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/config/config.go

@@ -92,12 +92,16 @@ type Config struct {
 	// Each starts with /.
 	RateLimitExemptPaths []string
 	// LookupSource is where each client's AS number and country are
-	// looked up (SWWAF_LOOKUP_SOURCE): geojs, or off for nowhere. A request
-	// waits up to LookupTimeout for its client's first answer while a
-	// setting needs it (SWWAF_LOOKUP_TIMEOUT), which cannot be off.
-	// AddLookupHeaders is true when the app is passed the client's AS
-	// number and country in headers (SWWAF_ADD_LOOKUP_HEADERS).
+	// looked up (SWWAF_LOOKUP_SOURCE): geojs, file, or off for nowhere.
+	// LookupDBPath is the lookup database, the IPinfo Lite file looked up
+	// in while LookupSource is file (SWWAF_LOOKUP_DB_PATH), and "" for any
+	// other source. A request waits up to LookupTimeout for its client's
+	// first answer from GeoJS while a setting needs it
+	// (SWWAF_LOOKUP_TIMEOUT), which cannot be off. AddLookupHeaders is true
+	// when the app is passed the client's AS number and country in headers
+	// (SWWAF_ADD_LOOKUP_HEADERS).
 	LookupSource     string
+	LookupDBPath     string
 	LookupTimeout    time.Duration
 	AddLookupHeaders bool
 	// DeniedCountries are the countries whose clients are refused
@@ -201,6 +205,10 @@ type Config struct {
 // off.
 const off = "off"
 
+// fileSource is the SWWAF_LOOKUP_SOURCE that looks clients up in the
+// lookup database, the file SWWAF_LOOKUP_DB_PATH names.
+const fileSource = "file"
+
 const (
 	day      = 24 * time.Hour
 	kibibyte = 1 << 10
@@ -242,8 +250,10 @@ var (
 		"is taken out of every request by Go's HTTP server, so it can never " +
 			"be logged")
 	errOnBothLists          = errors.New("is in SWWAF_DENIED_COUNTRIES too")
-	errNotLookupSource      = errors.New("is not geojs or off")
+	errNotLookupSource      = errors.New("is not geojs, file or off")
 	errNeedsLookups         = errors.New("it needs each client looked up")
+	errNeedsDBPath          = errors.New("it names the file to look clients up in")
+	errDBPathUnused         = errors.New("only file reads it")
 	errNotOver4K            = errors.New("is not a size of more than 4K, such as 32K")
 	errNotDurationAboveZero = errors.New(
 		"is not a duration above zero, such as 1h or 7d")
@@ -312,6 +322,7 @@ func FromEnvironment(lookupEnv func(string) (string, bool)) (*Config, error) {
 		RateLimitPerDay:         env.count("SWWAF_RATE_LIMIT_PER_DAY", "50000"),
 		RateLimitExemptPaths:    env.pathPrefixes("SWWAF_RATE_LIMIT_EXEMPT_PATHS", ""),
 		LookupSource:            env.lookupSource("SWWAF_LOOKUP_SOURCE", "geojs"),
+		LookupDBPath:            env.value("SWWAF_LOOKUP_DB_PATH", ""),
 		LookupTimeout:           env.durationNotOff("SWWAF_LOOKUP_TIMEOUT", "1s"),
 		AddLookupHeaders:        env.boolean("SWWAF_ADD_LOOKUP_HEADERS", "false"),
 		DeniedCountries:         env.countries("SWWAF_DENIED_COUNTRIES", ""),
@@ -353,6 +364,7 @@ func FromEnvironment(lookupEnv func(string) (string, bool)) (*Config, error) {
 		cfg.InstanceName, cfg.LogRemoteURL != nil)
 
 	env.checkInstanceNameForNtfy(cfg.InstanceName, cfg.AlertNtfyURL != nil)
+	env.checkLookupDBPath(cfg)
 	env.checkCountriesAndLookups(cfg)
 
 	if env.err != nil {
@@ -556,16 +568,30 @@ func (e *environment) countries(name, defaultValue string) []string {
 }
 
 // lookupSource reads the setting that is where clients are looked up:
-// geojs, or off.
+// geojs, file, or off.
 func (e *environment) lookupSource(name, defaultValue string) string {
 	source := e.value(name, defaultValue)
-	if source != "geojs" && source != off {
+	if source != "geojs" && source != fileSource && source != off {
 		e.check(name, fmt.Errorf("%q %w", source, errNotLookupSource))
 	}
 
 	return source
 }
 
+// checkLookupDBPath refuses SWWAF_LOOKUP_SOURCE=file without
+// SWWAF_LOOKUP_DB_PATH, and SWWAF_LOOKUP_DB_PATH with any other source:
+// one source at a time.
+func (e *environment) checkLookupDBPath(cfg *Config) {
+	switch {
+	case cfg.LookupSource == fileSource && cfg.LookupDBPath == "":
+		e.check("SWWAF_LOOKUP_SOURCE", fmt.Errorf(
+			"is file while SWWAF_LOOKUP_DB_PATH is unset; %w", errNeedsDBPath))
+	case cfg.LookupSource != fileSource && cfg.LookupDBPath != "":
+		e.check("SWWAF_LOOKUP_DB_PATH", fmt.Errorf(
+			"is set while SWWAF_LOOKUP_SOURCE is %s; %w", cfg.LookupSource, errDBPathUnused))
+	}
+}
+
 // checkCountriesAndLookups refuses a country on both country lists, and,
 // while SWWAF_LOOKUP_SOURCE is off, each setting that needs clients looked
 // up: the country lists and SWWAF_ADD_LOOKUP_HEADERS.