brontide+peer: incrementally release buffer after each write

This lets the GC free up the buffers sooner.

Author: Roasbeef

brontide/conn.go

@@ -290,3 +290,10 @@ func (c *Conn) RemotePub() *btcec.PublicKey {
 func (c *Conn) LocalPub() *btcec.PublicKey {
 	return c.noise.localStatic.PubKey()
 }
+
+// ClearPendingSend drops references to the next header and body buffers so
+// that the memory can be garbage collected.
+func (c *Conn) ClearPendingSend() {
+	c.noise.nextHeaderSend = nil
+	c.noise.nextBodySend = nil
+}

peer/brontide.go

@@ -19,6 +19,7 @@ import (
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/btcsuite/btclog/v2"
+	"github.com/lightningnetwork/lnd/brontide"
 	"github.com/lightningnetwork/lnd/buffer"
 	"github.com/lightningnetwork/lnd/chainntnfs"
 	"github.com/lightningnetwork/lnd/channeldb"
@@ -2705,6 +2706,13 @@ out:
 				goto retry
 			}
 
+			// Message has either been successfully sent or an
+			// unrecoverable error occurred.  Either way, we can
+			// free the memory used to store the message.
+			if bConn, ok := p.cfg.Conn.(*brontide.Conn); ok {
+				bConn.ClearPendingSend()
+			}
+
 			// The write succeeded, reset the idle timer to prevent
 			// us from disconnecting the peer.
 			if !idleTimer.Stop() {