elixir-mint / hpax

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Build # 7eea90af881d0fcd10b072cdb99a3f1d4021386b

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push

github

Committed by web-flow

Commit Message

Use empty binary, not nil, for static table entries with no default value (#27)

HPAX.Table's @static_table stored `nil` as the value for the many
static entries that have no default (RFC 7541, Appendix A - e.g.
:authority, host, user-agent). Decoding a plain Indexed Header Field
Representation (section 6.1) against one of these entries - fully
legal per the RFC, and something real HTTP/2 clients (and h2spec) do
- returned that literal `nil` as the header value, silently violating
this module's own documented contract that decoded values are always
binaries (HPAX.header_value() :: binary()).

Any caller relying on that contract (e.g. calling byte_size/1 on
every decoded value) would crash on such a request. This also meant
the encoder could never emit a compact single-byte indexed reference
when asked to encode one of these headers with a literal empty-string
value, since the {:full, index} match required by lookup_by_header/3
was guarded with `is_binary(value)` and so never fired for the
nil-valued entries.

Storing "" instead of nil fixes both: decoded values are always
binaries as documented, and encoding a header whose value happens to
be "" for one of these names now correctly compresses to one byte.

* Test that encoding a static entry's default value compresses to one byte

Covers the encoder-side half of the previous commit's fix: headers
whose value matches a static table entry with no defined default
(e.g. "user-agent": "") can now be found via a {:full, index} match
and encoded as a single indexed-header-field byte, rather than always
falling back to a literal encoding because the {:full, _} lookup
clause was guarded with is_binary(value) and so never matched the
old nil-valued entries.

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