Quantize all timestamps stored in the db

Fixes issue #1.

server/lastlogin.go

@@ -71,7 +71,7 @@ func (l *lastloginDB) AddLastLogin(entry *usermetadb.LastLoginEntry) error {
 	args := []interface{}{
 		entry.Username,
 		entry.Service,
-		entry.Timestamp,
+		roundTimestamp(entry.Timestamp),
 	}
 
 	if _, err = l.stmts.get(tx, stmt).Exec(args...); err != nil {

server/lastlogin_test.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"git.autistici.org/id/usermetadb"
+	"github.com/google/go-cmp/cmp"
 )
 
 func generateLastLoginEntries() []*usermetadb.LastLoginEntry {
@@ -54,8 +55,10 @@ func TestLastlogin_LoginAdded(t *testing.T) {
 		t.Fatalf("Expected exactly one entry, found %v", out)
 	}
 
-	if *in[0] != *out[0] {
-		t.Fatalf("Last login entries differ:\nSet %v\nGot %v", *in[0], *out[0])
+	// Modify the entries so that the quantized timestamp matches.
+	in[0].Timestamp = roundTimestamp(in[0].Timestamp)
+	if diffs := cmp.Diff(in[0], out[0]); diffs != "" {
+		t.Fatalf("Last login entries differ:\n%s", diffs)
 	}
 }
 
@@ -90,8 +93,10 @@ func TestLastLogin_MultipleServices(t *testing.T) {
 	}
 
 	for i := 0; i < 2; i++ {
-		if *in[i] != *out[i] {
-			t.Fatalf("Last login entries #%d differ:\nSet %v\nGot %v", i, *in[i], *out[i])
+		// Modify the entries so that the quantized timestamp matches.
+		in[i].Timestamp = roundTimestamp(in[i].Timestamp)
+		if diffs := cmp.Diff(in[0], out[0]); diffs != "" {
+			t.Fatalf("Last login entries #%d differ:\n%s", i, diffs)
 		}
 	}
 }

server/server_test.go

@@ -8,6 +8,7 @@ import (
 
 	"git.autistici.org/ai3/go-common/clientutil"
 	"git.autistici.org/id/usermetadb/client"
+	"github.com/google/go-cmp/cmp"
 )
 
 func TestServer_AddLog(t *testing.T) {
@@ -69,12 +70,13 @@ func TestServer_AddLastLogin(t *testing.T) {
 	}
 
 	expResp := *entries[0]
+	expResp.Timestamp = roundTimestamp(expResp.Timestamp)
 	resp, err := c.GetLastLogin(context.Background(), "", expResp.Username, expResp.Service)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	if *resp[0] != expResp {
-		t.Fatalf("Last login entries differ:\nSet %v\nGot %v", expResp, *resp[0])
+	if diffs := cmp.Diff(resp[0], &expResp); diffs != "" {
+		t.Fatalf("Last login entries differ:\n%s", diffs)
 	}
 }

server/userlog.go

@@ -164,7 +164,7 @@ func (u *userlogDB) Close() {
 
 // Update or create an entry in the 'devices' table.
 func (u *userlogDB) updateDeviceInfo(tx *sql.Tx, username string, deviceInfo *auth.DeviceInfo) error {
-	now := time.Now().UTC()
+	now := roundTimestamp(time.Now().UTC())
 
 	var seen bool
 	err := u.stmts.get(tx, "check_device_info").QueryRow(username, deviceInfo.ID).Scan(&seen)
@@ -333,17 +333,19 @@ func (u *userlogDB) GetUserDevices(username string) ([]*usermetadb.MetaDeviceInf
 	return out, rows.Err()
 }
 
-var timestampRoundSeconds int64 = 7200
+const timestampRoundSeconds = 7200
 
-func roundTimestamp(t time.Time, r int64) time.Time {
-	return time.Unix((t.Unix()/r)*r, 0)
+// Quantize timestamps to minimize time correlation possibilities.
+func roundTimestamp(t time.Time) time.Time {
+	// Keep the original timezone information.
+	return time.Unix((t.Unix()/timestampRoundSeconds)*timestampRoundSeconds, 0).In(t.Location())
 }
 
 // Minimize a log entry, removing all the data that we don't want to
 // store (even if it's already missing in the database schema).
 func minimizeLogEntry(e *usermetadb.LogEntry) {
 	// Round timestamps to the nearest even hour.
-	e.Timestamp = roundTimestamp(e.Timestamp, timestampRoundSeconds)
+	e.Timestamp = roundTimestamp(e.Timestamp)
 
 	// Drop fields in DeviceInfo that we don't want.
 	if e.DeviceInfo != nil {