envconfig: re-add AdvertiseCompressors temporarily (grpc#6764)

internal/envconfig/envconfig.go

@@ -28,6 +28,9 @@ import (
 var (
 	// TXTErrIgnore is set if TXT errors should be ignored ("GRPC_GO_IGNORE_TXT_ERRORS" is not "false").
 	TXTErrIgnore = boolFromEnv("GRPC_GO_IGNORE_TXT_ERRORS", true)
+	// AdvertiseCompressors is set if registered compressor should be advertised
+	// ("GRPC_GO_ADVERTISE_COMPRESSORS" is not "false").
+	AdvertiseCompressors = boolFromEnv("GRPC_GO_ADVERTISE_COMPRESSORS", true)
 	// RingHashCap indicates the maximum ring size which defaults to 4096
 	// entries but may be overridden by setting the environment variable
 	// "GRPC_RING_HASH_CAP".  This does not override the default bounds

internal/grpcutil/compressor.go

@@ -20,6 +20,8 @@ package grpcutil
 
 import (
 	"strings"
+
+	"google.golang.org/grpc/internal/envconfig"
 )
 
 // RegisteredCompressorNames holds names of the registered compressors.
@@ -38,5 +40,8 @@ func IsCompressorNameRegistered(name string) bool {
 // RegisteredCompressors returns a string of registered compressor names
 // separated by comma.
 func RegisteredCompressors() string {
+	if !envconfig.AdvertiseCompressors {
+		return ""
+	}
 	return strings.Join(RegisteredCompressorNames, ",")
 }