Make the cache TTL an explicit, configurable parameter

Author: jedisct1

dnscrypt-proxy/config.go

@@ -188,6 +188,7 @@ type SourceConfig struct {
 	CacheFile      string `toml:"cache_file"`
 	FormatStr      string `toml:"format"`
 	RefreshDelay   int    `toml:"refresh_delay"`
+	CacheTTL       int    `toml:"cache_ttl"`
 	Prefix         string
 }
 
@@ -716,6 +717,10 @@ func (config *Config) loadSource(proxy *Proxy, cfgSourceName string, cfgSource *
 		cfgSource.RefreshDelay = 72
 	}
 	cfgSource.RefreshDelay = Min(169, Max(25, cfgSource.RefreshDelay))
+	if cfgSource.CacheTTL <= 0 {
+		cfgSource.CacheTTL = 168
+	}
+	cfgSource.CacheTTL = Min(168, Max(cfgSource.RefreshDelay, cfgSource.CacheTTL))
 	source, err := NewSource(
 		cfgSourceName,
 		proxy.xTransport,
@@ -724,6 +729,7 @@ func (config *Config) loadSource(proxy *Proxy, cfgSourceName string, cfgSource *
 		cfgSource.CacheFile,
 		cfgSource.FormatStr,
 		time.Duration(cfgSource.RefreshDelay)*time.Hour,
+		time.Duration(cfgSource.CacheTTL)*time.Hour,
 		cfgSource.Prefix,
 	)
 	if err != nil {

dnscrypt-proxy/example-dnscrypt-proxy.toml

@@ -752,10 +752,14 @@ format = 'tsv'
 ##
 ## If the `urls` property is missing, cache files and valid signatures
 ## must already be present. This doesn't prevent these cache files from
-## expiring after `refresh_delay` hours.
-## `refreshed_delay` must be in the [24..168] interval.
-## The minimum delay of 24 hours (1 day) avoids unnecessary requests to servers.
-## The maximum delay of 168 hours (1 week) ensures cache freshness.
+## expiring after `cache_ttl` hours.
+##
+## `refresh_delay` controls how often to download updates during normal operation.
+## Must be in the [24..168] interval (1 day to 1 week).
+##
+## `cache_ttl` controls how old the cache can be at startup before requiring
+## an immediate download. Defaults to 168 hours if not set.
+## Must be in [refresh_delay..168] interval.
 
 [sources]
 

dnscrypt-proxy/sources.go

@@ -221,17 +221,24 @@ func NewSource(
 	cacheFile string,
 	formatStr string,
 	refreshDelay time.Duration,
+	cacheTTL time.Duration,
 	prefix string,
 ) (*Source, error) {
 	if refreshDelay < DefaultPrefetchDelay {
 		refreshDelay = DefaultPrefetchDelay
 	}
+	if cacheTTL < refreshDelay {
+		cacheTTL = refreshDelay
+	}
+	if cacheTTL > 168*time.Hour {
+		cacheTTL = 168 * time.Hour
+	}
 	source := &Source{
 		name:          name,
 		urls:          []*url.URL{},
 		cacheFile:     cacheFile,
-		cacheTTL:      refreshDelay,
-		prefetchDelay: DefaultPrefetchDelay,
+		cacheTTL:      cacheTTL,
+		prefetchDelay: refreshDelay,
 		prefix:        prefix,
 	}
 	if formatStr == "v2" {

dnscrypt-proxy/sources_test.go

@@ -350,7 +350,7 @@ func prepSourceTestDownload(
 	}
 	if e.success {
 		e.err = ""
-		e.delay = DefaultPrefetchDelay
+		e.delay = DefaultPrefetchDelay * 3 // matches cacheTTL/prefetchDelay set in setupSourceTestCase
 	} else {
 		e.delay = MinimumPrefetchInterval
 	}
@@ -371,7 +371,7 @@ func setupSourceTestCase(t *testing.T, d *SourceTestData, i int,
 	}
 	e.Source = &Source{
 		name: id, urls: []*url.URL{}, format: SourceFormatV2, minisignKey: d.key,
-		cacheFile: e.cachePath, cacheTTL: DefaultPrefetchDelay * 3, prefetchDelay: DefaultPrefetchDelay,
+		cacheFile: e.cachePath, cacheTTL: DefaultPrefetchDelay * 3, prefetchDelay: DefaultPrefetchDelay * 3,
 	}
 	if cacheTest != nil {
 		prepSourceTestCache(t, d, e, d.sources[i], *cacheTest)
@@ -401,13 +401,13 @@ func TestNewSource(t *testing.T) {
 	}
 	d.n++
 	for _, tt := range []struct {
-		v, key       string
-		refreshDelay time.Duration
-		e            *SourceTestExpect
+		v, key                 string
+		refreshDelay, cacheTTL time.Duration
+		e                      *SourceTestExpect
 	}{
-		{"", "", 0, &SourceTestExpect{err: " ", Source: &Source{name: "short refresh delay", urls: []*url.URL{}, cacheTTL: DefaultPrefetchDelay, prefetchDelay: DefaultPrefetchDelay, prefix: ""}}},
-		{"v1", d.keyStr, DefaultPrefetchDelay * 2, &SourceTestExpect{err: "Unsupported source format", Source: &Source{name: "old format", urls: []*url.URL{}, cacheTTL: DefaultPrefetchDelay * 2, prefetchDelay: DefaultPrefetchDelay}}},
-		{"v2", "", DefaultPrefetchDelay * 3, &SourceTestExpect{err: "Invalid encoded public key", Source: &Source{name: "invalid public key", urls: []*url.URL{}, cacheTTL: DefaultPrefetchDelay * 3, prefetchDelay: DefaultPrefetchDelay}}},
+		{"", "", 0, 0, &SourceTestExpect{err: " ", Source: &Source{name: "short refresh delay", urls: []*url.URL{}, cacheTTL: DefaultPrefetchDelay, prefetchDelay: DefaultPrefetchDelay, prefix: ""}}},
+		{"v1", d.keyStr, DefaultPrefetchDelay * 2, DefaultPrefetchDelay * 2, &SourceTestExpect{err: "Unsupported source format", Source: &Source{name: "old format", urls: []*url.URL{}, cacheTTL: DefaultPrefetchDelay * 2, prefetchDelay: DefaultPrefetchDelay * 2}}},
+		{"v2", "", DefaultPrefetchDelay * 3, DefaultPrefetchDelay * 3, &SourceTestExpect{err: "Invalid encoded public key", Source: &Source{name: "invalid public key", urls: []*url.URL{}, cacheTTL: DefaultPrefetchDelay * 3, prefetchDelay: DefaultPrefetchDelay * 3}}},
 	} {
 		t.Run(tt.e.Source.name, func(t *testing.T) {
 			got, err := NewSource(
@@ -418,6 +418,7 @@ func TestNewSource(t *testing.T) {
 				tt.e.cachePath,
 				tt.v,
 				tt.refreshDelay,
+				tt.cacheTTL,
 				tt.e.prefix,
 			)
 			checkResult(t, tt.e, got, err)
@@ -437,6 +438,7 @@ func TestNewSource(t *testing.T) {
 						e.cachePath,
 						"v2",
 						DefaultPrefetchDelay*3,
+						DefaultPrefetchDelay*3,
 						"",
 					)
 					checkResult(t, e, got, err)
@@ -483,7 +485,7 @@ func TestPrefetchSources(t *testing.T) {
 				cacheFile:     e.Source.cacheFile,
 				cacheTTL:      e.Source.cacheTTL,
 				prefetchDelay: e.Source.prefetchDelay,
-				refresh:       e.Source.refresh,
+				refresh:       d.timeUpd, // Set to trigger prefetch (source.refresh.After(now) will be false)
 				prefix:        e.Source.prefix,
 				// bin is intentionally left nil
 			}