==== Protocol Buffer (Protobuf) ====

This is a solution for the serialization of structured data, developed by Google. The interface description is also displayed for this data integration method.

Protobuf are designed to be a compact and efficient binary format for transmitting data over a network or storing it on disk. They use a binary format that is smaller and faster to serialize and deserialize than text-based formats such as XML or JSON.

More details can be found here:

https://developers.google.com/protocol-buffers/docs/tutorials

1.) Install the translator from the official website. https://github.com/protocolbuffers/protobuf/releases - in the case of Windows, unzip the file protoc-XXX.zip.

2.) Create a directory called ./proto and the file book.proto with the following content:

<code python>
syntax = "proto3";
 
message Book {
    int32 id = 1;
    string title = 2;
    string author = 3;
    float price = 4;
}
 
message Books {
    repeated Book books = 1;
}
</code>

We have created two messages named Book and Books. Books can contain several Books. = 1, = 2 at the end of the lines indicates the internal position of the structure field, numbering starts from one.

3.) Run the following command:

    .\protoc\bin\protoc.exe --python_out=.\ book.proto

After running, book_pb2.py is created, which is generated source code and contains the data interface. This can be used to manage (serialize and de-serialize) the data.

4.) Upgrade protobuf interface
   pip install –upgrade protobuf

5.) Create the server.py file with the following content:

<code python>
import socket
import book_pb2
import create_books as c

# protoc/bin/protoc --python_out=./ book.proto
# pip3 install --upgrade protobuf

books = c.create_books()

book_store = book_pb2.Books()
for book in books:
    book_store.books.append(book)

bytes_to_send = book_store.SerializeToString()

#TCP socket server
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((socket.gethostname(), 4100))
s.listen(10)

while True:
    client_socket, address = s.accept()
    print(f"server> Connection from {address} has been established!\n")

    client_socket.send(bytes_to_send)
    print(f"server> Message sent: {bytes_to_send}\n")

    msg = client_socket.recv(1024)
    print(f"client> {msg}\n")
    client_socket.close()

    if msg == b'bye':
        break

s.close()
</code>

6.) Create the create_books.py file with the following content:

<code python>
import book_pb2

def create_books():
    books = []

    books.append(book_pb2.Book())
    books[0].id = 1
    books[0].title = "Solaris"
    books[0].author = "Stanislaw Lem"
    books[0].price = 7.54

    books.append(book_pb2.Book())
    books[1].id = 2
    books[1].title = "Dune"
    books[1].author = "Frank Herbert"
    books[1].price = 9.87

    books.append(book_pb2.Book())
    books[2].id = 3
    books[2].title = "Foundation"
    books[2].author = "Isaac Asimov"
    books[2].price = 5.07

    return books
</code>

7.) Create the client.py file with the following content:
<code python>
import socket
import book_pb2
from google.protobuf.json_format import MessageToJson
import json

#TCP socket client
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((socket.gethostname(), 4100))

msg = s.recv(1024)
print(f"server> {msg}\n")

s.sendall(b'bye')
print(f"client> Message sent: {b'bye'}\n")

s.close()

books = book_pb2.Books()
books.ParseFromString(msg)

json_obj = MessageToJson(books)
print(f"client> The server's message in JSON:\n{json_obj}")

dict_obj = json.loads(json_obj)

with open('data.json', 'w', encoding='utf-8') as f:
    json.dump(dict_obj, f, ensure_ascii=False, indent=4)
    print("client> data.json saved\n")

with open('data.bytes', 'wb') as fb:
    fb.write(msg)
    print("client> data.bytes saved\n")
</code>
8.) Run the server and client. python server.py then python client.py commands and let's see and analyze what happens?