What causes "invalid `udp_weight`, must be in [0, 1]" in shadowsocks/shadowsocks-rust?

Set udp_weight within [0.0, 1.0], e.g. 0.5 for half weight

invalid `udp_weight`, must be in [0, 1]

Error message

invalid `udp_weight`, must be in [0, 1]

What it means

Thrown when a server entry specifies `udp_weight` outside [0.0, 1.0]. Like tcp_weight, this feeds ServerWeight for traffic balancing; the parser validates it immediately after tcp_weight and rejects values below 0 or above 1 with ErrorKind::Invalid. Defaults to 1.0 when omitted.

Source

Thrown at crates/shadowsocks-service/src/config.rs:2386

                }

                if let Some(remarks) = svr.remarks {
                    nsvr.set_remarks(remarks);
                }

                if let Some(id) = svr.id {
                    nsvr.set_id(id);
                }

                if svr.tcp_weight.is_some() || svr.udp_weight.is_some() {
                    let tcp_weight = svr.tcp_weight.unwrap_or(1.0);
                    if !(0.0..=1.0).contains(&tcp_weight) {
                        let err = Error::new(ErrorKind::Invalid, "invalid `tcp_weight`, must be in [0, 1]", None);
                        return Err(err);
                    }
                    let udp_weight = svr.udp_weight.unwrap_or(1.0);
                    if !(0.0..=1.0).contains(&udp_weight) {
                        let err = Error::new(ErrorKind::Invalid, "invalid `udp_weight`, must be in [0, 1]", None);
                        return Err(err);
                    }
                    let mut weight = ServerWeight::new();
                    weight.set_tcp_weight(tcp_weight);
                    weight.set_udp_weight(udp_weight);
                    nsvr.set_weight(weight);
                }

                let mut server_instance = ServerInstanceConfig::with_server_config(nsvr);

                if let Some(acl_path) = svr.acl {
                    let acl = match AccessControl::load_from_file(&acl_path) {
                        Ok(acl) => acl,
                        Err(err) => {
                            let err = Error::new(
                                ErrorKind::Invalid,
                                "acl loading failed",
                                Some(format!("file {acl_path}, error: {err}")),

View on GitHub (pinned to 8eb0f0a65b)

Solutions

Set udp_weight within [0.0, 1.0], e.g. 0.5 for half weight
Use 0.0 to disable UDP traffic for that server
Remove the field to accept the default of 1.0

Example fix

// before
{"server": "1.2.3.4", "server_port": 8388, "method": "aes-256-gcm", "password": "pw", "udp_weight": 80}
// after
{"server": "1.2.3.4", "server_port": 8388, "method": "aes-256-gcm", "password": "pw", "udp_weight": 0.8}

Defensive patterns

Strategy: validation

Validate before calling

if let Some(w) = svr.get("udp_weight").and_then(|w| w.as_f64()) {
    assert!((0.0..=1.0).contains(&w), "udp_weight {w} out of [0,1]");
}

Type guard

fn valid_udp_weight(w: f64) -> bool { (0.0..=1.0).contains(&w) }

Try / catch

let udp_weight = svr.udp_weight.unwrap_or(1.0);
if !(0.0..=1.0).contains(&udp_weight) {
    eprintln!("clamping udp_weight {udp_weight} to [0,1]");
}

Prevention

Validate tcp_weight and udp_weight together — either being present triggers both checks
Use a shared helper to normalize weights before generating configs
Default to omitting weights unless load-balancing is intentional

When it happens

Trigger: Setting `"udp_weight": 2.0`, `"udp_weight": -1`, etc. in a server entry while weight fields are present (the check runs whenever either tcp_weight or udp_weight is set).

Common situations: Percentage-scale confusion (using 0-100 numbers); typo'd decimals; assuming UDP weight is validated only when udp_weight itself is present.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

AI-assisted analysis of shadowsocks/shadowsocks-rust@8eb0f0a65b (2026-09-09). Data as JSON: /api/errors/f4140a6bbedfe65a. Report an issue: GitHub.