Butler — a Ruby HTTP client designed around modern Fiber-based concurrency

HTTP/1.1 and HTTP/2 with transparent ALPN negotiation, structured concurrency, built-in resilience, and security-conscious defaults — without ever exposing its transport in the public API.

gem install butler-http MIT licensed GitHub

Butler owns its own public API — Client, Request, Response, Headers — built around Ruby's Fiber::Scheduler rather than one Thread per in-flight request. That's the whole point of the design: real HTTP/2 multiplexing, structured concurrency you can actually reason about (client.async { |tasks| ... }), and a resilience layer (timeouts, deadlines, retries with backoff+jitter, a circuit breaker) that's part of the client, not four extra gems bolted onto Net::HTTP.

gem install butler-http

# HTTParty-style, zero setup:
Butler.get("https://api.example.com/users").json

# Or a configured Client, for connection pooling/retries/middleware tuned per-API:
client = Butler::Client.new(base_url: "https://api.example.com")

client.async do |tasks|
  users  = tasks.async { client.get("/users") }
  orders = tasks.async { client.get("/orders") }
  { users: users.wait.json, orders: orders.wait.json }
end

What it does

• HTTP/1.1 and HTTP/2 — transparent ALPN negotiation, multiplexed connection pooling per origin, and a per-call http_version: override when you need to force one or the other.
• Structured concurrency — client.async { |tasks| tasks.async { ... } } gives real parent/child task cancellation and exception propagation, backed by an Async::Barrier, not a bare Thread pool.
• Built-in resilience — a total-budget deadline: that survives every retry and redirect hop, exponential backoff with jitter, a CLOSED → OPEN → HALF_OPEN circuit breaker, and retry rules that actually respect HTTP semantics (POST is never auto-retried on a 5xx).
• Security-conscious defaults — TLS/hostname verification on by default, certificate-verification failures are never retried (a bad cert won't become valid on the next attempt), a host allow/block list, response/header size limits, and credential stripping on cross-origin redirects.
• Observability and testing — standalone instrumentation with optional OpenTelemetry and Rails/ActiveSupport::Notifications bridges, plus native request stubbing with no WebMock/VCR dependency.

How it compares

Capability	Butler	Faraday	Excon	Net::HTTP
Fiber-native concurrency	✓	—	—	limited
HTTP/2 (ALPN, multiplexed)	✓ (first-class)	adapter-dependent	limited	depends
Connection pooling	✓	adapter	✓	manual
Retries + backoff/jitter	built-in	middleware	limited	manual
Circuit breaker	built-in	external gem	external gem	external gem
Deadlines (total budget across retries)	✓	—	—	—
OpenTelemetry	first-class, optional	external	external	external
Native request stubbing	✓	via WebMock	via WebMock	via WebMock

The one architectural rule that keeps this from rotting into "Faraday but slower": Butler owns its public abstractions. async/async-http implement the real transport underneath, but nothing outside lib/butler/transport.rb ever touches those types — the public API doesn't change if the transport underneath it ever does. Full breakdown, including Excon/HTTParty and a real Sequential/Concurrent benchmark matrix, in the README.

Guides

• Fiber-based concurrency in Ruby, explained — what Fiber::Scheduler actually is, thread-per-request vs. Fiber-per-request, and why it fits I/O-bound HTTP work specifically.
• HTTP/2 multiplexing vs. HTTP/1.1 connection pooling — the conceptual difference, and what it actually buys you under real concurrency.
• Building resilient HTTP clients: timeouts, deadlines, retries, and circuit breakers — the concepts, and where a naive implementation of each one quietly goes wrong.
• Choosing a Ruby HTTP client: Butler vs. Faraday vs. Excon vs. HTTParty vs. Net::HTTP — a straight, contender-by-contender comparison.

Links