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_test.go

@@ -41,6 +41,7 @@ const (
 	rateLimitPerDay         = "SWWAF_RATE_LIMIT_PER_DAY"
 	rateLimitExemptPaths    = "SWWAF_RATE_LIMIT_EXEMPT_PATHS"
 	lookupSource            = "SWWAF_LOOKUP_SOURCE"
+	lookupDBPath            = "SWWAF_LOOKUP_DB_PATH"
 	lookupTimeout           = "SWWAF_LOOKUP_TIMEOUT"
 	addLookupHeaders        = "SWWAF_ADD_LOOKUP_HEADERS"
 	deniedCountries         = "SWWAF_DENIED_COUNTRIES"
@@ -123,8 +124,12 @@ const off = "off"
 // enabled is true, as a setting's value.
 const enabled = "true"
 
-// defaultLookupSource is the default of SWWAF_LOOKUP_SOURCE.
-const defaultLookupSource = "geojs"
+// defaultLookupSource is the default of SWWAF_LOOKUP_SOURCE, and
+// fileSource the source that is the lookup database.
+const (
+	defaultLookupSource = "geojs"
+	fileSource          = "file"
+)
 
 // environment is a set of environment variables, for FromEnvironment.
 type environment map[string]string
@@ -802,6 +807,47 @@ func TestLookupSettingsAsSet(t *testing.T) {
 	})
 }
 
+func TestLookupDBPathGoesWithTheFileSourceAlone(t *testing.T) {
+	t.Parallel()
+
+	const path = "/var/lib/ipinfo/ipinfo_lite.mmdb"
+
+	cfg := fromEnvironment(t, environment{lookupSource: fileSource, lookupDBPath: path})
+	if cfg.LookupSource != fileSource || cfg.LookupDBPath != path {
+		t.Errorf("lookups from %q in %q, want file in %q",
+			cfg.LookupSource, cfg.LookupDBPath, path)
+	}
+
+	for _, tc := range []struct {
+		env  environment
+		want string
+	}{
+		{
+			environment{lookupSource: fileSource},
+			lookupSource + ": is file while " + lookupDBPath +
+				" is unset; it names the file to look clients up in",
+		},
+		{
+			environment{lookupSource: fileSource, lookupDBPath: ""},
+			lookupSource + ": is file while " + lookupDBPath +
+				" is unset; it names the file to look clients up in",
+		},
+		{
+			environment{lookupDBPath: path},
+			lookupDBPath + ": is set while " + lookupSource + " is geojs; only file reads it",
+		},
+		{
+			environment{lookupSource: off, lookupDBPath: path},
+			lookupDBPath + ": is set while " + lookupSource + " is off; only file reads it",
+		},
+	} {
+		_, err := config.FromEnvironment(tc.env.lookupEnv)
+		if err == nil || err.Error() != tc.want {
+			t.Errorf("settings %v: error %v, want %s", tc.env, err, tc.want)
+		}
+	}
+}
+
 func TestSettingNeedingLookupsStopsTheStartWhileTheyAreOff(t *testing.T) {
 	t.Parallel()
 
@@ -950,7 +996,7 @@ func TestInvalidValueStopsTheStart(t *testing.T) {
 		{rateLimitPerHour, "1.5"},
 		{rateLimitPerDay, "-1"}, {rateLimitPerDay, "lots"},
 		{rateLimitExemptPaths, "/assets/,,/static/"},
-		{lookupSource, "file"}, {lookupSource, "GeoJS"}, {lookupSource, ""},
+		{lookupSource, "ipinfo"}, {lookupSource, "GeoJS"}, {lookupSource, ""},
 		{lookupTimeout, off}, {lookupTimeout, "0s"}, {lookupTimeout, "1"},
 		{addLookupHeaders, "yes"},
 		{deniedCountries, "nk"},
@@ -1241,6 +1287,7 @@ func TestLogsEachSettingWithItsValue(t *testing.T) {
 		rateLimitPerDay:         "50000",
 		rateLimitExemptPaths:    "",
 		lookupSource:            defaultLookupSource,
+		lookupDBPath:            "",
 		lookupTimeout:           "1s",
 		addLookupHeaders:        "false",
 		deniedCountries:         "",