Add "bad conn" for debugging UDP

pkg/debug/conn.go

@@ -0,0 +1,47 @@
+package debug
+
+import (
+	"bytes"
+	"math/rand"
+	"net"
+)
+
+type badConn struct {
+	net.Conn
+	delay int
+	buf   []byte
+}
+
+func NewBadConn(conn net.Conn) net.Conn {
+	return &badConn{Conn: conn}
+}
+
+const (
+	missChance  = 0.05
+	delayChance = 0.1
+)
+
+func (c *badConn) Read(b []byte) (n int, err error) {
+	if rand.Float32() < missChance {
+		if _, err = c.Conn.Read(b); err != nil {
+			return
+		}
+		//log.Printf("bad conn: miss")
+	}
+
+	if c.delay > 0 {
+		if c.delay--; c.delay == 0 {
+			n = copy(b, c.buf)
+			return
+		}
+	} else if rand.Float32() < delayChance {
+		if n, err = c.Conn.Read(b); err != nil {
+			return
+		}
+		c.delay = 1 + rand.Intn(5)
+		c.buf = bytes.Clone(b[:n])
+		//log.Printf("bad conn: delay %d", c.delay)
+	}
+
+	return c.Conn.Read(b)
+}