avoid initializing a math/rand.Rand in the connIDManager

math/rand.Source uses a lot of memory, as it keeps an array of 607
int64s as internal state.

conn_id_manager.go

@@ -1,10 +1,7 @@
 package quic
 
 import (
-	"crypto/rand"
-	"encoding/binary"
 	"fmt"
-	mrand "math/rand"
 
 	"github.com/lucas-clemente/quic-go/internal/protocol"
 	"github.com/lucas-clemente/quic-go/internal/qerr"
@@ -25,7 +22,7 @@ type connIDManager struct {
 	// protocol.PacketsPerConnectionID packets. The actual value is randomized
 	// hide the packet loss rate from on-path observers.
 	packetsSinceLastChange uint64
-	rand                   *mrand.Rand
+	rand                   utils.Rand
 	packetsPerConnectionID uint64
 
 	addStatelessResetToken    func(protocol.StatelessResetToken)
@@ -39,15 +36,11 @@ func newConnIDManager(
 	removeStatelessResetToken func(protocol.StatelessResetToken),
 	queueControlFrame func(wire.Frame),
 ) *connIDManager {
-	b := make([]byte, 8)
-	_, _ = rand.Read(b) // ignore the error here. Nothing bad will happen if the seed is not perfectly random.
-	seed := int64(binary.BigEndian.Uint64(b))
 	return &connIDManager{
 		activeConnectionID:        initialDestConnID,
 		addStatelessResetToken:    addStatelessResetToken,
 		removeStatelessResetToken: removeStatelessResetToken,
 		queueControlFrame:         queueControlFrame,
-		rand:                      mrand.New(mrand.NewSource(seed)),
 	}
 }
 
@@ -155,7 +148,7 @@ func (h *connIDManager) updateConnectionID() {
 	h.activeConnectionID = front.ConnectionID
 	h.activeStatelessResetToken = &front.StatelessResetToken
 	h.packetsSinceLastChange = 0
-	h.packetsPerConnectionID = protocol.PacketsPerConnectionID/2 + uint64(h.rand.Int63n(protocol.PacketsPerConnectionID))
+	h.packetsPerConnectionID = protocol.PacketsPerConnectionID/2 + uint64(h.rand.Int31n(protocol.PacketsPerConnectionID))
 	h.addStatelessResetToken(*h.activeStatelessResetToken)
 }