The side effect of #1832 has been that there are now two ways to determine if a header name is a token: one by using h2o_iovec_is_token (which refers to the address of the name) and the other by h2o_header_is_token (which refers to h2o_header_t::flags.token_index_plus1. To keep the two consistent, we introduced h2o_validate_header.

Now it seems to me that we can simplify the design by splitting h2o_header_flags_t into two structures: h2o_token_flags_t and h2o_header_flags_t.

The only flag that needs to be configurable (from outside the HTTP protocol implementation) is the dont_compress flag. We retain that in h2o_header_flags_t at the same time removing all the other fields.

h2o_token_flags_t is now part of h2o_token_t; functions that dealt with the redundant structure (i.e. h2o_validate_header, h2o_header_is_token) are removed.