apache/cassandra · error · IllegalArgumentException

%s is not a valid function resource name. It must end with "

Error message

%s is not a valid function resource name. It must end with "[]"

What it means

When FunctionResource.fromName sees a 3-part name, the last part must be the function name followed by a bracketed argument list. It throws IllegalArgumentException if the full name does not match the regex ^.+\[.*\]$, i.e. there is no trailing '[...]' argument block.

Source

Thrown at src/java/org/apache/cassandra/auth/FunctionResource.java:201

     * @return FunctionResource instance matching the name.
     */
    public static FunctionResource fromName(String name)
    {
        // Split the name into at most 3 parts.
        // The last part is the function name + args list, the name might contains '/'
        String[] parts = StringUtils.split(name, "/", 3);

        if (!parts[0].equals(ROOT_NAME))
            throw new IllegalArgumentException(String.format("%s is not a valid function resource name", name));

        if (parts.length == 1)
            return root();

        if (parts.length == 2)
            return keyspace(parts[1]);

        if (!name.matches("^.+\\[.*\\]$"))
            throw new IllegalArgumentException(String.format("%s is not a valid function resource name. It must end with \"[]\"", name));

        String function = parts[2];
        // The name must end with '[...]' block
        int lastStartingBracketIndex = function.lastIndexOf('[');
        String functionName = StringUtils.substring(function, 0, lastStartingBracketIndex);
        String functionArgs = StringUtils.substring(function,
                                                    // excludes the wrapping brackets [ ]
                                                    lastStartingBracketIndex + 1,
                                                    function.length() - 1);

        return function(parts[1], functionName, functionArgs.isEmpty() ? Collections.emptyList() : argsListFromString(functionArgs));
    }

    /**
     * @return Printable name of the resource.
     */
    public String getName()
    {

View on GitHub (pinned to 88fd0f6a0e)

Solutions

1. Append an argument list: 'functions/<ks>/<fn>[<type>,<type>]' — use '[]' for zero-arg overloads
2. Construct via FunctionResource.function(keyspace, name, argTypes) so formatting is handled for you
3. Inspect the stored name for truncation or missing brackets before parsing

Example fix

// before
FunctionResource r = FunctionResource.fromName("functions/ks/fn");
// after
FunctionResource r = FunctionResource.fromName("functions/ks/fn[int]");

boolean hasArgsBlock(String name) {
    return name.matches("^.+\\[.*\\]$");
}

try { FunctionResource r = FunctionResource.fromName(name); } catch (IllegalArgumentException e) { log.error("function resource missing [args] block: {}", name); }

When it happens

Trigger: Parsing a name like 'functions/ks/fn' (missing '[]'), 'functions/ks/fn(' (unclosed bracket), or 'functions/ks/[int]' where the regex-match fails on the whole name rather than the third part.

Common situations: Building function resource names by hand and forgetting the argument list; overloads recorded without '[]'; truncation of stored permission strings; generating names from signatures without argument types.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• %s is not a valid data resource name
• %s is not a valid function resource name
• %s is not a valid JMX resource name
• In this context function name must be explictly qualified by
• %s function resource has no function name

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/8e56b97b25abe362. Report an issue: GitHub.