5 files changed, 94 insertions, 0 deletions
diff --git a/include/grpc/impl/codegen/grpc_types.h b/include/grpc/impl/codegen/grpc_types.h
index 3e897b0b27..a03be05531 100644
--- a/include/grpc/impl/codegen/grpc_types.h
+++ b/include/grpc/impl/codegen/grpc_types.h
@@ -314,6 +314,9 @@ typedef struct {
     Defaults to "blend". In the current implementation "blend" is equivalent to
     "latency". */
 #define GRPC_ARG_OPTIMIZATION_TARGET "grpc.optimization_target"
+/** Channel arg that carries the bridged objective c object for custom metrics
+ * logging filter. */
+#define GRPC_ARG_MOBILE_LOG_CONFIG "grpc.mobile_log_config"
 /** \} */
 
 /** Result of a grpc call. If the caller satisfies the prerequisites of a
diff --git a/src/objective-c/GRPCClient/GRPCCall+MobileLog.h b/src/objective-c/GRPCClient/GRPCCall+MobileLog.h
new file mode 100644
index 0000000000..53b347d9ca
--- /dev/null
+++ b/src/objective-c/GRPCClient/GRPCCall+MobileLog.h
@@ -0,0 +1,30 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#import "GRPCCall.h"
+
+@interface GRPCCall (MobileLog)
+// Set the object to be passed down along channel stack with channel arg
+// GRPC_ARG_MOBILE_LOG_CONFIG. The setting may be used by custom channel
+// filters for metrics logging.
++ (void)setLogConfig:(id)logConfig;
+
+// Obtain the object to be passed down along channel stack with channel arg
+// GRPC_ARG_MOBILE_LOG_CONFIG.
++ (id)logConfig;
+@end
diff --git a/src/objective-c/GRPCClient/GRPCCall+MobileLog.m b/src/objective-c/GRPCClient/GRPCCall+MobileLog.m
new file mode 100644
index 0000000000..4dedb7de8b
--- /dev/null
+++ b/src/objective-c/GRPCClient/GRPCCall+MobileLog.m
@@ -0,0 +1,33 @@
+/*
+ *
+ * Copyright 2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#import "GRPCCall+MobileLog.h"
+
+static id globalLogConfig = nil;
+
+@implementation GRPCCall (MobileLog)
+
++ (void)setLogConfig:(id)logConfig {
+  globalLogConfig = logConfig;
+}
+
++ (id)logConfig {
+  return globalLogConfig;
+}
+
+@end
diff --git a/src/objective-c/GRPCClient/private/GRPCChannel.m b/src/objective-c/GRPCClient/private/GRPCChannel.m
index 87646f7895..b53d84159d 100644
--- a/src/objective-c/GRPCClient/private/GRPCChannel.m
+++ b/src/objective-c/GRPCClient/private/GRPCChannel.m
@@ -32,6 +32,24 @@
 #endif
 #import "GRPCCompletionQueue.h"
 
+static void* copy_pointer_arg(void *p) {
+  // Add ref count to the object when making copy
+  id obj = (__bridge id)p;
+  return (__bridge_retained void *)obj;
+}
+
+static void destroy_pointer_arg(void *p) {
+  // Decrease ref count to the object when destroying
+  CFRelease((CFTreeRef)p);
+}
+
+static int cmp_pointer_arg(void *p, void *q) {
+  return p == q;
+}
+
+static const grpc_arg_pointer_vtable objc_arg_vtable = {
+  copy_pointer_arg, destroy_pointer_arg, cmp_pointer_arg};
+
 static void FreeChannelArgs(grpc_channel_args *channel_args) {
   for (size_t i = 0; i < channel_args->num_args; ++i) {
     grpc_arg *arg = &channel_args->args[i];
@@ -75,6 +93,10 @@ static grpc_channel_args *BuildChannelArgs(NSDictionary *dictionary) {
     } else if ([value respondsToSelector:@selector(intValue)]) {
       arg->type = GRPC_ARG_INTEGER;
       arg->value.integer = [value intValue];
+    } else if (value != nil) {
+      arg->type = GRPC_ARG_POINTER;
+      arg->value.pointer.p = (__bridge_retained void *)value;
+      arg->value.pointer.vtable = &objc_arg_vtable;
     } else {
       [NSException raise:NSInvalidArgumentException
                   format:@"Invalid value type: %@", [value class]];
diff --git a/src/objective-c/GRPCClient/private/GRPCHost.m b/src/objective-c/GRPCClient/private/GRPCHost.m
index ceae9607d7..71b57cf1f6 100644
--- a/src/objective-c/GRPCClient/private/GRPCHost.m
+++ b/src/objective-c/GRPCClient/private/GRPCHost.m
@@ -21,6 +21,7 @@
 #include <grpc/grpc.h>
 #include <grpc/grpc_security.h>
 #import <GRPCClient/GRPCCall.h>
+#import <GRPCClient/GRPCCall+MobileLog.h>
 #ifdef GRPC_COMPILE_WITH_CRONET
 #import <GRPCClient/GRPCCall+ChannelArg.h>
 #import <GRPCClient/GRPCCall+Cronet.h>
@@ -231,6 +232,11 @@ static GRPCConnectivityMonitor *connectivityMonitor = nil;
         [NSNumber numberWithInt:_compressAlgorithm];
   }
 
+  id logConfig = [GRPCCall logConfig];
+  if (logConfig != nil) {
+    args[@GRPC_ARG_MOBILE_LOG_CONFIG] = logConfig;
+  }
+
   return args;
 }