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\section{Interprocess communication overview}\label{ipcoverview}
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Classes: \helpref{wxDDEServer}{wxddeserver}, \helpref{wxDDEConnection}{wxddeconnection},
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\helpref{wxDDEClient}{wxddeclient},
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\helpref{wxTCPServer}{wxtcpserver}, \helpref{wxTCPConnection}{wxtcpconnection},
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\helpref{wxTCPClient}{wxtcpclient}
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Classes: \helpref{wxServer}{wxddeserver},
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\helpref{wxConnection}{wxddeconnection},
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\helpref{wxClient}{wxddeclient}
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%\helpref{wxTCPServer}{wxtcpserver}, \helpref{wxTCPConnection}{wxtcpconnection},
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%\helpref{wxTCPClient}{wxtcpclient}
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wxWindows has a number of different classes to help with interprocess communication
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and network programming. This section only discusses one family of classes - the DDE-like
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protocol - but here's a list of other useful classes:
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wxWindows has a number of different classes to help with
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interprocess communication and network programming. This section
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only discusses one family of classes -- the DDE-like protocol --
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but here's a list of other useful classes:
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\begin{itemize}\itemsep=0pt
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\item \helpref{wxSocketEvent}{wxsocketevent},
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\helpref{wxSocketBase}{wxsocketbase},
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\helpref{wxSocketClient}{wxsocketclient},
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\item \helpref{wxSocketEvent}{wxsocketevent},
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\helpref{wxSocketBase}{wxsocketbase},
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\helpref{wxSocketClient}{wxsocketclient},
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\helpref{wxSocketServer}{wxsocketserver}: classes for the low-level TCP/IP API.
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\item \helpref{wxProtocol}{wxprotocol}, \helpref{wxURL}{wxurl}, \helpref{wxFTP}{wxftp}, wxHTTP: classes
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\item \helpref{wxProtocol}{wxprotocol}, \helpref{wxURL}{wxurl}, \helpref{wxFTP}{wxftp}, \helpref{wxHTTP}{wxhttp}: classes
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for programming popular Internet protocols.
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\end{itemize}
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Further information on these classes will be available in due course.
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wxWindows' DDE-like protocol is a high-level protocol based on
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Windows DDE. There are two implementations of this DDE-like
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protocol: one using real DDE running on Windows only, and another
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using TCP/IP (sockets) that runs on most platforms. Since the API
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and virtually all of the behaviour is the same apart from the
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names of the classes, you should find it easy to switch between
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the two implementations.
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Notice that by including {\tt <wx/ipc.h>} you may define convnient synonyms for
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the IPC classes: {\tt wxServer} for either {\tt wxDDEServer} or
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{\tt wxTCPServer} depending on whether DDE-based or socket-based implementation
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is used and the same thing for {\tt wxClient} and {\tt wxConnection}. By
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default, DDE implementation is used under Windows. If you want to use IPC
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between the different workstations you should define {\tt wxUSE\_DDE\_FOR\_IPC}
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as $0$ before including this header -- this will force using TCP/IP
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implementation even under Windows.
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Notice that by including {\tt <wx/ipc.h>} you may define
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convenient synonyms for the IPC classes: {\tt wxServer} for either
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{\tt wxDDEServer} or {\tt wxTCPServer} depending on whether
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DDE-based or socket-based implementation is used and the same
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thing for {\tt wxClient} and {\tt wxConnection}.
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By default, DDE implementation is used under Windows. DDE works
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only within one computer. If you want to use IPC between
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different workstations you should define {\tt
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wxUSE\_DDE\_FOR\_IPC} as $0$ before including this header -- this
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will force using TCP/IP implementation even under Windows.
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wxWindows has a high-level protocol based on Windows DDE.
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There are two implementations of this DDE-like protocol:
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one using real DDE running on Windows only, and another using TCP/IP (sockets) that runs
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on most platforms. Since the API is the same apart from the names of the classes, you
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should find it easy to switch between the two implementations.
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The following description refers to wx... but remember that the
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equivalent wxTCP... and wxDDE... classes can be used in much the
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same way.
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The following description refers to 'DDE' but remember that the equivalent wxTCP... classes
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can be used in much the same way.
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Three classes are central to the DDE API:
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Three classes are central to the DDE-like API:
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\begin{enumerate}\itemsep=0pt
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\item wxDDEClient. This represents the client application, and is used
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\item wxClient. This represents the client application, and is used
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only within a client program.
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\item wxDDEServer. This represents the server application, and is used
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\item wxServer. This represents the server application, and is used
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only within a server program.
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\item wxDDEConnection. This represents the connection from the current
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client or server to the other application (server or client), and can be used
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in both server and client programs. Most DDE
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transactions operate on this object.
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\item wxConnection. This represents the connection from the
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client to the server - both the client and the server use an
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instance of this class, one per connection. Most DDE transactions
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operate on this object.
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\end{enumerate}
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Messages between applications are usually identified by three variables:
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connection object, topic name and item name. A data string is a fourth
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element of some messages. To create a connection (a conversation in
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Windows parlance), the client application sends the message
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MakeConnection to the client object, with a string service name to
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identify the server and a topic name to identify the topic for the
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duration of the connection. Under Unix, the service name may be either an
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integer port identifier in which case an Internet domain socket will be used
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for the communications or a valid file name (which shouldn't exist and will be
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deleted afterwards) in which case a Unix domain socket is created.
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Messages between applications are usually identified by three
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variables: connection object, topic name and item name. A data
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string is a fourth element of some messages. To create a
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connection (a conversation in Windows parlance), the client
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application uses wxClient::MakeConnection to send a message to the
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server object, with a string service name to identify the server
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and a topic name to identify the topic for the duration of the
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connection. Under Unix, the service name may be either an integer
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port identifier in which case an Internet domain socket will be
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used for the communications or a valid file name (which shouldn't
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exist and will be deleted afterwards) in which case a Unix domain
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socket is created.
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{\bf SECURITY NOTE:} Using Internet domain sockets if extremely insecure for
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IPC as there is absolutely no access control for them, use Unix domain sockets
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whenever possible!
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The server then responds and either vetoes the connection or allows it.
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If allowed, a connection object is created which persists until the
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connection is closed. The connection object is then used for subsequent
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messages between client and server.
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The server then responds and either vetoes the connection or
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allows it. If allowed, both the server and client objects create
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wxConnection objects which persist until the connection is
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closed. The connection object is then used for sending and
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receiving subsequent messages between client and server -
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overriding virtual functions in your class derived from
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wxConnection allows you to handle the DDE messages.
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To create a working server, the programmer must:
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\begin{enumerate}\itemsep=0pt
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\item Derive a class from wxDDEServer.
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\item Override the handler OnAcceptConnection for accepting or rejecting a connection,
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on the basis of the topic argument. This member must create and return a connection
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object if the connection is accepted.
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\item Create an instance of your server object, and call Create to
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\item Derive a class from wxConnection, providing handlers for various messages sent to the server
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side of a wxConnection (e.g. OnExecute, OnRequest, OnPoke). Only
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the handlers actually required by the application need to be
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overridden.
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\item Derive a class from wxServer, overriding OnAcceptConnection
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to accept or reject a connection on the basis of the topic
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argument. This member must create and return an instance of the
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derived connection class if the connection is accepted.
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\item Create an instance of your server object and call Create to
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activate it, giving it a service name.
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\item Derive a class from wxDDEConnection.
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\item Provide handlers for various messages that are sent to the server
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side of a wxDDEConnection.
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\end{enumerate}
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To create a working client, the programmer must:
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\begin{enumerate}\itemsep=0pt
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\item Derive a class from wxDDEClient.
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\item Override the handler OnMakeConnection to create and return
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an appropriate connection object.
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\item Derive a class from wxConnection, providing handlers for various
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messages sent to the client side of a wxConnection (e.g.
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OnAdvise). Only the handlers actually required by the application
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need to be overridden.
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\item Derive a class from wxClient, overriding OnMakeConnection to
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create and return an instance of the derived connection class.
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\item Create an instance of your client object.
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\item Derive a class from wxDDEConnection.
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\item Provide handlers for various messages that are sent to the client
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side of a wxDDEConnection.
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\item When appropriate, create a new connection by sending a MakeConnection
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message to the client object, with arguments host name (processed in Unix only),
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service name, and topic name for this connection. The client object will call OnMakeConnection
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to create a connection object of the desired type.
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\item Use the wxDDEConnection member functions to send messages to the server.
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\item When appropriate, create a new connection using
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\helpref{wxClient::MakeConnection}{wxddeclientmakeconnection},
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with arguments host name (processed in Unix only, use `localhost'
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for local computer), service name, and topic name for this
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connection. The client object will call
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\helpref{OnMakeConnection}{wxddeclientonmakeconnection} to create
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a connection object of the derived class if the connection is
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successful.
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\item Use the wxConnection member functions to send messages to the server.
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\end{enumerate}
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\subsection{Data transfer}
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These are the ways that data can be transferred from one application to
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another.
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These are the ways that data can be transferred from one
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application to another. These are methods of wxConnection.
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\begin{itemize}\itemsep=0pt
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\item {\bf Execute:} the client calls the server with a data string representing
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@@ -140,31 +155,31 @@ that item to be highlighted in the client list box.
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\subsection{More DDE details}
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A wxDDEClient object represents the client part of a client-server DDE
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(Dynamic Data Exchange) conversation (available in both
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A wxClient object initiates the client part of a client-server
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DDE-like (Dynamic Data Exchange) conversation (available in both
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Windows and Unix).
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To create a client which can communicate with a suitable server,
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you need to derive a class from wxDDEConnection and another from wxDDEClient.
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The custom wxDDEConnection class will intercept communications in
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a `conversation' with a server, and the custom wxDDEServer is required
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so that a user-overridden \helpref{wxDDEClient::OnMakeConnection}{wxddeclientonmakeconnection} member can return
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a wxDDEConnection of the required class, when a connection is made.
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you need to derive a class from wxConnection and another from
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wxClient. The custom wxConnection class will receive
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communications in a `conversation' with a server. and the custom
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wxServer is required so that a user-overridden
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\helpref{wxDDEClient::OnMakeConnection}{wxddeclientonmakeconnection}
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member can return a wxDDEConnection of the required class, when a
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connection is made.
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For example:
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\begin{verbatim}
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class MyConnection: public wxDDEConnection
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{
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class MyConnection: public wxConnection {
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public:
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MyConnection(void)::wxDDEConnection(ipc_buffer, 3999) {}
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MyConnection(void)::wxConnection() {}
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~MyConnection(void) { }
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bool OnAdvise(const wxString& topic, const wxString& item, char *data, int size, wxIPCFormat format)
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{ wxMessageBox(topic, data); }
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};
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class MyClient: public wxDDEClient
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{
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class MyClient: public wxClient {
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public:
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MyClient(void) {}
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wxConnectionBase *OnMakeConnection(void) { return new MyConnection; }
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@@ -172,15 +187,20 @@ class MyClient: public wxDDEClient
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\end{verbatim}
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Here, {\bf MyConnection} will respond to \helpref{OnAdvise}{wxddeconnectiononadvise} messages sent
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by the server.
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Here, {\bf MyConnection} will respond to
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\helpref{OnAdvise}{wxddeconnectiononadvise} messages sent by the
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server by displaying a message box.
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When the client application starts, it must create an instance of the derived wxDDEClient. In the following, command line
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arguments are used to pass the host name (the name of the machine the server is running
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on) and the server name (identifying the server process). Calling \helpref{wxDDEClient::MakeConnection}{wxddeclientmakeconnection}\rtfsp
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implicitly creates an instance of {\bf MyConnection} if the request for a
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connection is accepted, and the client then requests an {\it Advise} loop
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from the server, where the server calls the client when data has changed.
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When the client application starts, it must create an instance of
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the derived wxClient. In the following, command line arguments
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are used to pass the host name (the name of the machine the
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server is running on) and the server name (identifying the server
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process). Calling
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\helpref{wxDDEClient::MakeConnection}{wxddeclientmakeconnection}\rtfsp
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implicitly creates an instance of {\bf MyConnection} if the
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request for a connection is accepted, and the client then
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requests an {\it Advise} loop from the server (an Advise loop is
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where the server calls the client when data has changed).
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\begin{verbatim}
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wxString server = "4242";
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Julian Smart