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

Every time the program stores, logs or compares is in UTC, whatever TZ says, and AbuseIPDB's day in `reputation.json` is a `YYYY-MM-DD` date. Times read from a state file are converted to UTC as they are read, so a file is written back with `Z` times only. A test runs `sww waf` with `TZ=Pacific/Kiritimati` and checks the process line, the request line and `clients.json`. `SPEC.md` states the rule and `AGENTS.md` makes it an iron rule.

- The rate limit's `day` and `day_bytes` buckets keep a start time: each is a 24-hour bucket begun at an instant, not a calendar day.
- New dependency `cloud.google.com/go`, of which only `civil` is built.
- No migration: a `reputation.json` holding the old day form fails to load, naming the file.

Model: opus-5-5

internal/sww/waf_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 TestMainRunsWAF starts
+	// finds the zone TZ names on any host.
+	_ "time/tzdata"
 
 	"sneak.berlin/go/smallwebwaf/internal/sww"
 	"sneak.berlin/go/smallwebwaf/internal/waf"
@@ -37,6 +41,14 @@ func TestMain(m *testing.M) {
 func TestMainRunsWAF(t *testing.T) {
 	t.Parallel()
 
+	// Kiritimati is 14 hours ahead of UTC; every time sww gives stays in 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)
@@ -45,14 +57,16 @@ func TestMainRunsWAF(t *testing.T) {
 	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+"="+wafCommand,
 		listenAddr+"="+localhost+":0",
-		stateDir+"="+t.TempDir(),
+		stateDir+"="+dir,
 		rulesDir+"="+t.TempDir(),
 		lookupSource+"=off")
 
@@ -66,9 +80,11 @@ func TestMainRunsWAF(t *testing.T) {
 		_ = cmd.Wait()
 	})
 
-	addr, _ := out.line(t, "msg", "starting")["address"].(string)
+	starting := out.line(t, "msg", "starting")
+	addr, _ := starting["address"].(string)
 	ask(t, addr, "/", http.StatusOK, waf.DispositionAllow)
 
+	// The files are written as sww stops.
 	err = cmd.Process.Signal(syscall.SIGTERM)
 	if err != nil {
 		t.Fatalf("signal: %v", err)
@@ -76,7 +92,39 @@ func TestMainRunsWAF(t *testing.T) {
 
 	err = cmd.Wait()
 	if err != nil {
-		t.Errorf("exit: %v; output:\n%s", err, out.text())
+		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 read from the log line or file that
+// where names, 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)
 	}
 }