What causes "Empty key in query string" in epi052/feroxbuster?

Add the missing key name before the `=` (e.g. `foo=bar` instead of `=bar`)

Empty key in query string

Error message

Empty key in query string

What it means

split_query splits a query string on `=` and requires a non-empty key before the first `=`. If the input starts with `=` (or the part before `=` is only whitespace after trimming), there is no parameter name to return, so it throws. This keeps CLI `--query` entries well-formed.

Solutions

Add the missing key name before the `=` (e.g. `foo=bar` instead of `=bar`)
Check the request file / CLI args for stray leading `=` characters and remove or fix them
Validate each query entry matches `key=value` format before passing it to the parser

Example fix

// before
xatu --query "=123"
// after
xatu --query "block=123"

Defensive patterns

Strategy: validation

Validate before calling

if !q.is_empty() && q != "=" && !q.starts_with('=') { /* safe to parse */ }

Try / catch

match split_query(entry) {
    Ok((k, v)) => insert_query(k, v),
    Err(e) => eprintln!("invalid query entry '{entry}': {e}"),
}

Prevention

Always write query parameters as key=value with a non-empty key
Check templated request files for variables that expand to empty names
Validate entries against a `^[^=\s][^=]*=.+$`-style pattern before parsing

When it happens

Trigger: Calling split_query("=value") or split_query("=") with surrounding whitespace like split_query(" =value") — the key is empty after trim.

Common situations: Typos in CLI flags (`--query =foo` from a misplaced space), templated request files where a variable name was dropped (`={{value}}` collapsing to `=value`), or copy-paste errors losing the parameter name.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

AI-assisted analysis of epi052/feroxbuster@1f595dab5c (2026-09-13). Data as JSON: /api/errors/976f16291e4ce35e. Report an issue: GitHub.

Appendix: source

Thrown at src/config/utils.rs:277

/// * `Result<(String, String)>` - A tuple containing the key and value as `String`s,
///   or an error if the input is invalid.
///
/// # Errors
///
/// This function will return an error if:
/// * The input string is empty or equal to `"="`.
/// * The key part of the query string is empty (i.e., if the string starts with `"="`).
pub fn split_query(query: &str) -> Result<(String, String)> {
    if query.is_empty() || query == "=" {
        bail!("Empty query string provided");
    }

    let mut split_val = query.split('=');

    let name = split_val.next().unwrap().trim();

    if name.is_empty() {
        bail!("Empty key in query string");
    }

    let value = split_val.collect::<Vec<&str>>().join("=");

    Ok((name.to_string(), value.to_string()))
}

/// Splits an HTTP header string into a key-value pair.
///
/// This function takes a header string in the format of `"Key: Value"` and splits it into
/// a tuple containing the key and value as separate strings. If the header string is
/// malformed (e.g., empty or missing a key), it returns an error.
///
/// # Arguments
///
/// * `header` - A string slice that holds the header string to be split.
///
/// # Returns

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