expression {
  call_expr {
    function: "_==_"
    args {
      call_expr {
        function: "_[_]"
	args {
	  select_expr {
	    operand {
	      ident_expr {
	        name: "request"
	      }
	    }
	    field: "headers"
	  }
	  const_expr {
	    string_value: "foo"
	  }
        }
      }
      const_expr {
        string_value: "bar"
      }
    }
  }
}
request_headers {
  headers{key: ":method" value : "GET"}
  headers{key: ":path" value : "/"}
  headers{key: ":scheme" value : "http"}
  headers{key: ":authority" value : "foo.com"}
  headers {key: "foo" value: "bar"}
  headers {}
  headers {}
  headers {}
  headers {}
}
response_headers {
  headers {
    key: ":status"
    value : "200"
  }
}
trailers {
  headers {}
}
stream_info {}