tls-proxy-tunnel

tls-proxy-tunnel (tpt) is a layer-4 proxy written in Rust. It listens on configured ports, peeks at the TLS SNI to select a route, and tunnels the connection to a remote address — optionally via an HTTP CONNECT proxy.

Features

• Listen on one or more ports and forward TCP connections
• SNI-based routing without terminating TLS
• DNS backend with periodic re-resolution (tcp://, tcp4://, tcp6://)
• HTTP CONNECT tunnelling with configurable headers and timeout (via)
• Environment-variable substitution in header values ($VARNAME)
• Per-server connection limit (maxclients)
• Prometheus metrics endpoint (/metrics)
• Built-in upstreams: ban, echo, health
• JSON or plain-text log format; log level configurable per config or RUST_LOG

Sequence diagram

sequenceDiagram
  participant CL AS Client
  participant LP AS tls-proxy-tunnel
  participant UP AS Upstream Proxy
  participant DS AS Destination Server

  CL->>LP: TCP connect (SNI used for routing)
  LP->>UP: TCP connect to upstream proxy
  LP->>UP: HTTP CONNECT {sni}:{port}
  UP->>DS: Connect to destination
  DS->>UP: Connection established
  UP->>LP: 200 Connection Established
  Note over CL,DS: Tunnel open
  CL->>DS: TLS handshake (SNI visible to destination)
  DS->>CL: TLS handshake complete
  Note over CL,DS: Encrypted traffic
  CL->>DS: Connection closed

Installation

Build from source (requires Rust toolchain):

cargo build --release
# binary: target/release/tls-proxy-tunnel

Install via Cargo:

cargo install tls-proxy-tunnel

Or download a pre-built binary from the Releases page.

Usage

tpt [OPTIONS]

OPTIONS:
    -c, --config <path>    Path to config file
    -h, --help             Show this help

When --config is not given, tpt searches for a config file in this order:

1. $TPT_CONFIG environment variable
2. /etc/tpt/tpt.yaml
3. /etc/tpt/config.yaml
4. ./tpt.yaml
5. ./config.yaml

If no arguments are given and no config file is found, the help text is printed.

Configuration

Config files use YAML. Versions 1 and 2 are supported.

Minimal example

version: 1
log: info

servers:
  proxy_server:
    listen:
      - "0.0.0.0:8443"
    tls: true
    sni:
      www.example.com: corp_proxy
    default: ban
    maxclients: 100
    via:
      use_sni_as_target: true
      target_port: 443
      connect_timeout: 30s

  health_server:
    listen:
      - "127.0.0.1:8080"
    default: health

upstream:
  corp_proxy: "tcp://proxy.internal:3128"

Full via reference

via:
  target: "host:port"          # static CONNECT target; ignored when use_sni_as_target: true
  use_sni_as_target: true      # derive CONNECT target from TLS SNI
  target_port: 443             # port appended to SNI (default: 443)
  connect_timeout: 30s         # upstream connect timeout (default: 30s)
  stats_interval: 30s          # log rx/tx counters every N seconds (0s = off)
  headers:
    Proxy-Authorization: "Basic $ENCODED_PW"   # $VARNAME resolved from env
    X-Custom-Header: "static-value"

via can be set at server level (inherited by all SNI entries) or overridden per SNI entry:

sni:
  www.example.com: corp_proxy          # plain string: inherits server via
  intern.corp.org:
    upstream: direct_host
    via: {}                            # via: {} → direct TCP (no CONNECT)
  api.example.com:
    upstream: corp_proxy
    via:                               # per-SNI override
      target: "api.example.com:8443"
      connect_timeout: 10s

Upstream protocols

upstream:
  corp_proxy:  "tcp://proxy.internal:3128"    # IPv4 or IPv6
  corp_proxy4: "tcp4://proxy.internal:3128"   # force IPv4
  corp_proxy6: "tcp6://proxy.internal:3128"   # force IPv6

Logging

log: info          # off | error | warn | info | debug | trace | disable
log_format: txt    # txt | text | json  (default: txt)

RUST_LOG takes precedence over the config log field.

Built-in upstreams

Name	Behaviour
ban	Closes the connection immediately
echo	Reflects received bytes back to the sender
health	HTTP/1.1: GET /health → 200 OK, GET /metrics → Prometheus text

Prometheus metrics

The health upstream exposes /metrics in Prometheus text format:

# HELP tpt_active_connections Current number of active connections
# TYPE tpt_active_connections gauge
tpt_active_connections{name="proxy_server",listen="0.0.0.0:8443"} 3

# HELP tpt_maxclients Maximum number of concurrent connections
# TYPE tpt_maxclients gauge
tpt_maxclients{name="proxy_server",listen="0.0.0.0:8443"} 100

Test run

TPT_CONFIG=container-files/etc/tpt/config.yaml cargo run

Docker

tls-proxy-tunnel on Docker Hub

Thanks

• fourth, of which this is a heavily modified fork.
• layer4-proxy

License

tls-proxy-tunnel is available under the terms of Apache-2.0.