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cmd/anubis: configurable difficulty per-bot rule (#53)

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Closes #30

Introduces the "challenge" field in bot rule definitions:

```json
{
  "name": "generic-bot-catchall",
  "user_agent_regex": "(?i:bot|crawler)",
  "action": "CHALLENGE",
  "challenge": {
    "difficulty": 16,
    "report_as": 4,
    "algorithm": "slow"
  }
}
```

This makes Anubis return a challenge page for every user agent with
"bot" or "crawler" in it (case-insensitively) with difficulty 16 using
the old "slow" algorithm but reporting in the client as difficulty 4.

This is useful when you want to make certain clients in particular
suffer.

Additional validation and testing logic has been added to make sure
that users do not define "impossible" challenge settings.

If no algorithm is specified, Anubis defaults to the "fast" algorithm.

Signed-off-by: Xe Iaso <me@xeiaso.net>
This commit is contained in:
Xe Iaso 2025-03-21 13:48:00 -04:00 • committed by GitHub
parent 90049001e9
commit d3e509517c
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GPG key ID: B5690EEEBB952194
17 changed files with 311 additions and 46 deletions
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26
cmd/anubis/policy.go
View file

@ -32,7 +32,8 @@ type Bot struct {
Name string
UserAgent *regexp.Regexp
Path *regexp.Regexp
Action config.Rule `json:"action"`
Action config.Rule
Challenge *config.ChallengeRules
}
func (b Bot) Hash() (string, error) {
@ -48,7 +49,7 @@ func (b Bot) Hash() (string, error) {
return sha256sum(fmt.Sprintf("%s::%s::%s", b.Name, pathRex, userAgentRex))
}
func parseConfig(fin io.Reader, fname string) (*ParsedConfig, error) {
func parseConfig(fin io.Reader, fname string, defaultDifficulty int) (*ParsedConfig, error) {
var c config.Config
if err := json.NewDecoder(fin).Decode(&c); err != nil {
return nil, fmt.Errorf("can't parse policy config JSON %s: %w", fname, err)
@ -96,6 +97,19 @@ func parseConfig(fin io.Reader, fname string) (*ParsedConfig, error) {
}
}
if b.Challenge == nil {
parsedBot.Challenge = &config.ChallengeRules{
Difficulty: defaultDifficulty,
ReportAs: defaultDifficulty,
Algorithm: config.AlgorithmFast,
}
} else {
parsedBot.Challenge = b.Challenge
if parsedBot.Challenge.Algorithm == config.AlgorithmUnknown {
parsedBot.Challenge.Algorithm = config.AlgorithmFast
}
}
result.Bots = append(result.Bots, parsedBot)
}
@ -142,5 +156,11 @@ func (s *Server) check(r *http.Request) (CheckResult, *Bot) {
}
}
return cr("default/allow", config.RuleAllow), nil
return cr("default/allow", config.RuleAllow), &Bot{
Challenge: &config.ChallengeRules{
Difficulty: defaultDifficulty,
ReportAs: defaultDifficulty,
Algorithm: config.AlgorithmFast,
},
}
}