upgrade deps; rewrite smtp session

vendor/github.com/jhillyerd/enmime/internal/stringutil/rand_source.go

@@ -0,0 +1,43 @@
+package stringutil
+
+import (
+	"math/rand"
+	"sync"
+	"time"
+)
+
+var globalRandSource rand.Source
+
+func init() {
+	globalRandSource = NewLockedSource(time.Now().UTC().UnixNano())
+}
+
+// NewLockedSource creates a source of randomness using the given seed.
+func NewLockedSource(seed int64) rand.Source64 {
+	return &lockedSource{
+		s: rand.NewSource(seed).(rand.Source64),
+	}
+}
+
+type lockedSource struct {
+	lock sync.Mutex
+	s    rand.Source64
+}
+
+func (x *lockedSource) Int63() int64 {
+	x.lock.Lock()
+	defer x.lock.Unlock()
+	return x.s.Int63()
+}
+
+func (x *lockedSource) Uint64() uint64 {
+	x.lock.Lock()
+	defer x.lock.Unlock()
+	return x.s.Uint64()
+}
+
+func (x *lockedSource) Seed(seed int64) {
+	x.lock.Lock()
+	defer x.lock.Unlock()
+	x.s.Seed(seed)
+}

vendor/github.com/jhillyerd/enmime/internal/stringutil/uuid.go

@@ -3,19 +3,15 @@ package stringutil
 import (
 	"fmt"
 	"math/rand"
-	"sync"
-	"time"
 )
 
-var uuidRand = rand.New(rand.NewSource(time.Now().UnixNano()))
-var uuidMutex = &sync.Mutex{}
-
-// UUID generates a random UUID according to RFC 4122.
-func UUID() string {
+// UUID generates a random UUID according to RFC 4122, using optional rand if supplied
+func UUID(rs rand.Source) string {
 	uuid := make([]byte, 16)
-	uuidMutex.Lock()
-	_, _ = uuidRand.Read(uuid)
-	uuidMutex.Unlock()
+	if rs == nil {
+		rs = globalRandSource
+	}
+	_, _ = rand.New(rs).Read(uuid)
 	// variant bits; see section 4.1.1
 	uuid[8] = uuid[8]&^0xc0 | 0x80
 	// version 4 (pseudo-random); see section 4.1.3