Rule files, and bans for a clear sign of attack (closes #24)

Every *.rules file in SWWAF_RULES_DIR is read at start and on each
change, and each request is checked against the rules after the rate
limits: log notes a match, block refuses with 403, ban refuses and bans
the netblock for SWWAF_ATTACK_BAN_DURATION, made permanent by its next
request or clear sign of attack. path, query and uri are matched as the
request line sent them. bans.json gains each ban's cause, and ban notes
count earlier bans by cause. The image ships 00-default.rules.

Judgement call: a header sent twice is matched with its values joined
by ", ".
Judgement call: SWWAF_MAX_BAN_DURATION does not cap a ban for an attack.
Not in this unit: offences for rule matches, with the error burst.

Model: opus-5-5

internal/proxy/proxy.go

@@ -17,6 +17,7 @@ import (
 	"sneak.berlin/go/smallwebwaf/internal/metrics"
 	"sneak.berlin/go/smallwebwaf/internal/ratelimit"
 	"sneak.berlin/go/smallwebwaf/internal/requestlog"
+	"sneak.berlin/go/smallwebwaf/internal/rules"
 )
 
 // How smallwebwaf keeps connections to the app open between requests.
@@ -51,6 +52,9 @@ type Params struct {
 	// limits, bans are made and run out, and GeoJS's answers are kept,
 	// normally time.Now in UTC, the time the state files give.
 	Now func() time.Time
+	// Rules are the rule files' rules, which each request is checked
+	// against.
+	Rules *rules.Files
 }
 
 // Server is the server smallwebwaf runs, with the parts of the proxy
@@ -90,6 +94,7 @@ func New(params Params) *Server {
 			LimitBanDuration:     params.Config.LimitBanDuration,
 			LimitBanRepeatWindow: params.Config.LimitBanRepeatWindow,
 			MaxBanDuration:       params.Config.MaxBanDuration,
+			AttackBanDuration:    params.Config.AttackBanDuration,
 			MaxBans:              params.Config.MaxBans,
 		}),
 		geojs: lookup.New(lookup.Params{
@@ -98,8 +103,10 @@ func New(params Params) *Server {
 			ProcessLog: params.ProcessLog,
 			Metrics:    m,
 		}),
+		rules: params.Rules,
 	}
 	m.AddBansAndClients(h.ledger, h.limiter, params.Now)
+	m.AddRules(params.Rules)
 
 	return &Server{
 		Server: &http.Server{
@@ -134,6 +141,7 @@ type handler struct {
 	limiter    *ratelimit.Limiter
 	ledger     *bans.Ledger
 	geojs      *lookup.GeoJS
+	rules      *rules.Files
 }
 
 // newTransport returns what carries requests to the app. It never goes