projectdiscovery/katana · error

unsupported captcha solver provider: %s

Error message

unsupported captcha solver provider: %s

What it means

NewSolver performs a lookup in solverRegistry, a map from provider name strings to constructor functions populated by each solver package's init() via captcha.RegisterSolver. If the given provider name has no entry, this error is returned. It is a configuration/name-resolution failure, not a network or API failure.

Source

Thrown at pkg/engine/headless/captcha/solver.go:20

import (
	"context"
	"fmt"
)

type Solution struct {
	Token    string
	Provider Provider
}

type Solver interface {
	Solve(ctx context.Context, info *Info) (*Solution, error)
}

func NewSolver(provider, apiKey string) (Solver, error) {
	constructor, ok := solverRegistry[provider]
	if !ok {
		return nil, fmt.Errorf("unsupported captcha solver provider: %s", provider)
	}
	return constructor(apiKey)
}

type SolverConstructor func(apiKey string) (Solver, error)

var solverRegistry = map[string]SolverConstructor{}

func RegisterSolver(name string, constructor SolverConstructor) {
	solverRegistry[name] = constructor
}

View on GitHub (pinned to e3e742739c)

Solutions

1. Compare the configured provider string against the registered keys (e.g. "capsolver") — exact match, lowercase
2. Ensure the solver package is imported so its init() registration runs
3. Trim whitespace and normalize case on config values before passing to NewSolver
4. Whitelist/validate provider names in your own config layer and fail fast with a clear message
5. Check the library docs for the current list of supported solvers

Example fix

// before
provider := strings.TrimSpace(opts.CaptchaSolver) // "Capsolver"

// after
provider := strings.ToLower(strings.TrimSpace(opts.CaptchaSolver))
if _, err := captcha.NewSolver(provider, apiKey); err != nil {
	return fmt.Errorf("invalid captcha solver %q: %w", provider, err)
}

func isValidSolver(name string) bool {
	return map[string]bool{"capsolver": true}[strings.ToLower(strings.TrimSpace(name))]
}
if !isValidSolver(cfg.CaptchaSolverProvider) {
	return errors.New("unsupported captcha solver provider in config")
}

solver, err := captcha.NewSolver(provider, apiKey)
if err != nil {
	return nil, fmt.Errorf("solver %q not registered: %w", provider, err)
}

When it happens

Trigger: Called by NewHandler at handler construction and directly in tests (TestNewSolver_UnsupportedProvider); fires when the provider string does not exactly match a registered key such as "capsolver".

Common situations: Case mismatch or whitespace in config ("Capsolver", " capsolver"); empty provider string; desired solver package not imported so its init() never ran; renamed provider in a newer library version.

Related errors

• captcha solver init: %w
• unsupported captcha provider for capsolver: %s
• create task: %w
• capsolver error %s: %s
• captcha solve timed out after %s

AI-assisted analysis of projectdiscovery/katana@e3e742739c (2026-09-03). Data as JSON: /api/errors/cf9b572ae2ccc144. Report an issue: GitHub.