Pollux - A Simple Gemini Server

Pollux is a lightweight Gemini server for serving static files securely. It supports virtual hosting, allowing multiple Gemini capsules on a single server instance. Features include TLS encryption, hostname validation, directory serving, and comprehensive security protections.

Requirements

Rust 1.70+ and Cargo.

Building

Clone or download the source, then run:

cargo build --release

This produces the target/release/pollux binary.

Virtual Hosting

Pollux supports virtual hosting, allowing you to serve multiple Gemini capsules from a single server. Each hostname can have its own root directory, certificates, and configuration.

Configuration

Create a config file at /etc/pollux/config.toml or use --config to specify a path:

# Global settings (optional)
bind_host = "0.0.0.0"
port = 1965
max_concurrent_requests = 1000   # requests processed at once (default 1000)
max_connections = 512            # connections handled at once (default 512)

# Virtual host configurations
["example.com"]
root = "/var/gemini/example.com"
cert = "/etc/ssl/example.com.crt"
key = "/etc/ssl/example.com.key"

["blog.example.com"]
root = "/var/gemini/blog"
cert = "/etc/ssl/blog.crt"
key = "/etc/ssl/blog.key"

["another-site.net"]
root = "/var/gemini/another"
cert = "/etc/ssl/another.crt"
key = "/etc/ssl/another.key"

Set the log level with the RUST_LOG environment variable (for example RUST_LOG=info) rather than in the config file.

Keep max_connections comfortably below the process file-descriptor limit (ulimit -n, or LimitNOFILE in the systemd unit). Connections above the limit are dropped immediately, which keeps the listener responsive.

Not implemented: per-host port and log_level keys are still parsed for backwards compatibility but have no effect — every host is served on the single global port. Pollux logs a warning at startup if it sees them.

Features

• Multiple hostnames on a single server instance
• Per-host TLS certificates selected by SNI, so each capsule presents its own identity
• Automatic content isolation - each host serves only its own files
• Path security - directory traversal and symlink escapes are blocked
• Hidden files are private - dotfiles and dot-directories (.git, .env) are never served
• Streamed responses - memory use is independent of file size, capped at 64 MiB per response
• Index file serving - index.gmi files are served automatically
• Hostname validation - DNS-compliant hostname checking, matched case-insensitively

Request Routing

• gemini://example.com/ → serves /var/gemini/example.com/index.gmi
• gemini://blog.example.com/article.gmi → serves /var/gemini/blog/article.gmi
• gemini://unknown.com/ → returns status 53 "Proxy request refused"

Single Host Mode (Legacy)

For backward compatibility, you can still use the old single-host format:

root = "/path/to/static/files"
cert = "/path/to/cert.pem"
key = "/path/to/key.pem"
hostname = "gemini.example.com"
bind_host = "0.0.0.0"
port = 1965
max_concurrent_requests = 1000

Development Setup

Quick Start with Self-Signed Certs

mkdir -p tmp
openssl req -x509 -newkey rsa:2048 \
  -keyout tmp/key.pem \
  -out tmp/cert.pem \
  -days 365 \
  -nodes \
  -subj "/CN=localhost"

Update config.toml:

cert = "tmp/cert.pem"
key = "tmp/key.pem"

Run the server:

./pollux --config /path/to/config.toml

Access with a Gemini client like Lagrange at gemini://yourdomain.com/.

Development Notes

• These certificates are for local testing only
• Browsers will show security warnings with self-signed certs
• Certificates in the dev/ directory are gitignored for security

Options

• --config (-C): Path to config file (default /etc/pollux/config.toml)
• --test-processing-delay (debug builds only): Add delay before processing requests (seconds) - for testing rate limiting

Logging

Pollux uses the tracing crate for structured logging. Configure log levels with the RUST_LOG environment variable:

# Basic usage
export RUST_LOG=info
./pollux

# Module-specific levels
export RUST_LOG=pollux=debug,sqlx=info

# Maximum verbosity
export RUST_LOG=trace

Available levels: error, warn, info, debug, trace

Security

Pollux is designed with security as a priority:

• Path traversal protection - requests like ../../../etc/passwd are blocked
• TLS encryption - all connections are encrypted with valid certificates
• Content isolation - virtual hosts cannot access each other's files
• Request validation - malformed requests are rejected
• Rate limiting - configurable concurrent request limits prevent abuse

Best Practices

Virtual Hosting Setup

• Use separate TLS certificates for each hostname when possible
• Keep host root directories separate and properly permissioned
• Use DNS-compliant hostnames (no underscores, proper formatting)
• Monitor logs for unknown hostname attempts

Certificate Management

• Never commit certificate files to version control
• Use development certificates only for local testing
• Production certificates should be obtained via Let's Encrypt or your CA
• Rotate certificates regularly and restart the server

File Organization

• Create index.gmi files in directories for automatic serving
• Use .gmi extension for Gemini text files
• Store certificates outside web-accessible directories
• Use proper file permissions (readable by server user only)

Limitations

• No dynamic content - Pollux serves only static files
• Single certificate per server - All hosts currently share the same TLS certificate (can be enhanced)
• No CGI support - No server-side processing or scripting
• Memory usage - All host configurations are loaded into memory
• No HTTP support - Gemini protocol only

Examples

The examples/ directory contains sample configuration files:

• virtual-hosting.toml - Multi-host setup with different certificates
• single-host.toml - Legacy single-host configuration
• development.toml - Local development with self-signed certificates

Testing

Run cargo test for the full test suite, which includes comprehensive integration tests covering:

• Virtual hosting with multiple hostnames
• TLS certificate validation
• Path security and isolation
• Concurrent request handling
• Performance validation

Note: Some integration tests use Python 3 for Gemini protocol validation. If Python 3 is not available, certain tests will be skipped automatically.