b/68276665: Raise isFromCache=true events when offline (#567)

* Plumbs FSTOnlineState changes through to views.
* View sets this.current to false on FSTOnlineStateFailed, triggering
	isFromCache=true events. It will automatically be returned to true
	once the listen is reestablished and we get a new CURRENT message.
* Updated tests (and added one new one) to verify behavior.
* Unifies setOnlineStateToUnknown, setOnlineStateToHealthy, and
	updateAndBroadcastOnlineState into a single updateOnlineState
	method.
* Split disableNetwork into (public) disableNetwork and
	(private) disableNetworkWithTargetOnlineState methods..
* Some miscellaneous comment cleanup.

* Add missing comment per CR feedback.

5 files changed, 187 insertions, 4 deletions

diff --git a/Firestore/Example/Tests/SpecTests/FSTSpecTests.m b/Firestore/Example/Tests/SpecTests/FSTSpecTests.m
index 2c1b8db..0bd7b43 100644
--- a/Firestore/Example/Tests/SpecTests/FSTSpecTests.m
+++ b/Firestore/Example/Tests/SpecTests/FSTSpecTests.m
@@ -156,7 +156,7 @@ static NSString *const kNoIOSTag = @"no-ios";
   FSTTargetID actualID = [self.driver addUserListenerWithQuery:query];
 
   FSTTargetID expectedID = [listenSpec[0] intValue];
-  XCTAssertEqual(actualID, expectedID);
+  XCTAssertEqual(actualID, expectedID, @"targetID assigned to listen");
 }
 
 - (void)doUnlisten:(NSArray *)unlistenSpec {
diff --git a/Firestore/Example/Tests/SpecTests/FSTSyncEngineTestDriver.h b/Firestore/Example/Tests/SpecTests/FSTSyncEngineTestDriver.h
index 3d031bd..7cb2726 100644
--- a/Firestore/Example/Tests/SpecTests/FSTSyncEngineTestDriver.h
+++ b/Firestore/Example/Tests/SpecTests/FSTSyncEngineTestDriver.h
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#import <Firestore/Source/Remote/FSTRemoteStore.h>
 #import <Foundation/Foundation.h>
 
 #import "Firestore/Source/Core/FSTTypes.h"
@@ -76,7 +77,7 @@ typedef NSDictionary<FSTUser *, NSArray<FSTOutstandingWrite *> *> FSTOutstanding
  *
  * Each method on the driver injects a different event into the system.
  */
-@interface FSTSyncEngineTestDriver : NSObject
+@interface FSTSyncEngineTestDriver : NSObject <FSTOnlineStateDelegate>
 
 /**
  * Initializes the underlying FSTSyncEngine with the given local persistence implementation and
diff --git a/Firestore/Example/Tests/SpecTests/FSTSyncEngineTestDriver.m b/Firestore/Example/Tests/SpecTests/FSTSyncEngineTestDriver.m
index 896a292..d618aee 100644
--- a/Firestore/Example/Tests/SpecTests/FSTSyncEngineTestDriver.m
+++ b/Firestore/Example/Tests/SpecTests/FSTSyncEngineTestDriver.m
@@ -119,7 +119,7 @@ NS_ASSUME_NONNULL_BEGIN
     _remoteStore.syncEngine = _syncEngine;
     _eventManager = [FSTEventManager eventManagerWithSyncEngine:_syncEngine];
 
-    _remoteStore.onlineStateDelegate = _eventManager;
+    _remoteStore.onlineStateDelegate = self;
 
     // Set up internal event tracking for the spec tests.
     NSMutableArray<FSTQueryEvent *> *events = [NSMutableArray array];
@@ -139,6 +139,11 @@ NS_ASSUME_NONNULL_BEGIN
   return self;
 }
 
+- (void)watchStreamDidChangeOnlineState:(FSTOnlineState)onlineState {
+  [self.syncEngine applyOnlineStateChange:onlineState];
+  [self.eventManager watchStreamDidChangeOnlineState:onlineState];
+}
+
 - (void)start {
   [self.localStore start];
   [self.remoteStore start];
diff --git a/Firestore/Example/Tests/SpecTests/json/listen_spec_test.json b/Firestore/Example/Tests/SpecTests/json/listen_spec_test.json
index e607710..7bfe557 100644
--- a/Firestore/Example/Tests/SpecTests/json/listen_spec_test.json
+++ b/Firestore/Example/Tests/SpecTests/json/listen_spec_test.json
@@ -1608,7 +1608,19 @@
         "stateExpect": {
           "activeTargets": {},
           "limboDocs": []
-        }
+        },
+        "expect": [
+          {
+            "query": {
+              "path": "collection",
+              "filters": [],
+              "orderBys": []
+            },
+            "errorCode": 0,
+            "fromCache": true,
+            "hasPendingWrites": false
+          }
+        ]
       },
       {
         "enableNetwork": true,
diff --git a/Firestore/Example/Tests/SpecTests/json/offline_spec_test.json b/Firestore/Example/Tests/SpecTests/json/offline_spec_test.json
index f542a6e..3981cec 100644
--- a/Firestore/Example/Tests/SpecTests/json/offline_spec_test.json
+++ b/Firestore/Example/Tests/SpecTests/json/offline_spec_test.json
@@ -294,5 +294,170 @@
         ]
       }
     ]
+  },
+  "Queries revert to fromCache=true when offline.": {
+    "describeName": "Offline:",
+    "itName": "Queries revert to fromCache=true when offline.",
+    "tags": [],
+    "config": {
+      "useGarbageCollection": true
+    },
+    "steps": [
+      {
+        "userListen": [
+          2,
+          {
+            "path": "collection",
+            "filters": [],
+            "orderBys": []
+          }
+        ],
+        "stateExpect": {
+          "activeTargets": {
+            "2": {
+              "query": {
+                "path": "collection",
+                "filters": [],
+                "orderBys": []
+              },
+              "resumeToken": ""
+            }
+          }
+        }
+      },
+      {
+        "watchAck": [
+          2
+        ]
+      },
+      {
+        "watchEntity": {
+          "docs": [
+            [
+              "collection/a",
+              1000,
+              {
+                "key": "a"
+              }
+            ]
+          ],
+          "targets": [
+            2
+          ]
+        }
+      },
+      {
+        "watchCurrent": [
+          [
+            2
+          ],
+          "resume-token-1000"
+        ],
+        "watchSnapshot": 1000,
+        "expect": [
+          {
+            "query": {
+              "path": "collection",
+              "filters": [],
+              "orderBys": []
+            },
+            "added": [
+              [
+                "collection/a",
+                1000,
+                {
+                  "key": "a"
+                }
+              ]
+            ],
+            "errorCode": 0,
+            "fromCache": false,
+            "hasPendingWrites": false
+          }
+        ]
+      },
+      {
+        "watchStreamClose": {
+          "error": {
+            "code": 14,
+            "message": "Simulated Backend Error"
+          }
+        },
+        "stateExpect": {
+          "activeTargets": {
+            "2": {
+              "query": {
+                "path": "collection",
+                "filters": [],
+                "orderBys": []
+              },
+              "resumeToken": "resume-token-1000"
+            }
+          }
+        }
+      },
+      {
+        "watchStreamClose": {
+          "error": {
+            "code": 14,
+            "message": "Simulated Backend Error"
+          }
+        }
+      },
+      {
+        "watchStreamClose": {
+          "error": {
+            "code": 14,
+            "message": "Simulated Backend Error"
+          }
+        },
+        "expect": [
+          {
+            "query": {
+              "path": "collection",
+              "filters": [],
+              "orderBys": []
+            },
+            "errorCode": 0,
+            "fromCache": true,
+            "hasPendingWrites": false
+          }
+        ]
+      },
+      {
+        "watchAck": [
+          2
+        ]
+      },
+      {
+        "watchEntity": {
+          "docs": [],
+          "targets": [
+            2
+          ]
+        }
+      },
+      {
+        "watchCurrent": [
+          [
+            2
+          ],
+          "resume-token-1000"
+        ],
+        "watchSnapshot": 1000,
+        "expect": [
+          {
+            "query": {
+              "path": "collection",
+              "filters": [],
+              "orderBys": []
+            },
+            "errorCode": 0,
+            "fromCache": false,
+            "hasPendingWrites": false
+          }
+        ]
+      }
+    ]
   }
 }