Re: [Rd] R as shared library

Byron Ellis Fri, 20 Aug 2004 11:33:07 -0700

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 ([EMAIL PROTECTED])
"Oook" -- The Librarian

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Re: [Rd] R as shared library

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