发送图像时出现Python套接字错误。无法解码字节/意外的EOF

Question

我正在使用python套接字将图像从笔记本电脑的摄像头（客户端）传输到raspberry pi（服务器）。下面是它的运行方式，我连接到套接字，然后我的客户机等待信号以便拍照。当信号（来自我的服务器）被发送时，我的客户机拍了一张照片并按顺序发送以下数据；首先，表示图片大小的数字的长度（例如，对于10000字节，数字为5，对于100000字节，数字为6，依此类推），然后发送实际大小，最后以字节字符串的形式发送照片。这个过程重复了无数次

Client.py

import cv2
import socket
import os

def send_msg(s, msg):
    s.sendall(msg)


s = socket.socket()
port = 24999
ip = '192.168.1.3'
s.connect((ip, port))

video = cv2.VideoCapture(0)

s.recv(1) #Wait until data is sent
while True:
    _, img = video.read()
    img = cv2.resize(img, (0,0), fx = 0.4, fy = 0.4) #reduce image size
    cv2.imwrite("test.jpg", img) #save img
    size = os.path.getsize("test.jpg") #get image size
    img_str = cv2.imencode('.jpg', img)[1].tostring() #convert to bytes string
    sizenum = str(len(str(size))) #how many digits the image size contains
    send_msg(s, sizenum.encode())
    send_msg(s, str(size).encode('utf-8')) #send actual image size
    send_msg(s, img_str) #finally send the image
    s.recv(1) #Wait until data is sent

Server.py

import socket
import ast

def send_msg(client, msg):
    client.sendall(msg+b'\r\n')

def recvall(sock, n):
    # Helper function to recv n bytes or return None if EOF is hit
    data = bytearray()
    while len(data) < n:
        packet = sock.recv(n - len(data))
        if not packet:
            return None
        data.extend(packet)
    return data

def take_photo(cl):
    #RECEIVE LENGTH OF SIZE
    while True:
        lensize = cl.recv(1)
        lensize = lensize.decode('utf-8')
        if lensize != "":
            break
    print("Size is a",lensize,"-digit number")
    lensize = lensize.replace("\n","").replace(" ","").replace("\r","")
    #RECEIVE SIZE
    size_pic = recvall(cl,ast.literal_eval(lensize)).decode('utf-8')
    size_pic = size_pic.replace("\n","").replace(" ","").replace("\r","")
    print("Exact size is",size_pic)
    #RECEIVE PHOTO
    return lensize,size_pic,bytearray(recvall(cl,ast.literal_eval(size_pic)))

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind(("192.168.1.3",24999))
s.listen(1)

while True:
    cl_image, addr = s.accept()
    break

while True:
    try:
        send_msg(cl_image, b"1") #Send signal
        size1, size2, photo = take_photo(cl_image)
        print(photo)

    except KeyboardInterrupt:
        print("error")
        s.close()

问题 运行服务器时，在运行几秒钟后会出现问题（有时在引发任何异常前仅运行1秒，有时运行5秒或更长时间）

示例运行1（服务器）

Size is a 5 -digit number
Exact size is 21263
7294 from 21263 Not all bytes were read
18974 from 21263 Not all bytes were read
Size is a 5 -digit number
Exact size is 21226
2915 from 21226 Not all bytes were read
4375 from 21226 Not all bytes were read
11675 from 21226 Not all bytes were read
18975 from 21226 Not all bytes were read
Size is a 5 -digit number
Exact size is 21412
2915 from 21412 Not all bytes were read
7295 from 21412 Not all bytes were read
14595 from 21412 Not all bytes were read
Size is a . -digit number
Traceback (most recent call last):
  File "sending_test.py", line 46, in <module>
    size1, size2, photo = take_photo(cl_image)
  File "sending_test.py", line 27, in take_photo
    size_pic = recvall(cl,ast.literal_eval(lensize)).decode('utf-8')
  File "/usr/lib/python3.7/ast.py", line 46, in literal_eval
    node_or_string = parse(node_or_string, mode='eval')
  File "/usr/lib/python3.7/ast.py", line 35, in parse
    return compile(source, filename, mode, PyCF_ONLY_AST)
  File "<unknown>", line 1
    .

示例运行2（服务器）

Size is a 5 -digit number
Exact size is 20653
7294 from 20653 Not all bytes were read
14594 from 20653 Not all bytes were read
18974 from 20653 Not all bytes were read
Size is a 5 -digit number
Exact size is 20595
2915 from 20595 Not all bytes were read
8755 from 20595 Not all bytes were read
10215 from 20595 Not all bytes were read
18975 from 20595 Not all bytes were read
Traceback (most recent call last):
  File "sending_test.py", line 46, in <module>
    size1, size2, photo = take_photo(cl_image)
  File "sending_test.py", line 21, in take_photo
    lensize = lensize.decode('utf-8')
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 0: invalid start byte

我还在服务器的循环中插入了一个print（photo）命令，以查看发生了什么，这就是结果（参见最后一行与其他行的比较）

Size is a 3 -digit number
Exact size is 828
bytearray(b'\xff\xd8\xff.......\xff\xd9')
Size is a 3 -digit number
Exact size is 831
bytearray(b'\xff\xd8\xff......\xff\xd9')
Size is a 3 -digit number
Exact size is 831
bytearray(b'\xff\xd8\xff.......\xff\xd9383')

这意味着它读取的字节数应该多一些（3）（3表示大小长度，83来自图像大小，类似于（83x）

Answer 1

根据评论，我做了如下几点修改：

• 与其将JPEG写入磁盘，然后计算其大小，然后再次将其编码到内存并转换为字符串并发送，我只是将JPEG编码到内存缓冲区，获取其大小并发送

• 我没有发送一个字符串来表示视频帧中的字节数，而是将字节数作为4字节网络顺序整数发送。它使生活更容易

它在我的机器上似乎工作得很可靠

这是客户：

#!/usr/bin/env python3

import cv2
import socket
import os
import struct

ip, port = '192.168.0.8', 24999
s = socket.socket()
s.connect((ip, port))

# Start video reader
video = cv2.VideoCapture(0)

while True:
    # Wait till data requested, as indicated by receipt of single byte
    s.recv(1)
    print('CLIENT: Image requested')

    # Read a frame of video and reduce size
    _, img = video.read()
    img = cv2.resize(img, (0,0), fx = 0.4, fy = 0.4)

    # JPEG-encode into memory buffer and get size
    _, buffer = cv2.imencode('.jpg', img)
    nBytes = buffer.size
    print(f'CLIENT: nBytes={nBytes}')

    # Send 4-byte network order frame size and image
    hdr = struct.pack('!i',nBytes)
    s.sendall(hdr)
    s.sendall(buffer)

这是服务器：

#!/usr/bin/env python3

import time
import socket
import struct

def recvall(sock, n):
    # Helper function to recv n bytes or return None if EOF is hit
    data = bytearray()
    while len(data) < n:
        packet = sock.recv(n - len(data))
        if not packet:
            return None
        data.extend(packet)
    return data

def take_photo(cl):
    # Get header with number of bytes
    header = cl.recv(4)
    nBytes = struct.unpack('!i',header)[0]

    # Receive actual image
    img = recvall(cl, nBytes)
    return img

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind(("192.168.0.8",24999))
s.listen(1)

while True:
    cl_image, addr = s.accept()
    break

while True:
    try:
        # Request image by sending a single byte
        cl_image.sendall(b'1')
        photo = take_photo(cl_image)
        time.sleep(1)
        print(f'SERVER: photo received, {len(photo)} bytes')

    except KeyboardInterrupt:
        print("error")
        s.close()

关键词：TCP套接字、流、基于流、基于流、消息、基于消息、成帧协议、成帧、htonl、网络顺序、数据包、主数据包