Add utility functions.

ogr_fdw_version() to return fdw and GDAL versions
ogr_fdw_drivers() to return array of driver names
Closes #196

META.json

@@ -2,7 +2,7 @@
    "name": "ogr_fdw",
    "abstract": "OGR foreign data wrapper",
    "description": "OGR FDW allows you to connect to any OGR supported data source.",
-   "version": "1.0.9",
+   "version": "1.1.0",
    "maintainer": [
       "Paul Ramsey <[email protected]>"
    ],
@@ -21,9 +21,9 @@
    },
    "provides": {
      "ogr_fdw": {
-       "file": "ogr_fdw--1.0.sql",
+       "file": "ogr_fdw--1.1.sql",
        "docfile": "README.md",
-       "version": "1.0.9",
+       "version": "1.1.0",
        "abstract": "OGR FDW wrapper"
      }
    },

Makefile

@@ -1,7 +1,14 @@
 # ogr_fdw/Makefile
 
 MODULE_big = ogr_fdw
-OBJS = ogr_fdw.o ogr_fdw_deparse.o ogr_fdw_common.o stringbuffer_pg.o
+
+OBJS = \
+	ogr_fdw.o \
+	ogr_fdw_deparse.o \
+	ogr_fdw_common.o \
+	ogr_fdw_func.o \
+	stringbuffer_pg.o
+
 EXTENSION = ogr_fdw
 DATA = ogr_fdw--1.0.sql
 

README.md

@@ -424,3 +424,16 @@ ALTER SERVER myserver_latin1
   );
 ```
 
+### Utility Functions
+
+To view the current FDW and GDAL version.
+
+```sql
+SELECT ogr_fdw_version();
+```
+
+To view the drivers supported by this GDAL.
+
+```sql
+SELECT unnest(ogr_fdw_drivers());
+```

ogr_fdw--1.0--1.1.sql

@@ -0,0 +1,13 @@
+CREATE OR REPLACE FUNCTION ogr_fdw_version()
+	RETURNS text
+	AS 'MODULE_PATHNAME', 'ogr_fdw_version'
+	LANGUAGE 'c'
+	IMMUTABLE STRICT
+	PARALLEL SAFE;
+
+CREATE OR REPLACE FUNCTION ogr_fdw_drivers()
+	RETURNS text[]
+	AS 'MODULE_PATHNAME', 'ogr_fdw_drivers'
+	LANGUAGE 'c'
+	IMMUTABLE STRICT
+	PARALLEL SAFE;

ogr_fdw--1.1.sql

@@ -0,0 +1,32 @@
+/* ogr_fdw/ogr_fdw--1.1.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION ogr_fdw" to load this file. \quit
+
+CREATE FUNCTION ogr_fdw_handler()
+	RETURNS fdw_handler
+	AS 'MODULE_PATHNAME'
+	LANGUAGE 'c' STRICT;
+
+CREATE FUNCTION ogr_fdw_validator(text[], oid)
+	RETURNS void
+	AS 'MODULE_PATHNAME'
+	LANGUAGE 'c' STRICT;
+
+CREATE FOREIGN DATA WRAPPER ogr_fdw
+	HANDLER ogr_fdw_handler
+	VALIDATOR ogr_fdw_validator;
+
+CREATE OR REPLACE FUNCTION ogr_fdw_version()
+	RETURNS text
+	AS 'MODULE_PATHNAME', 'ogr_fdw_version'
+	LANGUAGE 'c'
+	IMMUTABLE STRICT
+	PARALLEL SAFE;
+
+CREATE OR REPLACE FUNCTION ogr_fdw_drivers()
+	RETURNS text[]
+	AS 'MODULE_PATHNAME', 'ogr_fdw_drivers'
+	LANGUAGE 'c'
+	IMMUTABLE STRICT
+	PARALLEL SAFE;

ogr_fdw.control

@@ -1,5 +1,5 @@
 # ogr_fdw extension
 comment = 'foreign-data wrapper for GIS data access'
-default_version = '1.0'
+default_version = '1.1'
 module_pathname = '$libdir/ogr_fdw'
 relocatable = true

ogr_fdw.h

@@ -11,6 +11,8 @@
 #ifndef _OGR_FDW_H
 #define _OGR_FDW_H 1
 
+#define OGR_FDW_RELEASE_NAME "1.1"
+
 /*
  * PostgreSQL
  */

ogr_fdw_func.c

@@ -0,0 +1,77 @@
+
+/*-------------------------------------------------------------------------
+ *
+ * ogr_fdw_func.c
+ *          Helper functions for OGR FDW
+ *
+ * Copyright (c) 2020, Paul Ramsey <[email protected]>
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "ogr_fdw.h"
+#include "ogr_fdw_gdal.h"
+
+#include <postgres.h>
+#include <fmgr.h>
+#include <funcapi.h>
+#include <catalog/pg_type_d.h>
+#include <utils/array.h>
+#include <utils/builtins.h>
+
+
+/**
+*/
+Datum ogr_fdw_drivers(PG_FUNCTION_ARGS);
+PG_FUNCTION_INFO_V1(ogr_fdw_drivers);
+Datum ogr_fdw_drivers(PG_FUNCTION_ARGS)
+{
+
+	/* Array building */
+	size_t arr_nelems = 0;
+	Datum *arr_elems;
+	ArrayType *arr;
+	Oid elem_type = TEXTOID;
+	int16 elem_len;
+	bool elem_byval;
+	char elem_align;
+	int num_drivers;
+
+	if (GDALGetDriverCount() <= 0)
+		GDALAllRegister();
+
+	num_drivers = GDALGetDriverCount();
+	if (num_drivers < 1)
+		PG_RETURN_NULL();
+
+ 	arr_elems = palloc0(num_drivers * sizeof(Datum));
+    get_typlenbyvalalign(elem_type, &elem_len, &elem_byval, &elem_align);
+
+	for (int i = 0; i < num_drivers; i++) {
+		GDALDriverH hDriver = GDALGetDriver(i);
+		if (GDALGetMetadataItem(hDriver, GDAL_DCAP_VECTOR, NULL) != NULL) {
+			const char *strName = OGR_Dr_GetName(hDriver);
+			text *txtName = cstring_to_text(strName);
+			arr_elems[arr_nelems++] = PointerGetDatum(txtName);
+		}
+	}
+
+	arr = construct_array(arr_elems, arr_nelems, elem_type, elem_len, elem_byval, elem_align);
+	PG_RETURN_ARRAYTYPE_P(arr);
+}
+
+/**
+*/
+Datum ogr_fdw_version(PG_FUNCTION_ARGS);
+PG_FUNCTION_INFO_V1(ogr_fdw_version);
+Datum ogr_fdw_version(PG_FUNCTION_ARGS)
+{
+	const char *gdal_ver = GDAL_RELEASE_NAME;
+	const char *ogr_fdw_ver = OGR_FDW_RELEASE_NAME;
+	char ver_str[256];
+	snprintf(ver_str, sizeof(ver_str), "OGR_FDW=\"%s\" GDAL=\"%s\"", ogr_fdw_ver, gdal_ver);
+	text* ver_txt = cstring_to_text(ver_str);
+	PG_RETURN_TEXT_P(ver_txt);
+}
+
+