persistent connection

[Piyush-Goenka]

Summary

• Add Content-Length and Connection header negotiation as prerequisites for connection reuse.
• Add configurable idle timeout (default 30s) and per-request parsing timeout (default 10s) to protect against slow/malicious clients.

Changes

request_parser.rb

• Added create_stream(socket) so the IO stream is created once per connection and reused across requests.
• parse now accepts stream: and optional version: (cached after the first request) instead of creating a new stream from socket: each time.
• Returns nil on EOF instead of raising, letting the connection loop exit cleanly.
• parse_body reads exactly Content-Length bytes instead of stream.read (which would block forever on a persistent connection).
• Guards against nil from stream.gets during header parsing (client disconnect mid-request).

response_builder.rb

• Adds Content-Length header (file size for file bodies, bytesize for buffered bodies).
• Adds Connection: keep-alive or Connection: close based on negotiation.
• Removed socket.close — connection lifecycle is now managed by LowLoop#handle_connection.
• Uses socket.write for the body instead of socket.puts (avoids trailing newline that would break Content-Length).
• Filters Content-Length and Connection from the response headers loop so we don't emit duplicates when a handler sets them.

low_loop.rb

• Extracted handle_connection(socket) that owns the full connection lifecycle: create stream → loop (wait → parse → process → respond → check keep-alive) → close.
• keep_alive? negotiates per RFC 9112: HTTP/1.1 defaults keep-alive, HTTP/1.0 defaults close. Handles multi-token Connection headers (e.g. Connection: Upgrade, close) by splitting on commas.
• socket.wait_readable(keep_alive_timeout) for idle timeout (Fiber-scheduler-aware, unlike IO.select).
• socket.timeout = request_timeout during parsing to bound each read — prevents slowloris-style attacks where a client drip-feeds bytes to hold the connection open. IO::TimeoutError exits the loop cleanly.
• Configurable via config.keep_alive_timeout (default 30s) and config.request_timeout (default 10s).

response_factory.rb

• Fixed response version string from http/1.1 to HTTP/1.1 so clients correctly identify the protocol (curl was falling back to HTTP/1.0 parsing otherwise).

spec/units/low_loop_spec.rb

• Bumped concurrent-request timing threshold from 1.1s to 1.2s to account for the small keep-alive connection lifecycle overhead (one extra loop iteration per connection to detect client disconnect).