Sample file

default.vcl

backend default {
        .host = "127.0.0.1";
        .port = "80";
}

// Intialization
C{
        #include "/usr/src/wurfl/wurfl.h"
        int  is_mobile;
}C

// simple subroutine that fetches the useragent, checks if its a mobile device and
// sets the backend-request header accordingly
sub detectmobile {
C{
        char *ua = VRT_GetHdr(sp, HDR_REQ, "\013User-Agent:");
        is_mobile = wurfl_ismobile(ua);
        VRT_SetHdr(sp, HDR_BEREQ, "\011X-Mobile:", (is_mobile == 1)?"yes":"no", vrt_magic_string_end);
}C
}

// Miss, pass and pipe all make a request to the backend
sub vcl_miss {
        call detectmobile;
        return(fetch);
}
sub vcl_pipe {
        call detectmobile;
        return(pipe);
}
sub vcl_pass {
        call detectmobile;
        return(pass);
}


// Deliver sets the header to the response to the client as well
sub vcl_deliver {
C{
        VRT_SetHdr(sp, HDR_RESP, "\011X-Mobile:", (is_mobile == 1)?"yes":"no", vrt_magic_string_end);
}C
}

hello.php

<?php
  if ($_SERVER['HTTP_X_MOBILE'] == "yes") {
        print "Hello mobile!";
  } else {
        print "Hello!";
 }


print "<pre>";
print_r ($_SERVER);

wurfl.c

#include <string.h>
#include <libxml/parser.h>
#include <libxml/tree.h>
#include <libxml/xpath.h>
#include <libxml/xpathInternals.h>
#include "wurfl.h"

xmlDoc *doc = NULL;

// Load document
int wurfl_init(char *filename) {
        doc = xmlReadFile(filename, NULL, 0);
        return (doc != NULL);
}

int wurfl_ismobile(char *useragent) {
        xmlXPathContextPtr xpathCtx;
        xmlXPathObjectPtr xpathObj;

        // Lazy loading. Varnish does not support an init() function
        if (doc == NULL) wurfl_init("/etc/wurfl.xml");


        // Create new context
        xpathCtx = xmlXPathNewContext(doc);
        if (xpathCtx == NULL) return -1;

        // Create xpath expression
        char *expr = malloc(strlen(useragent) + 40);
        sprintf(expr, "//devices/device[@user_agent='%s']", (unsigned char *)useragent);
        xpathObj = xmlXPathEvalExpression(expr, xpathCtx);
        free(expr);

        // Nothing found?
        if (xpathObj == NULL) {
                xmlXPathFreeContext(xpathCtx);
                return -2;
        }

        // Fetch the number of nodes found
        xmlNodeSetPtr nodes = xpathObj->nodesetval;
        int size = (nodes) ? nodes->nodeNr : 0;

        // Something has been found...
        xmlXPathFreeObject(xpathObj);
        xmlXPathFreeContext(xpathCtx);
        return (size > 0);
}

wurfl.h

#ifndef __WURFL_H__
#define __WURFL_H__

int wurfl_ismobile(char *useragent);

#endif // __WURFL_H__