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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-579D7C32-B6C8-5C77-88A5-B3078729E1BA" xml:lang="en"><title>How

    13 to implement a simple client interface</title><shortdesc>Provides code snippets to help you to implement a simple client

    14 interface.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    15 <section id="GUID-EE1BFD0F-EE55-47BA-A8FD-D753EC132255"><title>Client side session with a server</title> <p>A client side

    16 session is represented by an instance of a class derived from <codeph>RSessionBase</codeph> which

    17 provides the behaviour for connecting to the server and sending messages to

    18 it. </p> <p>In the following code fragment, taken from the example that can

    19 be found at <filepath>...\examples\Base\IPC\ClientServer\simple</filepath>,

    20 the class <codeph>RCountServSession</codeph>, derived from <codeph>RSessionBase</codeph>,

    21 represents the client side session with a server. In the example, this may

    22 be referred to as the "count server". Note that sessions can not be shared

    23 in this example, and it just shows the basic mechanics of the client/server

    24 interaction. </p> <codeblock id="GUID-48AC1BF2-BA67-5959-A49A-AF57AC25E155" xml:space="preserve">class RCountServSession : public RSessionBase

    25     {

    26 public:

    27     RCountServSession();

    28     TInt Connect();

    29     TVersion Version() const;

    30     TInt UnsupportedRequest();

    31     TInt SetFromString(const TDesC& aString);

    32     void Increase();

    33     void Decrease();

    34     void IncreaseBy(TInt anInt);

    35     void DecreaseBy(TInt anInt);

    36     void Reset();

    37     TInt CounterValue();

    38     void BadRequest();

    39     void Close();

    40 private:

    41     RThread iServerThread;

    42     };</codeblock> <p>The important points are: </p> <ul>

    43 <li id="GUID-B6AC51AC-91A3-5794-815A-292E308735F6"><p>Use <codeph>Connect()</codeph> to

    44 start the count server. This calls <codeph>RSessionBase::CreateSession()</codeph> to

    45 create a session with the server. Note that in this simple example, the server

    46 is implemented as a separate thread, which is started by the example executable. </p> </li>

    47 <li id="GUID-EBDC7F23-8D2F-5093-8C32-50C3DE137EF5"><p>Use a client interface

    48 function, such as <codeph>Increase()</codeph>, to send a specific message

    49 to the server. The client interface function builds the message using the

    50 appropriate operation code and assembling a suitable <xref href="GUID-4AD02F14-1142-372F-9D11-224595932034.dita"><apiname>TIpcArgs</apiname></xref> object,

    51 i.e. the object containing the integers and/or the descriptor pointers to

    52 the message arguments in the client address space. </p> </li>

    53 </ul> <p>As an example, the function <codeph>SetFromString()</codeph> is implemented

    54 as follows: </p> <codeblock id="GUID-A673A2A4-0999-5EDE-9FFB-E0C7335B58D9" xml:space="preserve">TInt RCountServSession::SetFromString(const TDesC&amp; aString)

    55     {

    56     TIpcArgs args(&aString);

    57     return SendReceive(ECountServSetFromString, args);

    58     }</codeblock> <p> <codeph>SendReceive()</codeph> is called, specifying

    59 an operation code <codeph>ECountServSetFromString</codeph> and a <xref href="GUID-4AD02F14-1142-372F-9D11-224595932034.dita"><apiname>TIpcArgs</apiname></xref> object

    60 containing argument values. In this case, there is only one argument - a pointer

    61 to a <codeph>TDesC</codeph> object containing the string to be passed to the

    62 server. Typically, operation codes are enum values defined in a header file

    63 visible to both the client interface and the server. Note that the client

    64 descriptor must remain in existence until the server request completes. </p> </section>

    65 </conbody></concept>