New global discovery protocol over HTTPS (fixes #628, fixes #1907)

lib/discover/cache.go

@@ -0,0 +1,192 @@
+package discover
+
+import (
+	stdsync "sync"
+	"time"
+
+	"github.com/syncthing/protocol"
+	"github.com/syncthing/syncthing/lib/sync"
+	"github.com/thejerf/suture"
+)
+
+// The CachingMux aggregates results from multiple Finders. Each Finder has
+// an associated cache time and negative cache time. The cache time sets how
+// long we cache and return successfull lookup results, the negative cache
+// time sets how long we refrain from asking about the same device ID after
+// receiving a negative answer. The value of zero disables caching (positive
+// or negative).
+type CachingMux struct {
+	*suture.Supervisor
+	finders []cachedFinder
+	caches  []*cache
+	mut     sync.Mutex
+}
+
+// A cachedFinder is a Finder with associated cache timeouts.
+type cachedFinder struct {
+	Finder
+	cacheTime    time.Duration
+	negCacheTime time.Duration
+}
+
+func NewCachingMux() *CachingMux {
+	return &CachingMux{
+		Supervisor: suture.NewSimple("discover.cachingMux"),
+		mut:        sync.NewMutex(),
+	}
+}
+
+// Add registers a new Finder, with associated cache timeouts.
+func (m *CachingMux) Add(finder Finder, cacheTime, negCacheTime time.Duration) {
+	m.mut.Lock()
+	m.finders = append(m.finders, cachedFinder{finder, cacheTime, negCacheTime})
+	m.caches = append(m.caches, newCache())
+	m.mut.Unlock()
+
+	if svc, ok := finder.(suture.Service); ok {
+		m.Supervisor.Add(svc)
+	}
+}
+
+// Lookup attempts to resolve the device ID using any of the added Finders,
+// while obeying the cache settings.
+func (m *CachingMux) Lookup(deviceID protocol.DeviceID) (direct []string, relays []Relay, err error) {
+	m.mut.Lock()
+	for i, finder := range m.finders {
+		if cacheEntry, ok := m.caches[i].Get(deviceID); ok {
+			// We have a cache entry. Lets see what it says.
+
+			if cacheEntry.found && time.Since(cacheEntry.when) < finder.cacheTime {
+				// It's a positive, valid entry. Use it.
+				if debug {
+					l.Debugln("cached discovery entry for", deviceID, "at", finder.String())
+					l.Debugln("   ", cacheEntry)
+				}
+				direct = append(direct, cacheEntry.Direct...)
+				relays = append(relays, cacheEntry.Relays...)
+				continue
+			}
+
+			if !cacheEntry.found && time.Since(cacheEntry.when) < finder.negCacheTime {
+				// It's a negative, valid entry. We should not make another
+				// attempt right now.
+				if debug {
+					l.Debugln("negative cache entry for", deviceID, "at", finder.String())
+				}
+				continue
+			}
+
+			// It's expired. Ignore and continue.
+		}
+
+		// Perform the actual lookup and cache the result.
+		if td, tr, err := finder.Lookup(deviceID); err == nil {
+			if debug {
+				l.Debugln("lookup for", deviceID, "at", finder.String())
+				l.Debugln("   ", td)
+				l.Debugln("   ", tr)
+			}
+			direct = append(direct, td...)
+			relays = append(relays, tr...)
+			m.caches[i].Set(deviceID, CacheEntry{
+				Direct: td,
+				Relays: tr,
+				when:   time.Now(),
+				found:  len(td)+len(tr) > 0,
+			})
+		}
+	}
+	m.mut.Unlock()
+
+	if debug {
+		l.Debugln("lookup results for", deviceID)
+		l.Debugln("   ", direct)
+		l.Debugln("   ", relays)
+	}
+
+	return direct, relays, nil
+}
+
+func (m *CachingMux) String() string {
+	return "discovery cache"
+}
+
+func (m *CachingMux) Error() error {
+	return nil
+}
+
+func (m *CachingMux) ChildErrors() map[string]error {
+	m.mut.Lock()
+	children := make(map[string]error, len(m.finders))
+	for _, f := range m.finders {
+		children[f.String()] = f.Error()
+	}
+	m.mut.Unlock()
+	return children
+}
+
+func (m *CachingMux) Cache() map[protocol.DeviceID]CacheEntry {
+	// Res will be the "total" cache, i.e. the union of our cache and all our
+	// children's caches.
+	res := make(map[protocol.DeviceID]CacheEntry)
+
+	m.mut.Lock()
+	for i := range m.finders {
+		// Each finder[i] has a corresponding cache at cache[i]. Go through it
+		// and populate the total, if it's newer than what's already in there.
+		// We skip any negative cache entries.
+		for k, v := range m.caches[i].Cache() {
+			if v.found && v.when.After(res[k].when) {
+				res[k] = v
+			}
+		}
+
+		// Then ask the finder itself for it's cache and do the same. If this
+		// finder is a global discovery client, it will have no cache. If it's
+		// a local discovery client, this will be it's current state.
+		for k, v := range m.finders[i].Cache() {
+			if v.found && v.when.After(res[k].when) {
+				res[k] = v
+			}
+		}
+	}
+	m.mut.Unlock()
+
+	return res
+}
+
+// A cache can be embedded wherever useful
+
+type cache struct {
+	entries map[protocol.DeviceID]CacheEntry
+	mut     stdsync.Mutex
+}
+
+func newCache() *cache {
+	return &cache{
+		entries: make(map[protocol.DeviceID]CacheEntry),
+	}
+}
+
+func (c *cache) Set(id protocol.DeviceID, ce CacheEntry) {
+	c.mut.Lock()
+	c.entries[id] = ce
+	c.mut.Unlock()
+}
+
+func (c *cache) Get(id protocol.DeviceID) (CacheEntry, bool) {
+	c.mut.Lock()
+	ce, ok := c.entries[id]
+	c.mut.Unlock()
+	return ce, ok
+}
+
+func (c *cache) Cache() map[protocol.DeviceID]CacheEntry {
+	c.mut.Lock()
+	m := make(map[protocol.DeviceID]CacheEntry, len(c.entries))
+	for k, v := range c.entries {
+		m[k] = v
+	}
+	c.mut.Unlock()
+	return m
+}