Drop repeated response headers.

src/objective-c/GRPCClient/private/NSDictionary+GRPC.m

@@ -108,8 +108,8 @@
     // TODO(jcanizales): Verify in a C library test that it's converting header names to lower case
     // automatically.
     NSString *name = [NSString stringWithCString:entry->key encoding:NSASCIIStringEncoding];
-    if (!name) {
-      // log?
+    if (!name || metadata[name]) {
+      // Log if name is nil?
       continue;
     }
     id value;
@@ -119,10 +119,7 @@
     } else {
       value = [NSString grpc_stringFromMetadataValue:entry];
     }
-    if (!metadata[name]) {
-      metadata[name] = [NSMutableArray array];
-    }
-    [metadata[name] addObject:value];
+    metadata[name] = value;
   }
   return metadata;
 }

src/objective-c/tests/GRPCClientTests.m

@@ -165,7 +165,7 @@ static GRPCMethodName *kUnaryCallMethod;
     XCTAssertEqual(errorOrNil.code, 16, @"Finished with unexpected error: %@", errorOrNil);
     XCTAssertEqualObjects(call.responseMetadata, errorOrNil.userInfo[kGRPCStatusMetadataKey],
                           @"Metadata in the NSError object and call object differ.");
-    NSString *challengeHeader = call.responseMetadata[@"www-authenticate"][0];
+    NSString *challengeHeader = call.responseMetadata[@"www-authenticate"];
     XCTAssertGreaterThan(challengeHeader.length, 0,
                          @"No challenge in response headers %@", call.responseMetadata);
     [expectation fulfill];