force-set support for identity alg. in channel arg bitset

src/core/lib/channel/channel_args.c

@@ -199,7 +199,8 @@ static int find_compression_algorithm_states_bitset(const grpc_channel_args *a,
           !strcmp(GRPC_COMPRESSION_CHANNEL_ENABLED_ALGORITHMS_BITSET,
                   a->args[i].key)) {
         *states_arg = &a->args[i].value.integer;
-        return 1; /* GPR_TRUE */
+        **states_arg |= 0x1; /* forcefully enable support for no compression */
+        return 1;
       }
     }
   }
@@ -216,7 +217,7 @@ grpc_channel_args *grpc_channel_args_compression_algorithm_set_state(
   if (states_arg_found) {
     if (state != 0) {
       GPR_BITSET((unsigned *)states_arg, algorithm);
-    } else {
+    } else if (algorithm != GRPC_COMPRESS_NONE) {
       GPR_BITCLEAR((unsigned *)states_arg, algorithm);
     }
   } else {
@@ -228,7 +229,7 @@ grpc_channel_args *grpc_channel_args_compression_algorithm_set_state(
     tmp.value.integer = (1u << GRPC_COMPRESS_ALGORITHMS_COUNT) - 1;
     if (state != 0) {
       GPR_BITSET((unsigned *)&tmp.value.integer, algorithm);
-    } else {
+    } else if (algorithm != GRPC_COMPRESS_NONE) {
       GPR_BITCLEAR((unsigned *)&tmp.value.integer, algorithm);
     }
     result = grpc_channel_args_copy_and_add(*a, &tmp, 1);

src/core/lib/channel/compress_filter.c

@@ -296,8 +296,8 @@ static void init_channel_elem(grpc_exec_ctx *exec_ctx,
     channeld->default_compression_algorithm = GRPC_COMPRESS_NONE;
   }
 
-  channeld->supported_compression_algorithms = 0;
-  for (grpc_compression_algorithm algo_idx = 0;
+  channeld->supported_compression_algorithms = 1; /* always support identity */
+  for (grpc_compression_algorithm algo_idx = 1;
        algo_idx < GRPC_COMPRESS_ALGORITHMS_COUNT; ++algo_idx) {
     /* skip disabled algorithms */
     if (!GPR_BITGET(channeld->enabled_algorithms_bitset, algo_idx)) {