Migrate to capy post-#262 buffer API

[mvandeberg]

cppalliance/capy#262 removes the slice CPO machinery (capy::prefix, capy::sans_prefix, capy::remove_prefix, capy::remove_suffix, capy::keep_prefix, capy::slice_of<>) and the capy::const_buffer_pair / capy::mutable_buffer_pair aliases. boost::http migrates to the replacements:

• capy::const_buffer_pair / capy::mutable_buffer_pair --> std::array<capy::const_buffer, 2> / std::array<capy::mutable_buffer, 2>.

• capy::prefix(seq, n) returning a 2-element buffer pair --> local helper prefix_pair(seq, n) in src/parser.cpp that constructs the trimmed array directly. Retained for the call sites that consume the result as a std::array (i.e. assigning to a parser member or passing to filter::process).

• For one parser site where the result is consumed by capy::buffer_copy, the migration uses capy::buffer_slice directly: auto chunk = capy::buffer_slice(cb0_.data(), 0, n); then buffer_copy(target, chunk.data()). Demonstrates the by-value buffer_slice's idiomatic use; the slice owns its buffer-sequence copy and works with the prvalue cb0_.data().

• capy::remove_prefix(pair, n) / capy::remove_suffix(pair, n) on 2-element buffer pairs --> local helpers trim_prefix_pair / trim_suffix_pair in src/serializer.cpp. Retained for out_prepare()'s in-place std::array trim.

• capy::remove_prefix(buf, n) on a single buffer --> buf += n (member operator already provided by capy).

• capy::sans_prefix(seq, n) --> capy::buffer_slice(seq, n) (returns a Slice exposing the buffer sequence via .data()). In iterative consumption loops, advance an existing slice in place via slice.remove_prefix(n).

• filter::process now takes boost::span<const capy::mutable_buffer> and std::array<capy::const_buffer, 2> directly, and drives the loop using capy::buffer_slice internally.

• Test serializer.cpp's read_some builds a slice in one expression via capy::buffer_slice(sr.prepare().value(), 0, 256) and iterates .data(). Since capy's buffer_slice captures its underlying buffer sequence by value, the prvalue sr.prepare() .value() is safe — the slice owns its own copy.

Coordinated with capy PR cppalliance/capy#262. Merge order: this PR lands before #262 (so http remains buildable against capy's `develop` during the brief window).

[cppalliance-bot]

An automated preview of the documentation is available at https://270.http.prtest3.cppalliance.org/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-05-15 21:13:19 UTC