Here are the list of HTTP client libraries/wrappers, and some thoughts on HTTP client in general. I’d like to hear from others how they work with HTTP..

HTTP client libraries

• httpc — OTP 29.0.2 (inets 9.7.1) - erlang (part of OTP)
• GitHub - benoitc/hackney: simple HTTP client in Erlang · GitHub - erlang, socket pools
• GitHub - cmullaparthi/ibrowse: Erlang HTTP client · GitHub - erlang, pool/pipeline per destination
• GitHub - puzza007/katipo: HTTP2/HTTP3 client for Erlang based on libcurl and libevent · GitHub - erlang, libcurl
• GitHub - ninenines/gun: HTTP/1.1, HTTP/2, Websocket client (and more) for Erlang/OTP. · GitHub - erlang, HTTP/2, Websocket, keeping connection with supervisor
• GitHub - inaka/shotgun: For the times you need more than just a gun. · GitHub - erlang, on the top of gun, out-of-box support of Server-sent Events

HTTP Client Wrappers

• GitHub - elixir-tesla/tesla: The flexible HTTP client library for Elixir, with support for middleware and multiple adapters. · GitHub - elixir, support httpc, hackney, ibrowse
• GitHub - edgurgel/httpoison: Yet Another HTTP client for Elixir powered by hackney · GitHub - elixir, hackney
• GitHub - valpackett/httpotion: [Deprecated because ibrowse is not maintained] HTTP client for Elixir (use Tesla please) · GitHub - elixir, ibrowse
• GitHub - alexandrubagu/simplehttp: HTTP client for Elixir without dependencies · GitHub - elixir, httpc

Related links

• HTTP client libraries - need better one in standard library?
• Erlang httpc or Elixir third-party http libraries (httpoison, httppotion)?

Thoughts & Questions

• Although HTTP spec says headers are case-insensitive, http client libraries should not automatically downcase such values (especially for outgoing request) since there are applications require specific cases
• headers, form data, and query string should be a list not a map to preserve orders (both order of keys and order of values)
• For performance, what about using NIF to parse headers? For example, puma (app server in Ruby) uses C for this: puma/ext/puma_http11 at v3.12.0 · puma/puma · GitHub - such parser may be shared across client/server.
• How should HTTP libraries handle HTTP version upgrade?
• Should HTTP libraries make pure functional (zero side effect) or leverage more global states (connection pools, keeping connection, etc.)?
  • For example, Tesla allows creating new client on the fly, so that it “builds” client without any configuration from “global” config; however as it may use HTTP client library (application) which maintains some state in it.