Introduce a grpc-exp ALPN protocol identifier.

This patch introduces an additional ALPN protocol, grpc-exp, intended to
take preference to h2 and indicate to the server that the connection
contains only gRPC traffic. This allows servers and intermediate boxes
to distinguish gRPC from other HTTP/2 traffic.

The choice of grpc-exp as a protocol identifier indicates that this
scheme is currently experimental and should not be relied upon. The
protocol is not in the IANA TLS registry.

This patch also introduces client/server handshake tests that validate
the preferential treatment of grpc-exp in an end-to-end manner.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/core/ext/transport/chttp2/alpn/alpn.c b/src/core/ext/transport/chttp2/alpn/alpn.c
index 48b0217265..55710dc5ae 100644
--- a/src/core/ext/transport/chttp2/alpn/alpn.c
+++ b/src/core/ext/transport/chttp2/alpn/alpn.c
@@ -36,7 +36,7 @@
 #include <grpc/support/useful.h>
 
 /* in order of preference */
-static const char *const supported_versions[] = {"h2"};
+static const char *const supported_versions[] = {"grpc-exp", "h2"};
 
 int grpc_chttp2_is_alpn_version_supported(const char *version, size_t size) {
   size_t i;