Add ns_plugin_expandpath()

Implement a helper function which, given an input string:

  - copies it verbatim if it contains at least one path separator,
  - prepends the named plugin installation directory to it otherwise.

This function will allow configuration parsing code to conveniently
determine the full path to a plugin module given either a path or a
filename.

While other, simpler ways exist for making sure filenames passed to
dlopen() cause the latter to look for shared objects in a specific
directory, they are very platform-specific.  Using full paths is thus
likely the most portable and reliable solution.

Also added unit tests for ns_plugin_expandpath() to ensure it behaves
as expected for absolute paths, relative paths, and filenames, for
various target buffer sizes.

(Note: plugins share a directory with named on Windows; there is no
default plugin path. Therefore the source path is copied to the
destination path with no modification.)

lib/ns/tests/plugin_test.c

@@ -0,0 +1,205 @@
+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+#include <config.h>
+
+#if HAVE_CMOCKA
+
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <setjmp.h>
+
+#define UNIT_TESTING
+#include <cmocka.h>
+
+#include <limits.h>
+#include <stdbool.h>
+#include <string.h>
+
+#include <isc/mem.h>
+#include <isc/result.h>
+#include <isc/types.h>
+#include <isc/util.h>
+
+#include <ns/hooks.h>
+
+#include "nstest.h"
+
+static int
+_setup(void **state) {
+	isc_result_t result;
+
+	UNUSED(state);
+
+	result = ns_test_begin(NULL, false);
+	assert_int_equal(result, ISC_R_SUCCESS);
+
+	return (0);
+}
+
+static int
+_teardown(void **state) {
+	if (*state != NULL) {
+		isc_mem_free(mctx, *state);
+	}
+
+	ns_test_end();
+
+	return (0);
+}
+
+/*%
+ * Structure containing parameters for run_full_path_test().
+ */
+typedef struct {
+	const ns_test_id_t id;	/* libns test identifier */
+	const char *input;	/* source string - plugin name or path */
+	size_t output_size;	/* size of target char array to allocate */
+	isc_result_t result;	/* expected return value */
+	const char *output;	/* expected output string */
+} ns_plugin_expandpath_test_params_t;
+
+/*%
+ * Perform a single ns_plugin_expandpath() check using given parameters.
+ */
+static void
+run_full_path_test(const ns_plugin_expandpath_test_params_t *test,
+		   void **state)
+{
+	char **target = (char **)state;
+	isc_result_t result;
+
+	REQUIRE(test != NULL);
+	REQUIRE(test->id.description != NULL);
+	REQUIRE(test->input != NULL);
+	REQUIRE(test->result != ISC_R_SUCCESS || test->output != NULL);
+
+	/*
+	 * Prepare a target buffer of given size.  Store it in 'state' so that
+	 * it can get cleaned up by _teardown() if the test fails.
+	 */
+	*target = isc_mem_allocate(mctx, test->output_size);
+
+	/*
+	 * Call ns_plugin_expandpath().
+	 */
+	result = ns_plugin_expandpath(test->input,
+					 *target, test->output_size);
+
+	/*
+	 * Check return value.
+	 */
+	if (result != test->result) {
+		fail_msg("# test \"%s\" on line %d: "
+			 "expected result %d (%s), got %d (%s)",
+			 test->id.description, test->id.lineno,
+			 test->result, isc_result_totext(test->result),
+			 result, isc_result_totext(result));
+	}
+
+	/*
+	 * Check output string if return value indicates success.
+	 */
+	if (result == ISC_R_SUCCESS && strcmp(*target, test->output) != 0) {
+		fail_msg("# test \"%s\" on line %d: "
+			 "expected output \"%s\", got \"%s\"",
+			 test->id.description, test->id.lineno,
+			 test->output, *target);
+	}
+
+	isc_mem_free(mctx, *target);
+}
+
+/* test ns_plugin_expandpath() */
+static void
+ns_plugin_expandpath_test(void **state) {
+	size_t i;
+
+	const ns_plugin_expandpath_test_params_t tests[] = {
+		{
+			NS_TEST_ID("correct use with an absolute path"),
+			.input = "/usr/lib/named/foo.so",
+			.output_size = PATH_MAX,
+			.result = ISC_R_SUCCESS,
+			.output = "/usr/lib/named/foo.so",
+		},
+		{
+			NS_TEST_ID("correct use with a relative path"),
+			.input = "../../foo.so",
+			.output_size = PATH_MAX,
+			.result = ISC_R_SUCCESS,
+			.output = "../../foo.so",
+		},
+		{
+			NS_TEST_ID("correct use with a filename"),
+			.input = "foo.so",
+			.output_size = PATH_MAX,
+			.result = ISC_R_SUCCESS,
+#ifndef WIN32
+			.output = NAMED_PLUGINDIR "/foo.so",
+#else
+			.output = "foo.so",
+#endif
+		},
+		{
+			NS_TEST_ID("no space at all in target buffer"),
+			.input = "/usr/lib/named/foo.so",
+			.output_size = 0,
+			.result = ISC_R_NOSPACE,
+		},
+		{
+			NS_TEST_ID("target buffer too small to fit input"),
+			.input = "/usr/lib/named/foo.so",
+			.output_size = 1,
+			.result = ISC_R_NOSPACE,
+		},
+		{
+			NS_TEST_ID("target buffer too small to fit NULL byte"),
+			.input = "/foo.so",
+			.output_size = 7,
+			.result = ISC_R_NOSPACE,
+		},
+#ifndef WIN32
+		{
+			NS_TEST_ID("target buffer too small to fit full path"),
+			.input = "foo.so",
+			.output_size = 7,
+			.result = ISC_R_NOSPACE,
+		},
+#endif
+	};
+
+	for (i = 0; i < sizeof(tests) / sizeof(tests[0]); i++) {
+		run_full_path_test(&tests[i], state);
+	}
+}
+
+int
+main(void) {
+	const struct CMUnitTest tests[] = {
+		cmocka_unit_test_setup_teardown(ns_plugin_expandpath_test,
+						_setup, _teardown),
+	};
+
+	return (cmocka_run_group_tests(tests, NULL, NULL));
+}
+#else /* HAVE_CMOCKA */
+
+#include <stdio.h>
+
+int
+main(void) {
+	printf("1..0 # Skipped: cmocka not available\n");
+	return (0);
+}
+
+#endif