Address comments

src/core/ext/filters/workarounds/workaround_cronet_compression_filter.c

@@ -60,15 +60,10 @@ typedef struct channel_data {
 // Find the user agent metadata element in the batch
 static bool get_user_agent_mdelem(const grpc_metadata_batch* batch,
                                   grpc_mdelem* md) {
-  grpc_linked_mdelem* t = batch->list.head;
-  while (t != NULL) {
-    *md = t->md;
-    if (grpc_slice_eq(GRPC_MDKEY(*md), GRPC_MDSTR_USER_AGENT)) {
-      return true;
-    }
-    t = t->next;
+  if (batch->idx.named.user_agent != NULL) {
+    *md = batch->idx.named.user_agent->md;
+    return true;
   }
-
   return false;
 }
 
@@ -221,8 +216,7 @@ static bool register_workaround_cronet_compression(
   if (a->value.integer == 0) {
     return true;
   }
-  grpc_register_workaround(GRPC_WORKAROUND_ID_CRONET_COMPRESSION,
-                           parse_user_agent);
+  grpc_enable_workaround(GRPC_WORKAROUND_ID_CRONET_COMPRESSION);
   return grpc_channel_stack_builder_prepend_filter(
       builder, &grpc_workaround_cronet_compression_filter, NULL, NULL);
 }
@@ -231,6 +225,8 @@ void grpc_workaround_cronet_compression_filter_init(void) {
   grpc_channel_init_register_stage(
       GRPC_SERVER_CHANNEL, GRPC_WORKAROUND_PRIORITY_HIGH,
       register_workaround_cronet_compression, NULL);
+  grpc_register_workaround(GRPC_WORKAROUND_ID_CRONET_COMPRESSION,
+                           parse_user_agent);
 }
 
 void grpc_workaround_cronet_compression_filter_shutdown(void) {}

src/core/ext/filters/workarounds/workaround_utils.c

@@ -34,12 +34,17 @@
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 
+typedef struct {
+  bool enabled;
+  user_agent_parser ua_parser;
+} workaround_context;
+
+static workaround_context workarounds[GRPC_MAX_WORKAROUND_ID];
+
 static void destroy_user_agent_md(void *user_agent_md) {
   gpr_free(user_agent_md);
 }
 
-static user_agent_parser user_agent_parsers[GRPC_MAX_WORKAROUND_ID];
-
 grpc_user_agent_md *grpc_parse_user_agent(grpc_mdelem md) {
   grpc_user_agent_md *user_agent_md =
       (grpc_user_agent_md *)grpc_mdelem_get_user_data(md,
@@ -50,8 +55,8 @@ grpc_user_agent_md *grpc_parse_user_agent(grpc_mdelem md) {
   }
   user_agent_md = gpr_malloc(sizeof(grpc_user_agent_md));
   for (int i = 0; i < GRPC_MAX_WORKAROUND_ID; i++) {
-    if (user_agent_parsers[i]) {
-      user_agent_md->workaround_active[i] = user_agent_parsers[i](md);
+    if (workarounds[i].enabled && workarounds[i].ua_parser) {
+      user_agent_md->workaround_active[i] = workarounds[i].ua_parser(md);
     }
   }
   grpc_mdelem_set_user_data(md, destroy_user_agent_md, (void *)user_agent_md);
@@ -61,5 +66,10 @@ grpc_user_agent_md *grpc_parse_user_agent(grpc_mdelem md) {
 
 void grpc_register_workaround(uint32_t id, user_agent_parser parser) {
   GPR_ASSERT(id < GRPC_MAX_WORKAROUND_ID);
-  user_agent_parsers[id] = parser;
+  workarounds[id].ua_parser = parser;
+}
+
+void grpc_enable_workaround(uint32_t id) {
+  GPR_ASSERT(id < GRPC_MAX_WORKAROUND_ID);
+  workarounds[id].enabled = true;
 }

src/core/ext/filters/workarounds/workaround_utils.h

@@ -51,4 +51,6 @@ typedef bool (*user_agent_parser)(grpc_mdelem);
 
 void grpc_register_workaround(uint32_t id, user_agent_parser parser);
 
+void grpc_enable_workaround(uint32_t id);
+
 #endif