read http2 body empty

nginx version: openresty/1.19.9.1

server {
        listen       80 http2;
        server_name  localhost;

        #charset koi8-r;

        #access_log  logs/host.access.log  main;

        location / {
            content_by_lua_block {
                ngx.req.read_body()
                ngx.log(ngx.ERR, ngx.req.get_body_data())
            }
        }
} 

use curl to test, get_body_data can get data

curl --http2-prior-knowledge 'http://127.0.0.1:80'  -XPOST -d 'hello wrold'

use grpc client,https://github.com/grpc/grpc/blob/master/examples/python/helloworld/greeter_client.py
get_body_data return nil

Start by reproducing the configuration with curl over HTTP/2 and with the linked gRPC Python client. Trace how content_by_lua_block handles ngx.req.read_body() and ngx.req.get_body_data() for each request type. Done means the differing behavior is explained and get_body_data returns the expected request data or the limitation is documented.