Systems

The internal subsystems of libcurl. Each page here covers a single architectural concept that crosses many .c files. The protocol-specific details (HTTP, FTP, TLS, SSH, etc.) live under Features; this section covers the shared engine.

Page	Description
Transfer engine	The multi state machine that drives every transfer
Connection management	Connection cache, reuse, share handle, shutdown
Connection filters	The filter framework that stacks TLS, HTTP/2, HTTP/3, proxy, and socket layers
DNS resolution	Sync, threaded, c-ares, and DoH resolvers and the DNS cache
Protocol handlers	The Curl_protocol registry and how scheme dispatch works