GSproxy is a standalone Perl tool that reads a CSV list of remote targets and keeps a working SOCKS proxy alive for each of them. It brings up remote SOCKS servers over an MCP shell bridge, starts local gs-netcat SOCKS clients, watches every proxy, and exposes a single gateway SOCKS port that always points at the first healthy proxy.
## Overview
The tool turns a list of `endpoint,secret,port` rows into a self-healing set of SOCKS proxies. For each row it does three things:
- Brings up a remote SOCKS server through an MCP `Tools_Shell_Command` call, using a gs-netcat listener wrapped to look like `python`.
- Starts a local gs-netcat SOCKS client bound to `127.0.0.1` on the row's port.
- Monitors the local SOCKS proxy and logs every status change.
It then listens on a gateway SOCKS port and relays each incoming connection to the first proxy that is currently alive.
The whole tool is written with core Perl modules only, so it runs without extra installs.
## Features
- CSV driven config, one proxy per row.
- Remote bring-up through an MCP shell call, reusing the gs-netcat listener command shape.
- Local gs-netcat SOCKS client launched per row.
- Continuous monitoring with configurable interval and per-check timeout.
- Automatic re-bring-up of dead proxies in the background.
- A gateway SOCKS port that follows the first alive proxy.
- Daemon mode with pidfile, status, and stop commands.
- Remote and local teardown that kills leftover gs-netcat processes.
The config file is CSV. Each non-empty, non-comment line has the form:
```
endpoint,secret,port[,label]
```
-`endpoint` is the base URL of the MCP server that exposes `Tools_Shell_Command`.
-`secret` is the gs-netcat shared secret used by both the remote listener and the local client.
-`port` is the local SOCKS port for that row. It must be a number from 1 to 65535.
-`label` is an optional friendly name. When missing it defaults to `row` plus the line number.
Blank lines and lines starting with `#` are ignored. A header line such as `endpoint,secret,port,label` is detected and skipped when the third field is not a number. Invalid rows are reported on standard error and skipped.
Example:
```
endpoint,secret,port,label
https://mcp.example.org,sekret123,20001,alpha
https://mcp.other.org,topsecret9,20002,beta
```
The `endpoint` may be a base URL or a full MCP URL. If it does not already end in `/gradio_api/mcp` or `/mcp`, the value of `--mcp-path` is appended.
-`--gateway-auth FILE` requires SOCKS5 username/password auth on the gateway. The first non-empty, non-comment line of FILE is `user:pass`; keep the file mode 0600.
-`--target-sha256 HASH` pins the SHA-256 of the remote gs-netcat binary (64 hex chars). The remote bring-up verifies the extracted binary before running it; a mismatch aborts the bring-up.
The `--daemon` option is a negatable boolean and defaults to on. `--verbose` and `-v` increase logging to standard error.
## How it works
gsproxy has four moving parts: the remote bring-up, the local client, the monitor, and the gateway.
- Remote bring-up downloads a gs-netcat build with `curl`, unpacks it, and runs a gs-netcat listener with `-lSD -s SECRET`. The listening process is renamed to `python` so it blends into the host.
- The local client runs `gs-netcat -D -p PORT -s SECRET`, which opens a SOCKS listener on `127.0.0.1` at the row's port.
- The monitor performs a full SOCKS5 handshake against each local port, testing a real CONNECT to a probe host and port. A passing handshake marks the proxy alive.
- The gateway accepts SOCKS5 connections on `--bind:--gateway-port` and relays them to the first alive proxy listed in the state file.
### MCP bring-up
The remote call is an MCP JSON-RPC exchange over HTTP. The script sends an `initialize` request, captures the `Mcp-Session-Id` header, sends the `notifications/initialized` notification, then calls `tools/call` with the name `Tools_Shell_Command`. Responses may be plain JSON or server-sent events, so the body is parsed for the last `data:` line before decoding. Requests are retried up to three times on transport failures.
### Monitoring and state
On every interval the monitor checks each proxy, logs only status changes, and writes the list of alive ports to the state file. The first alive port from that list is the current gateway target. When a proxy is found dead, the tool forks a background bring-up unless `--no-bringup` is set. In `--once` mode the bring-up runs inline instead of forking.
### Gateway relay
The gateway listens, forks per connection, and reads the target port from the state file. It opens a TCP connection to that port and copies bytes in both directions with `IO::Select`, shutting down each direction as its side closes. If the state file has no valid port, the connection is dropped.
Without `--gateway-auth` the gateway is a transparent relay. With `--gateway-auth` the gateway performs the SOCKS5 username/password exchange itself (RFC 1929), then greets the upstream proxy and forwards the client's CONNECT request, so only authenticated clients can route through it.
Stopping the tool cleans up both sides. Locally it scans `/proc` for gs-netcat processes that match the `-D -p PORT` shape and sends them `TERM`. Remotely it runs a shell command over MCP that scans `/proc` for processes whose environment contains `GSOCKET_ARGS=-lSD -s SECRET` and kills them.
## Command reference
- Start as a daemon: `./gsproxy.pl`
- Start and stop: `./gsproxy.pl --stop`
- Check status: `./gsproxy.pl --status`
- List config rows: `./gsproxy.pl --list`
- One pass, foreground: `./gsproxy.pl --once --no-daemon`
Every event is written with a UTC timestamp in the form `[YYYY-MM-DDTHH:MM:SSZ] message`. Bring-up, MCP results, status changes, gateway startup, and teardown are all logged. The log is appended, never truncated, so it grows over time. With `--verbose`, log lines are also printed to standard error.
## Gateway behavior
- The gateway always targets the first alive proxy in listing order.
- It re-reads the state file on every new connection, so failover is immediate.
- A dead or missing target port causes the connection to be dropped without reply.
- Each connection is handled by a forked child, keeping the listener responsive.
The `--selftest` mode runs offline checks and prints `PASS` or `FAIL` per case. It writes a temporary CSV, a temporary state file, and a temporary log under `/tmp`. It covers config parsing, command string quoting, gs-netcat process discovery, secret redaction, the single-instance lock, zombie detection, gateway auth accept/reject, live and dead SOCKS detection, and a full gateway relay (with and without auth) against a fake SOCKS server. It exits non-zero if any check fails.
## Hardening
- **File permissions.** The script runs with `umask 0077`, creates the log, pidfile, state, and auth files with mode 0600, and tightens pre-existing files at startup. It warns when the CSV config or the gateway auth file is group/world readable.
- **Secret redaction.** Every log line passes through a redactor that replaces configured secrets with `**`. This includes MCP tool results that echo the full remote command, so secrets no longer leak into the log.
- **Single instance.** An advisory `flock` on the pidfile plus a `/proc` scan for already-daemonized gsproxy processes prevents the overlapping-instance failure mode. A second instance refuses to start, and `--once`/foreground runs refuse while a daemon is active.
- **Gateway supervision.** The gateway child reports bind success through a pipe before serving. A bind failure aborts startup instead of leaving a half-alive instance, and the monitor restarts a crashed gateway (reaping zombies on every pass).
- **Verified stop.** `--stop` only signals processes that are really gsproxy instances, waits up to five seconds for them to exit, escalates to `KILL` if needed, and also finds daemons that are missing from the pidfile.
- **Gateway auth.** `--gateway-auth FILE` turns the gateway into a SOCKS5 username/password front-end. Without it the gateway is an open relay, and a warning is logged whenever the gateway binds to a non-loopback address.
- **Binary pinning.** `--target-sha256 HASH` verifies the downloaded gs-netcat binary on the remote host before it runs, so a tampered download fails the bring-up.
- The gateway binds to `0.0.0.0` by default and is an open relay unless `--gateway-auth` is set. Restrict `--bind` to `127.0.0.1` or enable auth if the host should not expose the proxy to the network.
- If the daemon will not start, run `--status` to see whether it is already running, then use `--stop` first. A live daemon detected in `/proc` or a locked pidfile also refuses startup.
