Persist default sound so we can use it for fallback notifications

// FREEBIE

Signal.xcodeproj/project.pbxproj

@@ -327,6 +327,7 @@
 		458E38371D668EBF0094BD24 /* OWSDeviceProvisioningURLParser.m in Sources */ = {isa = PBXBuildFile; fileRef = 458E38361D668EBF0094BD24 /* OWSDeviceProvisioningURLParser.m */; };
 		458E383A1D6699FA0094BD24 /* OWSDeviceProvisioningURLParserTest.m in Sources */ = {isa = PBXBuildFile; fileRef = 458E38391D6699FA0094BD24 /* OWSDeviceProvisioningURLParserTest.m */; };
 		459311FC1D75C948008DD4F0 /* OWSDeviceTableViewCell.m in Sources */ = {isa = PBXBuildFile; fileRef = 459311FB1D75C948008DD4F0 /* OWSDeviceTableViewCell.m */; };
+		45A2F005204473A3002E978A /* NewMessage.aifc in Resources */ = {isa = PBXBuildFile; fileRef = 45A2F004204473A3002E978A /* NewMessage.aifc */; };
 		45A663C51F92EC760027B59E /* GroupTableViewCell.swift in Sources */ = {isa = PBXBuildFile; fileRef = 45A663C41F92EC760027B59E /* GroupTableViewCell.swift */; };
 		45A6DAD61EBBF85500893231 /* ReminderView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 45A6DAD51EBBF85500893231 /* ReminderView.swift */; };
 		45AE48511E0732D6004D96C2 /* TurnServerInfo.swift in Sources */ = {isa = PBXBuildFile; fileRef = 45AE48501E0732D6004D96C2 /* TurnServerInfo.swift */; };
@@ -901,6 +902,7 @@
 		459311FB1D75C948008DD4F0 /* OWSDeviceTableViewCell.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = OWSDeviceTableViewCell.m; sourceTree = "<group>"; };
 		4597E94E1D8313C100040CDE /* sq */ = {isa = PBXFileReference; lastKnownFileType = text.plist.strings; name = sq; path = translations/sq.lproj/Localizable.strings; sourceTree = "<group>"; };
 		4597E94F1D8313CB00040CDE /* bg */ = {isa = PBXFileReference; lastKnownFileType = text.plist.strings; name = bg; path = translations/bg.lproj/Localizable.strings; sourceTree = "<group>"; };
+		45A2F004204473A3002E978A /* NewMessage.aifc */ = {isa = PBXFileReference; lastKnownFileType = file; name = NewMessage.aifc; path = Signal/AudioFiles/NewMessage.aifc; sourceTree = SOURCE_ROOT; };
 		45A663C41F92EC760027B59E /* GroupTableViewCell.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GroupTableViewCell.swift; sourceTree = "<group>"; };
 		45A6DAD51EBBF85500893231 /* ReminderView.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ReminderView.swift; sourceTree = "<group>"; };
 		45AE48501E0732D6004D96C2 /* TurnServerInfo.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = TurnServerInfo.swift; sourceTree = "<group>"; };
@@ -1150,6 +1152,7 @@
 		34074F54203D0722004596AE /* Sounds */ = {
 			isa = PBXGroup;
 			children = (
+				45A2F004204473A3002E978A /* NewMessage.aifc */,
 				34CF0783203E6B77005C4D61 /* busy_tone_ansi.caf */,
 				34CF0786203E6B78005C4D61 /* end_call_tone_cept.caf */,
 				34F77044203F5E4B00C7CBB7 /* messageReceivedClassic-quiet.caf */,
@@ -2543,6 +2546,7 @@
 				34074FEE203E5436004596AE /* aurora.m4r in Resources */,
 				34330A5E1E787BD800DF2FB9 /* ElegantIcons.ttf in Resources */,
 				AD83FF451A73426500B5C81A /* audio_pause_button@2x.png in Resources */,
+				45A2F005204473A3002E978A /* NewMessage.aifc in Resources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

Signal/src/ViewControllers/DebugUI/DebugUITableViewController.m

@@ -102,9 +102,9 @@ NS_ASSUME_NONNULL_BEGIN
                    }];
     [subsectionItems addObject:sharedDataFileBrowserItem];
     OWSTableItem *documentsFileBrowserItem = [OWSTableItem
-        disclosureItemWithText:@"📁 Document Dir"
+        disclosureItemWithText:@"📁 App Container"
                    actionBlock:^{
-                       NSURL *baseURL = [NSURL URLWithString:[OWSFileSystem appDocumentDirectoryPath]];
+                       NSURL *baseURL = [NSURL URLWithString:[OWSFileSystem appLibraryDirectoryPath]];
                        DebugUIFileBrowser *fileBrowser = [[DebugUIFileBrowser alloc] initWithFileURL:baseURL];
                        [viewController.navigationController pushViewController:fileBrowser animated:YES];
                    }];

SignalMessaging/environment/OWSSounds.m

@@ -4,6 +4,7 @@
 
 #import "OWSSounds.h"
 #import "OWSAudioPlayer.h"
+#import <SignalServiceKit/OWSFileSystem.h>
 #import <SignalServiceKit/TSStorageManager.h>
 #import <SignalServiceKit/TSThread.h>
 #import <SignalServiceKit/YapDatabaseConnection+OWS.h>
@@ -245,6 +246,36 @@ NSString *const kOWSSoundsStorageGlobalNotificationKey = @"kOWSSoundsStorageGlob
 
 + (void)setGlobalNotificationSound:(OWSSound)sound
 {
+    // Fallback push notifications play a sound specified by the server, but we don't want to store this configuration
+    // on the server. Instead, we create a file with the same name as the default to be played when receiving
+    // a fallback notification.
+    NSString *dirPath = [[OWSFileSystem appLibraryDirectoryPath] stringByAppendingPathComponent:@"Sounds"];
+    [OWSFileSystem ensureDirectoryExists:dirPath];
+
+    // This name is specified in the payload by the Signal Service when requesting fallback push notifications.
+    NSString *kDefaultNotificationSoundFilename = @"NewMessage.aifc";
+    NSString *defaultSoundPath = [dirPath stringByAppendingPathComponent:kDefaultNotificationSoundFilename];
+
+    DDLogDebug(@"%@ writing new default sound to %@", self.logTag, defaultSoundPath);
+
+    NSURL *_Nullable soundURL = [OWSSounds soundURLForSound:sound quiet:NO];
+    OWSAssert(soundURL);
+
+    // Quick way to achieve an atomic "copy" operation that allows overwriting if the user has previously specified
+    // a default notification sound.
+    NSData *soundData = [NSData dataWithContentsOfURL:soundURL];
+    BOOL success = [soundData writeToFile:defaultSoundPath atomically:YES];
+
+    // The globally configured sound the user has configured is unprotected, so that we can still play the sound if the
+    // user hasn't authenticated after power-cycling their device.
+    [OWSFileSystem protectFileOrFolderAtPath:defaultSoundPath fileProtectionType:NSFileProtectionNone];
+
+    if (!success) {
+        OWSProdLogAndFail(
+            @"%@ Unable to write new default sound data from: %@ to :%@", self.logTag, soundURL, defaultSoundPath);
+        return;
+    }
+
     OWSSounds *instance = OWSSounds.sharedManager;
     [instance.dbConnection setObject:@(sound)
                               forKey:kOWSSoundsStorageGlobalNotificationKey

SignalServiceKit/src/Util/OWSFileSystem.h

@@ -9,10 +9,14 @@ NS_ASSUME_NONNULL_BEGIN
 - (instancetype)init NS_UNAVAILABLE;
 
 + (BOOL)protectFileOrFolderAtPath:(NSString *)path;
++ (BOOL)protectFileOrFolderAtPath:(NSString *)path fileProtectionType:(NSFileProtectionType)fileProtectionType;
+
 + (BOOL)protectRecursiveContentsAtPath:(NSString *)path;
 
 + (NSString *)appDocumentDirectoryPath;
 
++ (NSString *)appLibraryDirectoryPath;
+
 + (NSString *)appSharedDataDirectoryPath;
 
 + (NSString *)cachesDirectoryPath;

SignalServiceKit/src/Util/OWSFileSystem.m

@@ -37,6 +37,12 @@ NS_ASSUME_NONNULL_BEGIN
 }
 
 + (BOOL)protectFileOrFolderAtPath:(NSString *)path
+{
+    return
+        [self protectFileOrFolderAtPath:path fileProtectionType:NSFileProtectionCompleteUntilFirstUserAuthentication];
+}
+
++ (BOOL)protectFileOrFolderAtPath:(NSString *)path fileProtectionType:(NSFileProtectionType)fileProtectionType
 {
     DDLogVerbose(@"%@ protecting file at path: %@", self.logTag, path);
     if (![NSFileManager.defaultManager fileExistsAtPath:path]) {
@@ -44,7 +50,7 @@ NS_ASSUME_NONNULL_BEGIN
     }
 
     NSError *error;
-    NSDictionary *fileProtection = @{ NSFileProtectionKey : NSFileProtectionCompleteUntilFirstUserAuthentication };
+    NSDictionary *fileProtection = @{ NSFileProtectionKey : fileProtectionType };
     [[NSFileManager defaultManager] setAttributes:fileProtection ofItemAtPath:path error:&error];
 
     NSDictionary *resourcesAttrs = @{ NSURLIsExcludedFromBackupKey : @YES };
@@ -86,6 +92,14 @@ NS_ASSUME_NONNULL_BEGIN
     }
 }
 
++ (NSString *)appLibraryDirectoryPath
+{
+    NSFileManager *fileManager = [NSFileManager defaultManager];
+    NSURL *documentDirectoryURL =
+        [[fileManager URLsForDirectory:NSLibraryDirectory inDomains:NSUserDomainMask] lastObject];
+    return [documentDirectoryURL path];
+}
+
 + (NSString *)appDocumentDirectoryPath
 {
     NSFileManager *fileManager = [NSFileManager defaultManager];