/*
Copyright 2014 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.
*/

package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"net"
	"net/http"
	"net/url"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"sync/atomic"
	"time"

	utilnet "k8s.io/apimachinery/pkg/util/net"
)

var (
	httpPort    = 8080
	udpPort     = 8081
	shellPath   = "/bin/sh"
	serverReady = &atomicBool{0}
)

// atomicBool uses load/store operations on an int32 to simulate an atomic boolean.
type atomicBool struct {
	v int32
}

// set sets the int32 to the given boolean.
func (a *atomicBool) set(value bool) {
	if value {
		atomic.StoreInt32(&a.v, 1)
		return
	}
	atomic.StoreInt32(&a.v, 0)
}

// get returns true if the int32 == 1
func (a *atomicBool) get() bool {
	return atomic.LoadInt32(&a.v) == 1
}

type output struct {
	responses []string
	errors    []string
}

func init() {
	flag.IntVar(&httpPort, "http-port", 8080, "HTTP Listen Port")
	flag.IntVar(&udpPort, "udp-port", 8081, "UDP Listen Port")
}

func main() {
	flag.Parse()
	go startUDPServer(udpPort)
	startHTTPServer(httpPort)
}

func startHTTPServer(httpPort int) {
	http.HandleFunc("/", rootHandler)
	http.HandleFunc("/clientip", clientIpHandler)
	http.HandleFunc("/echo", echoHandler)
	http.HandleFunc("/exit", exitHandler)
	http.HandleFunc("/hostname", hostnameHandler)
	http.HandleFunc("/shell", shellHandler)
	http.HandleFunc("/upload", uploadHandler)
	http.HandleFunc("/dial", dialHandler)
	http.HandleFunc("/healthz", healthzHandler)
	// older handlers
	http.HandleFunc("/hostName", hostNameHandler)
	http.HandleFunc("/shutdown", shutdownHandler)
	log.Fatal(http.ListenAndServe(fmt.Sprintf(":%d", httpPort), nil))
}

func rootHandler(w http.ResponseWriter, r *http.Request) {
	log.Printf("GET /")
	fmt.Fprintf(w, "NOW: %v", time.Now())
}

func echoHandler(w http.ResponseWriter, r *http.Request) {
	log.Printf("GET /echo?msg=%s", r.FormValue("msg"))
	fmt.Fprintf(w, "%s", r.FormValue("msg"))
}

func clientIpHandler(w http.ResponseWriter, r *http.Request) {
	log.Printf("GET /clientip")
	fmt.Fprintf(w, r.RemoteAddr)
}

func exitHandler(w http.ResponseWriter, r *http.Request) {
	log.Printf("GET /exit?code=%s", r.FormValue("code"))
	code, err := strconv.Atoi(r.FormValue("code"))
	if err == nil || r.FormValue("code") == "" {
		os.Exit(code)
	}
	fmt.Fprintf(w, "argument 'code' must be an integer [0-127] or empty, got %q", r.FormValue("code"))
}

func hostnameHandler(w http.ResponseWriter, r *http.Request) {
	log.Printf("GET /hostname")
	fmt.Fprintf(w, getHostName())
}

// healthHandler response with a 200 if the UDP server is ready. It also serves
// as a health check of the HTTP server by virtue of being a HTTP handler.
func healthzHandler(w http.ResponseWriter, r *http.Request) {
	log.Printf("GET /healthz")
	if serverReady.get() {
		w.WriteHeader(200)
		return
	}
	w.WriteHeader(http.StatusPreconditionFailed)
}

func shutdownHandler(w http.ResponseWriter, r *http.Request) {
	log.Printf("GET /shutdown")
	os.Exit(0)
}

func dialHandler(w http.ResponseWriter, r *http.Request) {
	values, err := url.Parse(r.URL.RequestURI())
	if err != nil {
		http.Error(w, fmt.Sprintf("%v", err), http.StatusBadRequest)
		return
	}

	host := values.Query().Get("host")
	port := values.Query().Get("port")
	request := values.Query().Get("request") // hostName
	protocol := values.Query().Get("protocol")
	tryParam := values.Query().Get("tries")
	log.Printf("GET /dial?host=%s&protocol=%s&port=%s&request=%s&tries=%s", host, protocol, port, request, tryParam)
	tries := 1
	if len(tryParam) > 0 {
		tries, err = strconv.Atoi(tryParam)
	}
	if err != nil {
		http.Error(w, fmt.Sprintf("tries parameter is invalid. %v", err), http.StatusBadRequest)
		return
	}
	if len(request) == 0 {
		http.Error(w, fmt.Sprintf("request parameter not specified. %v", err), http.StatusBadRequest)
		return
	}
	if len(protocol) == 0 {
		protocol = "http"
	} else {
		protocol = strings.ToLower(protocol)
	}
	if protocol != "http" && protocol != "udp" {
		http.Error(w, fmt.Sprintf("unsupported protocol. %s", protocol), http.StatusBadRequest)
		return
	}

	hostPort := net.JoinHostPort(host, port)
	var udpAddress *net.UDPAddr
	if protocol == "udp" {
		udpAddress, err = net.ResolveUDPAddr("udp", hostPort)
		if err != nil {
			http.Error(w, fmt.Sprintf("host and/or port param are invalid. %v", err), http.StatusBadRequest)
			return
		}
	} else {
		_, err = net.ResolveTCPAddr("tcp", hostPort)
		if err != nil {
			http.Error(w, fmt.Sprintf("host and/or port param are invalid. %v", err), http.StatusBadRequest)
			return
		}
	}
	errors := make([]string, 0)
	responses := make([]string, 0)
	var response string
	for i := 0; i < tries; i++ {
		if protocol == "udp" {
			response, err = dialUDP(request, udpAddress)
		} else {
			response, err = dialHTTP(request, hostPort)
		}
		if err != nil {
			errors = append(errors, fmt.Sprintf("%v", err))
		} else {
			responses = append(responses, response)
		}
	}
	output := map[string][]string{}
	if len(response) > 0 {
		output["responses"] = responses
	}
	if len(errors) > 0 {
		output["errors"] = errors
	}
	bytes, err := json.Marshal(output)
	if err == nil {
		fmt.Fprintf(w, string(bytes))
	} else {
		http.Error(w, fmt.Sprintf("response could not be serialized. %v", err), http.StatusExpectationFailed)
	}
}

func dialHTTP(request, hostPort string) (string, error) {
	transport := utilnet.SetTransportDefaults(&http.Transport{})
	httpClient := createHTTPClient(transport)
	resp, err := httpClient.Get(fmt.Sprintf("http://%s/%s", hostPort, request))
	defer transport.CloseIdleConnections()
	if err == nil {
		defer resp.Body.Close()
		body, err := ioutil.ReadAll(resp.Body)
		if err == nil {
			return string(body), nil
		}
	}
	return "", err
}

func createHTTPClient(transport *http.Transport) *http.Client {
	client := &http.Client{
		Transport: transport,
		Timeout:   5 * time.Second,
	}
	return client
}

func dialUDP(request string, remoteAddress *net.UDPAddr) (string, error) {
	Conn, err := net.DialUDP("udp", nil, remoteAddress)
	if err != nil {
		return "", fmt.Errorf("udp dial failed. err:%v", err)
	}

	defer Conn.Close()
	buf := []byte(request)
	_, err = Conn.Write(buf)
	if err != nil {
		return "", fmt.Errorf("udp connection write failed. err:%v", err)
	}
	udpResponse := make([]byte, 1024)
	Conn.SetReadDeadline(time.Now().Add(5 * time.Second))
	count, err := Conn.Read(udpResponse)
	if err != nil || count == 0 {
		return "", fmt.Errorf("reading from udp connection failed. err:'%v'", err)
	}
	return string(udpResponse[0:count]), nil
}

func shellHandler(w http.ResponseWriter, r *http.Request) {
	cmd := r.FormValue("shellCommand")
	if cmd == "" {
		cmd = r.FormValue("cmd")
	}
	log.Printf("GET /shell?cmd=%s", cmd)
	cmdOut, err := exec.Command(shellPath, "-c", cmd).CombinedOutput()
	output := map[string]string{}
	if len(cmdOut) > 0 {
		output["output"] = string(cmdOut)
	}
	if err != nil {
		output["error"] = fmt.Sprintf("%v", err)
	}
	log.Printf("Output: %s", output)
	bytes, err := json.Marshal(output)
	if err == nil {
		fmt.Fprintf(w, string(bytes))
	} else {
		http.Error(w, fmt.Sprintf("response could not be serialized. %v", err), http.StatusExpectationFailed)
	}
}

func uploadHandler(w http.ResponseWriter, r *http.Request) {
	log.Printf("GET /upload")
	result := map[string]string{}
	file, _, err := r.FormFile("file")
	if err != nil {
		result["error"] = "Unable to upload file."
		bytes, err := json.Marshal(result)
		if err == nil {
			fmt.Fprintf(w, string(bytes))
		} else {
			http.Error(w, fmt.Sprintf("%s. Also unable to serialize output. %v", result["error"], err), http.StatusInternalServerError)
		}
		log.Printf("Unable to upload file: %s", err)
		return
	}
	defer file.Close()

	f, err := ioutil.TempFile("/uploads", "upload")
	if err != nil {
		result["error"] = "Unable to open file for write"
		bytes, err := json.Marshal(result)
		if err == nil {
			fmt.Fprintf(w, string(bytes))
		} else {
			http.Error(w, fmt.Sprintf("%s. Also unable to serialize output. %v", result["error"], err), http.StatusInternalServerError)
		}
		log.Printf("Unable to open file for write: %s", err)
		return
	}
	defer f.Close()
	if _, err = io.Copy(f, file); err != nil {
		result["error"] = "Unable to write file."
		bytes, err := json.Marshal(result)
		if err == nil {
			fmt.Fprintf(w, string(bytes))
		} else {
			http.Error(w, fmt.Sprintf("%s. Also unable to serialize output. %v", result["error"], err), http.StatusInternalServerError)
		}
		log.Printf("Unable to write file: %s", err)
		return
	}

	UploadFile := f.Name()
	if err := os.Chmod(UploadFile, 0700); err != nil {
		result["error"] = "Unable to chmod file."
		bytes, err := json.Marshal(result)
		if err == nil {
			fmt.Fprintf(w, string(bytes))
		} else {
			http.Error(w, fmt.Sprintf("%s. Also unable to serialize output. %v", result["error"], err), http.StatusInternalServerError)
		}
		log.Printf("Unable to chmod file: %s", err)
		return
	}
	log.Printf("Wrote upload to %s", UploadFile)
	result["output"] = UploadFile
	w.WriteHeader(http.StatusCreated)
	bytes, err := json.Marshal(result)
	fmt.Fprintf(w, string(bytes))
}

func hostNameHandler(w http.ResponseWriter, r *http.Request) {
	log.Printf("GET /hostName")
	fmt.Fprintf(w, getHostName())
}

// udp server supports the hostName, echo and clientIP commands.
func startUDPServer(udpPort int) {
	serverAddress, err := net.ResolveUDPAddr("udp", fmt.Sprintf(":%d", udpPort))
	assertNoError(err)
	serverConn, err := net.ListenUDP("udp", serverAddress)
	assertNoError(err)
	defer serverConn.Close()
	buf := make([]byte, 1024)

	log.Printf("Started UDP server")
	// Start responding to readiness probes.
	serverReady.set(true)
	defer func() {
		log.Printf("UDP server exited")
		serverReady.set(false)
	}()
	for {
		n, clientAddress, err := serverConn.ReadFromUDP(buf)
		assertNoError(err)
		receivedText := strings.ToLower(strings.TrimSpace(string(buf[0:n])))
		if receivedText == "hostname" {
			log.Println("Sending udp hostName response")
			_, err = serverConn.WriteToUDP([]byte(getHostName()), clientAddress)
			assertNoError(err)
		} else if strings.HasPrefix(receivedText, "echo ") {
			parts := strings.SplitN(receivedText, " ", 2)
			resp := ""
			if len(parts) == 2 {
				resp = parts[1]
			}
			log.Printf("Echoing %v\n", resp)
			_, err = serverConn.WriteToUDP([]byte(resp), clientAddress)
			assertNoError(err)
		} else if receivedText == "clientip" {
			log.Printf("Sending back clientip to %s", clientAddress.String())
			_, err = serverConn.WriteToUDP([]byte(clientAddress.String()), clientAddress)
			assertNoError(err)
		} else if len(receivedText) > 0 {
			log.Printf("Unknown udp command received: %v\n", receivedText)
		}
	}
}

func getHostName() string {
	hostName, err := os.Hostname()
	assertNoError(err)
	return hostName
}

func assertNoError(err error) {
	if err != nil {
		log.Fatal("Error occurred. error:", err)
	}
}