fix(server): use UTC and portable path composition

This diff implements portable path composition theoretically
allowing the server to run under Windows systems.

Additionally, this diff implements tests to ensure that we're
still composing the output file path correctly.

While there, notice we're not using UTC and enforce UTC.

server/server.go

@@ -34,6 +34,11 @@ type sessionInfo struct {
 	stamp time.Time
 }
 
+// timeNowUTC returns the current time using UTC.
+func timeNowUTC() time.Time {
+	return time.Now().UTC()
+}
+
 // dependencies abstracts the dependencies used by [*Handler].
 type dependencies struct {
 	GzipNewWriterLevel func(w io.Writer, level int) (*gzip.Writer, error)
@@ -104,7 +109,7 @@ func NewHandler(datadir string, logger model.Logger) *Handler {
 //
 // This method LOCKS and MUTATES the .sessions field.
 func (h *Handler) createSession(UUID string) {
-	now := time.Now()
+	now := timeNowUTC()
 	session := &sessionInfo{
 		stamp: now,
 		serverSchema: model.ServerSchema{
@@ -156,7 +161,7 @@ func (h *Handler) getSessionState(UUID string) sessionState {
 // The integer argument, currently ignored, contains the number of bytes
 // that were sent as part of the current DASH iteration.
 func (h *Handler) updateSession(UUID string, _ int) {
-	now := time.Now()
+	now := timeNowUTC()
 	h.mtx.Lock()
 	defer h.mtx.Unlock()
 	session, ok := h.sessions[UUID]
@@ -198,7 +203,7 @@ func (h *Handler) reapStaleSessions() {
 	h.mtx.Lock()
 	defer h.mtx.Unlock()
 	h.logger.Debugf("reapStaleSessions: inspecting %d sessions", len(h.sessions))
-	now := time.Now()
+	now := timeNowUTC()
 	var stale []string
 	for UUID, session := range h.sessions {
 		const toomuch = 60 * time.Second
@@ -381,9 +386,7 @@ func (h *Handler) savedata(session *sessionInfo) error {
 	}
 
 	// append the file name to the path
-	//
-	// TODO(bassosimone): this code does not work as intended on Windows
-	name += "/neubot-dash-" + session.stamp.Format("20060102T150405.000000000Z") + ".json.gz"
+	name = path.Join(name, "/neubot-dash-"+session.stamp.Format("20060102T150405.000000000Z")+".json.gz")
 
 	// open the results file
 	//

server/server_test.go

@@ -7,7 +7,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
 	"net/url"
@@ -72,7 +71,7 @@ func TestServerNegotiate(t *testing.T) {
 		if resp.StatusCode != 200 {
 			t.Fatal("Expected different status code")
 		}
-		data, err := ioutil.ReadAll(resp.Body)
+		data, err := io.ReadAll(resp.Body)
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -213,7 +212,7 @@ func TestServerDownload(t *testing.T) {
 		if resp.StatusCode != 200 {
 			t.Fatal("Expected different status code")
 		}
-		data, err := ioutil.ReadAll(resp.Body)
+		data, err := io.ReadAll(resp.Body)
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -268,7 +267,7 @@ func TestServerSaveData(t *testing.T) {
 		handler.deps.OSOpenFile = func(
 			name string, flag int, perm os.FileMode,
 		) (*os.File, error) {
-			return ioutil.TempFile("", "neubot-dash-tests")
+			return os.CreateTemp("", "neubot-dash-tests")
 		}
 		handler.deps.GzipNewWriterLevel = func(
 			w io.Writer, level int,
@@ -292,7 +291,7 @@ func TestServerSaveData(t *testing.T) {
 		handler.deps.OSOpenFile = func(
 			name string, flag int, perm os.FileMode,
 		) (*os.File, error) {
-			return ioutil.TempFile("", "neubot-dash-tests")
+			return os.CreateTemp("", "neubot-dash-tests")
 		}
 		handler.deps.JSONMarshal = func(v interface{}) ([]byte, error) {
 			return nil, errors.New("Mocked error")
@@ -311,15 +310,22 @@ func TestServerSaveData(t *testing.T) {
 		handler.deps.OSMkdirAll = func(path string, perm os.FileMode) error {
 			return nil
 		}
+		sessionInfo.stamp = time.Date(2024, time.January, 29, 20, 23, 0, 0, time.UTC) // predictable
+		expectFilename := "dash/2024/01/29/neubot-dash-20240129T202300.000000000Z.json.gz"
+		var gotFilename string
 		handler.deps.OSOpenFile = func(
 			name string, flag int, perm os.FileMode,
 		) (*os.File, error) {
-			return ioutil.TempFile("", "neubot-dash-tests")
+			gotFilename = name
+			return os.CreateTemp("", "neubot-dash-tests")
 		}
 		err := handler.savedata(sessionInfo)
 		if err != nil {
 			t.Fatal(err)
 		}
+		if gotFilename != expectFilename {
+			t.Fatal("expected", expectFilename, "got", gotFilename)
+		}
 	})
 }
 
@@ -335,7 +341,7 @@ func TestServerCollect(t *testing.T) {
 		}
 	})
 
-	t.Run("ioutil.ReadAll failure", func(t *testing.T) {
+	t.Run("io.ReadAll failure", func(t *testing.T) {
 		const session = "deadbeef"
 		handler := NewHandler("", log.Log)
 		handler.createSession(session)