Project description

The existing systems are two computers of Windows 10, one of which is used as a server and the other as a client. There is a folder pics in the server, which contains 10 pictures, as shown in the following figure:

This paper aims to use the Socket library in Python to transfer the pictures in the server to the client.

Implementation steps

The server:

• 1. socket object type declaration and connection protocol generation;
• 2. Bind the port to be monitored in the server and start listening;
• 3. After the client uploads the request, establish a connection instance from the server to the client;
• 4. Receiving data, obtaining commands about image names, and specifying pictures to be transmitted;
• 5. Download the picture data to the client in batches according to the number of bytes until the transmission is completed.

client:

• 1. Declare the protocol type and generate the socket connection object at the same time;
• 2. Connect the relevant ports of the server;
• 3. Sending a command about the image name to the server;
• 4. Obtain the data downloaded from the server to the client in batches according to the number of bytes and coexist in a file until the transmission is completed.

code implementation

The code implementation here is only to illustrate the role of some important functions, which is not complete. The complete code is posted at the end of the article.

The server

1. Import required libraries

import socket
import os

2. Declare the protocol type and generate the socket connection object at the same time

server = socket.socket()

3. Bind the port in the server that needs to listen and start listening

server.bind(('192.168.43.164', 1200))  # Bind the port to listen on = (server ip address + any port)
server.listen(5)  # monitor

The server ip address here can be found by entering ipconfig in the terminal. The port is arbitrarily specified. If it is occupied, it's good to change it to another one.

4. Get the picture information in the server

BASE_DIR = os.path.dirname(os.path.abspath(__file__))  # Get current directory
PIC_DIR = os.path.join(BASE_DIR, 'pics')  # Path to the picture folder
pic_names = sorted(os.listdir(PIC_DIR))  # Get the names of all sorted pictures and put them in a list ['1.jpg','2.jpg',...,'9.jpg']
# Put the picture name into a large string
pic_names = " ".join(i for i in pic_names)  # '0.jpg 1.jpg 2.jpg 3.jpg 4.jpg 5.jpg 6.jpg 7.jpg 8.jpg 9.jpg'

5. After the client uploads the request, the connection instance from the server to the client is established

conn, addr = server.accept()
print("Received from{}request".format(addr))

The conn generated here is a connection instance that the client connects to and the server generates for it.

6. Receive data and specify the picture name

When receiving data, you can specify the number of bytes received each time to prevent blocking. Here, it is set that up to 1024 bytes can be received each time.

data = conn.recv(1024)  # Receive data, obtain the command of image name, and specify the image to be transmitted
print("recv:", data)

7. Upload relevant picture information to the client

The communication between the client and the server is based on the information of bytes type, so after each transmission, the information of bytes type needs to be decoded into the information of string type.

In addition, the size of the image to be downloaded needs to be transmitted to the client, so that the client can specify the number of bytes to be uploaded each time.

img_name = data.decode('utf-8')  # Decode the picture name (bytes) transmitted from the client into a string
img_path = os.path.join(PIC_DIR, img_name)  # Get the absolute path of the corresponding picture
file_size = os.stat(img_path).st_size  # Get the size of the image file in bytes. When calling stat, it is used to return the system status information of relevant files
file_info = '%s|%s' % (img_name, file_size)  # Send the image information to the client (used to distinguish two tasks in the document)
conn.sendall(bytes(file_info, 'utf-8'))

8. Open relevant picture files, read bytes in batches and download them to the client

f = open(img_path, 'rb')  # Open a file in binary format for read-only
has_sent = 0  # Record the number of bytes that have been sent
while has_sent != file_size:  # If the number of bytes sent is not equal to the size of the image, it is then sent
	file = f.read(1024)  # 1024 bytes read at a time
	conn.sendall(file)  # Send to client
	has_sent += len(file)  # Update bytes sent
f.close()  # After sending, close the file

client

1. Import required libraries

import socket
import os

2. Declare the protocol type and generate the socket connection object at the same time

server = socket.socket()

3. Connect to the relevant port of the server

client.connect(('192.168.43.28', 1200))

The ip address here is the ip address of the server. In other words, the ip address and port number here are the same as those set in the server code.

4. Upload picture name information to the server

msg = input(">>:").strip()  # Get the information to be sent to the server in string format
client.send(msg.encode("utf-8"))  # Encode the string format into bytes and send

5. Receive the picture information returned by the server

data = client.recv(1024)  # Receive the content returned by the server

6. Open a file in binary format to store bytes downloaded by the server

f = open(path, 'ab')  # Open a file in binary format for appending. If the file does not exist, create a new file for writing.
has_receive = 0  # Count the number of bytes received
while has_receive != filesize:
	data1 = client.recv(1024)  # Receive 1024 bytes of data from the server at a time
	f.write(data1)  # write in
	has_receive += len(data1)  # Update bytes received
f.close()  # Close file

The number of bytes received at one time set here does not need to be the same as that in the server.

Complete code

The server

import socket
import os

server = socket.socket()  # 1. Declare the protocol type and generate socket link object at the same time
server.bind(('192.168.43.28', 1200))  # Bind the port to listen on = (server ip address + any port)
server.listen(5)  # monitor

BASE_DIR = os.path.dirname(os.path.abspath(__file__))  # Get current directory
PIC_DIR = os.path.join(BASE_DIR, 'pics')  # Path to the picture folder
pic_names = sorted(os.listdir(PIC_DIR))  # Get the names of all sorted pictures and put them in a list ['1.jpg','2.jpg',...,'9.jpg']
# Put the picture name into a large string
pic_names = " ".join(i for i in pic_names)  # '0.jpg 1.jpg 2.jpg 3.jpg 4.jpg 5.jpg 6.jpg 7.jpg 8.jpg 9.jpg'

print("I'm going to start waiting for the phone")

while True:
	conn, addr = server.accept()  # Wait for the call
	# conn is a connection instance that the client connects to and generates for it on the server
	print("Received from{}request".format(addr))

	while True:
		data = conn.recv(1024)  # Receive data, obtain the command of image name, and specify the image to be transmitted
		print("recv:", data)

		if not data:
			print("client has lost...")
			break
		if data.decode('utf-8') == 'get pics_names':  # The command to get the image name is defined as get pics_names
			conn.send(pic_names.encode('utf-8'))
		elif data.decode('utf-8') == 'break':
			break
		else:
			img_name = data.decode('utf-8')  # Decode the picture name (bytes) transmitted from the client into a string
			img_path = os.path.join(PIC_DIR, img_name)  # Get the absolute path of the corresponding picture
			file_size = os.stat(img_path).st_size  # Get the size of the image file in bytes. When calling stat, it is used to return the system status information of relevant files
			file_info = '%s|%s' % (img_name, file_size)  # Send the image information to the client (used to distinguish two tasks in the document)
			conn.sendall(bytes(file_info, 'utf-8'))

			f = open(img_path, 'rb')  # Open a file in binary format for read-only
			has_sent = 0  # Record the number of bytes that have been sent
			while has_sent != file_size:  # If the number of bytes sent is not equal to the size of the image, it is then sent
				file = f.read(1024)  # 1024 bytes read at a time
				conn.sendall(file)  # Send to client
				has_sent += len(file)  # Update bytes sent
			f.close()  # After sending, close the file
			print('Upload successful')
	break

server.close()

client

import socket
import os

client = socket.socket()  # Declare socket type and generate socket connection object at the same time
client.connect(('192.168.43.28', 1200))  # ip + port of linked server

BASE_DIR = os.path.dirname(os.path.abspath(__file__))  # Get current directory

while True:
	msg = input(">>:").strip()  # Get the information to be sent to the server in string format
	if len(msg) == 0:
		continue

	client.send(msg.encode("utf-8"))  # Encode the string format into bytes and send
	if msg == 'break':
		break
	data = client.recv(1024)  # Receive the content returned by the server
	if len(str(data, 'utf-8').split('|')) == 2:  # If the length of the returned string is 2, it indicates that a picture is returned from the server for task 2
		filename, filesize = str(data, 'utf8').split('|')  # Gets the name and size of the specified image
		path = os.path.join(BASE_DIR, filename)  # Specifies the path to save the image
		filesize = int(filesize)  # Convert image size to plastic

		f = open(path, 'ab')  # Open a file in binary format for appending. If the file does not exist, create a new file for writing.
		has_receive = 0  # Count the number of bytes received
		while has_receive != filesize:
			data1 = client.recv(1024)  # Receive 1024 bytes of data from the server at a time
			f.write(data1)  # write in
			has_receive += len(data1)  # Update bytes received
		f.close()  # Close file
	print("recv:", data.decode())

client.close()

report errors

The following error messages may appear:

The connection attempt failed because the connecting party did not reply correctly after a period of time or the connecting host did not respond!

At this time, we can go to the terminals of two computers and input:

ping 192.168.43.X

This X refers to the ip address of another computer.

The following prompt should appear

Is Ping 10.16.1.89 Data with 32 bytes:
From 192.168.2.135 Reply from: Unable to access the target host.
From 192.168.2.135 Reply from: Unable to access the target host.
From 192.168.2.135 Reply from: Unable to access the target host.
From 192.168.2.135 Reply from: Unable to access the target host.

But the normal prompt should be:

At this time, it is likely to be a network problem. You can try to use the mobile phone hotspot and turn on wifi for these two computers at the same time. The personal test is useful!