[IMPROVED] Memory growth on compressed websocket connections. (#4620)

Holding onto the compressor and not recycling the internal byte slice
could cause havoc with GC.

This needs to be improved but this at least should allow the GC to
cleanup more effectively.

Signed-off-by: Derek Collison <derek@nats.io>

server/websocket.go

@@ -115,7 +115,6 @@ type websocket struct {
 	nocompfrag bool // No fragment for compressed frames
 	maskread   bool
 	maskwrite  bool
-	compressor *flate.Writer
 	cookieJwt  string
 	clientIP   string
 }
@@ -1295,15 +1294,8 @@ func (c *client) wsCollapsePtoNB() (net.Buffers, int64) {
 		if mfs > 0 && c.ws.nocompfrag {
 			mfs = 0
 		}
-		buf := &bytes.Buffer{}
-
-		cp := c.ws.compressor
-		if cp == nil {
-			c.ws.compressor, _ = flate.NewWriter(buf, flate.BestSpeed)
-			cp = c.ws.compressor
-		} else {
-			cp.Reset(buf)
-		}
+		buf := bytes.NewBuffer(nbPoolGet(usz))
+		cp, _ := flate.NewWriter(buf, flate.BestSpeed)
 		var csz int
 		for _, b := range nb {
 			cp.Write(b)
@@ -1352,6 +1344,7 @@ func (c *client) wsCollapsePtoNB() (net.Buffers, int64) {
 			}
 			csz = len(h) + ol
 		}
+		nbPoolPut(b) // No longer needed as we copied from above.
 		// Add to pb the compressed data size (including headers), but
 		// remove the original uncompressed data size that was added
 		// during the queueing.