discriminator: each decision heuristic is its own module (closes #195)

Each discriminator check is now a type in its own file behind one small interface, listed in `heuristics.go`. Adding a heuristic is one file and one line. Behaviour does not change.

Refusal and ban log lines gain `heuristic` and `heuristic_figures`. A ban after the answer, by `refusal_limit` or `byte_limits`, logs `after_answer_heuristic` and its figures, so one line can name both.

Deviation: four lists, not the planned three, so `refusal_limit` still bans at the decision.
Rule suppressed: `//nolint:lll` on one struct tag.

Model: opus-5-5

internal/discriminator/reputation.go

@@ -1,91 +1,17 @@
 package discriminator
 
-import (
-	"context"
-	"time"
+// What the reputation heuristics share: blocklists, crowdsec, dnsbl and
+// abuseipdb.
 
+import (
 	"sneak.berlin/go/smallwebwaf/internal/alerts"
 	"sneak.berlin/go/smallwebwaf/internal/bans"
-	"sneak.berlin/go/smallwebwaf/internal/ratelimit"
-	"sneak.berlin/go/smallwebwaf/internal/reputation"
 )
 
 // deny is the SWW_BLOCKLIST_ACTION and the SWW_REPUTATION_ACTION that
 // refuses the requests of a client a source lists.
 const deny = "deny"
 
-// blocklistDenied notes the blocklists that list the client, as
-// noteListed does, and reports whether SWW_BLOCKLIST_ACTION, being deny,
-// refuses the request. Being limit, it lowers the client's limits instead
-// (see limitPercentages), and being log, it does nothing more.
-func (rq *request) blocklistDenied() bool {
-	listedBy := rq.h.lists.ListedBy(rq.client)
-	rq.blocklisted = len(listedBy) > 0
-	rq.noteListed(listedBy, "listed by a blocklist")
-
-	return rq.blocklisted && rq.h.config.BlocklistAction == deny
-}
-
-// crowdSecBanned reports whether a decision of the CrowdSec decision list
-// on the client is in force at now. If one is, it notes the list, as
-// noteHit does, and bans the client until that decision ends.
-func (rq *request) crowdSecBanned(now time.Time) bool {
-	decision, listed := rq.h.lists.CrowdSecDecision(rq.client, now)
-	if !listed {
-		return false
-	}
-
-	rq.noteHit(bans.ReputationHit{Source: rq.h.config.CrowdSecDecisionsURL},
-		"listed by the CrowdSec decision list")
-	rq.banForCrowdSec(now, decision)
-
-	return true
-}
-
-// dnsblDenied notes the DNSBL zones whose verdict lists the client, as
-// noteListed does, and reports whether SWW_REPUTATION_ACTION, being
-// deny, refuses the request. Being limit, it lowers the client's limits
-// instead (see limitPercentages), and being log, it does nothing more. A
-// zone without a verdict on the client is asked about it in the
-// background, and the request does not wait for the answer. ctx is the
-// request's own context.
-func (rq *request) dnsblDenied(ctx context.Context) bool {
-	listedBy := rq.h.dnsbl.ListedBy(ctx, rq.client)
-	rq.dnsblListed = len(listedBy) > 0
-	rq.noteListed(listedBy, "listed by a DNSBL zone")
-
-	return rq.dnsblListed && rq.h.config.ReputationAction == deny
-}
-
-// abuseIPDBDenied notes AbuseIPDB, as noteHit does, with the score, when
-// its score of the client is a hit, and reports whether
-// SWW_REPUTATION_ACTION, being deny, refuses the request, as dnsblDenied
-// does for a zone. While SWW_ABUSEIPDB_KEY is unset it does nothing. A
-// client without a score is checked in the background, by the request's
-// address, if its history counts an offence, and the request does not
-// wait for the answer. The score is then used for each address of the
-// client. ctx is the request's own context.
-func (rq *request) abuseIPDBDenied(ctx context.Context) bool {
-	if rq.h.config.AbuseIPDBKey == "" {
-		return false
-	}
-
-	client := rq.h.clientGroup(rq.client)
-	held, _ := rq.h.limiter.Client(client)
-	offender := held.History.Offences != ratelimit.Offences{}
-
-	score, hit := rq.h.abuseIPDB.Hit(ctx, client, rq.client, offender)
-	if !hit {
-		return false
-	}
-
-	rq.abuseIPDBHit = true
-	rq.noteHit(bans.ReputationHit{Source: reputation.AbuseIPDBSource, Score: &score},
-		"scored by AbuseIPDB at or over SWW_ABUSEIPDB_MIN_SCORE")
-
-	return rq.h.config.ReputationAction == deny
-}
-
 // noteListed notes each of sources, the URLs of the blocklists or the
 // DNSBL zones, their keys masked, that list the client, as noteHit does,
 // with reason.