
             let stateResolver = SPUAppcastItemStateResolver(hostVersion: hostVersion, applicationVersionComparator: versionComparator, standardVersionComparator: versionComparator)
 
             let appcast = try SUAppcast(xmlData: testData, relativeTo: nil, stateResolver: stateResolver)
-            XCTAssertEqual(5, appcast.items.count)
+            XCTAssertEqual(6, appcast.items.count)
 
             do {
                 let filteredAppcast = SUAppcastDriver.filterAppcast(appcast, forMacOSAndAllowedChannels: ["beta", "nightly"])