shadowsocks/shadowsocks-rust · error

method

Error message

method

What it means

In the server service `create`, the `ENCRYPT_METHOD` CLI value is parsed with `x.parse::<CipherKind>().expect("method")`. The panic means the provided encryption method string is not a valid `CipherKind`. This occurs while constructing a server from `--server-addr` CLI arguments (rather than a config file).

Source

Thrown at src/service/server.rs:336

                logging::init_with_file(path);
            }
            None => {
                logging::init_with_config("ssserver", &service_config.log);
            }
        }

        trace!("{:?}", service_config);

        let mut config = match config_path_opt {
            Some(cpath) => Config::load_from_file(&cpath, ConfigType::Server)
                .map_err(|err| ShadowsocksError::LoadConfigFailure(format!("loading config {cpath:?}, {err}")))?,
            None => Config::new(ConfigType::Server),
        };

        if let Some(svr_addr) = matches.get_one::<String>("SERVER_ADDR") {
            let method = matches
                .get_one::<String>("ENCRYPT_METHOD")
                .map(|x| x.parse::<CipherKind>().expect("method"))
                .expect("`method` is required");

            let password = match matches.get_one::<String>("PASSWORD") {
                Some(pwd) => read_variable_field_value(pwd).into(),
                None => {
                    // NOTE: svr_addr should have been checked by crate::vparser
                    if method.is_none() {
                        // If method doesn't need a key (none, plain), then we can leave it empty
                        String::new()
                    } else {
                        match crate::password::read_server_password(svr_addr) {
                            Ok(pwd) => pwd,
                            Err(..) => panic!("`password` is required for server {svr_addr}"),
                        }
                    }
                }
            };

View on GitHub (pinned to 8eb0f0a65b)

Solutions

1. Use an exact supported cipher: `aes-256-gcm`, `aes-128-gcm`, `chacha20-ietf-poly1305`, or SIP002 `2022-*` ciphers
2. Keep the method string identical on both client and server
3. Enable the required cargo feature if the cipher was compiled out
4. Put the method in the config file instead of CLI to avoid quoting/casing issues

Example fix

// before
--encrypt-method rc4-md5
// after
--encrypt-method chacha20-ietf-poly1305

const VALID: &[&str] = &["aes-128-gcm","aes-256-gcm","chacha20-ietf-poly1305"];
if let Some(m) = &cli.method {
    assert!(VALID.contains(&m.as_str()), "unknown method {m}");
}

fn is_known_cipher(s: &str) -> bool {
    matches!(s, "aes-128-gcm" | "aes-256-gcm" | "chacha20-ietf-poly1305")
}

// parse with a clear message
let kind: CipherKind = m.parse().map_err(|_| anyhow!("unsupported --encrypt-method {m}"))?;

When it happens

Trigger: Running `ssserver` with `--encrypt-method` set to an unrecognized cipher name — legacy ciphers (e.g. `aes-256-cfb`), wrong casing, extra whitespace, or a cipher not enabled in the build's feature flags.

Common situations: Following outdated tutorials referencing stream ciphers; mismatched method strings shared between client and server; typo in long cipher names like `2022-blake3-aes-128-gcm`.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• method
• `method` is required
• server-addr
• not supported `protocol` "{p}"
• `password` is required for server {svr_addr}

AI-assisted analysis of shadowsocks/shadowsocks-rust@8eb0f0a65b (2026-09-09). Data as JSON: /api/errors/089f30355ad59d3c. Report an issue: GitHub.