Fix memory leak in failed metadata preparation

src/core/lib/surface/call.c

@@ -554,21 +554,6 @@ static int prepare_application_metadata(grpc_call *call, int count,
   int i;
   grpc_metadata_batch *batch =
       &call->metadata_batch[0 /* is_receiving */][is_trailing];
-  if (prepend_extra_metadata) {
-    if (call->send_extra_metadata_count == 0) {
-      prepend_extra_metadata = 0;
-    } else {
-      for (i = 0; i < call->send_extra_metadata_count; i++) {
-        GRPC_MDELEM_REF(call->send_extra_metadata[i].md);
-      }
-      for (i = 1; i < call->send_extra_metadata_count; i++) {
-        call->send_extra_metadata[i].prev = &call->send_extra_metadata[i - 1];
-      }
-      for (i = 0; i < call->send_extra_metadata_count - 1; i++) {
-        call->send_extra_metadata[i].next = &call->send_extra_metadata[i + 1];
-      }
-    }
-  }
   for (i = 0; i < count; i++) {
     grpc_metadata *md = &metadata[i];
     grpc_linked_mdelem *l = (grpc_linked_mdelem *)&md->internal_data;
@@ -579,14 +564,37 @@ static int prepare_application_metadata(grpc_call *call, int count,
                                   GRPC_MDSTR_LENGTH(l->md->key))) {
       gpr_log(GPR_ERROR, "attempt to send invalid metadata key: %s",
               grpc_mdstr_as_c_string(l->md->key));
-      return 0;
+      break;
     } else if (!grpc_is_binary_header(grpc_mdstr_as_c_string(l->md->key),
                                       GRPC_MDSTR_LENGTH(l->md->key)) &&
                !grpc_header_nonbin_value_is_legal(
                    grpc_mdstr_as_c_string(l->md->value),
                    GRPC_MDSTR_LENGTH(l->md->value))) {
       gpr_log(GPR_ERROR, "attempt to send invalid metadata value");
-      return 0;
+      break;
+    }
+  }
+  if (i != count) {
+    for (int j = 0; j <= i; j++) {
+      grpc_metadata *md = &metadata[i];
+      grpc_linked_mdelem *l = (grpc_linked_mdelem *)&md->internal_data;
+      GRPC_MDELEM_UNREF(l->md);
+    }
+    return 0;
+  }
+  if (prepend_extra_metadata) {
+    if (call->send_extra_metadata_count == 0) {
+      prepend_extra_metadata = 0;
+    } else {
+      for (i = 0; i < call->send_extra_metadata_count; i++) {
+        GRPC_MDELEM_REF(call->send_extra_metadata[i].md);
+      }
+      for (i = 1; i < call->send_extra_metadata_count; i++) {
+        call->send_extra_metadata[i].prev = &call->send_extra_metadata[i - 1];
+      }
+      for (i = 0; i < call->send_extra_metadata_count - 1; i++) {
+        call->send_extra_metadata[i].next = &call->send_extra_metadata[i + 1];
+      }
     }
   }
   for (i = 1; i < count; i++) {