Fix race condition

Author: myleshorton

front.go

@@ -363,6 +363,8 @@ func NewStatusCodeValidator(reject []int) ResponseValidator {
 // slice of masquerade sorted by last vetted time
 type sortedFronts []Front
 
+var frontsMu sync.RWMutex
+
 func (m sortedFronts) Len() int      { return len(m) }
 func (m sortedFronts) Swap(i, j int) { m[i], m[j] = m[j], m[i] }
 func (m sortedFronts) Less(i, j int) bool {
@@ -377,11 +379,32 @@ func (m sortedFronts) Less(i, j int) bool {
 
 func (m sortedFronts) sortedCopy() sortedFronts {
 	c := make(sortedFronts, len(m))
+	frontsMu.Lock()
+	defer frontsMu.Unlock()
 	copy(c, m)
 	sort.Sort(c)
 	return c
 }
 
+func (m sortedFronts) addFronts(fronts sortedFronts) {
+	// Add new masquerades to the existing masquerades slice, but add them at the beginning.
+	frontsMu.Lock()
+	defer frontsMu.Unlock()
+	m = append(m, fronts...)
+}
+
+func (m sortedFronts) size() int {
+	frontsMu.Lock()
+	defer frontsMu.Unlock()
+	return len(m)
+}
+
+func (m sortedFronts) frontAt(i int) Front {
+	frontsMu.Lock()
+	defer frontsMu.Unlock()
+	return m[i]
+}
+
 func (fr *front) markCacheDirty() {
 	select {
 	case fr.cacheDirty <- nil:

fronted.go

@@ -260,7 +260,7 @@ func (f *fronted) onNewFronts(pool *x509.CertPool, providers map[string]*Provide
 	}
 	providersCopy := copyProviders(providers, f.countryCode)
 	f.addProviders(providersCopy)
-	f.addFronts(loadFronts(providersCopy, f.cacheDirty))
+	f.fronts.addFronts(loadFronts(providersCopy, f.cacheDirty))
 	f.certPool.Store(pool)
 
 	// The goroutine for finding working fronts runs forever, so only start it once.
@@ -320,8 +320,8 @@ func (f *fronted) tryAllFronts() {
 	pool := pond.NewPool(40)
 
 	// Submit all fronts to the worker pool.
-	for i := 0; i < f.frontSize(); i++ {
-		m := f.frontAt(i)
+	for i := 0; i < f.fronts.size(); i++ {
+		m := f.fronts.frontAt(i)
 		pool.Submit(func() {
 			if f.isStopped() {
 				return
@@ -348,18 +348,6 @@ func (f *fronted) hasEnoughWorkingFronts() bool {
 	return len(f.frontsCh) >= 4
 }
 
-func (f *fronted) frontSize() int {
-	f.frontsMu.Lock()
-	defer f.frontsMu.Unlock()
-	return len(f.fronts)
-}
-
-func (f *fronted) frontAt(i int) Front {
-	f.frontsMu.Lock()
-	defer f.frontsMu.Unlock()
-	return f.fronts[i]
-}
-
 func (f *fronted) vetFront(fr Front) bool {
 	conn, err := f.dialFront(fr)
 	if err != nil {
@@ -616,13 +604,6 @@ func (f *fronted) addProviders(providers map[string]*Provider) {
 	}
 }
 
-func (f *fronted) addFronts(fronts sortedFronts) {
-	// Add new masquerades to the existing masquerades slice, but add them at the beginning.
-	f.frontsMu.Lock()
-	defer f.frontsMu.Unlock()
-	f.fronts = append(fronts, f.fronts...)
-}
-
 func (f *fronted) providerFor(m Front) *Provider {
 	pid := m.getProviderID()
 	if pid == "" {