Server buildin into libgreattao and tao-network-client

In this entry I would describe network server, which were buildin into liobgreattao and client of this server(tao-network-client). These two projects are created by me. Both tools are ready for download from svn repository on sourceforge.


Calling each of these tool client of server is misunderstanding, because each of these tool can works both in server and client mode. Communication protocol is the same in both mode, the only difference between these two modes are in way connection is established. Exchanged messages are always the same, not dependent one of my solution is working as client or as sever.

Second mode was introduced to avoid unnecessary work on independent proxy application. It additionally allow to work by tao-network-client with many application written in libgreattao(Imagine one application was run another). In a result of adding second working mode, tao-network-client have two proxy mode:

  1. Libgreattao server proxy mode: tao-network-client is libgreattao application, so it can be run in proxy mode
  2. Second mode introduced by adding server mode to tao-network-client

First proxy mode allow to transport messages only from one libgreattao server.

The way it’s working

Entire protocol is designed to transfer messages associated with some libgreattao calls and to transfer files. Server sends icon, window class files or file created by application. It also sends command, like create a window of some class. Client sends messages requiring receive file and status of window creating operation

When server is working in server mode, it forks for each connection. When client is working in server mode, it run one thread for accept connection and runs additional thread for each connection request

Running server for application

To run application written in libgreattao as server, we need an certificate and a private key. If private key is is encrypted, we need to pass decrypt key as an parameter. Additionally we can type password, which will be required from client on connection step. We must give port number to listen on.

our_application --tao-network-port 1026 --tao-network-certificate-path /home/I/my_certificate.pem --tao-network-priv-key-path /home/I/my_private_key.pem --tao-network-priv-key-password OUR_KEY_TO_DECRYPT_PRIVATE_KEY --tao-network-password OUR_CONNECTION_PASSWORD

Two last parameters are optional. Password for connection can’t be bigger than 255 characters.

Running client

To run client, we need to single/double click(for example) on it. If no parameters are given, client ask for host name and port number. In the same case, in next step, client ask us for password, if server ask for it. We also run tao-network-client in command line, giving all needed arguments. This is example:

tao-netwrok-client --host localhost --port 1026 --password OUR_CONNECTION_PASSWORD

Client as proxy server for one application

You can run proxy server, using tao-nextwork-client. We run first type of proxy in this way:

tao-network-client --host locahost --port 1026 --password OUR_CONNECTION_PASSWORD --tao-network-port 1027 --tao-network-certificate-path /home/I/our_certificate.pem --tao-network-priv-key-path /home/I/our_private_key.pem --tao-network-priv-key-password OUR_PRIVATE_KEY_PASSWORD --tao-network-password OUR_PASSWORD_FOR_PROXY_SERVER

What was changed? We changed only port number, because proxy server can be ran on the same machine. We also assign different password for proxy server, because we had an fantasy. Certainly, we can skip two password, because:

  1. First – we will be asked for it as described before
  2. Second – tao-network-client is libgreattao application, so question for password of server application will be remote

Reverting roles

Imagine we would like to use many libgreattao applications with on client. In this situation, we need revert role of libgreattao process we want to use and tao-network-client. Servers will be clients and clients will be servers. We need also a way to establish remote connection to these application, so we start tao-network-client on server in second proxy mode and connects tao-network-client to it from our computer. In first proxy mode proxy server was a server for another tao-network-client and client for single instance of libgreattao application. In second proxy mode proxy instance is server for many libgreattao applications instance and server for one instance of libgreattao. Because in this mode proxy is still libgreattao server, it forks on each tao-network-client connection.
We can achieve our goal in this way:

tao-network-client --wait-on-port 1030 --path-to-certificate /home/I/our_certificate.pem --path-to-priv-key /home/I/our_private_key.pem --password-to-priv-key OUR_PRIVTE_KEY_PASSWORD --password PASSWORD_FOR_TAO_APPLICATION --tao-network-port 1027 --tao-network-certificate-path /home/I/our_certificate.pem --tao-network-priv-key-path /home/I/our_private_key.pem --tao-network-priv-key-password OUR_PASSWORD_FOR_PRIVATE_KEY --tao-network-password PASSWORD_FOR_TAO_NETWORK_CLIENT

In code placed above we had have one bug: we set port number, so we cannot connect many tao-network-client. The solution is rather simple. All we need is to not pass –wait-on-port parameter and pass –command instead. Example is showed below:

tao-network-client --path-to-certificate /home/I/our_certificate.pem --path-to-priv-key /home/I/our_private_key.pem --password-to-priv-key OUR_PRIVTE_KEY_PASSWORD --password PASSWORD_FOR_TAO_APPLICATION --tao-network-port 1027 --tao-network-certificate-path /home/I/our_certificate.pem --tao-network-priv-key-path /home/I/our_private_key.pem --tao-network-priv-key-password OUR_PASSWORD_FOR_PRIVATE_KEY --tao-network-password PASSWORD_FOR_TAO_NETWORK_CLIENT --tao-app-command-line --command our_tao_application

In this mode we don’t pass port number, so we can connects many clients, but we pass command to run instead. Command will be run on local machine, so this example is great for second proxy

Take a look at password argument. In two above examples, it is used to set password to authenticate to client instead of authenticate to server.

How to connect libgreattao application

In example below I demonstrate how to connect


Why we had use environment variables? The reason is simple: application can run another application and information should be passed to it. When our certificate are not valid(for example self signed or expired), our application will drop connection.To avoid this, we should pass additional environment variable, like below:


Passing argument

You can pass parameters to tao application by prefix name of parameter with –network-option-, for example to tell proxy to connect to application listen on port 1026 and host localhost, we can do this in way showed below:

tao-network-client --network-option-host localhost --network-option-port 1026


We can pass limit to downloaded file size. We can limit single file size with putting option –max-file-len size_in_bytes. We can limit sum of file sizes by putting option –max-files-len size_in_bytes. While one of the limit was reached, tao_network_client will asks to continue connection.


  • To develop custom client, you should use libgreatta/network.h
  • To support sending/receiving files selected in file dialogs, you should use functions tao_open_file, tao_close_file and tao_release_file

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