当我发送“ sendto”的数据报时，IS有效载荷大小与字节长度相同。

Question

我正在制作自己的协议，这是基于UDP的远程桌面协议。由于解决方案，我关心的是低潜伏期和时间效率。

在此之前，以前问题说UDP的最大安全有效负载大小为 508 。这是否意味着我每次发送508个字节？

我在做什么：

# RDP server.py
import cv2 as cv
import numpy as np
from time import time
from mss import mss
import pyautogui as pag
import socket

screenSize = pag.size()

# Optimization Config
'''
2160p = (3840, 2160)
1440p = (2560, 1440)
1080p = (1920, 1080)
720p  = (1280, 720)
480p  = (640, 480)
360p  = (480, 360)
240p  = (426, 240)
144p  = (256, 144)
'''
# resolution = screenSize # Uncomment for using server resolution
resolution = (640, 480) # Uncomment for using common resolution
compression = 5 # 100 means no compress, 0 is highest compression!
encodeParam = (int(cv.IMWRITE_JPEG_QUALITY), compression)


# Server Config
addrPortServer = ('0.0.0.0', 20001)
UDPServerSocket = socket.socket(family=socket.AF_INET, type=socket.SOCK_DGRAM)
UDPServerSocket.bind(addrPortServer)
UDPServerSocket.settimeout(0.5)
payloadSize = 508

monitor = {"top": 0, "left": 0, "width": screenSize[0], "height": screenSize[1]}

receivePeriode = time()

addrPortClient = None

print('RDU Server is running...')
with mss() as sct:
  while True:
    loopTime = time()

    if loopTime - receivePeriode > 3:
      try:
        dataFromClient, addrPortClient = UDPServerSocket.recvfrom(1024)
        if b'shutdown' in dataFromClient:
          print('Shutdown from client!')
          break
      except:
        addrPortClient = None
      receivePeriode = loopTime
      

    if addrPortClient is not None:
      frame = np.asarray(sct.grab(monitor))
      frame = cv.cvtColor(frame, cv.COLOR_BGRA2BGR)
      frame = cv.resize(frame, dsize=resolution)
      isSucceed, encImg = cv.imencode('.jpg', frame, encodeParam)
      bytesToSend = encImg.tobytes()
      for i in range(0, len(bytesToSend), payloadSize):
        UDPServerSocket.sendto(bytesToSend[i:i+payloadSize], addrPortClient)
    # print(time() - loopTime)

在client.py

# RDP client.py
import cv2 as cv
import numpy as np
from time import time
from mss import mss
import pyautogui as pag
import socket

# Client Config
addrPortServer = ('127.0.0.1', 20001)
UDPClientSocket = socket.socket(family=socket.AF_INET, type=socket.SOCK_DGRAM)
UDPClientSocket.settimeout(1)
payloadSize = 508
recvFromSize = payloadSize * 2

defaultFrame = np.fromfile('./waiting-server.jpg', dtype=np.uint8)
oldBytesFrame = defaultFrame
screenSize = pag.size() # uncomment for full screen
screenSize = (int(screenSize[0]*0.75), int(screenSize[1]*0.75)) # uncomment for windowed mode

sendPeriode = 0

currentDelay = []
avgDelay = 0
updateDelayTime = time()
with mss() as sct:
  while True:
    loopTime = time()

    if loopTime - sendPeriode > 3: 
      UDPClientSocket.sendto(b'?', addrPortServer)
      sendPeriode = loopTime
    bytesFrame = b''
    lenBytesFromServer = payloadSize
    try:
      while lenBytesFromServer == payloadSize:
        bytesFromServer = UDPClientSocket.recvfrom(recvFromSize)[0]
        lenBytesFromServer = len(bytesFromServer)
        bytesFrame += bytesFromServer
    except:
      bytesFrame = oldBytesFrame

    try:
      frame = cv.imdecode(np.frombuffer(bytesFrame, dtype=np.uint8), 1)
      frame = cv.resize(frame, screenSize)
    except Exception as e:
      print(e)
      frame = cv.imdecode(np.frombuffer(oldBytesFrame, dtype=np.uint8), 1)
      frame = cv.resize(frame, screenSize)

    # FPS Management
    currentDelay.append(time() - loopTime)
    if time() - updateDelayTime > 1:
      avgDelay = sum(currentDelay) / len(currentDelay)
      currentDelay = []
      print(len(bytesFrame))
      updateDelayTime = time()
    frame = cv.putText(frame, 
      text = str(avgDelay), 
      org = (10,40), 
      fontFace = cv.FONT_HERSHEY_SIMPLEX, 
      fontScale = 1, 
      thickness = 2, 
      lineType = cv.LINE_AA,
      color = (0,0,255))

    try:
      cv.imshow('RDU Client', frame)
    except:
      cv.imshow('RDU Client', cv.imdecode(defaultFrame,1))

    if cv.waitKey(1) == ord('q'):
      cv.destroyAllWindows()
      break
      
    oldBytesFrame = bytesFrame

UDPClientSocket.sendto(b'shutdown', addrPortServer)

focus.py to sendto 中，您可以看到我调用该函数并以长度508的方式发送字节，这是以前的问题的意思吗？

Answer 1

它说UDP的最大安全有效载荷大小为508。这是否意味着我发送508个字节？

我不太确定您的问题。但是，您似乎将“安全有效载荷尺寸”解释为保证交付并拥有其他可靠性保证。事实并非如此。

无论使用哪个有效载荷大小，UDP都是不可靠的协议，可能导致数据包丢失，重新排序和数据包重复。不过，使用比“安全”更大的有效载荷大小会增加问题，因为这样的数据报可能会在IP级别分为多个片段，即使在交付过程中丢失了一个片段，数据报也会丢失。

因此，使用UDP，您永远不能假设所有数据包都是按顺序全部和订单的，就像您当前的代码一样。没有数据包大小会导致UDP是可靠的协议，因此需要在代码中处理数据报，重复和重新排序。

（从评论中）是的，我知道UDP是不可靠的协议，这就是为什么我使用许多Try-Except处理它。

Try-Except对数据包丢失，数据包重复和重新排序根本无济于事

（从评论中）实际上是508个字节（如以前的问题答案），或者应该是512个字节？

IPv4中UDP数据报的理论最大有效载荷大小为65507字节。 IPv6 Jumbograms可能会更大 - 请参阅。

但是来自下端：IPv4标准说，主机必须能够接受最多576个字节的数据报，而使用IPv6则是1280。删除IP和UDP标头，这将导致“安全”有效载荷大小为508对于IPv4（最大60个字节IPv4标头，固定8个字节UDP标头），为IPv6（固定40个字节IPv6标头），固定8个字节UDP标头）。