Fix prefetch sometimes being skipped

Previously when the cache was written to disk, the modification time was unspecified.
At the next prefetch, it was possible for the cache to be expiring very soon (on the order of milliseconds) but still deemed valid.
Now the modification time is explicitly set to when the prefetch run began to make this situation much less likely.

dnscrypt-proxy/sources.go

@@ -77,7 +77,7 @@ func (source *Source) fetchFromCache(now time.Time) (delay time.Duration, err er
 	return
 }
 
-func (source *Source) writeToCache(bin, sig []byte) (err error) {
+func (source *Source) writeToCache(bin, sig []byte, now time.Time) (err error) {
 	f := source.cacheFile
 	var fSrc, fSig *safefile.File
 	if fSrc, err = safefile.Create(f, 0644); err != nil {
@@ -97,7 +97,10 @@ func (source *Source) writeToCache(bin, sig []byte) (err error) {
 	if err = fSrc.Commit(); err != nil {
 		return
 	}
-	return fSig.Commit()
+	if err = fSig.Commit(); err != nil {
+		return
+	}
+	return os.Chtimes(f, now, now)
 }
 
 func (source *Source) parseURLs(urls []string) {
@@ -159,7 +162,7 @@ func (source *Source) fetchWithCache(xTransport *XTransport, now time.Time) (del
 		return
 	}
 	source.in = bin
-	if writeErr := source.writeToCache(bin, sig); writeErr != nil { // an error here isn't fatal
+	if writeErr := source.writeToCache(bin, sig, now); writeErr != nil { // an error here isn't fatal
 		f := source.cacheFile
 		if absPath, absErr := filepath.Abs(f); absErr == nil {
 			f = absPath

dnscrypt-proxy/sources_test.go

@@ -60,6 +60,7 @@ type SourceTestExpect struct {
 	success        bool
 	err, cachePath string
 	cache          []SourceFixture
+	mtime          time.Time
 	urls           []string
 	Source         *Source
 	delay          time.Duration
@@ -73,12 +74,12 @@ func readFixture(t *testing.T, name string) []byte {
 	return bin
 }
 
-func writeSourceCache(t *testing.T, basePath string, fixtures []SourceFixture) {
+func writeSourceCache(t *testing.T, e *SourceTestExpect) {
-	for _, f := range fixtures {
+	for _, f := range e.cache {
 		if f.content == nil {
 			continue
 		}
-		path := basePath + f.suffix
+		path := e.cachePath + f.suffix
 		perms := f.perms
 		if perms == 0 {
 			perms = 0644
@@ -89,21 +90,35 @@ func writeSourceCache(t *testing.T, basePath string, fixtures []SourceFixture) {
 		if err := acl.Chmod(path, perms); err != nil {
 			t.Fatalf("Unable to set permissions on cache file %s: %v", path, err)
 		}
-		if f.mtime.IsZero() {
+		if f.suffix != "" {
 			continue
 		}
-		if err := os.Chtimes(path, f.mtime, f.mtime); err != nil {
+		mtime := f.mtime
+		if f.mtime.IsZero() {
+			mtime = e.mtime
+		}
+		if err := os.Chtimes(path, mtime, mtime); err != nil {
 			t.Fatalf("Unable to touch cache file %s to %v: %v", path, f.mtime, err)
 		}
 	}
 }
 
-func checkSourceCache(c *check.C, basePath string, fixtures []SourceFixture) {
+func checkSourceCache(c *check.C, e *SourceTestExpect) {
-	for _, f := range fixtures {
+	for _, f := range e.cache {
-		path := basePath + f.suffix
+		path := e.cachePath + f.suffix
 		_ = acl.Chmod(path, 0644) // don't worry if this fails, reading it will catch the same problem
 		got, err := ioutil.ReadFile(path)
-		c.DeepEqual(got, f.content, "Cache file '%s', err %v", path, err)
+		c.DeepEqual(got, f.content, "Unexpected content for cache file '%s', err %v", path, err)
+		if f.suffix != "" {
+			continue
+		}
+		if fi, err := os.Stat(path); err == nil { // again, if this failed it was already caught above
+			mtime := f.mtime
+			if f.mtime.IsZero() {
+				mtime = e.mtime
+			}
+			c.EQ(fi.ModTime(), mtime, "Unexpected timestamp for cache file '%s'", path)
+		}
 	}
 }
 
@@ -139,7 +154,7 @@ func generateFixtureState(t *testing.T, d *SourceTestData, suffix, file string,
 			return
 		}
 	}
-	f := SourceFixture{suffix: suffix, mtime: d.timeNow}
+	f := SourceFixture{suffix: suffix}
 	switch state {
 	case TestStateExpired:
 		f.content, f.mtime = d.fixtures[TestStateCorrect][file].content, d.timeOld
@@ -161,7 +176,6 @@ func loadFixtures(t *testing.T, d *SourceTestData) {
 			d.fixtures[TestStateCorrect][file] = SourceFixture{
 				suffix:  suffix,
 				content: readFixture(t, filepath.Join("sources", file)),
-				mtime:   d.timeNow,
 			}
 			for _, state := range [...]SourceTestState{
 				TestStateExpired,
@@ -277,7 +291,7 @@ func prepSourceTestCache(t *testing.T, d *SourceTestData, e *SourceTestExpect, s
 	case TestStateMissing, TestStateMissingSig, TestStateOpenErr, TestStateOpenSigErr:
 		e.err = "open"
 	}
-	writeSourceCache(t, e.cachePath, e.cache)
+	writeSourceCache(t, e)
 }
 
 func prepSourceTestDownload(t *testing.T, d *SourceTestData, e *SourceTestExpect, source string, downloadTest []SourceTestState) {
@@ -336,6 +350,7 @@ func setupSourceTestCase(t *testing.T, d *SourceTestData, i int,
 	id = strconv.Itoa(d.n) + "-" + strconv.Itoa(i)
 	e = &SourceTestExpect{
 		cachePath: filepath.Join(d.tempDir, id),
+		mtime:     d.timeNow,
 	}
 	e.Source = &Source{name: id, urls: []*url.URL{}, format: SourceFormatV2, minisignKey: d.key,
 		cacheFile: e.cachePath, cacheTTL: DefaultPrefetchDelay * 3, prefetchDelay: DefaultPrefetchDelay}
@@ -359,7 +374,7 @@ func TestNewSource(t *testing.T) {
 		}
 		c.DeepEqual(got, e.Source, "Unexpected return")
 		checkTestServer(c, d)
-		checkSourceCache(c, e.cachePath, e.cache)
+		checkSourceCache(c, e)
 	}
 	d.n++
 	for _, tt := range []struct {
@@ -402,7 +417,7 @@ func TestPrefetchSources(t *testing.T) {
 		c.InDelta(got, expectDelay, time.Second, "Unexpected return")
 		checkTestServer(c, d)
 		for _, e := range expects {
-			checkSourceCache(c, e.cachePath, e.cache)
+			checkSourceCache(c, e)
 		}
 	}
 	timeNow = func() time.Time { return d.timeUpd } // since the fixtures are prepared using real now, make the tested code think it's the future
@@ -412,6 +427,7 @@ func TestPrefetchSources(t *testing.T) {
 		expects := []*SourceTestExpect{}
 		for i := range d.sources {
 			_, e := setupSourceTestCase(t, d, i, nil, downloadTest)
+			e.mtime = d.timeUpd
 			sources = append(sources, e.Source)
 			expects = append(expects, e)
 		}