Defining the Functions that Implement the Tag

Define the functions that implement the tags in C, using NSAPI. Include the header shtml_public.h, which is in the directory install-dir/include/shtml. Link against the SHTML shared library in the install_-dir/lib directory. On Windows, the SHTML shared library is named sshtml.dll. On UNIX platforms, the library is named libShtml.so or libShtml.sl.

ShtmlTagExecuteFunc is the tag handler which gets called with the NSAPI pblock, Session, and Request variables. In addition, this handler also gets passed the TagUserData created from the result of executing the tag loading and page loading functions, if any such functions are defined for that tag.

The signature for the tag execution function is:

typedef int (*ShtmlTagExecuteFunc)
            (pblock*, Session*, Request*, TagUserData, TagUserData);

Write the body of the tag execution function to generate the output to replace the tag in the .shtml page. Use the net_write NSAPI function, which writes a specified number of bytes to a specified socket from a specified buffer.

For more information about writing NSAPI plug-ins, see Chapter 2, Creating Custom Server Application Functions.

For more information about net_write and other NSAPI functions, see Chapter 6, NSAPI Function and Macro Reference.

The tag execution function must return an int value that indicates whether the server should proceed to the next instruction in obj.conf, which is one of the following:

• REQ_PROCEED — the execution was successful

• REQ_NOACTION — nothing happened

• REQ_ABORTED — an error occurred

• REQ_EXIT — the connection was lost

The other functions you must define for your tag are:

• ShtmlTagInstanceLoad — Called when a page containing the tag is parsed. This function is not called if the page is retrieved from the browser's cache. It serves as a constructor, the result of which is cached and is passed into ShtmlTagExecuteFunc whenever the execution function is called.

• ShtmlTagInstanceUnload — A destructor for cleaning up whatever was created in the ShtmlTagInstanceLoad function. This function gets passed the result that was originally returned from the ShtmlTagInstanceLoad function.

• ShtmlTagPageLoadFunc — Called when a page containing the tag is executed, regardless of whether the page is still in the browser's cache. This function provides a way to make information persistent between occurrences of the same tag on the same page.

• ShtmlTagPageUnLoadFn — Called after a page containing the tag has executed. This function provides a way to clean up any allocations done in a ShtmlTagPageLoadFunc and hence gets passed the result returned from the ShtmlTagPageLoadFunc.

The signature for these functions are:

#define TagUserData void*
typedef TagUserData (*ShtmlTagInstanceLoad)
                    (const char* tag, pblock*, const char*, size_t);
typedef void (*ShtmlTagInstanceUnload)(TagUserData);
typedef int (*ShtmlTagExecuteFunc)
            (pblock*, Session*, Request*, TagUserData, TagUserData);
typedef TagUserData (*ShtmlTagPageLoadFunc)
                    (block* pb, Session*, Request*);
typedef void (*ShtmlTagPageUnLoadFunc)(TagUserData);

      

The following code example implements the HELLO tag:

/*
 * mytag.c: NSAPI functions to implement #HELLO SSI calls
*/
#include "nsapi.h"
#include "shtml/shtml_public.h"
/* FUNCTION : mytag_con
 *
 * DESCRIPTION: ShtmlTagInstanceLoad function
 */
#ifdef __cplusplus
extern "C"
#endif
TagUserData
mytag_con(const char* tag, pblock* pb, const char* c1, size_t t1)
{
    return NULL;
}
/* FUNCTION : mytag_des
 *
 * DESCRIPTION: ShtmlTagInstanceUnload
 */
#ifdef __cplusplus
extern "C"
#endif
void
mytag_des(TagUserData v1)
{
}
/* FUNCTION : mytag_load
 * DESCRIPTION: ShtmlTagPageLoadFunc
 */
#ifdef __cplusplus
extern "C"
#endif
TagUserData
mytag_load(pblock *pb, Session *sn, Request *rq)
{
    return NULL;
}
/* FUNCTION : mytag_unload
 *
 * DESCRIPTION: ShtmlTagPageUnloadFunc
 */
#
#ifdef __cplusplus
extern "C"
#endif
void
mytag_unload(TagUserData v2)
{
}
/* FUNCTION : mytag
    * DESCRIPTION: ShtmlTagExecuteFunc
 */
#ifdef __cplusplus
extern "C"
#endif
int
mytag(pblock* pb, Session* sn, Request* rq, TagUserData t1, TagUserData t2)
{
    char* buf;
    int length;
    char* client;
    buf = (char *) MALLOC(100*sizeof(char));
    length = util_sprintf(buf, "<h1>Hello World! </h1>", client);
    if (net_write(sn->csd, buf, length) == IO_ERROR)
    {
        FREE(buf);
        return REQ_ABORTED;
    }
    FREE(buf);
    return REQ_PROCEED;
}
/* FUNCTION : mytag_init
    * DESCRIPTION: initialization function, calls shtml_add_tag() to
* load new tag
*/
#
#ifdef __cplusplus
extern "C"
#endif
int
mytag_init(pblock* pb, Session* sn, Request* rq)
{
    int retVal = 0;
// NOTE: ALL arguments are required in the shtml_add_tag() function
    retVal = shtml_add_tag("HELLO", mytag_con, mytag_des, mytag, mytag_load, mytag_unload);
return retVal;
}
/* end mytag.c */