rust-web-server 17.2.0

Static file web server and HTTP toolkit written in Rust. Supports HTTP/3, HTTP/2, and HTTP/1.1. HTTP/3 and HTTP/2 require a TLS certificate; without one the server falls back to plain HTTP/1.1 automatically.
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[Read Me](README.md) > Configuration

# Configuration

`rws` can be started with no configuration and will bind to `127.0.0.1:7878` with 200 threads, CORS enabled for all origins.

Configuration is applied in order from lowest to highest priority:

1. Built-in defaults (`src/entry_point/mod.rs`)
2. System environment variables (`rws.variables`)
3. `rws.config.toml` in the working directory
4. Command-line arguments (`rws.command_line`)

## HTTPS, HTTP/2, and HTTP/3

TLS is built into the default `rws` binary. Providing a certificate and key enables HTTPS on the configured port. HTTP/2 is negotiated automatically via ALPN alongside HTTP/1.1 on the same TCP port. HTTP/3 listens on the same port number over UDP (QUIC) simultaneously.

To obtain a free certificate for a public domain use [Let's Encrypt](https://letsencrypt.org/).

For local development, generate a self-signed certificate:
```bash
openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365 -nodes \
  -subj "/CN=localhost" -addext "subjectAltName=DNS:localhost,IP:127.0.0.1"
```

### TLS configuration

| Environment variable | Config file key | Command-line arg | Description |
|---|---|---|---|
| `RWS_CONFIG_TLS_CERT_FILE` | `tls_cert_file` | `--tls-cert-file` / `-s` | Path to PEM certificate file |
| `RWS_CONFIG_TLS_KEY_FILE` | `tls_key_file` | `--tls-key-file` / `-k` | Path to PEM private key file |

Example — environment variables:
```bash
export RWS_CONFIG_TLS_CERT_FILE="/path/to/cert.pem"
export RWS_CONFIG_TLS_KEY_FILE="/path/to/key.pem"
```

Example — `rws.config.toml`:
```toml
tls_cert_file = '/path/to/cert.pem'
tls_key_file  = '/path/to/key.pem'
```

Example — command line:
```bash
rws --tls-cert-file=/path/to/cert.pem --tls-key-file=/path/to/key.pem
```

## All configuration options

| Environment variable | Config file key | Command-line arg | Default | Description |
|---|---|---|---|---|
| `RWS_CONFIG_IP` | `ip` | `--ip` / `-i` | `127.0.0.1` | Bind IP address |
| `RWS_CONFIG_PORT` | `port` | `--port` / `-p` | `7878` | Bind port |
| `RWS_CONFIG_THREAD_COUNT` | `thread_count` | `--thread-count` / `-t` | `200` | Thread pool size |
| `RWS_CONFIG_TLS_CERT_FILE` | `tls_cert_file` | `--tls-cert-file` / `-s` | _(none)_ | PEM certificate file |
| `RWS_CONFIG_TLS_KEY_FILE` | `tls_key_file` | `--tls-key-file` / `-k` | _(none)_ | PEM private key file |
| `RWS_CONFIG_CORS_ALLOW_ALL` | `cors_allow_all` | `--cors-allow-all` / `-a` | `true` | Allow all CORS origins |
| `RWS_CONFIG_CORS_ALLOW_ORIGINS` | `cors_allow_origins` | `--cors-allow-origins` / `-o` | _(none)_ | Allowed origins (comma-separated) |
| `RWS_CONFIG_CORS_ALLOW_METHODS` | `cors_allow_methods` | `--cors-allow-methods` / `-m` | _(none)_ | Allowed methods |
| `RWS_CONFIG_CORS_ALLOW_HEADERS` | `cors_allow_headers` | `--cors-allow-headers` / `-h` | _(none)_ | Allowed headers |
| `RWS_CONFIG_CORS_ALLOW_CREDENTIALS` | `cors_allow_credentials` | `--cors-allow-credentials` / `-c` | `false` | Allow credentials |
| `RWS_CONFIG_CORS_EXPOSE_HEADERS` | `cors_expose_headers` | `--cors-expose-headers` / `-e` | _(none)_ | Exposed headers |
| `RWS_CONFIG_CORS_MAX_AGE` | `cors_max_age` | `--cors-max-age` / `-g` | _(none)_ | Preflight cache duration (seconds) |
| `RWS_CONFIG_REQUEST_ALLOCATION_SIZE` | `request_allocation_size` | `--request-allocation-size-in-bytes` / `-r` | `16000` | Read buffer size per request |
| `RWS_CONFIG_CSP` | — | — | `default-src 'self'` | `Content-Security-Policy` header value; set to empty string to disable |

## Memory

`rws` allocates one read buffer per request (default 16 KB). If you serve large files, use HTTP Range Requests on the client side to fetch them in parts, or increase `request_allocation_size` with caution.