4 files changed, 38 insertions, 22 deletions

diff --git a/src/objective-c/GRPCClient/private/GRPCRequestHeaders.h b/src/objective-c/GRPCClient/private/GRPCRequestHeaders.h
index cf5a1be9d6..b580f19406 100644
--- a/src/objective-c/GRPCClient/private/GRPCRequestHeaders.h
+++ b/src/objective-c/GRPCClient/private/GRPCRequestHeaders.h
@@ -32,21 +32,14 @@
  */
 
 #import <Foundation/Foundation.h>
-#include <grpc/grpc.h>
 
 #import "../GRPCCall.h"
 
-@interface GRPCRequestHeaders : NSObject<GRPCRequestHeaders>
-
-@property(nonatomic, readonly) NSUInteger count;
-@property(nonatomic, readonly) grpc_metadata *grpc_metadataArray;
+@interface GRPCRequestHeaders : NSMutableDictionary
 
 - (instancetype)initWithCall:(GRPCCall *)call;
 
-- (id)objectForKeyedSubscript:(NSString *)key;
-- (void)setObject:(id)obj forKeyedSubscript:(NSString *)key;
-
-- (void)removeAllObjects;
-- (void)removeObjectForKey:(NSString *)key;
+- (instancetype)initWithCall:(GRPCCall *)call
+                     storage:(NSMutableDictionary *)storage NS_DESIGNATED_INITIALIZER;
 
 @end
diff --git a/src/objective-c/GRPCClient/private/GRPCRequestHeaders.m b/src/objective-c/GRPCClient/private/GRPCRequestHeaders.m
index d23f21c0f9..c6a03c145e 100644
--- a/src/objective-c/GRPCClient/private/GRPCRequestHeaders.m
+++ b/src/objective-c/GRPCClient/private/GRPCRequestHeaders.m
@@ -68,17 +68,44 @@ static void CheckKeyValuePairIsValid(NSString *key, id value) {
 
 @implementation GRPCRequestHeaders {
   __weak GRPCCall *_call;
+  // The NSMutableDictionary superclass doesn't hold any storage (so that people can implement their
+  // own in subclasses). As that's not the reason we're subclassing, we just delegate storage to the
+  // default NSMutableDictionary subclass returned by the cluster (e.g. __NSDictionaryM on iOS 9).
   NSMutableDictionary *_delegate;
 }
 
+- (instancetype)init {
+  return [self initWithCall:nil];
+}
+
+- (instancetype)initWithCapacity:(NSUInteger)numItems {
+  return [self init];
+}
+
+- (instancetype)initWithCoder:(NSCoder *)aDecoder {
+  return [self init];
+}
+
 - (instancetype)initWithCall:(GRPCCall *)call {
+  return [self initWithCall:call storage:[NSMutableDictionary dictionary]];
+}
+
+// Designated initializer
+- (instancetype)initWithCall:(GRPCCall *)call storage:(NSMutableDictionary *)storage {
+  // TODO(jcanizales): Throw if call or storage are nil.
   if ((self = [super init])) {
     _call = call;
-    _delegate = [NSMutableDictionary dictionary];
+    _delegate = storage;
   }
   return self;
 }
 
+- (instancetype)initWithObjects:(const id  _Nonnull __unsafe_unretained *)objects
+                        forKeys:(const id<NSCopying>  _Nonnull __unsafe_unretained *)keys
+                          count:(NSUInteger)cnt {
+  return [self init];
+}
+
 - (void)checkCallIsNotStarted {
   if (_call.state != GRXWriterStateNotStarted) {
     [NSException raise:@"Invalid modification"
@@ -86,11 +113,11 @@ static void CheckKeyValuePairIsValid(NSString *key, id value) {
   }
 }
 
-- (id)objectForKeyedSubscript:(NSString *)key {
+- (id)objectForKey:(NSString *)key {
   return _delegate[key.lowercaseString];
 }
 
-- (void)setObject:(id)obj forKeyedSubscript:(NSString *)key {
+- (void)setObject:(id)obj forKey:(NSString *)key {
   [self checkCallIsNotStarted];
   CheckIsNonNilASCII(@"Header name", key);
   key = key.lowercaseString;
@@ -103,16 +130,12 @@ static void CheckKeyValuePairIsValid(NSString *key, id value) {
   [_delegate removeObjectForKey:key.lowercaseString];
 }
 
-- (void)removeAllObjects {
-  [self checkCallIsNotStarted];
-  [_delegate removeAllObjects];
-}
-
 - (NSUInteger)count {
   return _delegate.count;
 }
 
-- (grpc_metadata *)grpc_metadataArray {
-  return _delegate.grpc_metadataArray;
+- (NSEnumerator * _Nonnull)keyEnumerator {
+  return [_delegate keyEnumerator];
 }
+
 @end
diff --git a/src/objective-c/GRPCClient/private/GRPCWrappedCall.h b/src/objective-c/GRPCClient/private/GRPCWrappedCall.h
index 7747aa53ef..71e7e0e54e 100644
--- a/src/objective-c/GRPCClient/private/GRPCWrappedCall.h
+++ b/src/objective-c/GRPCClient/private/GRPCWrappedCall.h
@@ -45,7 +45,7 @@
 
 @interface GRPCOpSendMetadata : GRPCOperation
 
-- (instancetype)initWithMetadata:(GRPCRequestHeaders *)metadata
+- (instancetype)initWithMetadata:(NSDictionary *)metadata
                          handler:(void(^)())handler NS_DESIGNATED_INITIALIZER;
 
 @end
diff --git a/src/objective-c/GRPCClient/private/GRPCWrappedCall.m b/src/objective-c/GRPCClient/private/GRPCWrappedCall.m
index cea7c479e0..fe3d51da53 100644
--- a/src/objective-c/GRPCClient/private/GRPCWrappedCall.m
+++ b/src/objective-c/GRPCClient/private/GRPCWrappedCall.m
@@ -65,7 +65,7 @@
   return [self initWithMetadata:nil handler:nil];
 }
 
-- (instancetype)initWithMetadata:(GRPCRequestHeaders *)metadata handler:(void (^)())handler {
+- (instancetype)initWithMetadata:(NSDictionary *)metadata handler:(void (^)())handler {
   if (self = [super init]) {
     _op.op = GRPC_OP_SEND_INITIAL_METADATA;
     _op.data.send_initial_metadata.count = metadata.count;