[Rd] R as shared library

[Byron Ellis]

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 :-))

On Aug 18, 2004, at 1:08 PM, Jeffrey Horner wrote:

> 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
>
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>
---
Byron Ellis (bellis at hsph.harvard.edu)
"Oook" -- The Librarian