From 9c806d59df0b39e5059cda21c7553865298fb9b8 Mon Sep 17 00:00:00 2001
From: Matthew Chen <matthew@signal.org>
Date: Fri, 25 Jan 2019 15:33:32 -0500
Subject: [PATCH] Safely ignore invalid link preview images.

---
 .../ConversationView/ConversationViewItem.m       | 15 +++++++++++++--
 Signal/src/views/LinkPreviewView.swift            |  6 ++++--
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/Signal/src/ViewControllers/ConversationView/ConversationViewItem.m b/Signal/src/ViewControllers/ConversationView/ConversationViewItem.m
index 539788ee5..fa13720a0 100644
--- a/Signal/src/ViewControllers/ConversationView/ConversationViewItem.m
+++ b/Signal/src/ViewControllers/ConversationView/ConversationViewItem.m
@@ -669,10 +669,21 @@ NSString *NSStringForOWSMessageCellType(OWSMessageCellType cellType)
     if (self.hasBodyText && attachment == nil && message.linkPreview) {
         self.linkPreview = message.linkPreview;
         if (message.linkPreview.imageAttachmentId.length > 0) {
-            self.linkPreviewAttachment =
+            TSAttachment *_Nullable linkPreviewAttachment =
                 [TSAttachment fetchObjectWithUniqueID:message.linkPreview.imageAttachmentId transaction:transaction];
-            if (!self.linkPreviewAttachment) {
+            if (!linkPreviewAttachment) {
                 OWSFailDebug(@"Could not load link preview image attachment.");
+            } else if (!linkPreviewAttachment.isImage) {
+                OWSFailDebug(@"Link preview attachment isn't an image.");
+            } else if ([linkPreviewAttachment isKindOfClass:[TSAttachmentStream class]]) {
+                TSAttachmentStream *attachmentStream = (TSAttachmentStream *)linkPreviewAttachment;
+                if (!attachmentStream.isValidImage) {
+                    OWSFailDebug(@"Link preview image attachment isn't valid.");
+                } else {
+                    self.linkPreviewAttachment = linkPreviewAttachment;
+                }
+            } else {
+                self.linkPreviewAttachment = linkPreviewAttachment;
             }
         }
     }
diff --git a/Signal/src/views/LinkPreviewView.swift b/Signal/src/views/LinkPreviewView.swift
index f5395683c..2f1448ca0 100644
--- a/Signal/src/views/LinkPreviewView.swift
+++ b/Signal/src/views/LinkPreviewView.swift
@@ -188,7 +188,8 @@ public class LinkPreviewSent: NSObject, LinkPreviewState {
         guard let attachmentStream = imageAttachment as? TSAttachmentStream else {
             return .loading
         }
-        guard attachmentStream.isValidImage else {
+        guard attachmentStream.isImage,
+            attachmentStream.isValidImage else {
             return .invalid
         }
         return .loaded
@@ -201,7 +202,8 @@ public class LinkPreviewSent: NSObject, LinkPreviewState {
             owsFailDebug("Could not load image.")
             return nil
         }
-        guard attachmentStream.isValidImage else {
+        guard attachmentStream.isImage,
+            attachmentStream.isValidImage else {
             return nil
         }
         guard let imageFilepath = attachmentStream.originalFilePath else {