ReadMe (user documentation) file for the sm_vpn_stack_suite (Android VPN Stack Suite) tool.
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In this document user can find necessary info about usage of this tool
(sm_vpn_stack_suite - Android VPN Stack Suite) and reference of all functionality of this tool.

Features of the Android VPN Stack Suite:
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    - Simple TCP/UDP socket server (with multi-thread support) (Linux platform), that implements open simple
        communication protocol (application level):
            - TCP:
                - The Client connects to the TCP Server;
                - The Client sends "socket_client: Hello" to the Server;
                - The Server reads message from the Client; 
                - The Server sends "socket_server: Hello" to the Client;
                - The Client reads message from the Server;
                - The Client sends some text message (size 1024 with '\0' symbol) to the Server;
                - The Server reads text message from the Client and generates inverted message (src: "1234567890" 
                    -> inverted "0987654321");
                - The Server sends inverted message to the Client;
                - The Client reads message from the Server;
                - The Client send read message to the Server;
                - The Server reads text message from the Client and generates inverted message (src: "0987654321"
                    -> inverted "1234567890");
                - The Server sends inverted message to the Client;
                - The Client reads message from the Server;
                - Last received message by the Client should be similar to the first message sent by 
                    Client to the Server;
            - UDP:
                - The Client connects to the TCP Server;
                - The Client sends "socket_client: Hello" to the Server;
                - The Server reads message from the Client; 
                - The Server opens new UDP connection on new socket port;
                - The Server sends new UDP port number to the Client (using first connection);
                - The Client reads the UDP port number and closes first connection;
                - The Client creates new UDP connection, using received from Server port number;
                - The Client sends "socket_client: Hello" to the Server;
                - The Server reads message from the Client; 
                - The Server sends "socket_server: Hello" to the Client;
                - ... Then communication protocol (application level) is same as described in TCP section; 
    - Simple TCP/UDP socket client (Microsoft Visual Studio C++, Windows platform), that implements previous described protocol;
    - Simple TCP/UDP socket client (Android Studio/Android SDK, Android platform), that implements previous described protocol;
    - VPN Stack Application, that (Android Studio/Android SDK/Android NDK/C, Android platform), that is based on
        VpnService (Android platform) and implements intermediate IP/TCP/UDP stack (JNI/C/Sockets);
    - VPN Stack Application provides catching, monitoring and processing TCP/UDP/ICMP/IP packages; Then these packages
        are processed (via JNI) at the Native API level;
    - VPN Stack Application, can catch packages from some defined application (if text edit "Filtered Package Name" is defined)
        or from all applications (if text edit "Filtered Package Name" is empty);
    - VPN Stack Application creates tun0 device (after launching), which is used for catching
        TCP/UDP/ICMP/IP packages;
    - VPN Stack Application reads packages, sent from Android application(s) from tun0 device, provides processing these packages
        and creates new or uses saved (sessions) TCP connections (if Android Application sends TCP package)
        or just uses sendto (if Android Application sends TCP package);
    - VPN Stack Application receives all packages from network, provides processing these packages
        and writes packages to tun0 device, then packages will be received by Android application(s);
    - VPN Stack Application doesn't use Raw Sockets;
    - VPN Stack Application writes detailed log to Logcat and to the file
        /data/data/com.smansoft.vpn_stack/files/logs/vpn_stack.log;
    - Follow applications from this suite:
            - Simple TCP/UDP socket server (with multi-thread support) (Linux platform)
            - Simple TCP/UDP socket client (Microsoft Visual Studio C++, Windows platform)
            - Simple TCP/UDP socket client (Android Studio/Android SDK, Android platform)
        have been created and have been used for testing network connections and for testing the VPN Stack Application;

Downloading the Android VPN Stack Suite source files:
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    Source files of the sm_vpn_stack_suite (Android VPN Stack Suite) tool can be found here:
        http://smansoft.com/sm_vpn_stack_suite/
        https://github.com/smansoft/sm_vpn_stack_suite
    .
    
Demo, Screenshots and Log files of the Android VPN Stack Suite:
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    Demo, Screenshots and Log files of the sm_vpn_stack_suite (Android VPN Stack Suite) 
        can be found here:
        http://smansoft.com/sm_vpn_stack_suite/0.0.1.1/examples/
    .

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    Copyright (C) 2021 SManSoft <http://www.smansoft.com/>
                        Sergey Manoylo <info@smansoft.com>