Add 10 second timeout waiting for connection before client behaves as-if offline. (#872)

[Port of https://github.com/firebase/firebase-js-sdk/commit/0fa319e5e019dd0d40ab441d2ff9f8f6d4724e43]

* Refactored FSTOnlineState tracking out of FSTRemoteStore and into new
  FSTOnlineStateTracker component.
* Added a 10 second timeout to transition from OnlineState.Unknown to
  OnlineState.Offline rather than waiting indefinitely for the stream to
  succeed or fail.
* Removed hack to run SpecTests using an FSTDispatchQueue that wrapped
  dispatch_get_main_queue(). This was incompatible with [FSTDispatchQueue
  runDelayedCallbacksUntil:] since it queues work and blocks waiting for
  it to complete. Now spec tests create / use a proper FSTDispatchQueue.
* Added a SpecTest to verify OnlineState timeout behavior.
* Misc cleanup:
    * Renamed FSTOnlineState states: Failed => Offline, Healthy => Online
    * Renamed FSTTimerIds (ListenStreamConnection => ListenStreamConnectionBackoff)
    * Added ability to run timers from spec tests.

2 files changed, 27 insertions, 3 deletions

diff --git a/Firestore/Source/Util/FSTDispatchQueue.h b/Firestore/Source/Util/FSTDispatchQueue.h
index 9b28c9c..7922600 100644
--- a/Firestore/Source/Util/FSTDispatchQueue.h
+++ b/Firestore/Source/Util/FSTDispatchQueue.h
@@ -23,11 +23,24 @@ NS_ASSUME_NONNULL_BEGIN
  * can then be used from tests to check for the presence of callbacks or to run them early.
  */
 typedef NS_ENUM(NSInteger, FSTTimerID) {
-  FSTTimerIDAll,  // Sentinel value to be used with runDelayedCallbacksUntil: to run all blocks.
+  /** All can be used with runDelayedCallbacksUntil: to run all timers. */
+  FSTTimerIDAll,
+
+  /**
+   * The following 4 timers are used in FSTStream for the listen and write streams. The "Idle" timer
+   * is used to close the stream due to inactivity. The "ConnectionBackoff" timer is used to
+   * restart a stream once the appropriate backoff delay has elapsed.
+   */
   FSTTimerIDListenStreamIdle,
-  FSTTimerIDListenStreamConnection,
+  FSTTimerIDListenStreamConnectionBackoff,
   FSTTimerIDWriteStreamIdle,
-  FSTTimerIDWriteStreamConnection
+  FSTTimerIDWriteStreamConnectionBackoff,
+
+  /**
+   * A timer used in FSTOnlineStateTracker to transition from FSTOnlineState Unknown to Offline
+   * after a set timeout, rather than waiting indefinitely for success or failure.
+   */
+  FSTTimerIDOnlineStateTimeout
 };
 
 /**
@@ -81,6 +94,13 @@ typedef NS_ENUM(NSInteger, FSTTimerID) {
 - (void)dispatchAsyncAllowingSameQueue:(void (^)(void))block;
 
 /**
+ * Wrapper for dispatch_sync(). Mostly meant for use in tests.
+ *
+ * @param block The block to run.
+ */
+- (void)dispatchSync:(void (^)(void))block;
+
+/**
  * Schedules a callback after the specified delay.
  *
  * Unlike dispatchAsync: this method does not require you to dispatch to a different queue than
diff --git a/Firestore/Source/Util/FSTDispatchQueue.mm b/Firestore/Source/Util/FSTDispatchQueue.mm
index 5bd7f27..3184d29 100644
--- a/Firestore/Source/Util/FSTDispatchQueue.mm
+++ b/Firestore/Source/Util/FSTDispatchQueue.mm
@@ -187,6 +187,10 @@ NS_ASSUME_NONNULL_BEGIN
   dispatch_async(self.queue, block);
 }
 
+- (void)dispatchSync:(void (^)(void))block {
+  dispatch_sync(self.queue, block);
+}
+
 - (FSTDelayedCallback *)dispatchAfterDelay:(NSTimeInterval)delay
                                    timerID:(FSTTimerID)timerID
                                      block:(void (^)(void))block {