e2e agnhost functionality to RST TCP connections

add a new functionality to the agnhost image to run a server that
closes the connections received by sending a RST.

If a TCP servers closes the connection before all the socket is read,
it sends a RST. This implementations just reads only one byte from the
connection and closes it after that, that means that in order for this
to work the client has to send at least 2 bytes of data.

Using a simple curl is enough to trigger a RST:

curl http://127.0.0.1:8080
curl: (56) Recv failure: Connection reset by peer

Change-Id: I238fba0f790f2c92b37c732f51910a8b125f65db

test/images/agnhost/README.md

@@ -621,6 +621,29 @@ Usage:
     kubectl exec test-agnhost -- /agnhost serve-hostname [--tcp] [--udp] [--http] [--close] [--port <port>]
 ```
 
+### tcp-reset
+
+Starts a simple TCP servers that reads only one byte of the connection and then closes it,
+having the effect of sending a TCP RST to the client.
+
+The subcommand can accept the following flags:
+
+- `port` (default: `8080`): The port number to listen to.
+
+Usage:
+
+```console
+    kubectl exec test-agnhost -- /agnhost tcp-reset [--port <port>]
+```
+
+Important: This behavior only works if the client send more than 1 byte and is OS
+dependant, it is guaranteed to work on Linux.
+
+```console
+echo -n 1 | nc 192.168.1.4:8080  # FIN
+echo -n 12 | nc 192.168.1.4:8080 # RST
+```
+
 ### test-webserver
 
 Starts a simple HTTP fileserver which serves any file specified in the URL path, if it exists.

test/images/agnhost/VERSION

@@ -1 +1 @@
-2.43
+2.44

test/images/agnhost/agnhost.go

@@ -45,6 +45,7 @@ import (
 	"k8s.io/kubernetes/test/images/agnhost/porter"
 	resconsumerctrl "k8s.io/kubernetes/test/images/agnhost/resource-consumer-controller"
 	servehostname "k8s.io/kubernetes/test/images/agnhost/serve-hostname"
+	tcpreset "k8s.io/kubernetes/test/images/agnhost/tcp-reset"
 	testwebserver "k8s.io/kubernetes/test/images/agnhost/test-webserver"
 	"k8s.io/kubernetes/test/images/agnhost/webhook"
 )
@@ -81,6 +82,7 @@ func main() {
 	rootCmd.AddCommand(resconsumerctrl.CmdResourceConsumerController)
 	rootCmd.AddCommand(servehostname.CmdServeHostname)
 	rootCmd.AddCommand(testwebserver.CmdTestWebserver)
+	rootCmd.AddCommand(tcpreset.CmdTCPReset)
 	rootCmd.AddCommand(webhook.CmdWebhook)
 	rootCmd.AddCommand(openidmetadata.CmdTestServiceAccountIssuerDiscovery)
 	rootCmd.AddCommand(grpchealthchecking.CmdGrpcHealthChecking)

test/images/agnhost/tcp-reset/tcp_reset.go

@@ -0,0 +1,78 @@
+/*
+Copyright 2023 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// A small utility to send RST on the TCP connection
+// Ref: https://gosamples.dev/connection-reset-by-peer/
+
+package tcpreset
+
+import (
+	"fmt"
+	"log"
+	"net"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"github.com/spf13/cobra"
+)
+
+// CmdTCPReset is used by agnhost Cobra.
+var CmdTCPReset = &cobra.Command{
+	Use:   "tcp-reset",
+	Short: "Serves on a tcp port and RST the connections received",
+	Long:  `Serves on a tcp port and RST the connections received.`,
+	Args:  cobra.MaximumNArgs(0),
+	Run:   main,
+}
+
+var (
+	port int
+)
+
+func init() {
+	CmdTCPReset.Flags().IntVar(&port, "port", 8080, "Port number.")
+}
+
+func main(cmd *cobra.Command, args []string) {
+
+	listener, err := net.Listen("tcp", fmt.Sprintf(":%d", port))
+	if err != nil {
+		log.Fatalf("Error from net.Listen(): %s", err)
+	}
+	go func() {
+		for {
+			conn, err := listener.Accept()
+			if err != nil {
+				log.Fatalf("Error from Accept(): %s", err)
+			}
+			// if there are still data in the buffer to read
+			// and the connection is closed, it will send a RST.
+			buf := make([]byte, 1)
+			conn.Read(buf)
+			conn.Close()
+			log.Printf("TCP request from %s", conn.RemoteAddr().String())
+		}
+	}()
+
+	log.Printf("Serving on port %d.\n", port)
+	signals := make(chan os.Signal, 1)
+	signal.Notify(signals, syscall.SIGTERM)
+	sig := <-signals
+	log.Printf("Shutting down after receiving signal: %s.\n", sig)
+	log.Printf("Awaiting pod deletion.\n")
+
+}