kataras/iris · error
invalid arguments
Error message
invalid arguments
What it means
ErrInvalidArgs is returned by the internal Func.call method when a function registered via Context (Context.CallFunc / registered Func) is invoked with an invalid number of arguments, detected through reflection against the raw function's signature. The library throws it to fail fast on programming mistakes rather than panicking deep inside reflection.
Source
Thrown at context/context_func.go:11
package context
import (
"errors"
"reflect"
"sync"
)
// ErrInvalidArgs fires when the `Context.CallFunc`
// is called with invalid number of arguments.
var ErrInvalidArgs = errors.New("invalid arguments")
// Func represents a function registered by the Context.
// See its `buildMeta` and `call` internal methods.
type Func struct {
RegisterName string // the name of which this function is registered, for information only.
Raw any // the Raw function, can be used for custom casting.
PersistenceArgs []any // the persistence input arguments given on registration.
once sync.Once // guards build once, on first call.
// Available after the first call.
Meta *FuncMeta
}
func newFunc(name string, fn any, persistenceArgs ...any) *Func {
return &Func{
RegisterName: name,
Raw: fn,
PersistenceArgs: persistenceArgs,View on GitHub (pinned to 7bedaf55a0)
Solutions
- Match the argument count to the registered function's signature: inspect the Func.Raw signature and supply exactly that many arguments.
- Wrap the call with errors.Is(err, context.ErrInvalidArgs) and log the expected vs provided argument count.
- If the count is dynamic, build the args slice from reflect.TypeOf(fn.Raw).NumIn() before calling.
- Add a unit test that invokes every registered Func with its intended argument list to catch arity drift after refactors.
Example fix
// before
fn := app.Context().Func("handler") // expects (ctx, arg1, arg2)
err := fn.Call(ctx) // missing args -> ErrInvalidArgs
// after
fn := app.Context().Func("handler")
if n := reflect.TypeOf(fn.Raw).NumIn(); n != len(args)+1 {
return fmt.Errorf("func %s: want %d args, got %d", fn.RegisterName, n-1, len(args))
}
err := fn.Call(ctx, args...) Defensive patterns
Strategy: validation
Validate before calling
want := reflect.TypeOf(fn.Raw).NumIn()
if got := len(args) + 1 /* +ctx */; got != want {
return fmt.Errorf("%s: want %d args, got %d", fn.RegisterName, want, got)
} Type guard
func isInvalidArgs(err error) bool {
return errors.Is(err, context.ErrInvalidArgs)
} Try / catch
if err := fn.Call(ctx, args...); err != nil {
if errors.Is(err, context.ErrInvalidArgs) {
// log expected vs provided arity and skip/abort the call
return nil
}
return err
} Prevention
- Keep registered function signatures and call sites in sync; update all callers on signature changes.
- Derive argument counts from reflect.TypeOf(fn.Raw).NumIn() instead of hardcoding.
- Write a smoke test that calls each registered Func with its intended arguments.
- Avoid dynamic arg construction without validating length before the call.
When it happens
Trigger: Calling ctx.CallFunc (or the registered function through Context) with fewer or more arguments than the wrapped function's signature declares; registering a variadic-mismatched or wrong-arity function and invoking it with an incompatible argument list; framework internals dispatching to a Func whose expected input count doesn't match what's provided.
Common situations: Refactoring a registered function's signature without updating all call sites; passing nil or zero arguments to a function that expects parameters; dynamic invocation from plugins/handlers building the argument slice at runtime; middleware calling framework-registered funcs with wrong payloads.
Related errors
AI-assisted analysis of kataras/iris@7bedaf55a0 (2026-08-30).
Data as JSON: /api/errors/d6d1b5918c73b022.
Report an issue: GitHub.