Improve handling of incomplete and failed attachment downloads.

// FREEBIE

src/Messages/Attachments/OWSAttachmentsProcessor.m

@@ -331,7 +331,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (void)setAttachment:(TSAttachmentPointer *)pointer isDownloadingInMessage:(nullable TSMessage *)message
 {
-    pointer.downloading = YES;
+    pointer.state = TSAttachmentPointerStateDownloading;
     [pointer save];
     if (message) {
         [message touch];
@@ -340,8 +340,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (void)setAttachment:(TSAttachmentPointer *)pointer didFailInMessage:(nullable TSMessage *)message
 {
-    pointer.downloading = NO;
-    pointer.failed = YES;
+    pointer.state = TSAttachmentPointerStateFailed;
     [pointer save];
     if (message) {
         [message touch];

src/Messages/Attachments/TSAttachment.h

@@ -39,6 +39,8 @@ NS_ASSUME_NONNULL_BEGIN
 // that represent downloaded incoming attachments.
 - (instancetype)initWithPointer:(TSAttachment *)pointer;
 
+- (nullable instancetype)initWithCoder:(NSCoder *)coder;
+
 - (void)upgradeFromAttachmentSchemaVersion:(NSUInteger)attachmentSchemaVersion;
 
 @end

src/Messages/Attachments/TSAttachmentPointer.h

@@ -6,6 +6,12 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
+typedef NS_ENUM(NSUInteger, TSAttachmentPointerState) {
+    TSAttachmentPointerStateEnqueued = 0,
+    TSAttachmentPointerStateDownloading = 1,
+    TSAttachmentPointerStateFailed = 2,
+};
+
 /**
  * A TSAttachmentPointer is a yet-to-be-downloaded attachment.
  */
@@ -18,8 +24,7 @@ NS_ASSUME_NONNULL_BEGIN
                            relay:(NSString *)relay NS_DESIGNATED_INITIALIZER;
 
 @property (nonatomic, readonly) NSString *relay;
-@property (atomic, readwrite, getter=isDownloading) BOOL downloading;
-@property (atomic, readwrite, getter=hasFailed) BOOL failed;
+@property (atomic) TSAttachmentPointerState state;
 
 // Though now required, `digest` may be null for pre-existing records or from
 // messages received from other clients

src/Messages/Attachments/TSAttachmentPointer.m

@@ -8,6 +8,23 @@ NS_ASSUME_NONNULL_BEGIN
 
 @implementation TSAttachmentPointer
 
+- (nullable instancetype)initWithCoder:(NSCoder *)coder
+{
+    self = [super initWithCoder:coder];
+    if (!self) {
+        return self;
+    }
+
+    // A TSAttachmentPointer is a yet-to-be-downloaded attachment.
+    // If this is an old TSAttachmentPointer from another session,
+    // we know that it failed to complete before the session completed.
+    if (![coder containsValueForKey:@"state"]) {
+        _state = TSAttachmentPointerStateFailed;
+    }
+
+    return self;
+}
+
 - (instancetype)initWithServerId:(UInt64)serverId
                              key:(NSData *)key
                           digest:(nullable NSData *)digest
@@ -20,8 +37,7 @@ NS_ASSUME_NONNULL_BEGIN
     }
 
     _digest = digest;
-    _failed = NO;
-    _downloading = NO;
+    _state = TSAttachmentPointerStateEnqueued;
     _relay = relay;
 
     return self;

src/Messages/OWSFailedMessagesJob.m

@@ -21,6 +21,8 @@ static NSString *const OWSFailedMessagesJobMessageStateIndex = @"index_outoing_m
 
 @end
 
+#pragma mark -
+
 @implementation OWSFailedMessagesJob
 
 - (instancetype)initWithStorageManager:(TSStorageManager *)storageManager