C Examples -- Example 3: counter

### Example 3: counter

The following example implements a request function that generates the popular odometer-like page count image. The code is based on the popular odometer.c CGI program available at many archive sites, but because it's loaded directly into the AOLserver it generates the odometer at lightening speed, easily 10x faster!

This example can be found in the `examples/c/counter` directory.

        /*-
         *
         * This code implements an odometer-like page counter extension to the
         * AOLserver.  The code is based on the popular "odometer" CGI
         * by Chris Stephens, stephenc@pcmail.cbil.vcu.edu, and
         * Fred Christiansen, fredch@fc.hp.com (see below).
         *
         * Why use this module instead of the CGI?  By loading the code directly
         * into the AOLserver, you avoid all the painful overhead of CGI.
         * The result is this module is more than 10 times as fast as the CGI!
         * Plus, it compiles and run on all platforms!
         *
         * To use the counter, load the module and insert an image
         * link of the form <IMG SRC="/NS/Counter/my/page.htm">.
         * The NsCounter() function will return a small odometer image of the
         * number of hits to the corresponding page (i.e., /my/page.htm).  The
         * page count is kept in a file prefixed by .odo (i.e., /my/.odo.page.htm).
         *
         * To load this module, add the following to the [ns\server\<vs>\modules]
         * section of your nsd.ini file where <vs> is the name of the
         * server you want to add the counter too:
         *
         * counter=counter.dll    ; or counter.so on Unix platforms
         *
         * This prefix(s) of the count URL can be set with the "UrlPrefix"
         * key in the module's nsd.ini configuration file section (i.e.,
         * [ns\server\<vs>\module\counter]).  The value is a comma separated
         * list of URL prefixes.  For example, if the list includes the
         * "/cnt,/count" prefixes, then any URL which begins with /cnt or
         * /count will be processed by the NsCounter() function.
         *
         * Note: the setup interface in AOLserver 2.0 is open-ended, so you can
         * use it to view/edit these parameters by using the "List AOLserver
         * Configuration Sections"  available from the "Setup Home" page in expert
         * mode
         *
         */

        #include "ns.h"

        #include <errno.h>
        #include <assert.h>
        #include <string.h>
        #ifdef WIN32
        #include <io.h>
        #include <fcntl.h>
        #else
        #include <unistd.h>
        #endif

        #define CONFIG_PREFIX	"UrlPrefix"
        #define DEFAULT_PREFIX	"/cgi-bin/counter,/NS/Counter,/ns/counter"
        #define COUNT_PREFIX	".odo"

        static Ns_OpProc	NsCounter;

        int   Ns_ModuleVersion = 1;

        int
        Ns_ModuleInit(char *hServer, char *hModule)
        {
            char           *configPath;
            char	   *urlPrefix;
            char	   *next;
            Ns_DString	    dsBuf;
            Ns_DString	    dsPath;

            /*
             * Fetch the UrlPrefix from the config file.
             */
            configPath = Ns_ConfigGetPath(hServer, hModule, NULL);
            urlPrefix = Ns_ConfigGetValue(configPath, CONFIG_PREFIX);
            if (urlPrefix == NULL) {
        	urlPrefix = DEFAULT_PREFIX;
            }

            /*
             * Register NsCounter at each of the URL's specified
             * in the comma seperated UrlPrefix list.
             */
            Ns_DStringInit(&dsBuf);
            Ns_DStringInit(&dsPath);
            Ns_DStringAppend(&dsBuf, urlPrefix);
            next = dsBuf.string;

                do {
        	urlPrefix = next;
        	next = strchr(urlPrefix, `,');
        	if (next != NULL) {
        		*next++ = `\0';
        	}
        	if (*urlPrefix != `/') {
        	    Ns_Log(Warning, "%s(%s):  Invalid URL prefix skipped:  %s",
                                                                            hModule, hServer, urlPrefix);
        	} else {
        	    Ns_NormalizePath(&dsPath, urlPrefix);
        	    urlPrefix = Ns_DStringExport(&dsPath);
            	    Ns_RegisterRequest(hServer, "GET", urlPrefix, NsCounter, ns_free,
                                                                            urlPrefix, 0);
        	}
            } while (next != NULL);
                Ns_DStringFree(&dsBuf);
            Ns_DStringFree(&dsPath);

            return NS_OK;
        }

        /*-
        ** Originally count.c, by Chris Stephens, stephenc@pcmail.cbil.vcu.edu, (c)1995.
        ** Code cleaned up and enhanced by Fred Christiansen, fredch@fc.hp.com,
        ** as odometer.c; supports:
        ** - 8 digits instead of 7 (and by changing ODO_DIGITS, up to 10 (number
        **      of digits in an unsigned long))
        */

        #define NL              `\n'		/* new line char */
        #define ODO_DIGITS      8		/* # digits displayed */
        #define BUFSIZE         (ODO_DIGITS+2)	/* 8 digits + NL + nul */
        #define BM_HT           16		/* bitmap height */
        #define BM_WD           8		/* bitmap width */

        static char           *bitmap[] = {
        "0xff", "0xff", "0xff", "0xc3", "0x99", "0x99", "0x99", "0x99",	/* rows 1-8  of 0 */
        "0x99", "0x99", "0x99", "0x99", "0xc3", "0xff", "0xff", "0xff",	/* rows 9-16 of 0 */
        "0xff", "0xff", "0xff", "0xcf", "0xc7", "0xcf", "0xcf", "0xcf",	/* rows 1-8  of 1 */
        "0xcf", "0xcf", "0xcf", "0xcf", "0xcf", "0xff", "0xff", "0xff",	/* rows 9-16 of 1 */
        "0xff", "0xff", "0xff", "0xc3", "0x99", "0x9f", "0x9f", "0xcf",	/* rows 1-8  of 2 */
        "0xe7", "0xf3", "0xf9", "0xf9", "0x81", "0xff", "0xff", "0xff",	/* rows 9-16 of 2 */
        "0xff", "0xff", "0xff", "0xc3", "0x99", "0x9f", "0x9f", "0xc7",	/* rows 1-8  of 3 */
        "0x9f", "0x9f", "0x9f", "0x99", "0xc3", "0xff", "0xff", "0xff",	/* rows 9-16 of 3 */
        "0xff", "0xff", "0xff", "0xcf", "0xcf", "0xc7", "0xc7", "0xcb",	/* rows 1-8  of 4 */
        "0xcb", "0xcd", "0x81", "0xcf", "0x87", "0xff", "0xff", "0xff",	/* rows 9-16 of 4 */
        "0xff", "0xff", "0xff", "0x81", "0xf9", "0xf9", "0xf9", "0xc1",	/* rows 1-8  of 5 */
        "0x9f", "0x9f", "0x9f", "0x99", "0xc3", "0xff", "0xff", "0xff",	/* rows 9-16 of 5 */
        "0xff", "0xff", "0xff", "0xc7", "0xf3", "0xf9", "0xf9", "0xc1",	/* rows 1-8  of 6 */
        "0x99", "0x99", "0x99", "0x99", "0xc3", "0xff", "0xff", "0xff",	/* rows 9-16 of 6 */
        "0xff", "0xff", "0xff", "0x81", "0x99", "0x9f", "0x9f", "0xcf",	/* rows 1-8  of 7 */
        "0xcf", "0xe7", "0xe7", "0xf3", "0xf3", "0xff", "0xff", "0xff",	/* rows 9-16 of 7 */
        "0xff", "0xff", "0xff", "0xc3", "0x99", "0x99", "0x99", "0xc3",	/* rows 1-8  of 8 */
        "0x99", "0x99", "0x99", "0x99", "0xc3", "0xff", "0xff", "0xff",	/* rows 9-16 of 8 */
        "0xff", "0xff", "0xff", "0xc3", "0x99", "0x99", "0x99", "0x99",	/* rows 1-8  of 9 */
        "0x83", "0x9f", "0x9f", "0xcf", "0xe3", "0xff", "0xff", "0xff"	/* rows 9-16 of 9 */
        };

        /*
         * NsCounter -
         *
         * Handle a request of the form "/NS/Counter/my/page.htm" to create an
         * odometer-like count of visits to the /my/page.htm page.
         *
         */
        static int
        NsCounter(void *context, Ns_Conn *conn)
        {
            char            buf[BUFSIZE], dial[ODO_DIGITS];
            unsigned long   cnt;
            int             status, i, l;
            char           *p;
            Ns_DString      ds;
            int		    fd;
            char           *uri;
            char	   *hServer;
            char	   *urlPrefix;
            int		    nPrefix;

            hServer = Ns_ConnServer(conn);
            urlPrefix = (char *) context;

            /*
             * Figure out how many parts are in the
             * prefix, i.e., /NS/Counter has 2 parts.
             */
            nPrefix = 0;
            p = urlPrefix;
            while ((p = strchr(p, `/')) != NULL) {
        	++p;
        	++nPrefix;
            }
            if (conn->request->urlc > nPrefix) {
        	uri = Ns_SkipUrl(conn->request, nPrefix);
            } else {
        	return Ns_ConnReturnBadRequest(conn, "Missing URI");
            }

            /*
             * Convert the URI to the file, sneaking in counter prefix before the last
             * path element.
             */
            Ns_DStringInit(&ds);
            p = strrchr(uri, `/');
            *p = `\0';
            Ns_UrlToFile(&ds, hServer, uri);
            Ns_DStringAppend(&ds, "/");
            Ns_DStringAppend(&ds, COUNT_PREFIX);
            *p++ = `/';
            Ns_DStringAppend(&ds, ".");
            Ns_DStringAppend(&ds, p);

            /*
             * Open (or create) the counter file and increment the page count.
             */
            fd = open(ds.string, O_RDWR | O_CREAT, 0660);
            if (fd < 0) {
        	Ns_Log(Error, "Could not open counter file `%s' for URI `%s':  %s",
        	    ds.string, uri, strerror(errno));
            	Ns_DStringFree(&ds);
        	return Ns_ConnReturnInternalError(conn);
            }
            Ns_DStringFree(&ds);
            i = read(fd, buf, BUFSIZE);
            if (i > 0) {
        	buf[i] = `\0';
        	cnt = strtoul(buf, (char **) NULL, 10);
            } else {
        	cnt = 0;
            }
            lseek(fd, 0, SEEK_SET);
            sprintf(buf, "%u\n", ++cnt);
            write(fd, buf, strlen(buf));
            close(fd);

            /* Calc length (ignoring NL) and copy right-to-left into dial */

            for (l = 0, p = buf; *p != `\0' && *p != NL; l++, p++);
            for (i = 0, p = buf; i < l; i++, p++)
        	dial[ODO_DIGITS - l + i] = *p;
            for (i = 0; i < (ODO_DIGITS - l); i++)	/* backfill with zeros */
        	dial[i] = `0';

            /*
             * Build up the odometer xbm.
             */
            Ns_DStringPrintf(&ds, "#define odo_width  %d\n", (BM_WD * ODO_DIGITS));
            Ns_DStringPrintf(&ds, "#define odo_height %d\n", BM_HT);
            Ns_DStringAppend(&ds, "static char odo_bits[] = {\n");
            for (i = 0; i < BM_HT; i++) {
        	for (l = 0; l < ODO_DIGITS; l++) {
        	    Ns_DStringAppend(&ds, bitmap[(((dial[l] - `0') * BM_HT) + i)]);
        	    Ns_DStringAppend(&ds, ", ");
        	    if (l == 7)
        		Ns_DStringAppend(&ds, "\n");
        	}
        	if (i == 15) {
        	    Ns_DStringAppend(&ds, "};");
        	}
            }
            Ns_DStringAppend(&ds, "\n");

            /*
             * Setup the HTTP headers.
             */
            Ns_ConnSetRequiredHeaders(conn, "image/x-xbitmap", ds.length);
            status = Ns_ConnFlushHeaders(conn, 200);
            if (status == NS_OK) {
        	/*
        	 * Send the bitmap if the headers were sent o.k.
        	 *
        	 * Note that the underlying communications driver may send
        	 * less than the number of bytes requested so we need to
        	 * call Ns_ConnWrite() in a while loop to ensure all the
        	 * bytes are sent.  If the connection is shut down while
        	 * attempting to send, the communication driver returns
        	 * -1 and we set status to NS_ERROR and immediately break
        	 * out of the loop.  Whenever a status other than NS_OK
        	 * is returned from a request function, the AOLserver does
        	 * not run the registered trace functions (trace functions
        	 * are normally used for access logging and you shouldn't
        	 * normally log aborted connections).
        	 *
        	 * Actually, in this trivial case, you could simply use:
        	 *
        	 * 	status = Ns_ConnPuts(conn, ds.string)
        	 *
        	 * which pretty much implements the loop below.
        	 */
        	p = ds.string;
        	i = ds.length;
        	while (i > 0) {
        		cnt = Ns_ConnWrite(conn, p, i);
        		if (cnt < 0) {
        			status = NS_ERROR;
        			break;
        		}
        		i -= cnt;
        		p += cnt;
        	}
            }
            Ns_DStringFree(&ds);
            return status;
        }

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