Sticky packet problem is caused by the way of streaming data transmission in tcp protocol
 Give an example:

How to solve the sticky packet problem: the receiver can accurately collect every packet without any residue

Simple Edition for Solving Sticky Packing Problem

from socket import *
import struct

client = socket(AF_INET, SOCK_STREAM)
client.connect(('127.0.0.1', 8081))

# Communication cycle
while True:
    cmd=input('>>: ').strip()
    if len(cmd) == 0:continue
    client.send(cmd.encode('utf-8'))
    #1. Receive the headlines first,Get the length of the data from the header
    header=client.recv(4)
    total_size=struct.unpack('i',header)[0]
    #2. Receiving real data
    cmd_res=b''
    recv_size=0
    while recv_size < total_size:
        data=client.recv(1024)
        recv_size+=len(data)
        cmd_res+=data

    print(cmd_res.decode('gbk'))

client.close()

# The server must satisfy at least three points:
# 1. Binding a fixed ip and port
# 2. Always providing services to the outside world,stable operation
# 3. Ability to support concurrency
from socket import *
import subprocess
import struct

server = socket(AF_INET, SOCK_STREAM)
server.bind(('127.0.0.1', 8081))
server.listen(5)

# Link loop
while True:
    conn, client_addr = server.accept()
    print(client_addr)

    # Communication cycle
    while True:
        try:
            cmd = conn.recv(1024) #cmd=b'dir'
            if len(cmd) == 0: break  # In the light of linux system
            obj=subprocess.Popen(cmd.decode('utf-8'),
                             shell=True,
                             stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE
                             )
            stdout=obj.stdout.read()
            stderr=obj.stderr.read()
            # 1. Make a fixed-length headline first
            header=struct.pack('i',len(stdout) + len(stderr))
            # 2. Re-send header
            conn.send(header)
            # 3. Finally send real data
            conn.send(stdout)
            conn.send(stderr)
        except ConnectionResetError:
            break

    conn.close()

server.close()

Simulated ssh final version for solving sticky package problem

from socket import *
import struct
import json

client = socket(AF_INET, SOCK_STREAM)
client.connect(('127.0.0.1', 8081))

# Communication cycle
while True:
    cmd=input('>>: ').strip()
    if len(cmd) == 0:continue
    client.send(cmd.encode('utf-8'))
    #1. Receive 4 first bytes,Unscramble the length of the header
    header_size=struct.unpack('i',client.recv(4))[0]

    #2. Receive headers again,Get header_dic
    header_bytes=client.recv(header_size)
    header_json=header_bytes.decode('utf-8')
    header_dic=json.loads(header_json)
    print(header_dic)
    total_size=header_dic['total_size']

    #3. Receiving real data
    cmd_res=b''
    recv_size=0
    while recv_size < total_size:
        data=client.recv(1024)
        recv_size+=len(data)
        cmd_res+=data

    print(cmd_res.decode('gbk'))

client.close()

# The server must satisfy at least three points:
# 1. Binding a fixed ip and port
# 2. Always providing services to the outside world,stable operation
# 3. Ability to support concurrency
from socket import *
import subprocess
import struct
import json

server = socket(AF_INET, SOCK_STREAM)
server.bind(('127.0.0.1', 8081))
server.listen(5)

# Link loop
while True:
    conn, client_addr = server.accept()
    print(client_addr)

    # Communication cycle
    while True:
        try:
            cmd = conn.recv(1024)  # cmd=b'dir'
            if len(cmd) == 0: break  # In the light of linux system
            obj = subprocess.Popen(cmd.decode('utf-8'),
                                   shell=True,
                                   stdout=subprocess.PIPE,
                                   stderr=subprocess.PIPE
                                   )
            stdout = obj.stdout.read()
            stderr = obj.stderr.read()
            # 1. Make headlines first
            header_dic = {
                'filename': 'a.txt',
                'md5': 'asdfasdf123123x1',
                'total_size': len(stdout) + len(stderr)
            }
            header_json = json.dumps(header_dic)
            header_bytes = header_json.encode('utf-8')

            # 2. Send 4 first bytes(Length with headers)
            conn.send(struct.pack('i', len(header_bytes)))
            # 3  Re-send header
            conn.send(header_bytes)

            # 4. Finally send real data
            conn.send(stdout)
            conn.send(stderr)
        except ConnectionResetError:
            break

    conn.close()

server.close()

struct module

import struct

obj1=struct.pack('i',1332)
print(obj1,len(obj1))
# Result: b'4\x05\x00\x00' 4
res1=struct.unpack('i',obj1)
print(res1[0])
#Results: 1332
obj1=struct.pack('q',1332)
print(obj1,len(obj1))
# Result: b'4\x05\x00\x00\x00\x00\x00\x00' 8



import json

header_dic={
                'filename':'a.txt',
                'md5':'asdfasdf123123x1',
                'total_size':12312311111111111111111111111111111111111111123
            }

header_json=json.dumps(header_dic)
print(header_json)
#Result:
# {"filename": "a.txt", "md5": "asdfasdf123123x1", "total_size": 123123111111111111111111. . . }
header_bytes=header_json.encode('utf-8')
print(len(header_bytes))
# Results: 502

Topics: Python socket JSON Linux shell