usocks

SOCKS5 proxy for Linux 6.1 or newer on io_uring. CONNECT to IPv4, IPv6 and domain names; one event loop thread per worker process, libc only. Domain names are resolved by getaddrinfo() in 16 threads per worker. A lookup that waits 10 s for a thread fails untried; one in progress takes as long as the system resolver allows, which options timeout:1 attempts:2 in /etc/resolv.conf shortens. Half-close and data sent before the reply are relayed. The handshake and each connect attempt time out after 10 s; relayed connections have no idle timeout and rely on TCP keepalive. Each connection slot reserves 130 KB of buffers, resident once used and kept for later connections; past the limit, clients wait in the listen backlog. Connections that fail before relaying log one line to stderr.

A worker relays on one CPU core. With -w, workers share the port through SO_REUSEPORT and nothing else: the kernel spreads new connections among them by address hash, -m applies to each, and when one exits, all exit.

Destinations are not filtered: clients reach whatever the host can, including its loopback services, so listening beyond loopback without -u makes an open proxy. RFC 1929 sends the password in plaintext. -p is visible in ps until usocks blanks it at startup; USOCKS_PASS is not. A unix socket takes its mode from the umask; a stale socket at its path is replaced, a live one is not. Container seccomp profiles often block io_uring.

Build

make
make install

Needs a C99 compiler and Linux headers (Alpine: build-base linux-headers). PREFIX defaults to /usr/local; DESTDIR is honored. For a static binary, use make LDFLAGS=-static, preferably with musl.

Usage

usocks [-l addr:port|path] [-m maxconn] [-w workers] [-u user -p pass]

-l  listen on addr:port, [addr6]:port or a unix socket path
    (default 127.0.0.1:1080)
-m  connection limit per worker, 1 to 16384 (default 1024)
-w  worker processes, 1 to 64 (default 1); not with a unix socket
-u  require RFC 1929 authentication with this username
-p  password for -u

USOCKS_LISTEN, USOCKS_MAXCONN, USOCKS_WORKERS, USOCKS_USER and USOCKS_PASS set the same values. Flags take precedence.

Testing

make && ./test

Needs python3; takes about 15 s.