Every time in UTC, and every day as YYYY-MM-DD (closes #313)

AbuseIPDB's daily count keeps its day as a civil.Date, taken from the UTC
clock and written to reputation.json as "YYYY-MM-DD"; it was a time.Time
at midnight. A test runs sww discriminator with TZ 14 hours ahead of UTC
and checks the process line, the request line and clients.json are in
UTC. SPEC.md states the rule near its start; AGENTS.md makes it an iron
rule.

Model: opus-5-5

internal/lookup/file.go

@@ -26,7 +26,7 @@ type FileParams struct {
 	// Path is the lookup database, the IPinfo Lite file in its .mmdb form
 	// (SWW_LOOKUP_DB_PATH).
 	Path string
-	// Now tells the time, normally time.Now.
+	// Now tells the time, normally time.Now in UTC.
 	Now func() time.Time
 	// ProcessLog receives each reading of the file, and why a replacement
 	// of it cannot be read.

internal/lookup/lookup.go

@@ -74,7 +74,7 @@ type Params struct {
 	// Answered, unless nil, is given each answer GeoJS gives, once it is
 	// kept.
 	Answered func(Answer)
-	// Now tells the time, normally time.Now.
+	// Now tells the time, normally time.Now in UTC.
 	Now func() time.Time
 	// ProcessLog receives GeoJS's failures.
 	ProcessLog *slog.Logger

internal/reputation/abuseipdb.go

@@ -14,6 +14,7 @@ import (
 	"sync"
 	"time"
 
+	"cloud.google.com/go/civil"
 	"github.com/hashicorp/golang-lru/v2/simplelru"
 	"sneak.berlin/go/smallwebwaf/internal/alerts"
 )
@@ -27,8 +28,6 @@ const (
 	AbuseIPDBSource = "abuseipdb"
 	// maxAnswerBytes is the most of an answer of AbuseIPDB that is read.
 	maxAnswerBytes = 64 << 10
-	// day is the length of the day the checks are counted in, in UTC.
-	day = 24 * time.Hour
 )
 
 var (
@@ -50,9 +49,9 @@ type Score struct {
 // AbuseIPDB: the day, in UTC, of the checks Spent counts, zero before the
 // first, and the scores still in use.
 type Checks struct {
-	Day    time.Time `json:"day,omitzero"`
-	Spent  int       `json:"spent"`
-	Scores []Score   `json:"scores"`
+	Day    civil.Date `json:"day,omitzero"`
+	Spent  int        `json:"spent"`
+	Scores []Score    `json:"scores"`
 }
 
 // AbuseIPDBParams are what NewAbuseIPDB needs.
@@ -93,7 +92,7 @@ type AbuseIPDB struct {
 	// checking are the clients whose check is under way.
 	checking map[netip.Prefix]bool
 	// day is the day, in UTC, of the checks spent counts.
-	day   time.Time
+	day   civil.Date
 	spent int
 	// checks and failures count the checks made and those that failed,
 	// and retryAt is when a client may be checked again after the last
@@ -143,7 +142,7 @@ func (a *AbuseIPDB) Hit(
 		return kept.Score, kept.Score >= a.params.MinScore
 	}
 
-	if today := now.Truncate(day); !a.day.Equal(today) {
+	if today := civil.DateOf(now.UTC()); a.day != today {
 		a.day, a.spent = today, 0
 	}
 
@@ -190,7 +189,7 @@ func (a *AbuseIPDB) BudgetLeft() int {
 	a.mu.Lock()
 	defer a.mu.Unlock()
 
-	if !a.day.Equal(a.params.Now().Truncate(day)) {
+	if a.day != civil.DateOf(a.params.Now().UTC()) {
 		return a.params.DailyBudget
 	}
 

internal/reputation/abuseipdb_test.go

@@ -202,6 +202,43 @@ func TestDailyBudgetKeptAcrossARestartAndWholeAgainAsTheDayEnds(t *testing.T) {
 	})
 }
 
+func TestChecksAreCountedInUTCDaysWhateverTheClocksZone(t *testing.T) {
+	t.Parallel()
+
+	synctest.Test(t, func(t *testing.T) {
+		// A clock 14 hours ahead of UTC, whose day starts at 10:00 UTC.
+		ahead := time.FixedZone("UTC+14", 14*60*60)
+		p := abuseIPDBParams()
+		p.DailyBudget = 1
+		p.Now = func() time.Time { return time.Now().In(ahead) }
+		abuseIPDB := &abuseIPDBStandIn{scores: map[string]int64{suspect: 100}}
+		checker := newAbuseIPDB(abuseIPDB, p)
+
+		// At 09:00 UTC the one check is spent.
+		time.Sleep(9 * time.Hour)
+		hitFrom(t, checker, suspect, true)
+		synctest.Wait()
+		wantBudgetLeft(t, checker, 0)
+
+		// At 11:00 UTC the clock's day has changed, but the UTC day has not.
+		time.Sleep(2 * time.Hour)
+		wantBudgetLeft(t, checker, 0)
+
+		encoded, err := json.Marshal(checker.Snapshot())
+		if err != nil {
+			t.Fatalf("encode: %v", err)
+		}
+
+		if !strings.Contains(string(encoded), `"day":"2000-01-01"`) {
+			t.Errorf("reputation.json would hold %s, want the day 2000-01-01", encoded)
+		}
+
+		// At 00:00 UTC the budget is whole again.
+		time.Sleep(13 * time.Hour)
+		wantBudgetLeft(t, checker, 1)
+	})
+}
+
 func TestFailedCheckGivesNoScoreAndNoClientIsCheckedForAMinute(t *testing.T) {
 	t.Parallel()
 

internal/state/state_test.go

@@ -21,6 +21,7 @@ import (
 	"testing/synctest"
 	"time"
 
+	"cloud.google.com/go/civil"
 	"sneak.berlin/go/smallwebwaf/internal/alerts"
 	"sneak.berlin/go/smallwebwaf/internal/anomaly"
 	"sneak.berlin/go/smallwebwaf/internal/bans"
@@ -258,7 +259,7 @@ const filledReputationJSON = `{
         }
     ],
     "abuseipdb": {
-        "day": "2026-10-06T00:00:00Z",
+        "day": "2026-10-06",
         "spent": 3,
         "scores": [
             {
@@ -1306,7 +1307,7 @@ func TestEditOfEachFileTakenIn(t *testing.T) {
 		`"tried": "2026-10-06T00:00:00Z", "fetched": "2026-10-06T00:00:00Z", `+
 		`"lines": ["198.51.100.7"]}], "verdicts": [{"zone": "`+dnsblZone+`", `+
 		`"client": "198.51.100.7", "listed": true, "fetched": "2026-10-06T00:00:00Z"}], `+
-		`"abuseipdb": {"day": "2026-10-06T00:00:00Z", "spent": 9, "scores": [`+
+		`"abuseipdb": {"day": "2026-10-06", "spent": 9, "scores": [`+
 		`{"client": "198.51.100.7/32", "score": 80, "fetched": "2026-10-06T00:00:00Z"}]}}`)
 	wantTakenIn(t, lines, dir, reputationJSON)
 
@@ -1321,7 +1322,7 @@ func TestEditOfEachFileTakenIn(t *testing.T) {
 	}})
 
 	checks := reputation.Checks{
-		Day: midnight(), Spent: 9,
+		Day: civil.DateOf(midnight()), Spent: 9,
 		Scores: []reputation.Score{{Client: client, Score: 80, Fetched: midnight()}},
 	}
 	if got := params.AbuseIPDB.Snapshot(); !reflect.DeepEqual(got, checks) {
@@ -1837,10 +1838,12 @@ func fill(params state.Params) {
 		},
 		{Zone: dnsblZone, Client: client.Addr(), Listed: true, Fetched: now.Add(-time.Hour)},
 	})
-	params.AbuseIPDB.Load(reputation.Checks{Day: now, Spent: 3, Scores: []reputation.Score{
-		{Client: netip.MustParsePrefix("2001:db8::/64"), Fetched: now.Add(-2 * time.Hour)},
-		{Client: client, Score: 100, Fetched: now.Add(-time.Hour)},
-	}})
+	params.AbuseIPDB.Load(reputation.Checks{
+		Day: civil.DateOf(now), Spent: 3, Scores: []reputation.Score{
+			{Client: netip.MustParsePrefix("2001:db8::/64"), Fetched: now.Add(-2 * time.Hour)},
+			{Client: client, Score: 100, Fetched: now.Add(-time.Hour)},
+		},
+	})
 
 	// An alert waiting, a repeat of it the cooldown holds back, another
 	// alert waiting, and one past the two an hour, for the hour's summary.

internal/sww/discriminator_test.go

@@ -9,10 +9,14 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"regexp"
 	"strings"
 	"syscall"
 	"testing"
 	"time"
+	// The time zone database, so that the process TestTimesAreInUTCWhateverTZSays
+	// starts finds the zone TZ names on any host.
+	_ "time/tzdata"
 
 	"sneak.berlin/go/smallwebwaf/internal/discriminator"
 	"sneak.berlin/go/smallwebwaf/internal/sww"
@@ -80,6 +84,95 @@ func TestMainRunsDiscriminator(t *testing.T) {
 	}
 }
 
+func TestTimesAreInUTCWhateverTZSays(t *testing.T) {
+	t.Parallel()
+
+	// Kiritimati is 14 hours ahead of UTC.
+	const zone = "Pacific/Kiritimati"
+
+	_, err := time.LoadLocation(zone)
+	if err != nil {
+		t.Fatalf("load %s: %v", zone, err)
+	}
+
+	binary, err := os.Executable()
+	if err != nil {
+		t.Fatalf("find the test binary: %v", err)
+	}
+
+	ctx, cancel := context.WithTimeout(t.Context(), 3*waitLimit)
+	defer cancel()
+
+	dir := t.TempDir()
+	out := &output{}
+	cmd := exec.CommandContext(ctx, binary) //nolint:gosec // this test binary
+	cmd.Stdout = out
+
+	cmd.Env = append(os.Environ(),
+		"TZ="+zone,
+		commandForMain+"="+discriminatorCommand,
+		listenAddr+"="+localhost+":0",
+		stateDir+"="+dir,
+		rulesDir+"="+t.TempDir(),
+		lookupSource+"=off")
+
+	err = cmd.Start()
+	if err != nil {
+		t.Fatalf("start: %v", err)
+	}
+
+	t.Cleanup(func() {
+		_ = cmd.Process.Kill()
+		_ = cmd.Wait()
+	})
+
+	starting := out.line(t, "msg", "starting")
+	addr, _ := starting["address"].(string)
+	ask(t, addr, "/", http.StatusOK, discriminator.DispositionAllow)
+
+	// The files are written as sww stops.
+	err = cmd.Process.Signal(syscall.SIGTERM)
+	if err != nil {
+		t.Fatalf("signal: %v", err)
+	}
+
+	err = cmd.Wait()
+	if err != nil {
+		t.Fatalf("exit: %v; output:\n%s", err, out.text())
+	}
+
+	wantUTC(t, "the process line", starting["time"])
+	wantUTC(t, "the request line", out.line(t, "type", "request")["time"])
+
+	path := filepath.Join(dir, "clients.json")
+
+	clients, err := os.ReadFile(path) //nolint:gosec // a file in the test's directory
+	if err != nil {
+		t.Fatalf("read clients.json: %v", err)
+	}
+
+	stamp := regexp.MustCompile(`"\d{4}-\d\d-\d\dT[^"]*"`)
+
+	times := stamp.FindAllString(string(clients), -1)
+	if len(times) == 0 {
+		t.Errorf("clients.json holds no time:\n%s", clients)
+	}
+
+	for _, stored := range times {
+		wantUTC(t, "clients.json", strings.Trim(stored, `"`))
+	}
+}
+
+// wantUTC checks that value, a time where, is in UTC.
+func wantUTC(t *testing.T, where string, value any) {
+	t.Helper()
+
+	text, _ := value.(string)
+	if !strings.HasSuffix(text, "Z") {
+		t.Errorf("%s gives the time %v, want one in UTC", where, value)
+	}
+}
+
 func TestMainWithoutACommandItKnowsPrintsTheCommands(t *testing.T) {
 	t.Parallel()