local-proxy

Flow chart by Psuedo code

How to run

Check detail proxy setting here

cd src
python3 proxy.py 8080

How it works

Parsing for get “User-Agent” data

request_data_dict = {}

for line in request_data.decode().splitlines():
    try:
        title, content = line.split(": ")
        request_data_dict[title] = content
    except:
        pass

response_user_agent = request_data_dict['User-Agent']
end_index = response_user_agent.find(")")
cleaned_user_agent = response_user_agent[:end_index+1].replace("User-Agent: ", "")

Redirection to “mnet.Yonsei.ac.kr” when URL has “korea”

# Connect to the destination server
server_socket = None
response_data = None

try: 
    server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    if url_filter == "O":
        destination_host = "mnet.yonsei.ac.kr"
    server_socket.connect((destination_host,  80))
except Exception as e:
    print("\nServer socket error: " + str(e))
    

server_socket.sendall(request_data)

Image Filtering
Log response through proxy
It logs also http status, content-type, content-length and send response_data to client
But It don’t send response_data when drop image

# Print log for the received response
print(f"[CLI <== PRX --- SRV]")

if image_filter == "O":
    if response_content.startswith("image"):
        print(f" > 404 Not Found")
    else:
        print(f" > {cleaned_status}")
        print(f" > {response_content} {response_bytes}bytes")
        client_socket.sendall(response_data)
else:
    print(f" > {cleaned_status}")
    print(f" > {response_content} {response_bytes}bytes")

    # Forward the modified response to the client
    client_socket.sendall(response_data)

Snapshots

Mac proxy server setup

Image filtering

Image filtering at test page

Redirection

Redirection from Korea univ page to Yonsei univ page

Image filtering with Redirection

Environment

OS: Mac Sonoma
Language: Python(3.8.5)