Look clients up in the IPinfo Lite file with SWWAF_LOOKUP_SOURCE=file (closes #22)

SWWAF_LOOKUP_SOURCE=file looks every client up in the file
SWWAF_LOOKUP_DB_PATH names, without GeoJS. file without the path, the
path with another source, or a file that cannot be read stops the start.
The file is read whole into memory, so overwriting it in place cannot
disturb a lookup, and read again 2 seconds after its last change; a
replacement that cannot be read is logged, counted and sent as a
file_error alert, and the old one stays in use. Metrics give when it
was read and the failed reads. Tests write their databases through
internal/lookup/lookuptest.

Deviation: go.mod and go.sum written by hand; go runs only through make.
Judgement call: the 2-second wait, as the rule files have.

Model: opus-5-5

internal/proxy/proxy.go

@@ -54,9 +54,12 @@ type Params struct {
 	RequestLog io.Writer
 	// ProcessLog receives the process's own messages.
 	ProcessLog *slog.Logger
-	// GeoJSURL is where clients' AS numbers and countries are looked up,
-	// normally lookup.URL, unless SWWAF_LOOKUP_SOURCE is off.
+	// GeoJSURL is where clients' AS numbers and countries are looked up
+	// while SWWAF_LOOKUP_SOURCE is geojs, normally lookup.URL.
 	GeoJSURL string
+	// LookupFile is the lookup database they are looked up in while
+	// SWWAF_LOOKUP_SOURCE is file, and nil otherwise.
+	LookupFile *lookup.File
 	// Now tells the time by which requests are counted for the rate
 	// limits, bans are made and run out, and GeoJS's answers are kept,
 	// normally time.Now in UTC, the time the state files give.
@@ -70,14 +73,16 @@ type Params struct {
 }
 
 // Server is the server smallwebwaf runs, with the parts of the proxy
-// whose state the state files keep, and the metrics.
+// whose state the state files keep, the lookup database, nil unless
+// SWWAF_LOOKUP_SOURCE is file, and the metrics.
 type Server struct {
 	*http.Server
 
-	Ledger  *bans.Ledger
-	Limiter *ratelimit.Limiter
-	GeoJS   *lookup.GeoJS
-	Metrics *metrics.Metrics
+	Ledger     *bans.Ledger
+	Limiter    *ratelimit.Limiter
+	GeoJS      *lookup.GeoJS
+	LookupFile *lookup.File
+	Metrics    *metrics.Metrics
 }
 
 // New returns the server smallwebwaf runs: each request it reads passes
@@ -109,8 +114,9 @@ func New(params Params) *Server {
 			AttackBanDuration:    params.Config.AttackBanDuration,
 			MaxBans:              params.Config.MaxBans,
 		}),
-		rules:  params.Rules,
-		alerts: params.Alerts,
+		lookupFile: params.LookupFile,
+		rules:      params.Rules,
+		alerts:     params.Alerts,
 	}
 	h.geojs = lookup.New(lookup.Params{
 		URL:     params.GeoJSURL,
@@ -142,10 +148,11 @@ func New(params Params) *Server {
 			MaxHeaderBytes: int(params.Config.ClientRequestHeaderMaxBytes - 4<<10),
 			ErrorLog:       errorLog,
 		},
-		Ledger:  h.ledger,
-		Limiter: h.limiter,
-		GeoJS:   h.geojs,
-		Metrics: m,
+		Ledger:     h.ledger,
+		Limiter:    h.limiter,
+		GeoJS:      h.geojs,
+		LookupFile: h.lookupFile,
+		Metrics:    m,
 	}
 }
 
@@ -162,6 +169,7 @@ type handler struct {
 	limiter    *ratelimit.Limiter
 	ledger     *bans.Ledger
 	geojs      *lookup.GeoJS
+	lookupFile *lookup.File
 	rules      *rules.Files
 	alerts     *alerts.Queue
 }