Details
Major Description
QUESTION: How can I trigger my C code and set variable in response header BUT still retain original Response body which server is generating for client.
Requirement: Write custom Apache module to read POST request body >> Take out data from request body >> Set particular response header attribute using request body >> Send response back to client
Details: I am using Apache as proxy for my ElasticSearch. I have successfully developed Apache Module in C and added it to httpd.conf. I have used "SetHandler" directive to trigger my custom C code.
It is all working fine. Request generated from client browser is going through my custom C Apache Module and in my C code, I am able to read POST request body from request_rec. I am also able to set response header with that value I am readying from request body.
Issue: If I invoke my module/code using SetHandler, when it comes out it does not have any response body and blank response body is sent to client browser. Where as when I disable my module/code, response is well generated a sent to client. So looks like by using SetHandler, response is lost.
My config/code are below:
1. httpd.conf
LoadModule example_module /usr/lib64/httpd/modules/mycustommodule.so
<VirtualHost HOSTNAME:80>
<Location /elasticsearch/_msearch>
#SetHandler readbody-handler #calling my custom module
</Location>
#My KIBANA application is running on 5601 on same machine
ProxyPass / http://localhost:5601/
ProxyPassReverse / http://localhost:5601/
</VirtualHost>
2. My custom C module
module AP_MODULE_DECLARE_DATA readbody_module = {
STANDARD20_MODULE_STUFF,
NULL, /*Per-directory configuration handler */
NULL, /*Merge handler for per-directory configurations */
NULL, /*Per-server configuration handler */
NULL, /*Merge handler for per-server configurations */
NULL,
regiter_hooks /*Our hook registering function */
};
static void register_hooks(apr_pool_t *pool)
{
ap_hook_handler(readbody_handler, NULL, NULL, -10);
}
static int readbody_handler(request_rec *r)
{
const char *buffer;
if (!r->handler || strcmp(r->handler, "readbody-handler")) return (DECLINED);
if (util_read(r, &buffer) == OK) //reading the body and assigning it into buffer
{
char s[2] = ":";
char s2[2] = "\"";
char *indexname;
indexname = strtok(buffer, s);
indexname = strtok(NULL, s);
indexname = strtok(indexname, s2);
indexname = strtok(NULL, s2);
apr_table_setn(r->headers_out, "IndexPattern", indexname); //setting up response header
}
return OK;
}
static int util_read(request_rec *r, const char **rbuf)
{
int rc;
if ((rc = ap_setup_client_block(r, REQUEST_CHUNKED_ERROR)) != OK)
{
return rc;
}
if (ap_should_client_block(r))
{
char argsbuffer[HUGE_STRING_LEN];
int rsize, len_read, rpos = 0;
long length = r->remaining;
*rbuf = apr_pcalloc(r->pool, length + 1);
while ((len_read = ap_get_client_block(r, argsbuffer, sizeof(argsbuffer))) > 0)
{
if ((rpos + len_read) > length)
{
rsize = length - rpos;
}
else
{
rsize = len_read;
}
memcpy((char*) *rbuf + rpos, argsbuffer, rsize);
rpos += rsize;
}
}
}
return rc;