shadowsocks/shadowsocks-rust · error

`method` is required

Error message

`method` is required

What it means

After mapping the optional `ENCRYPT_METHOD` value, the code calls `.expect("`method` is required")`. This panics when `--server-addr` was given on the CLI but `--encrypt-method` was not — the inner map produced None. The server requires a cipher method when a server is defined via command-line arguments.

Source

Thrown at src/service/server.rs:337

            }
            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}"),
                        }
                    }
                }
            };

            let svr_addr = svr_addr.parse::<ServerAddr>().expect("server-addr");

View on GitHub (pinned to 8eb0f0a65b)

Solutions

1. Add `--encrypt-method aes-256-gcm` (or another supported cipher) to the command line
2. Or use a config file with the `method` field instead of CLI flags
3. In scripts, assert the method variable is non-empty before invoking ssserver

Example fix

// before
ssserver -s "0.0.0.0:8388" -p "pass"
// after
ssserver -s "0.0.0.0:8388" -p "pass" -m aes-256-gcm

// enforce method presence when server-addr is used
if cli.server_addr.is_some() {
    assert!(cli.method.is_some(), "--encrypt-method is required with --server-addr");
}

fn method_present(addr: Option<&str>, method: Option<&str>) -> bool {
    addr.is_none() || method.is_some()
}

null

When it happens

Trigger: Running `ssserver -s 0.0.0.0:8388 -p password` without `--encrypt-method`/-m; the server address path is taken but no method was supplied.

Common situations: New users omitting `-m` because a config file normally supplies it; scripts that pass the server address but forget the method; migrating from tools with implicit default ciphers.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

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

AI-assisted analysis of shadowsocks/shadowsocks-rust@8eb0f0a65b (2026-09-09). Data as JSON: /api/errors/b781f6012dd4ccb3. Report an issue: GitHub.