Implement -hash and -copy of GDLLogEvent, copy on log, and don't assign extensionBytes in log writer (#2204)

* Implement -hash and -copy of GDLLogEvent

Also implements a custom setter for setting the extension that changes the default behavior to set extensionBytes upon assignment of extension.

Copy the log upon logging, as the comments promised.

Remove setting extensionBytes in the log writer.

Implement a missing method

* Copy the log object upon logging

* Don't assign extensionBytes in the log writer

* Make an implicit loss of precision explicit.

* Add a comment on performance

Author: mikehaney24

GoogleDataLogger/GoogleDataLogger/Classes/GDLLogEvent.m

@@ -31,6 +31,31 @@ - (instancetype)initWithLogMapID:(NSString *)logMapID logTarget:(NSInteger)logTa
   return self;
 }
 
+- (instancetype)copy {
+  GDLLogEvent *copy = [[GDLLogEvent alloc] initWithLogMapID:_logMapID logTarget:_logTarget];
+  copy.extension = _extension;
+  copy.extensionBytes = _extensionBytes;
+  copy.qosTier = _qosTier;
+  copy.clockSnapshot = _clockSnapshot;
+  return copy;
+}
+
+- (NSUInteger)hash {
+  // This loses some precision, but it's probably fine.
+  NSUInteger timeHash = (NSUInteger)(_clockSnapshot.timeMillis ^ _clockSnapshot.uptimeMillis);
+  return [_logMapID hash] ^ _logTarget ^ [_extensionBytes hash] ^ _qosTier ^ timeHash;
+}
+
+- (void)setExtension:(id<GDLLogProto>)extension {
+  // If you're looking here because of a performance issue in -protoBytes slowing the assignment
+  // of extension, one way to address this is to add a queue to this class,
+  // dispatch_(barrier_ if concurrent)async here, and implement the getter with a dispatch_sync.
+  if (extension != _extension) {
+    _extension = extension;
+    _extensionBytes = [extension protoBytes];
+  }
+}
+
 #pragma mark - NSSecureCoding and NSCoding Protocols
 
 /** NSCoding key for logMapID property. */

GoogleDataLogger/GoogleDataLogger/Classes/GDLLogWriter.m

@@ -61,17 +61,6 @@ - (void)writeLog:(GDLLogEvent *)log
         return;
       }
     }
-
-    // Convert the extension to bytes after transforming.
-    NSAssert([log.extension respondsToSelector:@selector(protoBytes)],
-             @"The log event's extension must respond to -protoBytes.");
-    if ([log.extension respondsToSelector:@selector(protoBytes)]) {
-      log.extensionBytes = [log.extension protoBytes];
-      log.extension = nil;
-    } else {
-      GDLLogWarning(GDLMCWExtensionMissingBytesImpl, @"%@",
-                    @"The log event's extension must respond to -protoBytes.");
-    }
     // TODO(mikehaney24): [[GDLLogStorage sharedInstance] storeLog:transformedLog];
   });
 }

GoogleDataLogger/GoogleDataLogger/Classes/GDLLogger.m

@@ -50,12 +50,14 @@ - (instancetype)initWithLogMapID:(NSString *)logMapID
 
 - (void)logTelemetryEvent:(GDLLogEvent *)logEvent {
   NSAssert(logEvent, @"You can't log a nil event");
-  [[GDLLogWriter sharedInstance] writeLog:logEvent afterApplyingTransformers:_logTransformers];
+  GDLLogEvent *copiedLog = [logEvent copy];
+  [[GDLLogWriter sharedInstance] writeLog:copiedLog afterApplyingTransformers:_logTransformers];
 }
 
 - (void)logDataEvent:(GDLLogEvent *)logEvent {
   NSAssert(logEvent, @"You can't log a nil event");
-  [[GDLLogWriter sharedInstance] writeLog:logEvent afterApplyingTransformers:_logTransformers];
+  GDLLogEvent *copiedLog = [logEvent copy];
+  [[GDLLogWriter sharedInstance] writeLog:copiedLog afterApplyingTransformers:_logTransformers];
 }
 
 - (GDLLogEvent *)newEvent {