R as shared library

Hello folks,

I'm embarking on a project to embed R into the Apache web server, and 
I'd like your help. Currently, I'm looking for a way for R code to 
call back into a shared library from which the R shared library was 
loaded.

Essentially, apache starts and loads mod_R.so which runs an 
initialization routine which calls  Rf_initEmbeddedR() and the 
following code:

 /* override to call apache library write routine */
 ptr_R_WriteConsole = Rapache_WriteConsole;

 /* load source(). I assume this is appropriate. I could
    always move this to the code that handles the requst */
 PROTECT(R_source_fun = allocVector(LANGSXP, 2));
 SETCAR(R_source_fun, Rf_install("source"));
 SETCAR(CDR(R_source_fun), R_source_arg = NEW_CHARACTER(1));

Then each request is serviced by the following code:

 /* r is apache request, r->filename is url translated to
    apsolute path to filename */
 SET_STRING_ELT(R_source_arg, 0, COPY_TO_USER_STRING(r->filename));
 errorOccurred=1;
 /* R code: source(filename) */
 val = R_tryEval(R_source_fun,NULL,&errorOccurred);
 if (errorOccurred){
   // Send a message to stderr (apache redirects this to the error log)
   fprintf(stderr,"apache2_mod_R: source(%s) failed!\n",r->filename);
   fflush(stderr);
 } else {
   return ok;
 }

I would like to write R routines which hook into apache specific 
library calls to get at the CGI and system data. The apache specific 
calls need a request structure (the r variable) which is available in 
mod_R.so (already loaded) on each request. If I use the .C, .Call, or 
.External interface, then I must load a shared library with the 
appropriate routines. I would like to place those routines in mod_R.so 
to take advantage of access to the request structure. Is this doable?

Another approach is to turn the CGI data into R variables and just 
place those in the top level environment, foregoing any callbacks into 
apache again until the R code has run to completion. This is similar 
to how PHP is embedded into Apache. Other languages that _do_ provide 
callbacks into apache include Perl, Python, and Ruby.


-- 
Jeffrey Horner       Computer Systems Analyst         School of 
Medicine
615-322-8606         Department of Biostatistics   Vanderbilt 
University

Building the callbacks is possible. Basically, you need to construct a 
fake DllInfo object for Apache and then use R_registerRoutines to attach 
the callbacks to R as it if were a normal R package registering its 
routines.

I might have a simple example of this lying around, I'll see if I can 
find it (especially since it seems I'll be needing it myself soon :-))