routewatch/internal/geo/locator_internal_test.go

package geo

import (
	"bytes"
	"compress/gzip"
	"context"
	"database/sql"
	"errors"
	"io/fs"
	"log/slog"
	"net"
	"net/http"
	"net/http/httptest"
	"net/netip"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"sync/atomic"
	"testing"
	"time"

	"git.eeqj.de/sneak/routewatch/internal/cachedb"
	lru "github.com/hashicorp/golang-lru/v2"
	"github.com/maxmind/mmdbwriter"
	"github.com/maxmind/mmdbwriter/mmdbtype"
)

// The addresses and networks of the tests, from the documentation ranges.
const (
	testAddress    = "192.0.2.10"
	otherAddress   = "2001:db8::10"
	thirdAddress   = "203.0.113.10"
	coveredNetwork = "192.0.2.0/24"
	testCity       = "Testville"
	databaseCity   = "Databaseville"
	databaseMonth  = "2026-01"
	databasePath   = "/dbip-city-lite-" + databaseMonth + ".mmdb.gz"
	geojsPath      = "/geo.json"

	// testTimeLimit replaces geojsTimeLimit in the tests that use a real
	// server, so that a stall on a busy host cannot use it up.
	testTimeLimit = 2 * time.Minute

	// shortTimeLimit is the limit of the test in which geojs never answers.
	shortTimeLimit = 50 * time.Millisecond
)

// The bodies the fake geojs sends.
const (
	geojsTwoAddresses = `[
		{"accuracy": 20, "city": "` + testCity + `", "continent_code": "EU",
		 "country": "Germany", "country_code": "DE", "ip": "` + testAddress + `",
		 "latitude": "52.6171", "longitude": "13.1207",
		 "region": "Brandenburg", "timezone": "Europe/Berlin"},
		{"ip": "` + otherAddress + `", "latitude": "nil", "longitude": "nil"}
	]`
	geojsOneAddress = `[{"ip": "` + testAddress + `", "city": "` + testCity + `"}]`
)

// fixedTime returns the time a test's clock starts at.
func fixedTime() time.Time {
	return time.Date(2026, time.January, 2, 3, 4, 5, 0, time.UTC)
}

// parseAddresses returns the given addresses parsed.
func parseAddresses(t *testing.T, addresses ...string) []netip.Addr {
	t.Helper()

	addrs := make([]netip.Addr, len(addresses))

	for i, address := range addresses {
		addr, err := netip.ParseAddr(address)
		if err != nil {
			t.Fatalf("parsing %s: %v", address, err)
		}

		addrs[i] = addr
	}

	return addrs
}

// fakeGeoJS is a geojs server. It sends body, or status when that is set, or
// waits for the request to end when hang is true. It keeps each request's
// address list.
type fakeGeoJS struct {
	server *httptest.Server
	body   string
	status int
	hang   bool

	mu       sync.Mutex
	requests []string
}

// newFakeGeoJS starts a fake geojs that sends body.
func newFakeGeoJS(t *testing.T, body string) *fakeGeoJS {
	t.Helper()

	fake := &fakeGeoJS{body: body}
	fake.server = httptest.NewServer(http.HandlerFunc(fake.serve))
	t.Cleanup(fake.server.Close)

	return fake
}

func (f *fakeGeoJS) serve(w http.ResponseWriter, r *http.Request) {
	f.mu.Lock()
	f.requests = append(f.requests, r.URL.Query().Get("ip"))
	f.mu.Unlock()

	if f.hang {
		<-r.Context().Done()

		return
	}

	if f.status != 0 {
		w.WriteHeader(f.status)

		return
	}

	_, _ = w.Write([]byte(f.body))
}

// requestsSeen returns the address list of each request so far.
func (f *fakeGeoJS) requestsSeen() []string {
	f.mu.Lock()
	defer f.mu.Unlock()

	return append([]string{}, f.requests...)
}

// openCacheDB opens a new cache.db in a temporary directory.
func openCacheDB(t *testing.T, dir string) *sql.DB {
	t.Helper()

	db, err := cachedb.Open(t.Context(), dir)
	if err != nil {
		t.Fatalf("opening cache.db: %v", err)
	}

	t.Cleanup(func() { _ = db.Close() })

	return db
}

// newTestLocator returns a Locator that asks fake and uses db and dir, with
// its clock stopped at fixedTime.
func newTestLocator(
	t *testing.T, fake *fakeGeoJS, db *sql.DB, dir string,
) *Locator {
	t.Helper()

	locator, err := New(Params{
		DB:                db,
		Dir:               dir,
		GeoJSURL:          fake.server.URL + geojsPath,
		DatabaseURLFormat: fake.server.URL + "/dbip-city-lite-%s.mmdb.gz",
		Logger:            slog.New(slog.DiscardHandler),
	})
	if err != nil {
		t.Fatalf("New: %v", err)
	}

	locator.timeLimit = testTimeLimit
	locator.now = fixedTime

	t.Cleanup(locator.closeDatabase)

	return locator
}

// lookupOne returns the location of one address.
func lookupOne(t *testing.T, locator *Locator, address string) *Location {
	t.Helper()

	return locator.Lookup(t.Context(), parseAddresses(t, address))[0]
}

// databaseFile returns an MMDB file with the shape of City Lite. It covers
// coveredNetwork, with no time zone or accuracy radius, as the real file has
// none.
func databaseFile(t *testing.T) []byte {
	t.Helper()

	tree, err := mmdbwriter.New(mmdbwriter.Options{
		DatabaseType:            "DBIP-City-Lite",
		IncludeReservedNetworks: true,
	})
	if err != nil {
		t.Fatalf("creating the test database: %v", err)
	}

	_, network, err := net.ParseCIDR(coveredNetwork)
	if err != nil {
		t.Fatalf("parsing the network: %v", err)
	}

	names := func(name string) mmdbtype.Map {
		return mmdbtype.Map{"names": mmdbtype.Map{"en": mmdbtype.String(name)}}
	}

	country := names("Germany")
	country["iso_code"] = mmdbtype.String("DE")

	err = tree.Insert(network, mmdbtype.Map{
		"city":         names(databaseCity),
		"continent":    mmdbtype.Map{"code": mmdbtype.String("EU")},
		"country":      country,
		"subdivisions": mmdbtype.Slice{names("Brandenburg")},
		"location": mmdbtype.Map{
			"latitude":  mmdbtype.Float64(52.5),
			"longitude": mmdbtype.Float64(13.5),
		},
	})
	if err != nil {
		t.Fatalf("inserting the test record: %v", err)
	}

	var file bytes.Buffer

	_, err = tree.WriteTo(&file)
	if err != nil {
		t.Fatalf("writing the test database: %v", err)
	}

	return file.Bytes()
}

// gzipped returns data compressed with gzip.
func gzipped(t *testing.T, data []byte) []byte {
	t.Helper()

	var packed bytes.Buffer

	writer := gzip.NewWriter(&packed)

	_, err := writer.Write(data)
	if err != nil {
		t.Fatalf("compressing: %v", err)
	}

	err = writer.Close()
	if err != nil {
		t.Fatalf("compressing: %v", err)
	}

	return packed.Bytes()
}

// giveDatabase puts a copy of the test database in the locator's directory, and
// opens it.
func giveDatabase(t *testing.T, locator *Locator) {
	t.Helper()

	path := filepath.Join(locator.dir, databaseFileName)

	err := os.WriteFile(path, databaseFile(t), 0o600)
	if err != nil {
		t.Fatalf("writing the database copy: %v", err)
	}

	locator.openDatabaseCopy()
}

// requireCity checks where a location says it is, and its source.
func requireCity(t *testing.T, got *Location, city, source string) {
	t.Helper()

	if got == nil {
		t.Fatal("no location")
	}

	if got.City == nil || *got.City != city {
		t.Errorf("city %v, want %s", got.City, city)
	}

	if got.Source != source {
		t.Errorf("source %s, want %s", got.Source, source)
	}
}

// TestLookupAsksGeoJSOnceForEveryAddress looks up two addresses, and expects a
// single request that names both, and each answer in its own place.
func TestLookupAsksGeoJSOnceForEveryAddress(t *testing.T) {
	t.Parallel()

	fake := newFakeGeoJS(t, geojsTwoAddresses)
	dir := t.TempDir()
	locator := newTestLocator(t, fake, openCacheDB(t, dir), dir)

	got := locator.Lookup(t.Context(),
		parseAddresses(t, otherAddress, testAddress))

	requests := fake.requestsSeen()
	if len(requests) != 1 || requests[0] != otherAddress+","+testAddress {
		t.Fatalf("requests %v, want one naming both addresses", requests)
	}

	first := got[1]
	requireCity(t, first, testCity, sourceGeoJS)

	if *first.CountryCode != "DE" || *first.Country != "Germany" ||
		*first.ContinentCode != "EU" || *first.Region != "Brandenburg" ||
		*first.Latitude != 52.6171 || *first.Longitude != 13.1207 ||
		*first.AccuracyRadiusKm != 20 || *first.TimeZone != "Europe/Berlin" {
		t.Errorf("wrong location %+v", first)
	}

	if !first.Updated.Equal(fixedTime()) {
		t.Errorf("updated %v, want %v", first.Updated, fixedTime())
	}
}

// TestLookupGivesUnknownPartsAsNil checks an answer whose coordinates are the
// string "nil" and which has no other part: the parts are nil, and the answer
// is still an answer.
func TestLookupGivesUnknownPartsAsNil(t *testing.T) {
	t.Parallel()

	fake := newFakeGeoJS(t, geojsTwoAddresses)
	dir := t.TempDir()
	locator := newTestLocator(t, fake, openCacheDB(t, dir), dir)

	got := lookupOne(t, locator, otherAddress)
	if got == nil {
		t.Fatal("no location for an address geojs answered")
	}

	if got.Latitude != nil || got.Longitude != nil || got.City != nil ||
		got.CountryCode != nil || got.AccuracyRadiusKm != nil ||
		got.TimeZone != nil {
		t.Errorf("unknown parts are not nil: %+v", got)
	}

	if got.Source != sourceGeoJS {
		t.Errorf("source %s, want %s", got.Source, sourceGeoJS)
	}
}

// TestLookupRejectsNumbersJSONCannotCarry checks that a coordinate that is not
// a finite number is nil.
func TestLookupRejectsNumbersJSONCannotCarry(t *testing.T) {
	t.Parallel()

	for _, text := range []string{"NaN", "Inf", "-Inf", "not a number", ""} {
		if got := knownNumber(text); got != nil {
			t.Errorf("knownNumber(%q) = %v, want nil", text, *got)
		}
	}
}

// TestLookupFallsBackToTheDatabase makes geojs fail in each way the fallback
// covers, and expects the database's answer.
func TestLookupFallsBackToTheDatabase(t *testing.T) {
	t.Parallel()

	tests := []struct {
		name   string
		body   string
		status int
		hang   bool
	}{
		{name: "timeout", hang: true},
		{name: "error status", status: http.StatusBadGateway},
		{name: "unreadable answer", body: "not JSON"},
		{name: "address left out", body: "[]"},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			fake := newFakeGeoJS(t, tt.body)
			fake.status = tt.status
			fake.hang = tt.hang
			dir := t.TempDir()
			locator := newTestLocator(t, fake, openCacheDB(t, dir), dir)
			locator.timeLimit = shortTimeLimit

			if !tt.hang {
				locator.timeLimit = testTimeLimit
			}

			giveDatabase(t, locator)

			got := lookupOne(t, locator, testAddress)
			requireCity(t, got, databaseCity, sourceDBIP)

			if *got.CountryCode != "DE" || *got.Country != "Germany" ||
				*got.ContinentCode != "EU" || *got.Region != "Brandenburg" ||
				*got.Latitude != 52.5 || *got.Longitude != 13.5 {
				t.Errorf("wrong location %+v", got)
			}

			if got.TimeZone != nil || got.AccuracyRadiusKm != nil {
				t.Errorf("parts the database lacks are not nil: %+v", got)
			}

			// The fallback is local, so it is not cached: the next lookup
			// asks geojs again.
			lookupOne(t, locator, testAddress)

			if requests := fake.requestsSeen(); len(requests) != 2 {
				t.Errorf("%d requests, want 2", len(requests))
			}
		})
	}
}

// TestLookupIsNilWhenNeitherSourceAnswers makes geojs fail with no database
// copy, and then with a copy that does not cover the address.
func TestLookupIsNilWhenNeitherSourceAnswers(t *testing.T) {
	t.Parallel()

	fake := newFakeGeoJS(t, "")
	fake.status = http.StatusBadGateway
	dir := t.TempDir()
	locator := newTestLocator(t, fake, openCacheDB(t, dir), dir)

	if got := lookupOne(t, locator, testAddress); got != nil {
		t.Errorf("location %+v before the first download, want nil", got)
	}

	giveDatabase(t, locator)

	if got := lookupOne(t, locator, thirdAddress); got != nil {
		t.Errorf("location %+v for an address outside the database, want nil", got)
	}
}

// TestAnsweredAddressesAreNotAskedAgain checks that an address held in memory
// makes no request, and that only the others go to geojs.
func TestAnsweredAddressesAreNotAskedAgain(t *testing.T) {
	t.Parallel()

	fake := newFakeGeoJS(t, geojsTwoAddresses)
	dir := t.TempDir()
	locator := newTestLocator(t, fake, openCacheDB(t, dir), dir)

	lookupOne(t, locator, testAddress)

	second := locator.Lookup(t.Context(),
		parseAddresses(t, testAddress, otherAddress))

	requireCity(t, second[0], testCity, sourceGeoJS)

	requests := fake.requestsSeen()
	if len(requests) != 2 || requests[1] != otherAddress {
		t.Errorf("requests %v, want the second to name only %s",
			requests, otherAddress)
	}
}

// TestCacheSurvivesARestart writes an answer, then starts a new Locator on the
// same cache.db. It answers with no request, each part as it was.
func TestCacheSurvivesARestart(t *testing.T) {
	t.Parallel()

	fake := newFakeGeoJS(t, geojsTwoAddresses)
	dir := t.TempDir()
	db := openCacheDB(t, dir)
	locator := newTestLocator(t, fake, db, dir)

	want := locator.Lookup(t.Context(),
		parseAddresses(t, testAddress, otherAddress))
	locator.flush(t.Context())

	restarted := newTestLocator(t, fake, db, dir)

	err := restarted.load(t.Context())
	if err != nil {
		t.Fatalf("load: %v", err)
	}

	got := restarted.Lookup(t.Context(),
		parseAddresses(t, testAddress, otherAddress))

	if requests := fake.requestsSeen(); len(requests) != 1 {
		t.Errorf("%d requests, want only the first", len(requests))
	}

	requireCity(t, got[0], testCity, sourceGeoJS)

	if *got[0].Latitude != *want[0].Latitude ||
		*got[0].AccuracyRadiusKm != *want[0].AccuracyRadiusKm ||
		!got[0].Updated.Equal(want[0].Updated) {
		t.Errorf("reloaded %+v, want %+v", got[0], want[0])
	}

	if got[1].Latitude != nil || got[1].City != nil {
		t.Errorf("unknown parts came back set: %+v", got[1])
	}
}

// TestStopWritesWhatIsPending starts a Locator, takes an answer and stops it.
// The answer is in cache.db afterwards.
func TestStopWritesWhatIsPending(t *testing.T) {
	t.Parallel()

	fake := newFakeGeoJS(t, geojsTwoAddresses)
	dir := t.TempDir()
	db := openCacheDB(t, dir)
	locator := newTestLocator(t, fake, db, dir)

	err := locator.Start(t.Context())
	if err != nil {
		t.Fatalf("Start: %v", err)
	}

	lookupOne(t, locator, testAddress)
	locator.Stop(t.Context())

	stored, err := locator.readRow(t.Context(), testAddress)
	if err != nil {
		t.Fatalf("readRow: %v", err)
	}

	requireCity(t, stored, testCity, sourceGeoJS)
}

// TestAnswersExpireAfterSevenDays checks an answer just before and at the end
// of its lifetime, and that the sweep deletes its row and memory entry.
func TestAnswersExpireAfterSevenDays(t *testing.T) {
	t.Parallel()

	fake := newFakeGeoJS(t, geojsOneAddress)
	dir := t.TempDir()
	db := openCacheDB(t, dir)
	locator := newTestLocator(t, fake, db, dir)

	lookupOne(t, locator, testAddress)
	locator.flush(t.Context())

	locator.now = func() time.Time { return fixedTime().Add(entryLifetime - time.Second) }
	lookupOne(t, locator, testAddress)

	if requests := fake.requestsSeen(); len(requests) != 1 {
		t.Fatalf("%d requests just before expiry, want 1", len(requests))
	}

	expiry := fixedTime().Add(entryLifetime)
	locator.now = func() time.Time { return expiry }

	locator.sweep(t.Context())

	if locator.entries.Len() != 0 {
		t.Errorf("%d entries in memory after the sweep, want 0", locator.entries.Len())
	}

	var rows int

	err := db.QueryRowContext(t.Context(),
		"SELECT COUNT(*) FROM geolocations").Scan(&rows)
	if err != nil {
		t.Fatalf("counting rows: %v", err)
	}

	if rows != 0 {
		t.Errorf("%d rows after the sweep, want 0", rows)
	}

	lookupOne(t, locator, testAddress)

	if requests := fake.requestsSeen(); len(requests) != 2 {
		t.Errorf("%d requests after expiry, want 2", len(requests))
	}
}

// limitMemory makes the locator's memory hold at most size answers.
func limitMemory(t *testing.T, locator *Locator, size int) {
	t.Helper()

	entries, err := lru.New[string, *Location](size)
	if err != nil {
		t.Fatalf("lru.New: %v", err)
	}

	locator.entries = entries
	locator.maxEntries = size
}

// answerFor returns a location for store to keep, fetched at the time given.
func answerFor(fetched time.Time) *Location {
	return &Location{City: new(testCity), Source: sourceGeoJS, Updated: fetched}
}

// TestMemoryDropsTheLeastRecentlyUsedAnswer fills memory with two answers,
// uses the older one and stores a third. The unused one leaves memory, and its
// row still answers without a request.
func TestMemoryDropsTheLeastRecentlyUsedAnswer(t *testing.T) {
	t.Parallel()

	fake := newFakeGeoJS(t, "[]")
	dir := t.TempDir()
	locator := newTestLocator(t, fake, openCacheDB(t, dir), dir)
	limitMemory(t, locator, 2)

	locator.store(testAddress, answerFor(fixedTime()))
	locator.store(otherAddress, answerFor(fixedTime()))
	locator.flush(t.Context())

	lookupOne(t, locator, testAddress)
	locator.store(thirdAddress, answerFor(fixedTime()))

	if locator.entries.Contains(otherAddress) {
		t.Fatal("the least recently used answer stayed in memory")
	}

	if !locator.entries.Contains(testAddress) {
		t.Fatal("the recently used answer left memory")
	}

	requireCity(t, lookupOne(t, locator, otherAddress), testCity, sourceGeoJS)

	if requests := fake.requestsSeen(); len(requests) != 0 {
		t.Errorf("requests %v, want the row to answer", requests)
	}
}

// TestLoadKeepsTheNewestAnswers loads more rows than memory holds. The newest
// are in memory, and the newest of all is the last to be dropped.
func TestLoadKeepsTheNewestAnswers(t *testing.T) {
	t.Parallel()

	fake := newFakeGeoJS(t, "[]")
	dir := t.TempDir()
	locator := newTestLocator(t, fake, openCacheDB(t, dir), dir)

	locator.store(testAddress, answerFor(fixedTime().Add(-3*time.Hour)))
	locator.store(otherAddress, answerFor(fixedTime().Add(-2*time.Hour)))
	locator.store(thirdAddress, answerFor(fixedTime().Add(-time.Hour)))
	locator.flush(t.Context())

	limitMemory(t, locator, 2)

	err := locator.load(t.Context())
	if err != nil {
		t.Fatalf("load: %v", err)
	}

	if locator.entries.Contains(testAddress) {
		t.Error("the oldest answer was loaded")
	}

	locator.entries.Add("192.0.2.99", answerFor(fixedTime()))

	if !locator.entries.Contains(thirdAddress) {
		t.Error("the newest answer was the first to be dropped")
	}
}

// fakeDownload serves file for the January 2026 database and counts requests.
func fakeDownload(t *testing.T, file []byte) *httptest.Server {
	t.Helper()

	server := httptest.NewServer(http.HandlerFunc(
		func(w http.ResponseWriter, r *http.Request) {
			if r.URL.Path != databasePath {
				http.NotFound(w, r)

				return
			}

			_, _ = w.Write(file)
		}))
	t.Cleanup(server.Close)

	return server
}

// newDownloadLocator returns a locator that downloads file.
func newDownloadLocator(t *testing.T, file []byte) *Locator {
	t.Helper()

	fake := newFakeGeoJS(t, "[]")
	fake.status = http.StatusBadGateway
	dir := t.TempDir()
	locator := newTestLocator(t, fake, openCacheDB(t, dir), dir)
	locator.databaseURLFormat = fakeDownload(t, file).URL +
		"/dbip-city-lite-%s.mmdb.gz"

	return locator
}

// requireNoDownloadFile checks that a download left no temporary file.
func requireNoDownloadFile(t *testing.T, locator *Locator) {
	t.Helper()

	_, err := os.Stat(filepath.Join(locator.dir,
		databaseFileName+databaseDownloadSuffix))
	if !errors.Is(err, fs.ErrNotExist) {
		t.Errorf("the download's file is still there: %v", err)
	}
}

// TestDownloadPutsTheDatabaseInUse downloads this month's file, unpacks it, and
// answers from it. A restart opens the copy.
func TestDownloadPutsTheDatabaseInUse(t *testing.T) {
	t.Parallel()

	file := gzipped(t, databaseFile(t))
	locator := newDownloadLocator(t, file)

	err := locator.downloadDatabase(t.Context(), fixedTime())
	if err != nil {
		t.Fatalf("downloadDatabase: %v", err)
	}

	requireNoDownloadFile(t, locator)

	got := lookupOne(t, locator, testAddress)
	requireCity(t, got, databaseCity, sourceDBIP)

	if !got.Updated.Equal(fixedTime().Truncate(time.Second)) {
		t.Errorf("updated %v, want the download's time", got.Updated)
	}

	restarted := newDownloadLocator(t, file)
	restarted.dir = locator.dir
	restarted.openDatabaseCopy()
	requireCity(t, lookupOne(t, restarted, testAddress), databaseCity, sourceDBIP)
}

// TestDownloadIsDueOnceAMonth checks when a copy needs replacing: with no copy,
// not again in the month it was fetched, and in the next month.
func TestDownloadIsDueOnceAMonth(t *testing.T) {
	t.Parallel()

	locator := newDownloadLocator(t, gzipped(t, databaseFile(t)))

	if !locator.databaseDue(fixedTime()) {
		t.Error("no download due with no copy")
	}

	err := locator.downloadDatabase(t.Context(), fixedTime())
	if err != nil {
		t.Fatalf("downloadDatabase: %v", err)
	}

	if locator.databaseDue(fixedTime().AddDate(0, 0, 20)) {
		t.Error("a download is due in the same month")
	}

	if !locator.databaseDue(fixedTime().AddDate(0, 1, 0)) {
		t.Error("no download due in the next month")
	}
}

// TestFailedDownloadKeepsTheCopy serves a copy that cannot replace the one in
// use, in each way, and expects the old copy to go on answering.
func TestFailedDownloadKeepsTheCopy(t *testing.T) {
	t.Parallel()

	tests := []struct {
		name string
		file func(t *testing.T) []byte
		max  int64
	}{
		{
			name: "not gzip",
			file: func(*testing.T) []byte { return []byte("not gzip") },
		},
		{
			name: "not a database",
			file: func(t *testing.T) []byte {
				t.Helper()

				return gzipped(t, []byte("not a database"))
			},
		},
		{
			name: "cut off",
			file: func(t *testing.T) []byte {
				t.Helper()

				packed := gzipped(t, databaseFile(t))

				return packed[:len(packed)/2]
			},
		},
		{
			name: "over the size limit",
			file: func(t *testing.T) []byte {
				t.Helper()

				return gzipped(t, databaseFile(t))
			},
			max: 10,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			locator := newDownloadLocator(t, tt.file(t))
			if tt.max != 0 {
				locator.maxDatabaseBytes = tt.max
			}

			giveDatabase(t, locator)

			err := locator.downloadDatabase(t.Context(), fixedTime())
			if err == nil {
				t.Fatal("the download succeeded")
			}

			requireNoDownloadFile(t, locator)
			requireCity(t, lookupOne(t, locator, testAddress),
				databaseCity, sourceDBIP)
		})
	}
}

// TestMissingFileIsAFailedDownload checks that a month whose file is not
// published yet is an error and leaves no copy.
func TestMissingFileIsAFailedDownload(t *testing.T) {
	t.Parallel()

	locator := newDownloadLocator(t, nil)

	err := locator.downloadDatabase(t.Context(), fixedTime().AddDate(0, 1, 0))
	if !errors.Is(err, errDatabaseStatus) {
		t.Fatalf("error %v, want %v", err, errDatabaseStatus)
	}

	if !locator.databaseDue(fixedTime()) {
		t.Error("a copy is in use after a failed download")
	}
}

// TestUnopenableCopyIsDownloadedAgain leaves a damaged copy from this month. It
// counts as no copy, so the download is due.
func TestUnopenableCopyIsDownloadedAgain(t *testing.T) {
	t.Parallel()

	locator := newDownloadLocator(t, nil)

	err := os.WriteFile(filepath.Join(locator.dir, databaseFileName),
		[]byte("damaged"), 0o600)
	if err != nil {
		t.Fatalf("writing the copy: %v", err)
	}

	locator.openDatabaseCopy()

	if !locator.databaseDue(fixedTime()) {
		t.Error("no download due with a copy that does not open")
	}
}

// TestLookupDuringReplaceIsSafe looks up addresses while the copy is replaced.
// The race detector and the mapped file both catch a lookup of a closed copy.
func TestLookupDuringReplaceIsSafe(t *testing.T) {
	t.Parallel()

	file := gzipped(t, databaseFile(t))
	locator := newDownloadLocator(t, file)
	giveDatabase(t, locator)

	addrs := parseAddresses(t, testAddress)

	ctx, cancel := context.WithCancel(t.Context())
	defer cancel()

	var readers sync.WaitGroup

	readers.Go(func() {
		for ctx.Err() == nil {
			locator.fromDatabase(addrs[0])
		}
	})

	for range 5 {
		err := locator.downloadDatabase(t.Context(), fixedTime())
		if err != nil {
			t.Fatalf("downloadDatabase: %v", err)
		}
	}

	cancel()
	readers.Wait()
}

// TestRequestNamesRouteWatch checks the header each outside request carries,
// which tells geojs and DB-IP who is asking.
func TestRequestNamesRouteWatch(t *testing.T) {
	t.Parallel()

	var seen atomic.Pointer[string]

	server := httptest.NewServer(http.HandlerFunc(
		func(_ http.ResponseWriter, r *http.Request) {
			seen.Store(new(r.Header.Get(userAgentHeader)))
		}))
	t.Cleanup(server.Close)

	fake := newFakeGeoJS(t, "[]")
	dir := t.TempDir()
	locator := newTestLocator(t, fake, openCacheDB(t, dir), dir)
	locator.geojsURL = server.URL + geojsPath

	lookupOne(t, locator, testAddress)

	got := seen.Load()
	if got == nil || !strings.HasPrefix(*got, "routewatch") {
		t.Errorf("User-Agent %v", got)
	}
}