6 files changed, 36 insertions, 6 deletions
diff --git a/src/core/lib/surface/call.h b/src/core/lib/surface/call.h
index 185bfccb77..d537637cbb 100644
--- a/src/core/lib/surface/call.h
+++ b/src/core/lib/surface/call.h
@@ -19,6 +19,10 @@
 #ifndef GRPC_CORE_LIB_SURFACE_CALL_H
 #define GRPC_CORE_LIB_SURFACE_CALL_H
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #include "src/core/lib/channel/channel_stack.h"
 #include "src/core/lib/channel/context.h"
 #include "src/core/lib/surface/api_trace.h"
@@ -26,10 +30,6 @@
 #include <grpc/grpc.h>
 #include <grpc/impl/codegen/compression_types.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 typedef void (*grpc_ioreq_completion_func)(grpc_exec_ctx *exec_ctx,
                                            grpc_call *call, int success,
                                            void *user_data);
@@ -89,7 +89,7 @@ grpc_call_error grpc_call_start_batch_and_execute(grpc_exec_ctx *exec_ctx,
 /* Given the top call_element, get the call object. */
 grpc_call *grpc_call_from_top_element(grpc_call_element *surface_element);
 
-void grpc_call_log_batch(char *file, int line, gpr_log_severity severity,
+void grpc_call_log_batch(const char *file, int line, gpr_log_severity severity,
                          grpc_call *call, const grpc_op *ops, size_t nops,
                          void *tag);
 
diff --git a/src/core/lib/surface/call_log_batch.c b/src/core/lib/surface/call_log_batch.c
index 4443aba58a..4a1c265817 100644
--- a/src/core/lib/surface/call_log_batch.c
+++ b/src/core/lib/surface/call_log_batch.c
@@ -103,7 +103,7 @@ char *grpc_op_string(const grpc_op *op) {
   return out;
 }
 
-void grpc_call_log_batch(char *file, int line, gpr_log_severity severity,
+void grpc_call_log_batch(const char *file, int line, gpr_log_severity severity,
                          grpc_call *call, const grpc_op *ops, size_t nops,
                          void *tag) {
   char *tmp;
diff --git a/src/core/lib/transport/metadata_batch.c b/src/core/lib/transport/metadata_batch.c
index 8f24b8527c..a077052561 100644
--- a/src/core/lib/transport/metadata_batch.c
+++ b/src/core/lib/transport/metadata_batch.c
@@ -105,6 +105,7 @@ static grpc_error *maybe_link_callout(grpc_metadata_batch *batch,
     return GRPC_ERROR_NONE;
   }
   if (batch->idx.array[idx] == NULL) {
+    if (grpc_static_callout_is_default[idx]) ++batch->list.default_count;
     batch->idx.array[idx] = storage;
     return GRPC_ERROR_NONE;
   }
@@ -120,6 +121,7 @@ static void maybe_unlink_callout(grpc_metadata_batch *batch,
   if (idx == GRPC_BATCH_CALLOUTS_COUNT) {
     return;
   }
+  if (grpc_static_callout_is_default[idx]) --batch->list.default_count;
   GPR_ASSERT(batch->idx.array[idx] != NULL);
   batch->idx.array[idx] = NULL;
 }
diff --git a/src/core/lib/transport/metadata_batch.h b/src/core/lib/transport/metadata_batch.h
index 1b11a3e252..57d298c75c 100644
--- a/src/core/lib/transport/metadata_batch.h
+++ b/src/core/lib/transport/metadata_batch.h
@@ -41,6 +41,7 @@ typedef struct grpc_linked_mdelem {
 
 typedef struct grpc_mdelem_list {
   size_t count;
+  size_t default_count;  // Number of default keys.
   grpc_linked_mdelem *head;
   grpc_linked_mdelem *tail;
 } grpc_mdelem_list;
diff --git a/src/core/lib/transport/static_metadata.c b/src/core/lib/transport/static_metadata.c
index 28f05d5c44..b20d94aeac 100644
--- a/src/core/lib/transport/static_metadata.c
+++ b/src/core/lib/transport/static_metadata.c
@@ -823,6 +823,31 @@ grpc_mdelem_data grpc_static_mdelem_table[GRPC_STATIC_MDELEM_COUNT] = {
      {.refcount = &grpc_static_metadata_refcounts[97],
       .data.refcounted = {g_bytes + 1040, 13}}},
 };
+bool grpc_static_callout_is_default[GRPC_BATCH_CALLOUTS_COUNT] = {
+    true,  // :path
+    true,  // :method
+    true,  // :status
+    true,  // :authority
+    true,  // :scheme
+    true,  // te
+    true,  // grpc-message
+    true,  // grpc-status
+    true,  // grpc-payload-bin
+    true,  // grpc-encoding
+    true,  // grpc-accept-encoding
+    true,  // grpc-server-stats-bin
+    true,  // grpc-tags-bin
+    true,  // grpc-trace-bin
+    true,  // content-type
+    true,  // content-encoding
+    true,  // accept-encoding
+    true,  // grpc-internal-encoding-request
+    true,  // grpc-internal-stream-encoding-request
+    true,  // user-agent
+    true,  // host
+    true,  // lb-token
+};
+
 const uint8_t grpc_static_accept_encoding_metadata[8] = {0,  76, 77, 78,
                                                          79, 80, 81, 82};
 
diff --git a/src/core/lib/transport/static_metadata.h b/src/core/lib/transport/static_metadata.h
index 93ab90dff8..f03a9d23b1 100644
--- a/src/core/lib/transport/static_metadata.h
+++ b/src/core/lib/transport/static_metadata.h
@@ -571,6 +571,8 @@ typedef union {
              GRPC_BATCH_CALLOUTS_COUNT)                 \
        : GRPC_BATCH_CALLOUTS_COUNT)
 
+extern bool grpc_static_callout_is_default[GRPC_BATCH_CALLOUTS_COUNT];
+
 extern const uint8_t grpc_static_accept_encoding_metadata[8];
 #define GRPC_MDELEM_ACCEPT_ENCODING_FOR_ALGORITHMS(algs)                       \
   (GRPC_MAKE_MDELEM(                                                           \