[Cronet] Add CronetMetricsDelegate and add/remove methods to Cronet

This adds a CronetMetricsDelegate interface, as well as addMetricsDelegate
and removeMetricsDelegate methods, which are used to register/unregister
metrics callbacks.

Currently the callback is never actually called; this is simply defining the
interface and registration methods.

Bug: 702796
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I0a3933bf623265d675e3a10ef5ed25149c89e101
Reviewed-on: https://chromium-review.googlesource.com/748819
Commit-Queue: Lily Houghton <lilyhoughton@chromium.org>
Reviewed-by: Andrei Kapishnikov <kapishnikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515456}

components/cronet/ios/Cronet.h

@@ -33,6 +33,17 @@ FOUNDATION_EXPORT GRPC_SUPPORT_EXPORT NSString* const CRNInvalidArgumentKey;
 // be handled.
 typedef BOOL (^RequestFilterBlock)(NSURLRequest* request);
 
+// A delegate that a client can pass to Cronet to collect metrics for a
+// session task. The delegate can be added and removed by calling
+// [Cronet addMetricsDelegate:] and [Cronet removeMetricsDelegate:] methods
+// respectively.
+@protocol CronetMetricsDelegate <NSObject>
+// Is invoked by Cronet when the metrics for the task are ready.
+- (void)URLSession:(NSURLSession*)session task:(NSURLSessionTask*)task
+                    didFinishCollectingMetrics:(NSURLSessionTaskMetrics*)metrics
+    NS_AVAILABLE_IOS(10.0);
+@end
+
 // Interface for installing Cronet.
 // TODO(gcasto): Should this macro be separate from the one defined in
 // bidirectional_stream_c.h?
@@ -195,4 +206,19 @@ GRPC_SUPPORT_EXPORT
 // This method only has any effect before |start| is called.
 + (void)enableTestCertVerifierForTesting;
 
+// Registers a CronetMetricsDelegate callback.  The client is responsible for
+// creating an object which implements CronetMetricsDelegate, and passing
+// that as a |delegate|.  Returns |YES| if the delegate is added successfully,
+// and |NO| if it was not (because there is already an identical delegate
+// registered).
++ (BOOL)addMetricsDelegate:(id<CronetMetricsDelegate>)delegate
+    NS_AVAILABLE_IOS(10.0);
+
+// Unregisters a CronetMetricsDelegate callback.  |delegate| should be a
+// pointer to the delegate which is to be removed.  It returns |YES| if the
+// delegate is successfully removed and |NO| if the delegate is not
+// contained in the set of delegates (and therefore cannot be removed).
++ (BOOL)removeMetricsDelegate:(id<CronetMetricsDelegate>)delegate
+    NS_AVAILABLE_IOS(10.0);
+
 @end

components/cronet/ios/Cronet.mm

@@ -64,6 +64,7 @@ BOOL gEnableTestCertVerifierForTesting;
 std::unique_ptr<net::CertVerifier> gMockCertVerifier;
 NSString* gAcceptLanguages;
 BOOL gEnablePKPBypassForLocalTrustAnchors;
+NSMutableSet<id<CronetMetricsDelegate>>* gMetricsDelegates;
 
 // CertVerifier, which allows any certificates for testing.
 class TestCertVerifier : public net::CertVerifier {
@@ -510,6 +511,27 @@ class CronetHttpProtocolHandlerDelegate
   gMockCertVerifier.reset(nullptr);
   gAcceptLanguages = nil;
   gEnablePKPBypassForLocalTrustAnchors = YES;
+  gMetricsDelegates = [NSMutableSet set];
+}
+
++ (BOOL)addMetricsDelegate:(id<CronetMetricsDelegate>)delegate {
+  @synchronized(gMetricsDelegates) {
+    if ([gMetricsDelegates containsObject:delegate]) {
+      return NO;
+    }
+    [gMetricsDelegates addObject:delegate];
+    return YES;
+  }
+}
+
++ (BOOL)removeMetricsDelegate:(id<CronetMetricsDelegate>)delegate {
+  @synchronized(gMetricsDelegates) {
+    if ([gMetricsDelegates containsObject:delegate]) {
+      [gMetricsDelegates removeObject:delegate];
+      return YES;
+    }
+    return NO;
+  }
 }
 
 @end

components/cronet/ios/test/cronet_metrics_test.mm

@@ -6,11 +6,26 @@
 
 #include "components/cronet/ios/cronet_metrics.h"
 #include "components/cronet/ios/test/cronet_test_base.h"
+
 #include "testing/gtest_mac.h"
 
+@interface TestMetricsDelegate : NSObject<CronetMetricsDelegate>
+@end
+
+@implementation TestMetricsDelegate
+- (void)URLSession:(NSURLSession*)session task:(NSURLSessionTask*)task
+                    didFinishCollectingMetrics:(NSURLSessionTaskMetrics*)metrics
+    NS_AVAILABLE_IOS(10.0) {
+  // This is never actually called, so its definition currently doesn't matter.
+}
+@end
+
 namespace cronet {
 
 class CronetMetricsTest : public CronetTestBase {
+ protected:
+  CronetMetricsTest() {}
+  ~CronetMetricsTest() override {}
 };
 
 TEST_F(CronetMetricsTest, Setters) {
@@ -72,4 +87,15 @@ TEST_F(CronetMetricsTest, Setters) {
   }
 }
 
+TEST_F(CronetMetricsTest, Delegate) {
+  if (@available(iOS 10, *)) {
+    TestMetricsDelegate* metrics_delegate =
+        [[TestMetricsDelegate alloc] init];
+    EXPECT_TRUE([Cronet addMetricsDelegate:metrics_delegate]);
+    EXPECT_FALSE([Cronet addMetricsDelegate:metrics_delegate]);
+    EXPECT_TRUE([Cronet removeMetricsDelegate:metrics_delegate]);
+    EXPECT_FALSE([Cronet removeMetricsDelegate:metrics_delegate]);
+  }
+}
+
 }  // namespace cronet