Rename internal/proxy to internal/servewaf (closes #173)

The package passes nothing on since the one-process mode went: it answers rproxy's questions, takes its reports and answers servewaf's own endpoints. It is now named after the command it serves, with `git mv`, and its constructor is `servewaf.New`. `SPEC.md` and the other documents follow. No change of behaviour.

Model: opus-5-5

internal/servewaf/rules.go

@@ -0,0 +1,64 @@
+package servewaf
+
+import (
+	"slices"
+	"time"
+
+	"sneak.berlin/go/smallwebwaf/internal/bans"
+	"sneak.berlin/go/smallwebwaf/internal/requestlog"
+	"sneak.berlin/go/smallwebwaf/internal/rules"
+)
+
+// trapPath reports whether the request asks for a path in
+// SWWAF_TRAP_PATHS: its path as a path rule sees it, without the query,
+// as sent or once percent-decoded, is one of them. Such a request is a
+// clear sign of attack, as a ban rule's match is: it bans the client's
+// netblock, or in observe mode raises the alert for the ban it would have
+// made. The ban's notes give the path as sent.
+func (rq *request) trapPath(now time.Time) bool {
+	path := rules.Path(rq.in)
+	if !slices.Contains(rq.h.config.TrapPaths, path) &&
+		!slices.Contains(rq.h.config.TrapPaths, rules.DecodeOnce(path)) {
+		return false
+	}
+
+	rq.attack = true
+	rq.banForAttack(now, bans.Notes{TrapPath: path})
+
+	return true
+}
+
+// checkRules checks the request against the rules of the rule files at
+// now, notes the ids of those it matches in the log line, and returns the
+// action of the rule that refuses it, ActionRuleBlocked for a block rule
+// and ActionBanned for a ban rule, or "" when none does. A ban rule bans
+// the client's netblock for a clear sign of attack, or in observe mode
+// raises the alert for the ban it would have made. Either rule's match
+// is noted as an offence, for the client's history.
+func (rq *request) checkRules(now time.Time) string {
+	matched := rq.h.rules.Match(rq.in)
+
+	for _, rule := range matched {
+		rq.line.RuleIDs = append(rq.line.RuleIDs, rule.ID)
+		rq.h.metrics.RuleMatched(rule.ID, rule.Action)
+	}
+
+	if len(matched) == 0 {
+		return ""
+	}
+
+	// Only the last rule matched can refuse the request.
+	switch last := matched[len(matched)-1]; last.Action {
+	case rules.ActionBlock:
+		rq.ruleBlocked = true
+
+		return requestlog.ActionRuleBlocked
+	case rules.ActionBan:
+		rq.attack = true
+		rq.banForAttack(now, bans.Notes{RuleID: last.ID, Target: last.Target})
+
+		return requestlog.ActionBanned
+	default:
+		return ""
+	}
+}