Why is cohttp 3 not installable on opam (an answer)

[mseri]

This was put clearly by @hannesm on the discord channel, and is worth saving here until the new release is out, to help whoever is currently trying to use cohttp 3.0.0:

Currently, cohttp 3.0.0 is marked as avalable: false on the opam repository -- reasons include #733 and further down the road some discussion about the new conduit interface (see mirage/ocaml-conduit#337 and mirage/ocaml-conduit#338 and also mirage/ocaml-conduit#339). There's quite some movement in conduit, and there'll soon be a next release, and a corresponding cohttp release.

Until then, you can still try the current version of the new cohttp with opam by pinning it opam pin add cohttp.3.0.0~dev --dev-repo (see also ocaml/opam-repository#17691)

[mseri]

With the release of 4.0.0 this should no longer be an issue: https://discuss.ocaml.org/t/ann-release-of-cohttp-4-0-0/7537