Allow the file provider to fail without crashing

If you start the file provider before opening the app for the first
time, it can't open the rootfs and won't be able to display anything.
Make it return an error in this case instead of crashing.

Fixes #978

app/FileProvider/FileProviderExtension.m

@@ -17,15 +17,13 @@
 struct task *fake_task;
 
 @interface FileProviderExtension () {
-    dispatch_once_t _mountOnce;
+    struct mount *_mount;
 };
 @property NSURL *root;
-@property (readonly) struct mount *mount;
 @property NSTimer *cleanupStorageTimer;
 @end
 
 @implementation FileProviderExtension
-@synthesize mount = _mount;
 
 - (instancetype)init {
     if (self = [super init]) {
@@ -34,25 +32,38 @@ - (instancetype)init {
     return self;
 }
 
-- (struct mount *)mount {
-    dispatch_once(&_mountOnce, ^{
-        _mount = malloc(sizeof(struct mount));
-        if (!_mount)
-            return;
-        _mount->fs = &fakefs;
-        NSURL *container = ContainerURL();
-        _root = [[[container URLByAppendingPathComponent:@"roots"]
-                  URLByAppendingPathComponent:self.domain.identifier]
-                 URLByAppendingPathComponent:@"data"];
-        _mount->source = strdup(self.root.fileSystemRepresentation);
-        int err = _mount->fs->mount(_mount);
-        if (err < 0) {
-            NSLog(@"error opening root: %d", err);
-            _mount = NULL;
-            return;
+- (BOOL)getMount:(struct mount **)mount error:(NSError **)error {
+    @synchronized (self) {
+        if (_mount == NULL) {
+            if (self.domain == nil) {
+                *error = [NSError errorWithDomain:NSFileProviderErrorDomain code:NSFileProviderErrorServerUnreachable userInfo:nil];
+                return NO;
+            }
+            _mount = malloc(sizeof(struct mount));
+            if (_mount == NULL) {
+                *error = [NSError errorWithDomain:NSPOSIXErrorDomain code:ENOMEM userInfo:nil];
+                return NO;
+            }
+            _mount->fs = &fakefs;
+            NSURL *container = ContainerURL();
+            _root = [[[container URLByAppendingPathComponent:@"roots"]
+                      URLByAppendingPathComponent:self.domain.identifier]
+                     URLByAppendingPathComponent:@"data"];
+            _mount->source = strdup(self.root.fileSystemRepresentation);
+            int err = _mount->fs->mount(_mount);
+            if (err < 0) {
+                NSLog(@"error opening root: %d", err);
+                *error = [NSError errorWithISHErrno:err itemIdentifier:NSFileProviderRootContainerItemIdentifier];
+                free((void *) _mount->source);
+                free(_mount);
+                _mount = NULL;
+                return NO;
+            }
         }
-    });
-    return _mount;
+        NSAssert(_mount != NULL, @"mount initialization should have succeeded");
+        *mount = _mount;
+        return YES;
+    }
 }
 
 - (NSURL *)storageURL {
@@ -63,9 +74,11 @@ - (NSURL *)storageURL {
 }
 
 - (nullable NSFileProviderItem)itemForIdentifier:(NSFileProviderItemIdentifier)identifier error:(NSError * _Nullable *)error {
+    struct mount *mount;
+    if (![self getMount:&mount error:error]) return nil;
     NSLog(@"item for id %@", identifier);
     NSError *err;
-    FileProviderItem *item = [[FileProviderItem alloc] initWithIdentifier:identifier mount:self.mount error:&err];
+    FileProviderItem *item = [[FileProviderItem alloc] initWithIdentifier:identifier mount:mount error:&err];
     if (item == nil) {
         if (error != nil)
             *error = err;
@@ -156,52 +169,53 @@ - (void)itemChangedAtURL:(NSURL *)url {
 #pragma mark - Action helpers
 
 // FIXME: not dry enough
+// It's ok to use _mount in these because in each case the caller has already invoked itemForIdentifier:error: at least once
 - (BOOL)doCreateDirectoryAt:(NSString *)path inode:(ino_t *)inode error:(NSError **)error {
-    NSURL *url = [[NSURL fileURLWithPath:[NSString stringWithUTF8String:self.mount->source]] URLByAppendingPathComponent:path];
-    db_begin(self.mount);
+    NSURL *url = [[NSURL fileURLWithPath:[NSString stringWithUTF8String:_mount->source]] URLByAppendingPathComponent:path];
+    db_begin(_mount);
     if (![NSFileManager.defaultManager createDirectoryAtURL:url
                                 withIntermediateDirectories:NO
                                                  attributes:@{NSFilePosixPermissions: @0777}
                                                       error:error]) {
-        db_rollback(self.mount);
+        db_rollback(_mount);
         return nil;
     }
     struct ish_stat stat;
     NSString *parentPath = [path substringToIndex:[path rangeOfString:@"/" options:NSBackwardsSearch].location];
-    if (!path_read_stat(self.mount, parentPath.fileSystemRepresentation, &stat, NULL)) {
-        db_rollback(self.mount);
+    if (!path_read_stat(_mount, parentPath.fileSystemRepresentation, &stat, NULL)) {
+        db_rollback(_mount);
         *error = [NSError errorWithDomain:NSFileProviderErrorDomain code:NSFileProviderErrorNoSuchItem userInfo:nil];
         return nil;
     }
     stat.mode = (stat.mode & ~S_IFMT) | S_IFDIR;
-    path_create(self.mount, path.fileSystemRepresentation, &stat);
+    path_create(_mount, path.fileSystemRepresentation, &stat);
     if (inode != NULL)
-        *inode = path_get_inode(self.mount, path.fileSystemRepresentation);
-    db_commit(self.mount);
+        *inode = path_get_inode(_mount, path.fileSystemRepresentation);
+    db_commit(_mount);
     return YES;
 }
 
 - (BOOL)doCreateFileAt:(NSString *)path importFrom:(NSURL *)importURL inode:(ino_t *)inode error:(NSError **)error {
-    NSURL *url = [[NSURL fileURLWithPath:[NSString stringWithUTF8String:self.mount->source]] URLByAppendingPathComponent:path];
-    db_begin(self.mount);
+    NSURL *url = [[NSURL fileURLWithPath:[NSString stringWithUTF8String:_mount->source]] URLByAppendingPathComponent:path];
+    db_begin(_mount);
     if (![NSFileManager.defaultManager copyItemAtURL:importURL
                                                toURL:url
                                                error:error]) {
-        db_rollback(self.mount);
+        db_rollback(_mount);
         return nil;
     }
     struct ish_stat stat;
     NSString *parentPath = [path substringToIndex:[path rangeOfString:@"/" options:NSBackwardsSearch].location];
-    if (!path_read_stat(self.mount, parentPath.fileSystemRepresentation, &stat, NULL)) {
-        db_rollback(self.mount);
+    if (!path_read_stat(_mount, parentPath.fileSystemRepresentation, &stat, NULL)) {
+        db_rollback(_mount);
         *error = [NSError errorWithDomain:NSFileProviderErrorDomain code:NSFileProviderErrorNoSuchItem userInfo:nil];
         return nil;
     }
     stat.mode = (stat.mode & ~S_IFMT & ~0111) | S_IFREG;
-    path_create(self.mount, path.fileSystemRepresentation, &stat);
+    path_create(_mount, path.fileSystemRepresentation, &stat);
     if (inode != NULL)
-        *inode = path_get_inode(self.mount, path.fileSystemRepresentation);
-    db_commit(self.mount);
+        *inode = path_get_inode(_mount, path.fileSystemRepresentation);
+    db_commit(_mount);
     return YES;
 }
 
@@ -270,7 +284,7 @@ - (void)importDocumentAtURL:(NSURL *)fileURL toParentItemIdentifier:(NSFileProvi
 }
 
 - (NSString *)pathFromURL:(NSURL *)url {
-    NSURL *root = [NSURL fileURLWithPath:[NSString stringWithUTF8String:self.mount->source]];
+    NSURL *root = [NSURL fileURLWithPath:[NSString stringWithUTF8String:_mount->source]];
     assert([url.path hasPrefix:root.path]);
     NSString *path = [url.path substringFromIndex:root.path.length];
     assert([path hasPrefix:@"/"]);
@@ -280,7 +294,7 @@ - (NSString *)pathFromURL:(NSURL *)url {
 }
 
 - (BOOL)doDelete:(NSString *)path itemIdentifier:(NSFileProviderItemIdentifier)identifier error:(NSError **)error {
-    NSURL *url = [[NSURL fileURLWithPath:[NSString stringWithUTF8String:self.mount->source]] URLByAppendingPathComponent:path];
+    NSURL *url = [[NSURL fileURLWithPath:[NSString stringWithUTF8String:_mount->source]] URLByAppendingPathComponent:path];
     NSDirectoryEnumerator<NSURL *> *enumerator = [NSFileManager.defaultManager enumeratorAtURL:url
                                                                     includingPropertiesForKeys:nil
                                                                                        options:NSDirectoryEnumerationSkipsSubdirectoryDescendants
@@ -289,9 +303,9 @@ - (BOOL)doDelete:(NSString *)path itemIdentifier:(NSFileProviderItemIdentifier)i
         if (![self doDelete:[self pathFromURL:suburl] itemIdentifier:identifier error:error])
             return NO;
     }
-    int err = fakefs.unlink(self.mount, path.fileSystemRepresentation);
+    int err = fakefs.unlink(_mount, path.fileSystemRepresentation);
     if (err < 0)
-        err = fakefs.rmdir(self.mount, path.fileSystemRepresentation);
+        err = fakefs.rmdir(_mount, path.fileSystemRepresentation);
     if (err < 0) {
         *error = [NSError errorWithISHErrno:err itemIdentifier:identifier];
         return NO;
@@ -313,7 +327,7 @@ - (void)deleteItemWithIdentifier:(NSFileProviderItemIdentifier)itemIdentifier co
 }
 
 - (BOOL)doRename:(NSString *)src to:(NSString *)dst itemIdentifier:(NSFileProviderItemIdentifier)identifier error:(NSError **)error {
-    int err = fakefs.rename(self.mount, src.fileSystemRepresentation, dst.fileSystemRepresentation);
+    int err = fakefs.rename(_mount, src.fileSystemRepresentation, dst.fileSystemRepresentation);
     if (err < 0) {
         *error = [NSError errorWithISHErrno:err itemIdentifier:identifier];
         return NO;
@@ -367,8 +381,10 @@ - (void)reparentItemWithIdentifier:(NSFileProviderItemIdentifier)itemIdentifier
 }
 
 - (void)dealloc {
-    self.mount->fs->umount(self.mount);
-    free(self.mount);
+    if (_mount) {
+        _mount->fs->umount(_mount);
+        free(_mount);
+    }
 }
 
 #pragma mark - Storage deletion
@@ -387,13 +403,22 @@ - (void)startCleanupTimer {
 }
 
 - (void)cleanupStorage {
+    struct mount *mount;
+    @synchronized (self) {
+        mount = _mount;
+    }
+    if (_mount == NULL) {
+        NSLog(@"no mount, can't cleanup storage");
+        return;
+    }
+
     NSFileManager *manager = NSFileManager.defaultManager;
     NSArray<NSURL *> *storageDirs = [manager contentsOfDirectoryAtURL:self.storageURL includingPropertiesForKeys:nil options:0 error:nil];
     for (NSURL *dir in storageDirs) {
         ino_t inode = dir.lastPathComponent.longLongValue;
         if (inode == 0)
             continue;
-        struct fd *fd = fakefs_open_inode(self.mount, inode);
+        struct fd *fd = fakefs_open_inode(_mount, inode);
         if (IS_ERR(fd)) {
             NSLog(@"removing dead inode %llu", inode);
             NSError *err;