Add H5PLget and use it to set the plugin path on load

R/H5PL.R

@@ -8,4 +8,18 @@ H5PLprepend <- function(path) {
 H5PLsize <- function() {
   size <- .Call("_H5PLsize", PACKAGE = 'rhdf5')
   return(size)
+}
+
+H5PLget <- function(index) {
+  path <- .Call("_H5PLget", as.integer(index-1), PACKAGE = "rhdf5")
+  return(path)
+}
+
+h5getPluginPaths <- function() {
+
+  n_paths <- H5PLsize()
+  paths <- vapply(seq_len(n_paths), 
+                  FUN = H5PLget, 
+                  FUN.VALUE = character(1))
+  return(paths)
 }

R/zzz.R

@@ -2,4 +2,10 @@
 .onLoad <- function(libname, pkgname) {
   h5constants <<- H5loadConstants()
   h5errorHandling()
+
+  if(requireNamespace('rhdf5filters')) {
+    plugin_path <- rhdf5filters::hdf5_plugin_path()
+    H5PLprepend(plugin_path)
+  }
+
 }

src/H5PL.c

@@ -14,21 +14,38 @@ SEXP _H5PLprepend( SEXP _search_path ) {
   res = H5PLprepend(search_path);
 
   if(res < 0) {
-    error("Unable to prepend value to plugin search path");
+    error("Unable to prepend value to plugin search path\n");
   }
 
   SEXP Rval = ScalarLogical(1);
   return Rval;
 }
 
+/* ssize_t H5PLget	(	unsigned int index, char *path_buf, size_t 	buf_size ) */
+SEXP _H5PLget( SEXP index ) {
+
+  int i = asInteger(index);
+  char buf[512];
+  SEXP Rval;
+
+  if(H5PLget(i, buf, 512) < 0) {
+    error("Unable to read plugin path position\n");
+  }
+
+  PROTECT(Rval = mkString(buf));
+  UNPROTECT(1);
+  return Rval;
+}
+
+
 /* herr_t H5PLsize	(	unsigned int * 	num_paths	) */
 SEXP _H5PLsize() {
 
   SEXP Rval;
   unsigned int nvals = 0;
 
   if(H5PLsize( &nvals ) < 0 ) {
-    error("Unable to prepend value to plugin search path");
+    error("Unable to determine size of the plugin path\n");
   }
 
   if(nvals <= INT32_MAX) {

src/H5PL.h

@@ -10,5 +10,6 @@
 
 SEXP _H5PLprepend( SEXP _search_path );
 SEXP _H5PLsize();
+SEXP _H5PLget( SEXP index );
 
 #endif

src/wrap.c

@@ -338,6 +338,7 @@ static R_CallMethodDef libraryRCalls[] = {
   {"_h5getEnumValues", (DL_FUNC) &_h5getEnumValues, 1},
   {"_H5PLprepend", (DL_FUNC) &_H5PLprepend, 1},
   {"_H5PLsize", (DL_FUNC) &_H5PLsize, 0},
+  {"_H5PLget", (DL_FUNC) &_H5PLget, 1},
 #ifdef _H5P_filters
   {"_H5Pset_lzf", (DL_FUNC) &_H5Pset_lzf, 2},
   {"_H5Pset_bzip2", (DL_FUNC) &_H5Pset_bzip2, 2},