WebSocket: Ensure full writes to compressor

Signed-off-by: Neil Twigg <neil@nats.io>

server/websocket.go

@@ -1367,7 +1367,12 @@ func (c *client) wsCollapsePtoNB() (net.Buffers, int64) {
 		}
 		var csz int
 		for _, b := range nb {
-			cp.Write(b)
+			wb := bytes.NewBuffer(b)
+			if _, err := io.Copy(cp, wb); err != nil {
+				c.Errorf("Error during compression: %v", err)
+				c.markConnAsClosed(WriteError)
+				return nil, 0
+			}
 			nbPoolPut(b) // No longer needed as contents written to compressor.
 		}
 		if err := cp.Flush(); err != nil {