testing: move echosvr into testutils

pkg/testutils/echosvr/main.go

@@ -0,0 +1,38 @@
+// Echosvr is a simple TCP echo server
+//
+// It prints its listen address on stdout
+//    127.0.0.1:xxxxx
+//  A test should wait for this line, parse it
+//  and may then attempt to connect.
+package main
+
+import (
+	"fmt"
+	"net"
+)
+
+func main() {
+	listener, err := net.Listen("tcp", ":")
+	if err != nil {
+		panic(err)
+	}
+	_, port, err := net.SplitHostPort(listener.Addr().String())
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("127.0.0.1:%s\n", port)
+	for {
+		conn, err := listener.Accept()
+		if err != nil {
+			panic(err)
+		}
+		go handleConnection(conn)
+	}
+}
+
+func handleConnection(conn net.Conn) {
+	buf := make([]byte, 512)
+	nBytesRead, _ := conn.Read(buf)
+	conn.Write(buf[0:nBytesRead])
+	conn.Close()
+}