Revisit the [UIScrollView _adjustContentOffsetIfNecessary] issue. Fix glitches in the initial scroll state in message view. Don't reset scroll state when returning to the message view.

// FREEBIE

Podfile

@@ -5,8 +5,8 @@ target 'Signal' do
     pod 'ATAppUpdater'
     pod 'AxolotlKit',                 git: 'https://github.com/WhisperSystems/SignalProtocolKit.git'
     #pod 'AxolotlKit',                 path: '../SignalProtocolKit'
-    pod 'JSQMessagesViewController',  git: 'https://github.com/WhisperSystems/JSQMessagesViewController.git', branch: 'signal-master'
+    #pod 'JSQMessagesViewController',  git: 'https://github.com/WhisperSystems/JSQMessagesViewController.git', branch: 'signal-master'
-    #pod 'JSQMessagesViewController',   path: '../JSQMessagesViewController'
+    pod 'JSQMessagesViewController',   path: '../JSQMessagesViewController'
     pod 'PureLayout'
     pod 'OpenSSL',                    git: 'https://github.com/WhisperSystems/OpenSSL-Pod'
     pod 'Reachability'

Podfile.lock

@@ -43,7 +43,7 @@ PODS:
   - Reachability (3.2)
   - SAMKeychain (1.5.2)
   - SignalServiceKit (0.9.0):
-    - '25519'
+    - 25519
     - AFNetworking
     - AxolotlKit
     - CocoaLumberjack
@@ -114,7 +114,7 @@ PODS:
 DEPENDENCIES:
   - ATAppUpdater
   - AxolotlKit (from `https://github.com/WhisperSystems/SignalProtocolKit.git`)
-  - JSQMessagesViewController (from `https://github.com/WhisperSystems/JSQMessagesViewController.git`, branch `signal-master`)
+  - JSQMessagesViewController (from `../JSQMessagesViewController`)
   - OpenSSL (from `https://github.com/WhisperSystems/OpenSSL-Pod`)
   - PureLayout
   - Reachability
@@ -125,8 +125,7 @@ EXTERNAL SOURCES:
   AxolotlKit:
     :git: https://github.com/WhisperSystems/SignalProtocolKit.git
   JSQMessagesViewController:
-    :branch: signal-master
+    :path: ../JSQMessagesViewController
-    :git: https://github.com/WhisperSystems/JSQMessagesViewController.git
   OpenSSL:
     :git: https://github.com/WhisperSystems/OpenSSL-Pod
   SignalServiceKit:
@@ -138,9 +137,6 @@ CHECKOUT OPTIONS:
   AxolotlKit:
     :commit: 6e9d5e8c3dc87e397b4b7485172507b0990a22dd
     :git: https://github.com/WhisperSystems/SignalProtocolKit.git
-  JSQMessagesViewController:
-    :commit: 9e452ee59cbcebf2c67f0dc499988b6725de776e
-    :git: https://github.com/WhisperSystems/JSQMessagesViewController.git
   OpenSSL:
     :commit: b2d3c149102032a09aefbfb470885db4aa83efad
     :git: https://github.com/WhisperSystems/OpenSSL-Pod
@@ -149,7 +145,7 @@ CHECKOUT OPTIONS:
     :git: https://github.com/facebook/SocketRocket.git
 
 SPEC CHECKSUMS:
-  '25519': dc4bad7e2dbcbf1efa121068a705a44cd98c80fc
+  25519: dc4bad7e2dbcbf1efa121068a705a44cd98c80fc
   AFNetworking: 5e0e199f73d8626b11e79750991f5d173d1f8b67
   ATAppUpdater: a9f7027060959d47e58733d3b48f6b9a28cb8de1
   AxolotlKit: ba0ab24b879d34559a68e1270b079cc9bd7b3417
@@ -171,6 +167,6 @@ SPEC CHECKSUMS:
   UnionFind: c33be5adb12983981d6e827ea94fc7f9e370f52d
   YapDatabase: cd911121580ff16675f65ad742a9eb0ab4d9e266
 
-PODFILE CHECKSUM: 2f847bb25e70d1d376f38cf21ae08624fa6ed67d
+PODFILE CHECKSUM: 4a6db311736b5ab36b660af813dcdf0af62da48c
 
-COCOAPODS: 1.2.1
+COCOAPODS: 1.3.1

Signal.xcodeproj/project.pbxproj

@@ -2052,7 +2052,7 @@
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 			shellPath = /bin/sh;
-			shellScript = "diff \"${PODS_PODFILE_DIR_PATH}/Podfile.lock\" \"${PODS_ROOT}/Manifest.lock\" > /dev/null\nif [ $? != 0 ] ; then\n    # print error to STDERR\n    echo \"error: The sandbox is not in sync with the Podfile.lock. Run 'pod install' or update your CocoaPods installation.\" >&2\n    exit 1\nfi\n";
+			shellScript = "diff \"${PODS_PODFILE_DIR_PATH}/Podfile.lock\" \"${PODS_ROOT}/Manifest.lock\" > /dev/null\nif [ $? != 0 ] ; then\n    # print error to STDERR\n    echo \"error: The sandbox is not in sync with the Podfile.lock. Run 'pod install' or update your CocoaPods installation.\" >&2\n    exit 1\nfi\n# This output is used by Xcode 'outputs' to avoid re-running this script phase.\necho \"SUCCESS\" > \"${SCRIPT_OUTPUT_FILE_0}\"\n";
 			showEnvVarsInLog = 0;
 		};
 		3465F381B1856CC06933B3A8 /* [CP] Copy Pods Resources */ = {
@@ -2062,13 +2062,13 @@
 			);
 			inputPaths = (
 				"${SRCROOT}/Pods/Target Support Files/Pods-Signal/Pods-Signal-resources.sh",
-				"${PODS_ROOT}/JSQMessagesViewController/JSQMessagesViewController/Assets/JSQMessagesAssets.bundle",
+				"${PODS_ROOT}/../../JSQMessagesViewController/JSQMessagesViewController/Assets/JSQMessagesAssets.bundle",
-				"${PODS_ROOT}/JSQMessagesViewController/JSQMessagesViewController/Controllers/JSQMessagesViewController.xib",
+				"${PODS_ROOT}/../../JSQMessagesViewController/JSQMessagesViewController/Controllers/JSQMessagesViewController.xib",
-				"${PODS_ROOT}/JSQMessagesViewController/JSQMessagesViewController/Views/JSQMessagesCollectionViewCellIncoming.xib",
+				"${PODS_ROOT}/../../JSQMessagesViewController/JSQMessagesViewController/Views/JSQMessagesCollectionViewCellIncoming.xib",
-				"${PODS_ROOT}/JSQMessagesViewController/JSQMessagesViewController/Views/JSQMessagesCollectionViewCellOutgoing.xib",
+				"${PODS_ROOT}/../../JSQMessagesViewController/JSQMessagesViewController/Views/JSQMessagesCollectionViewCellOutgoing.xib",
-				"${PODS_ROOT}/JSQMessagesViewController/JSQMessagesViewController/Views/JSQMessagesLoadEarlierHeaderView.xib",
+				"${PODS_ROOT}/../../JSQMessagesViewController/JSQMessagesViewController/Views/JSQMessagesLoadEarlierHeaderView.xib",
-				"${PODS_ROOT}/JSQMessagesViewController/JSQMessagesViewController/Views/JSQMessagesToolbarContentView.xib",
+				"${PODS_ROOT}/../../JSQMessagesViewController/JSQMessagesViewController/Views/JSQMessagesToolbarContentView.xib",
-				"${PODS_ROOT}/JSQMessagesViewController/JSQMessagesViewController/Views/JSQMessagesTypingIndicatorFooterView.xib",
+				"${PODS_ROOT}/../../JSQMessagesViewController/JSQMessagesViewController/Views/JSQMessagesTypingIndicatorFooterView.xib",
 				"${PODS_ROOT}/SAMKeychain/Support/SAMKeychain.bundle",
 				"${PODS_ROOT}/../SignalServiceKit/src/Security/PinningCertificate/textsecure.cer",
 				"${PODS_ROOT}/../SignalServiceKit/src/Security/PinningCertificate/GIAG2.crt",
@@ -2160,7 +2160,7 @@
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 			shellPath = /bin/sh;
-			shellScript = "diff \"${PODS_PODFILE_DIR_PATH}/Podfile.lock\" \"${PODS_ROOT}/Manifest.lock\" > /dev/null\nif [ $? != 0 ] ; then\n    # print error to STDERR\n    echo \"error: The sandbox is not in sync with the Podfile.lock. Run 'pod install' or update your CocoaPods installation.\" >&2\n    exit 1\nfi\n";
+			shellScript = "diff \"${PODS_PODFILE_DIR_PATH}/Podfile.lock\" \"${PODS_ROOT}/Manifest.lock\" > /dev/null\nif [ $? != 0 ] ; then\n    # print error to STDERR\n    echo \"error: The sandbox is not in sync with the Podfile.lock. Run 'pod install' or update your CocoaPods installation.\" >&2\n    exit 1\nfi\n# This output is used by Xcode 'outputs' to avoid re-running this script phase.\necho \"SUCCESS\" > \"${SCRIPT_OUTPUT_FILE_0}\"\n";
 			showEnvVarsInLog = 0;
 		};
 		B4E9B04E862FB64FC9A8F79B /* [CP] Embed Pods Frameworks */ = {
@@ -2580,11 +2580,7 @@
 					"DEBUG=1",
 					"$(inherited)",
 				);
-				"GCC_PREPROCESSOR_DEFINITIONS[arch=*]" = (
+				"GCC_PREPROCESSOR_DEFINITIONS[arch=*]" = "DEBUG=1 $(inherited) SSK_BUILDING_FOR_TESTS=1";
-					"DEBUG=1",
-					"$(inherited)",
-					"SSK_BUILDING_FOR_TESTS=1",
-				);
 				GCC_TREAT_IMPLICIT_FUNCTION_DECLARATIONS_AS_ERRORS = YES;
 				GCC_TREAT_INCOMPATIBLE_POINTER_TYPE_WARNINGS_AS_ERRORS = YES;
 				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;

Signal/src/ViewControllers/ConversationView/MessagesViewController.m

@@ -243,6 +243,7 @@ typedef NS_ENUM(NSInteger, MessagesRangeSizeMode) {
 @property (nonatomic) BOOL isViewVisible;
 @property (nonatomic) BOOL isAppInBackground;
 @property (nonatomic) BOOL shouldObserveDBModifications;
+@property (nonatomic) BOOL viewHasEverAppeared;
 
 @end
 
@@ -639,7 +640,10 @@ typedef NS_ENUM(NSInteger, MessagesRangeSizeMode) {
     [((OWSMessagesToolbarContentView *)self.inputToolbar.contentView)ensureSubviews];
 
     [self.view layoutSubviews];
-    [self scrollToDefaultPosition];
+
+    if (!self.viewHasEverAppeared) {
+        [self scrollToDefaultPosition];
+    }
 }
 
 - (NSIndexPath *_Nullable)indexPathOfUnreadMessagesIndicator
@@ -1059,6 +1063,8 @@ typedef NS_ENUM(NSInteger, MessagesRangeSizeMode) {
     [ProfileFetcherJob runWithThread:self.thread networkManager:self.networkManager];
 
     [self markVisibleMessagesAsRead];
+
+    self.viewHasEverAppeared = YES;
 }
 
 - (void)viewWillDisappear:(BOOL)animated
@@ -3506,6 +3512,12 @@ typedef NS_ENUM(NSInteger, MessagesRangeSizeMode) {
 
 - (BOOL)isScrolledToBottom
 {
+    if (self.collectionView.contentSize.height < 1) {
+        // If the collection view hasn't determined its content size yet,
+        // scroll state is not yet coherent.
+        return NO;
+    }
+
     const CGFloat kIsAtBottomTolerancePts = 5;
     return (self.collectionView.contentOffset.y + self.collectionView.bounds.size.height + kIsAtBottomTolerancePts
         >= self.collectionView.contentSize.height);
@@ -4149,6 +4161,7 @@ typedef NS_ENUM(NSInteger, MessagesRangeSizeMode) {
 
 - (void)scrollToBottomAnimated:(BOOL)animated
 {
+    OWSAssert([NSThread isMainThread]);
 
     if (self.isUserScrolling) {
         return;