feat: socks5 proxy server

[qdm12]

Description

New options:

• SOCKS5_ENABLED=off
• SOCKS5_LISTENING_ADDRESS=":1080"
• SOCKS5_USER=
• SOCKS5_PASSWORD=

Issue

Fixes #234

Assertions

• I am aware that we do not accept manual changes to the servers.json file
• I am aware that any changes to settings should be reflected in the wiki

[Copilot]

Pull request overview

This PR introduces a new internal SOCKS5 proxy server (with optional username/password auth), wires it into Gluetun startup/shutdown, and adds configuration/env var plumbing plus unit/integration-style tests to support the feature request in #2409.

Changes:

• Add internal/socks5 package implementing a SOCKS5 CONNECT proxy with RFC1929 username/password auth.
• Add configuration settings/env vars for SOCKS5 and surface them in the global settings output.
• Start the SOCKS5 server loop from cmd/gluetun/main.go and add tests for the new package.

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
internal/socks5/socks5.go	Core SOCKS5 handshake + CONNECT handling and TCP relay.
internal/socks5/server.go	TCP listener accept loop and per-connection handling.
internal/socks5/loop.go	Restarting loop wrapper around the SOCKS5 server.
internal/socks5/usernamepassword.go	RFC1929 username/password subnegotiation.
internal/socks5/response.go	SOCKS5 response encoding helpers.
internal/socks5/constants.go	SOCKS5 protocol constants and stringers.
internal/socks5/settings.go	Internal settings struct for the SOCKS5 package.
internal/socks5/interfaces.go	Logger interface for the SOCKS5 package.
internal/socks5/socks5_test.go	Unit + end-to-end proxy tests for the SOCKS5 package.
internal/socks5/mocks_generate_test.go / internal/socks5/mocks_test.go	Generated GoMock logger for tests.
internal/configuration/settings/socks5.go	New config/env parsing + defaults + validation for SOCKS5.
internal/configuration/settings/settings.go	Add SOCKS5 settings to the global settings lifecycle (read/validate/defaults/string).
internal/configuration/settings/settings_test.go	Update settings string snapshot for SOCKS5 section.
Dockerfile	Add default SOCKS5 env vars.
cmd/gluetun/main.go	Start/stop SOCKS5 loop and include it in crash monitoring.

Files not reviewed (1)

• internal/socks5/mocks_test.go: Language not supported

Comments suppressed due to low confidence (1)

internal/socks5/loop.go:41

• runErrorCh is returned to the caller but nothing ever writes to it (and it is never closed). In cmd/gluetun/main.go the main select waits on this channel, so SOCKS5 loop failures will never be reported and the goroutine can leak. Consider returning runDone directly, or forwarding errors from run/server.Start into runErrorCh and closing it on exit.

	runDone := make(chan error)
	l.runDone = runDone
	runErrorCh := make(chan error)

	go run(runCtx, runDone, l.settings)

	return runErrorCh, nil
}

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[Copilot]

Pull request overview

Copilot reviewed 15 out of 16 changed files in this pull request and generated 4 comments.

Files not reviewed (1)

• internal/socks5/mocks_test.go: Language not supported

[Copilot]

Pull request overview

Copilot reviewed 15 out of 16 changed files in this pull request and generated 6 comments.

Files not reviewed (1)

• internal/socks5/mocks_test.go: Language not supported

[Copilot]

Pull request overview

Copilot reviewed 15 out of 16 changed files in this pull request and generated 5 comments.

Files not reviewed (1)

• internal/socks5/mocks_test.go: Language not supported

[Copilot]

Pull request overview

Copilot reviewed 15 out of 16 changed files in this pull request and generated 3 comments.

Files not reviewed (1)

• internal/socks5/mocks_test.go: Language not supported