add env variable

Author: Pranjali-2501

internal/envconfig/envconfig.go

@@ -126,6 +126,18 @@ var (
 	// enabled by setting the env variable
 	// GRPC_EXPERIMENTAL_ENABLE_PRIORITY_LB_CHILD_POLICY_CACHE to true.
 	EnablePriorityLBChildPolicyCache = boolFromEnv("GRPC_EXPERIMENTAL_ENABLE_PRIORITY_LB_CHILD_POLICY_CACHE", false)
+
+	// DefaultHeaderListSize indicates that default maximum header list size is
+	// restricted to 8KB. This is disabled by default, but can be enabled by
+	// setting the env variable "GRPC_GO_EXPERIMENTAL_DEFAULT_HEADER_LIST_SIZE"
+	// to "true". When disabled, the default maximum header list size of 16MB is
+	// used.
+	//
+	// When enabled RPCs with a total size of headers exceeding 8KB will fail
+	// unless explicitly configured otherwise by the user.
+	//
+	// TODO: After a release, we will enable the env var by default.
+	DefaultHeaderListSize = boolFromEnv("GRPC_GO_EXPERIMENTAL_DEFAULT_HEADER_LIST_SIZE", false)
 )
 
 func boolFromEnv(envVar string, def bool) bool {

internal/transport/http2_client.go

@@ -39,6 +39,7 @@ import (
 	"google.golang.org/grpc/internal"
 	"google.golang.org/grpc/internal/channelz"
 	icredentials "google.golang.org/grpc/internal/credentials"
+	"google.golang.org/grpc/internal/envconfig"
 	"google.golang.org/grpc/internal/grpclog"
 	"google.golang.org/grpc/internal/grpcsync"
 	"google.golang.org/grpc/internal/grpcutil"
@@ -317,6 +318,9 @@ func NewHTTP2Client(connectCtx, ctx context.Context, addr resolver.Address, opts
 	writeBufSize := opts.WriteBufferSize
 	readBufSize := opts.ReadBufferSize
 	maxHeaderListSize := defaultClientMaxHeaderListSize
+	if envconfig.DefaultHeaderListSize {
+		maxHeaderListSize = upcomingDefaultHeaderListSize
+	}
 	if opts.MaxHeaderListSize != nil {
 		maxHeaderListSize = *opts.MaxHeaderListSize
 	}
@@ -877,7 +881,7 @@ func (t *http2Client) NewStream(ctx context.Context, callHdr *CallHdr, handler s
 				return false
 			}
 		}
-		if sz > int64(upcomingDefaultHeaderListSize) {
+		if !envconfig.DefaultHeaderListSize && sz > int64(upcomingDefaultHeaderListSize) {
 			t.logger.Warningf("Header list size to send (%d bytes) is larger than the upcoming default limit (%d bytes). In a future release, this will be restricted to %d bytes.", sz, upcomingDefaultHeaderListSize, upcomingDefaultHeaderListSize)
 		}
 		return true

internal/transport/http2_server.go

@@ -38,6 +38,7 @@ import (
 	"google.golang.org/protobuf/proto"
 
 	"google.golang.org/grpc/internal"
+	"google.golang.org/grpc/internal/envconfig"
 	"google.golang.org/grpc/internal/grpclog"
 	"google.golang.org/grpc/internal/grpcutil"
 	"google.golang.org/grpc/internal/pretty"
@@ -166,6 +167,9 @@ func NewServerTransport(conn net.Conn, config *ServerConfig) (_ ServerTransport,
 	writeBufSize := config.WriteBufferSize
 	readBufSize := config.ReadBufferSize
 	maxHeaderListSize := defaultServerMaxHeaderListSize
+	if envconfig.DefaultHeaderListSize {
+		maxHeaderListSize = upcomingDefaultHeaderListSize
+	}
 	if config.MaxHeaderListSize != nil {
 		maxHeaderListSize = *config.MaxHeaderListSize
 	}
@@ -948,7 +952,7 @@ func (t *http2Server) checkForHeaderListSize(hf []hpack.HeaderField) bool {
 			return false
 		}
 	}
-	if sz > int64(upcomingDefaultHeaderListSize) {
+	if !envconfig.DefaultHeaderListSize && sz > int64(upcomingDefaultHeaderListSize) {
 		t.logger.Warningf("Header list size to send (%d bytes) is larger than the upcoming default limit (%d bytes). In a future release, this will be restricted to %d bytes.", sz, upcomingDefaultHeaderListSize, upcomingDefaultHeaderListSize)
 	}
 	return true