Refactor connectivity monitor

src/objective-c/GRPCClient/GRPCCall.m

@@ -209,6 +209,8 @@ static NSString * const kBearerPrefix = @"Bearer ";
   } else {
     [_responseWriteable enqueueSuccessfulCompletion];
   }
+
+  [GRPCConnectivityMonitor unregisterObserver:self];
 }
 
 - (void)cancelCall {
@@ -473,16 +475,8 @@ static NSString * const kBearerPrefix = @"Bearer ";
     // TODO(jcanizales): Check this on init.
     [NSException raise:NSInvalidArgumentException format:@"host of %@ is nil", _host];
   }
-  _connectivityMonitor = [GRPCConnectivityMonitor monitorWithHost:host];
+  [GRPCConnectivityMonitor registerObserver:self
-  __weak typeof(self) weakSelf = self;
+                                   selector:@selector(connectivityChanged:)];
-  void (^handler)(void) = ^{
-    typeof(self) strongSelf = weakSelf;
-    [strongSelf finishWithError:[NSError errorWithDomain:kGRPCErrorDomain
-                                                    code:GRPCErrorCodeUnavailable
-                                                userInfo:@{ NSLocalizedDescriptionKey : @"Connectivity lost." }]];
-  };
-  [_connectivityMonitor handleLossWithHandler:handler
-                      wifiStatusChangeHandler:nil];
 }
 
 - (void)startWithWriteable:(id<GRXWriteable>)writeable {
@@ -546,4 +540,12 @@ static NSString * const kBearerPrefix = @"Bearer ";
   }
 }
 
+- (void)connectivityChanged:(NSNotification *)note {
+  [self maybeFinishWithError:[NSError errorWithDomain:kGRPCErrorDomain
+                                                 code:GRPCErrorCodeUnavailable
+                                             userInfo:@{ NSLocalizedDescriptionKey : @"Connectivity lost." }]];
+  // Cancel underlying call upon this notification
+  [self cancelCall];
+}
+
 @end

src/objective-c/GRPCClient/private/GRPCConnectivityMonitor.h

@@ -19,44 +19,30 @@
 #import <Foundation/Foundation.h>
 #import <SystemConfiguration/SystemConfiguration.h>
 
-@interface GRPCReachabilityFlags : NSObject
+typedef NS_ENUM(NSInteger, GRPCConnectivityStatus) {
-
+  GRPCConnectivityUnknown = 0,
-+ (nonnull instancetype)flagsWithFlags:(SCNetworkReachabilityFlags)flags;
+  GRPCConnectivityNoNetwork = 1,
-
+  GRPCConnectivityCellular = 2,
-/**
+  GRPCConnectivityWiFi = 3,
- * One accessor method to query each of the different flags. Example:
+};
-
+
-@property(nonatomic, readonly) BOOL isCell;
+extern NSString * _Nonnull kGRPCConnectivityNotification;
-
+
- */
+// This interface monitors OS reachability interface for any network status
-#define GRPC_XMACRO_ITEM(methodName, FlagName) \
+// change. Parties interested in these events should register themselves as
-@property(nonatomic, readonly) BOOL methodName;
+// observer.
-
-#include "GRPCReachabilityFlagNames.xmacro.h"
-#undef GRPC_XMACRO_ITEM
-
-@property(nonatomic, readonly) BOOL isHostReachable;
-@end
-
 @interface GRPCConnectivityMonitor : NSObject
 
-+ (nullable instancetype)monitorWithHost:(nonnull NSString *)hostName;
-
 - (nonnull instancetype)init NS_UNAVAILABLE;
 
-/**
+// Register an object as observer of network status change. \a observer
- * Queue on which callbacks will be dispatched. Default is the main queue. Set it before calling
+// must have a notification method with one parameter of type
- * handleLossWithHandler:.
+// (NSNotification *) and should pass it to parameter \a selector. The
- */
+// parameter of this notification method is not used for now.
-// TODO(jcanizales): Default to a serial background queue instead.
++ (void)registerObserver:(_Nonnull id)observer
-@property(nonatomic, strong, null_resettable) dispatch_queue_t queue;
+                selector:(_Nonnull SEL)selector;
-
+
-/**
+// Ungegister an object from observers of network status change.
- * Calls handler every time the connectivity to this instance's host is lost. If this instance is
++ (void)unregisterObserver:(_Nonnull id)observer;
- * released before that happens, the handler won't be called.
+
- * Only one handler is active at a time, so if this method is called again before the previous
- * handler has been called, it might never be called at all (or yes, if it has already been queued).
- */
-- (void)handleLossWithHandler:(nullable void (^)(void))lossHandler
-      wifiStatusChangeHandler:(nullable void (^)(void))wifiStatusChangeHandler;
 @end

src/objective-c/GRPCClient/private/GRPCConnectivityMonitor.m

@@ -18,175 +18,74 @@
 
 #import "GRPCConnectivityMonitor.h"
 
-#pragma mark Flags
+#include <netinet/in.h>
 
-@implementation GRPCReachabilityFlags {
+NSString *kGRPCConnectivityNotification = @"kGRPCConnectivityNotification";
-  SCNetworkReachabilityFlags _flags;
-}
 
-+ (instancetype)flagsWithFlags:(SCNetworkReachabilityFlags)flags {
+static SCNetworkReachabilityRef reachability;
-  return [[self alloc] initWithFlags:flags];
+static GRPCConnectivityStatus currentStatus;
-}
 
-- (instancetype)initWithFlags:(SCNetworkReachabilityFlags)flags {
+// Aggregate information in flags into network status.
-  if ((self = [super init])) {
+GRPCConnectivityStatus CalculateConnectivityStatus(SCNetworkReachabilityFlags flags) {
-    _flags = flags;
+  GRPCConnectivityStatus result = GRPCConnectivityUnknown;
+  if (((flags & kSCNetworkReachabilityFlagsReachable) == 0) ||
+      ((flags & kSCNetworkReachabilityFlagsConnectionRequired) != 0)) {
+    return GRPCConnectivityNoNetwork;
   }
-  return self;
+  result = GRPCConnectivityWiFi;
-}
+#if TARGET_OS_IPHONE
-
+  if (flags & kSCNetworkReachabilityFlagsIsWWAN) {
-/*
+    return result = GRPCConnectivityCellular;
- * One accessor method implementation per flag. Example:
-
-- (BOOL)isCell { \
-  return !!(_flags & kSCNetworkReachabilityFlagsIsWWAN); \
-}
-
- */
-#define GRPC_XMACRO_ITEM(methodName, FlagName) \
-- (BOOL)methodName { \
-  return !!(_flags & kSCNetworkReachabilityFlags ## FlagName); \
-}
-#include "GRPCReachabilityFlagNames.xmacro.h"
-#undef GRPC_XMACRO_ITEM
-
-- (BOOL)isHostReachable {
-  // Note: connectionOnDemand means it'll be reachable only if using the CFSocketStream API or APIs
-  // on top of it.
-  // connectionRequired means we can't tell until a connection is attempted (e.g. for VPN on
-  // demand).
-  return self.reachable && !self.interventionRequired && !self.connectionOnDemand;
-}
-
-- (NSString *)description {
-  NSMutableArray *activeOptions = [NSMutableArray arrayWithCapacity:9];
-
-  /*
-   * For each flag, add its name to the array if it's ON. Example:
-
-  if (self.isCell) {
-    [activeOptions addObject:@"isCell"];
   }
-
+#endif
-   */
+  return result;
-  #define GRPC_XMACRO_ITEM(methodName, FlagName) \
-    if (self.methodName) {                       \
-      [activeOptions addObject:@ #methodName];   \
-    }
-  #include "GRPCReachabilityFlagNames.xmacro.h"
-  #undef GRPC_XMACRO_ITEM
-
-  return activeOptions.count == 0 ? @"(none)" : [activeOptions componentsJoinedByString:@", "];
-}
-
-- (BOOL)isEqual:(id)object {
-  return [object isKindOfClass:[GRPCReachabilityFlags class]] &&
-      _flags == ((GRPCReachabilityFlags *)object)->_flags;
-}
-
-- (NSUInteger)hash {
-  return _flags;
-}
-@end
-
-#pragma mark Connectivity Monitor
-
-// Assumes the third argument is a block that accepts a GRPCReachabilityFlags object, and passes the
-// received ones to it.
-static void PassFlagsToContextInfoBlock(SCNetworkReachabilityRef target,
-                                        SCNetworkReachabilityFlags flags,
-                                        void *info) {
-  #pragma unused (target)
-  // This can be called many times with the same info. The info is retained by SCNetworkReachability
-  // while this function is being executed.
-  void (^handler)(GRPCReachabilityFlags *) = (__bridge void (^)(GRPCReachabilityFlags *))info;
-  handler([[GRPCReachabilityFlags alloc] initWithFlags:flags]);
 }
 
-@implementation GRPCConnectivityMonitor {
+static void ReachabilityCallback(
-  SCNetworkReachabilityRef _reachabilityRef;
+    SCNetworkReachabilityRef target, SCNetworkReachabilityFlags flags, void* info) {
-  GRPCReachabilityFlags *_previousReachabilityFlags;
+  GRPCConnectivityStatus newStatus = CalculateConnectivityStatus(flags);
-}
 
-- (nullable instancetype)initWithReachability:(nullable SCNetworkReachabilityRef)reachability {
+  if (newStatus != currentStatus) {
-  if (!reachability) {
+    [[NSNotificationCenter defaultCenter] postNotificationName:kGRPCConnectivityNotification
-    return nil;
+                                                        object:nil];
+    currentStatus = newStatus;
   }
-  if ((self = [super init])) {
-    _reachabilityRef = CFRetain(reachability);
-    _queue = dispatch_get_main_queue();
-    _previousReachabilityFlags = nil;
-  }
-  return self;
 }
 
-+ (nullable instancetype)monitorWithHost:(nonnull NSString *)host {
+@implementation GRPCConnectivityMonitor
-  const char *hostName = host.UTF8String;
-  if (!hostName) {
-    [NSException raise:NSInvalidArgumentException
-                format:@"host.UTF8String returns NULL for %@", host];
-  }
-  SCNetworkReachabilityRef reachability =
-      SCNetworkReachabilityCreateWithName(NULL, hostName);
 
-  GRPCConnectivityMonitor *returnValue = [[self alloc] initWithReachability:reachability];
++ (void)initialize {
-  if (reachability) {
+  if (self == [GRPCConnectivityMonitor self]) {
-    CFRelease(reachability);
+    struct sockaddr_in addr = {0};
-  }
+    addr.sin_len = sizeof(addr);
-  return returnValue;
+    addr.sin_family = AF_INET;
-}
+    reachability = SCNetworkReachabilityCreateWithAddress(NULL, (struct sockaddr *)&addr);
+    currentStatus = GRPCConnectivityUnknown;
 
-- (void)handleLossWithHandler:(nullable void (^)(void))lossHandler
+    SCNetworkConnectionFlags flags;
-      wifiStatusChangeHandler:(nullable void (^)(void))wifiStatusChangeHandler {
+    if (SCNetworkReachabilityGetFlags(reachability, &flags)) {
-  __weak typeof(self) weakSelf = self;
+      currentStatus = CalculateConnectivityStatus(flags);
-  [self startListeningWithHandler:^(GRPCReachabilityFlags *flags) {
-    typeof(self) strongSelf = weakSelf;
-    if (strongSelf) {
-      if (lossHandler && !flags.reachable) {
-        lossHandler();
-#if TARGET_OS_IPHONE
-      } else if (wifiStatusChangeHandler &&
-                 strongSelf->_previousReachabilityFlags &&
-                 (flags.isWWAN ^
-                  strongSelf->_previousReachabilityFlags.isWWAN)) {
-        wifiStatusChangeHandler();
-#endif
-      }
-      strongSelf->_previousReachabilityFlags = flags;
     }
-  }];
-}
 
-- (void)startListeningWithHandler:(void (^)(GRPCReachabilityFlags *))handler {
+    SCNetworkReachabilityContext context = {0, (__bridge void *)(self), NULL, NULL, NULL};
-  // Copy to ensure the handler block is in the heap (and so can't be deallocated when this method
+    if (!SCNetworkReachabilitySetCallback(reachability, ReachabilityCallback, &context) ||
-  // returns).
+        !SCNetworkReachabilityScheduleWithRunLoop(
-  void (^copiedHandler)(GRPCReachabilityFlags *) = [handler copy];
+            reachability, CFRunLoopGetMain(), kCFRunLoopCommonModes)) {
-  SCNetworkReachabilityContext context = {
+      NSLog(@"gRPC connectivity monitor fail to set");
-    .version = 0,
+    }
-    .info = (__bridge void *)copiedHandler,
+  }
-    .retain = CFRetain,
-    .release = CFRelease,
-  };
-  // The following will retain context.info, and release it when the callback is set to NULL.
-  SCNetworkReachabilitySetCallback(_reachabilityRef, PassFlagsToContextInfoBlock, &context);
-  SCNetworkReachabilitySetDispatchQueue(_reachabilityRef, _queue);
-}
-
-- (void)stopListening {
-  // This releases the block on context.info.
-  SCNetworkReachabilitySetCallback(_reachabilityRef, NULL, NULL);
-  SCNetworkReachabilitySetDispatchQueue(_reachabilityRef, NULL);
 }
 
-- (void)setQueue:(dispatch_queue_t)queue {
++ (void)registerObserver:(_Nonnull id)observer
-  _queue = queue ?: dispatch_get_main_queue();
+                selector:(SEL)selector {
+  [[NSNotificationCenter defaultCenter] addObserver:observer
+                                           selector:selector
+                                               name:kGRPCConnectivityNotification
+                                             object:nil];
 }
 
-- (void)dealloc {
++ (void)unregisterObserver:(_Nonnull id)observer {
-  if (_reachabilityRef) {
+  [[NSNotificationCenter defaultCenter] removeObserver:observer];
-    [self stopListening];
-    CFRelease(_reachabilityRef);
-  }
 }
 
 @end

src/objective-c/GRPCClient/private/GRPCHost.m

@@ -37,12 +37,6 @@ NS_ASSUME_NONNULL_BEGIN
 
 static NSMutableDictionary *kHostCache;
 
-// This connectivity monitor flushes the host cache when connectivity status
-// changes or when connection switch between Wifi and Cellular data, so that a
-// new call will use a new channel. Otherwise, a new call will still use the
-// cached channel which is no longer available and will cause gRPC to hang.
-static GRPCConnectivityMonitor *connectivityMonitor = nil;
-
 @implementation GRPCHost {
   // TODO(mlumish): Investigate whether caching channels with strong links is a good idea.
   GRPCChannel *_channel;
@@ -90,17 +84,7 @@ static GRPCConnectivityMonitor *connectivityMonitor = nil;
       kHostCache[address] = self;
       _compressAlgorithm = GRPC_COMPRESS_NONE;
     }
-    // Keep a single monitor to flush the cache if the connectivity status changes
+    [GRPCConnectivityMonitor registerObserver:self selector:@selector(connectivityChange:)];
-    // Thread safety guarded by @synchronized(kHostCache)
-    if (!connectivityMonitor) {
-      connectivityMonitor =
-      [GRPCConnectivityMonitor monitorWithHost:hostURL.host];
-      void (^handler)(void) = ^{
-        [GRPCHost flushChannelCache];
-      };
-      [connectivityMonitor handleLossWithHandler:handler
-                         wifiStatusChangeHandler:handler];
-    }
   }
   return self;
 }
@@ -281,6 +265,13 @@ static GRPCConnectivityMonitor *connectivityMonitor = nil;
   }
 }
 
+// Flushes the host cache when connectivity status changes or when connection switch between Wifi
+// and Cellular data, so that a new call will use a new channel. Otherwise, a new call will still
+// use the cached channel which is no longer available and will cause gRPC to hang.
+- (void)connectivityChange:(NSNotification *)note {
+  [GRPCHost flushChannelCache];
+}
+
 @end
 
 NS_ASSUME_NONNULL_END