c-netapi3.html

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<div class="CellBody"><a name="89802"> </a><b class="routine"><i class="routine">zbufSockRecv</i></b><b>(&nbsp;)</b></div>

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<div class="CellBody"><a name="89804"> </a>Receive data in a zbuf from a TCP socket.</div>

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<div class="CellBody"><a name="89807"> </a><b class="routine"><i class="routine">zbufSockRecvfrom</i></b><b>(&nbsp;)</b></div>

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<div class="CellBody"><a name="89809"> </a>Receive a message in a zbuf from a UDP socket.</div>

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<dd><p class="Body"><a name="89810"> </a>For a detailed description of each routine, see the corresponding reference entry.</p>
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<font face="Helvetica, sans-serif" class="sans">
<h4 class="H4"><i><a name="89811">Standard Socket Calls and Zbuf Socket Calls</a></i></h4>
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<dl class="margin">

<dd><p class="Body"><a name="89812"> </a>The zbuf socket calls are particularly useful when large data transfer is a significant part of your socket application.  For example, many socket applications contain sections of code like the following fragment:</p>
<dl class="margin">

<dd><pre class="Code2"><b><a name="89813">pBuffer = malloc (BUFLEN); 
while ((readLen = read (fdDevice, pBuffer, BUFLEN))  &gt; 0) 
    write (fdSock, pBuffer, readLen);</a></b></pre>
</dl>

<dd><p class="Body"><a name="89815"> </a>You can eliminate the overhead of copying from the application buffer <b class="symbol_lc">pBuffer</b> into the internal socket buffers by changing the code to use zbuf socket calls.  For example, the following fragment is a zbuf version of the preceding loop:</p>
<dl class="margin">

<dd><pre class="Code2"><b><a name="89816">pBuffer = malloc (BUFLEN * BUFNUM);           /* allocate memory */ 
for (ix = 0; ix &lt; (BUFNUM - 1); ix++, pBuffer += BUFLEN) 
    appBufRetn (pBuffer);                    /* fill list of free bufs */ 
 
while ((readLen = read (fdDevice, pBuffer, BUFLEN)) &gt; 0) 
    { 
    zId = zbufCreate ();                     /* insert into new zbuf */ 
    zbufInsertBuf (zId, NULL, 0, pBuffer, readLen, appBufRetn, 0); 
    zbufSockSend (fdSock, zId, readLen, 0);   /* send zbuf */ 
    pBuffer = appBufGet (WAIT_FOREVER);       /* get a fresh buffer */ 
    }</a></b></pre>
</dl>

<dd><p class="Body"><a name="89827"> </a>The <b class="routine"><i class="routine">appBufGet</i></b><b>(&nbsp;)</b> and <b class="routine"><i class="routine">appBufRetn</i></b><b>(&nbsp;)</b> references in the preceding code fragment stand for application-specific buffer management routines, analogous to <b class="routine"><i class="routine">malloc</i></b><b>(&nbsp;)</b> and <b class="routine"><i class="routine">free</i></b><b>(&nbsp;)</b>.  In many applications, these routines do nothing more than manipulate a linked list of free fixed-length buffers.</p>
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<h4 class="EntityTitle"><a name="89829"><font face="Helvetica, sans-serif" size="-1" class="sans">Example 7-5:&nbsp;&nbsp;The TCP Example Server Using Zbufs</font></a></h4>
<dl class="margin">

<dl class="margin">

<dd><p class="Body"><a name="89831"> </a>For a small but complete example that illustrates the mechanics of using the zbuf socket library, consider the conversion of the client-server example in <a href="c-netapi2.html#88737">Example&nbsp;7-1</a> to use zbuf socket calls. </p>
<dd><p class="Body"><a name="89835"> </a>No conversion is needed for the client side of the example; the client operates the same regardless of whether or not the server uses zbufs.  The next example illustrates the following changes to convert the server side to use zbufs:</p>
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<dl class="margin">

<p class="listspace">
<ul class="Dash" type="circle"><li><a name="89836"> </a>Instead of including the header file <b class="file">sockLib.h</b>, include <b class="file">zbufSockLib.h</b>.</li></ul>
</p><p class="listspace">
<ul class="Dash" type="circle"><li><a name="89837"> </a>The data processing component must be capable of dealing with potentially non-contiguous data in successive zbuf segments.  In the TCP example, this component displays a message using <b class="routine"><i class="routine">printf</i></b><b>(&nbsp;)</b>; we can use the <b class="routine"><i class="routine">zbufDisplay</i></b><b>(&nbsp;)</b> routine from <a href="c-netapi3.html#89723">Example&nbsp;7-4</a> instead.</li></ul>
</p><p class="listspace">
<ul class="Dash" type="circle"><li><a name="89841"> </a>The original TCP example exploits <b class="routine"><i class="routine">fioRead</i></b><b>(&nbsp;)</b> to collect the complete message, rather than calling <b class="routine"><i class="routine">recv</i></b><b>(&nbsp;)</b> directly.  To achieve the same end while avoiding data copying by using zbufs, the following example defines a <b class="routine"><i class="routine">zbufFioSockRecv</i></b><b>(&nbsp;)</b> subroutine to call <b class="routine"><i class="routine">zbufSockRecv</i></b><b>(&nbsp;)</b> repeatedly until the complete message is received.</li></ul>
</p><p class="listspace">
<ul class="Dash" type="circle"><li><a name="89842"> </a>A new version of the worker routine <b class="routine"><i class="routine">tcpServerWorkTask</i></b><b>(&nbsp;)</b> must tie together these separate modifications, and must explicitly extract the <b class="symbol_lc">reply</b> and <b class="symbol_lc">msgLen</b> fields from the client's transmission to do so.  When using zbufs, these fields cannot be extracted by reference to the C structure in <b class="file">tcpExample.h</b> because of the possibility that the data is not contiguous.</li></ul>
</p></dl>

<dl class="margin">

<dd><p class="Body"><a name="89843"> </a>The following example shows the auxiliary <b class="routine"><i class="routine">zbufFioSockRecv</i></b><b>(&nbsp;)</b> routine and the zbuf version of <b class="routine"><i class="routine">tcpServerWorkTask</i></b><b>(&nbsp;)</b>.  To run this code:</p>
</dl>

<dl class="margin">

<p><ol class="List"><li value="1."><a name="89847"> </a>Start with <b class="file">tcpServer.c</b> as defined in <a href="c-netapi2.html#88737">Example&nbsp;7-1</a>.</li></ol></p>
<p><ol class="List"><li value="2."><a name="89848"> </a>Include the header file <b class="file">zbufSockLib.h</b>.</li></ol></p>
<p><ol class="List"><li value="3."><a name="89852"> </a>Insert the <b class="routine"><i class="routine">zbufDisplay</i></b><b>(&nbsp;)</b> routine from <a href="c-netapi3.html#89723">Example&nbsp;7-4</a>.</li></ol></p>
<p><ol class="List"><li value="4."><a name="89853"> </a>Replace the <b class="routine"><i class="routine">tcpServerWorkTask</i></b><b>(&nbsp;)</b> definition with the following two routines:</li></ol></p>
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<dl class="margin">

<dd><pre class="Code"><b><a name="89854">/************************************************************************ 
* 
* zbufFioSockRecv - receive &lt;len&gt; bytes from a socket into a zbuf 
* 
* This routine receives a specified amount of data from a socket into a 
* zbuf, by repeatedly calling zbufSockRecv() until &lt;len&gt; bytes 
* are read. 
* 
* RETURNS: 
* The ID of the zbuf containing &lt;len&gt; bytes of data, 
* or NULL if there is an error during the zbufSockRecv() operation. 
* 
* SEE ALSO: zbufSockRecv() 
*/</a></b><dd>
 
<b><a name="92809">ZBUF_ID zbufFioSockRecv 
    ( 
    int         fd,             /* file descriptor of file to read */ 
    int         len             /* maximum number of bytes to read */ 
    ) 
    { 
    BOOL        first = TRUE;           /* first time thru ? */ 
    ZBUF_ID     zRecvTotal = NULL;      /* zbuf to return */ 
    ZBUF_ID     zRecv;                  /* zbuf read from sock */ 
    int         nbytes;                 /* number of recv bytes */</a></b><dd>
 
<b><a name="92811">    for (; len &gt; 0; len -= nbytes) 
        { 
        nbytes = len;                   /* set number of bytes wanted */</a></b><dd>
 
<b><a name="89860">        /* read a zbuf from the socket */</a></b><dd>
 
<b><a name="89862">        if (((zRecv = zbufSockRecv (fd, 0, &amp;nbytes)) == NULL) || 
            (nbytes &lt;= 0)) 
            { 
            if (zRecvTotal != NULL) 
                zbufDelete (zRecvTotal); 
            return (NULL); 
            }</a></b><dd>
 
<b><a name="89864">        /* append recv'ed zbuf onto end of zRecvTotal */</a></b><dd>
 
<b><a name="89865">        if (first) 
            zRecvTotal = zRecv;         /* cannot append to empty zbuf */ 
        else if (zbufInsert (zRecvTotal, NULL, ZBUF_END, zRecv) == NULL) 
            { 
            zbufDelete (zRecv); 
            zbufDelete (zRecvTotal); 
            return (NULL); 
            }</a></b><dd>
 
<b><a name="89866">        first = FALSE;                  /* can append now... */ 
        }</a></b><dd>
 
<b><a name="89867">    return (zRecvTotal); 
    }</a></b><dd>
 
<b><a name="89869">/************************************************************************ 
* 
* tcpServerWorkTask - process client requests 
* 
* This routine reads from the server's socket, and processes client 
* requests.  If the client requests a reply message, this routine 
* sends a reply to the client. 
* 
* RETURNS: N/A. 
*/</a></b><dd>
 
<b><a name="89871">VOID tcpServerWorkTask 
    ( 
    int                 sFd,            /* server's socket fd */ 
    char *              address,        /* client's socket address */ 
    u_short             port            /* client's socket port */ 
    ) 
    { 
    static char         replyMsg[] = "Server received your message"; 
    ZBUF_ID             zReplyOrig;     /* original reply msg */ 
    ZBUF_ID             zReplyDup;      /* duplicate reply msg */ 
    ZBUF_ID             zRequest;       /* request msg from client */ 
    int                 msgLen;         /* request msg length */ 
    int                 reply;          /* reply requested ? */</a></b><dd>
 
<b><a name="89873">    /* create original reply message zbuf */</a></b><dd>
 
<b><a name="89874">    if ((zReplyOrig = zbufCreate ()) == NULL) 
        { 
        perror ("zbuf create"); 
        free (address);                 /* free malloc from inet_ntoa() */ 
        return; 
        }</a></b><dd>
 
<b><a name="89876">    /* insert reply message into zbuf */</a></b><dd>
 
<b><a name="89877">    if (zbufInsertBuf (zReplyOrig, NULL, 0, replyMsg,  
        sizeof (replyMsg), NULL, 0) == NULL) 
        { 
        perror ("zbuf insert"); 
        zbufDelete (zReplyOrig); 
        free (address);                 /* free malloc from inet_ntoa() */ 
        return; 
        }</a></b><dd>
 
<b><a name="89879">    /* read client request, display message */</a></b><dd>
 
<b><a name="89880">    while ((zRequest = zbufFioSockRecv (sFd, sizeof(struct request))) != NULL) 
        { 
        /* extract reply field into &lt;reply&gt; */</a></b><dd>
 
<b><a name="89882">        (void) zbufExtractCopy (zRequest, NULL, 0, 
            (char *) &amp;reply, sizeof (reply)); 
        (void) zbufCut (zRequest, NULL, 0, sizeof (reply));</a></b><dd>
 
<b><a name="89884">        /* extract msgLen field into &lt;msgLen&gt; */</a></b><dd>
 
<b><a name="89886">        (void) zbufExtractCopy (zRequest, NULL, 0, 
            (char *) &amp;msgLen, sizeof (msgLen)); 
        (void) zbufCut (zRequest, NULL, 0, sizeof (msgLen));</a></b><dd>
 
<b><a name="89888">        /* duplicate reply message zbuf, preserving original */</a></b><dd>
 
<b><a name="89890">        if ((zReplyDup = zbufDup (zReplyOrig, NULL, 0, ZBUF_END)) == NULL) 
            { 
            perror ("zbuf duplicate"); 
            zbufDelete (zRequest); 
            break; 
            }</a></b><dd>
 
<b><a name="89892">        printf ("MESSAGE FROM CLIENT (Internet Address %s, port %d):\n", 
             address, port); 
                           
        /* display request message zbuf */</a></b><dd>
 
<b><a name="89894">        (void) zbufDisplay (zRequest, NULL, 0, msgLen, TRUE); 
        printf ("\n"); 
        if (reply)  
            { 
            if (zbufSockSend (sFd, zReplyDup, sizeof (replyMsg), 0) &lt; 0) 
                perror ("zbufSockSend"); 
            }</a></b><dd>
 
<b><a name="89896">        /* finished with request message zbuf */</a></b><dd>
 
<b><a name="89898">        zbufDelete (zRequest); 
        }</a></b><dd>
 
<b><a name="89900">    free (address);                     /* free malloc from inet_ntoa() */ 
    zbufDelete (zReplyOrig); 
    close (sFd); 
    }</a></b></pre>
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<hr><div class="CalloutCell"><a name="93513"><b class="symbol_UC"><font face="Helvetica, sans-serif" size="-1" class="sans">CAUTION:  </font></b></a>In the interests of brevity, the <b class="symbol_UC">STATUS</b> return values for several zbuf socket calls are discarded with casts to <b class="keyword">void</b>.  In a real application, check these return values for possible errors. </div>
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