id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	uname	nginx_version
1538	gRPC upstreams cannot use dynamic HPACK	swolter.google.com@…		"""upstream sent invalid http2 table index: 64 while reading response header from upstream,""

gRPC uses the HPACK header compression (https://tools.ietf.org/html/rfc7541), which allows for dynamic header compression by assigning each key/value pair an ID in an HPACK table. There is a static, pre-shared part of the HPACK table (values 0 .. 60), and a dynamic part. When a gRPC upstream uses a header for the first time, it sends ""literal header with incremental indexing"" (header name/value + id), and afterwards sends only the id (""indexed header"").

nginx has the static HPACK values compiled in, but errors out on any attempt of the upstream to set a dynamic value (> 61). The client will only receive a 502. For example, any golang gRPC server is incompatible with nginx because the upstream will set content-type/application-grpc, which is not in the static HPACK table.

The offending code is https://github.com/nginx/nginx/blob/master/src/http/modules/ngx_http_grpc_module.c#L2626, which hardcodes the static table."	defect	closed	major		other	1.13.x	invalid				1.13.10