pbx_functions.c: Manually update ast_str strlen.

When ast_func_read2 is used to read a function using
its read function (as opposed to a native ast_str read2
function), the result is copied directly by the function
into the ast_str buffer. As a result, the ast_str length
remains initialized to 0, which is a bug because this is
not the real string length.

This can cascade and have issues elsewhere, such as when
reading substrings of functions that only register read
as opposed to read2 callbacks. In this case, since reading
ast_str_strlen returns 0, the returned substring is empty
as opposed to the actual substring. This has caused
the ast_str family of functions to behave inconsistently
and erroneously, in contrast to the pbx_variables substitution
functions which work correctly.

This fixes this issue by manually updating the ast_str length
when the result is copied directly into the ast_str buffer.

Additionally, an assertion and a unit test that previously
exposed these issues are added, now that the issue is fixed.

ASTERISK-29966 #close

Change-Id: I4e2dba41410f9d4dff61c995d2ca27718248e07f

main/pbx_functions.c

@@ -678,6 +678,7 @@ int ast_func_read2(struct ast_channel *chan, const char *function, struct ast_st
 				ast_str_make_space(str, maxsize);
 			}
 			res = acfptr->read(chan, copy, args, ast_str_buffer(*str), maxsize);
+			ast_str_update(*str); /* Manually set the string length */
 		}
 		if (acfptr->mod && u) {
 			__ast_module_user_remove(acfptr->mod, u);

main/pbx_variables.c

@@ -40,6 +40,7 @@
 #include "asterisk/paths.h"
 #include "asterisk/pbx.h"
 #include "asterisk/stasis_channels.h"
+#include "asterisk/test.h"
 #include "pbx_private.h"
 
 /*** DOCUMENTATION
@@ -189,6 +190,8 @@ static const char *ast_str_substring(struct ast_str *value, int offset, int leng
 
 	lr = ast_str_strlen(value); /* compute length after copy, so we never go out of the workspace */
 
+	ast_assert(lr == strlen(ast_str_buffer(value))); /* ast_str_strlen should always agree with strlen */
+
 	/* Quick check if no need to do anything */
 	if (offset == 0 && length >= lr)	/* take the whole string */
 		return ast_str_buffer(value);
@@ -1292,6 +1295,74 @@ void pbx_builtin_clear_globals(void)
 	ast_rwlock_unlock(&globalslock);
 }
 
+#ifdef TEST_FRAMEWORK
+AST_TEST_DEFINE(test_variable_substrings)
+{
+	int i, res = AST_TEST_PASS;
+	struct ast_channel *chan; /* dummy channel */
+	struct ast_str *str; /* fancy string for holding comparing value */
+
+	const char *test_strings[][5] = {
+		{"somevaluehere", "CALLERID(num):0:25", "somevaluehere"},
+		{"somevaluehere", "CALLERID(num):0:5", "somev"},
+		{"somevaluehere", "CALLERID(num):4:5", "value"},
+		{"somevaluehere", "CALLERID(num):0:-4", "somevalue"},
+		{"somevaluehere", "CALLERID(num):-4", "here"},
+	};
+
+	switch (cmd) {
+	case TEST_INIT:
+		info->name = "variable_substrings";
+		info->category = "/main/pbx/";
+		info->summary = "Test variable substring resolution";
+		info->description = "Verify that variable substrings are calculated correctly";
+		return AST_TEST_NOT_RUN;
+	case TEST_EXECUTE:
+		break;
+	}
+
+	if (!(chan = ast_dummy_channel_alloc())) {
+		ast_test_status_update(test, "Unable to allocate dummy channel\n");
+		return AST_TEST_FAIL;
+	}
+
+	if (!(str = ast_str_create(64))) {
+		ast_test_status_update(test, "Unable to allocate dynamic string buffer\n");
+		ast_channel_release(chan);
+		return AST_TEST_FAIL;
+	}
+
+	for (i = 0; i < ARRAY_LEN(test_strings); i++) {
+		char substituted[512], tmp[512] = "";
+
+		ast_set_callerid(chan, test_strings[i][0], NULL, test_strings[i][0]);
+
+		snprintf(tmp, sizeof(tmp), "${%s}", test_strings[i][1]);
+
+		/* test ast_str_substitute_variables */
+		ast_str_substitute_variables(&str, 0, chan, tmp);
+		ast_debug(1, "Comparing STR %s with %s\n", ast_str_buffer(str), test_strings[i][2]);
+		if (strcmp(test_strings[i][2], ast_str_buffer(str))) {
+			ast_test_status_update(test, "Format string '%s' substituted to '%s' using str sub.  Expected '%s'.\n", test_strings[i][0], ast_str_buffer(str), test_strings[i][2]);
+			res = AST_TEST_FAIL;
+		}
+
+		/* test pbx_substitute_variables_helper */
+		pbx_substitute_variables_helper(chan, tmp, substituted, sizeof(substituted) - 1);
+		ast_debug(1, "Comparing PBX %s with %s\n", substituted, test_strings[i][2]);
+		if (strcmp(test_strings[i][2], substituted)) {
+			ast_test_status_update(test, "Format string '%s' substituted to '%s' using pbx sub.  Expected '%s'.\n", test_strings[i][0], substituted, test_strings[i][2]);
+			res = AST_TEST_FAIL;
+		}
+	}
+	ast_free(str);
+
+	ast_channel_release(chan);
+
+	return res;
+}
+#endif
+
 static struct ast_cli_entry vars_cli[] = {
 	AST_CLI_DEFINE(handle_show_globals, "Show global dialplan variables"),
 	AST_CLI_DEFINE(handle_show_chanvar, "Show channel variables"),
@@ -1306,6 +1377,7 @@ static void unload_pbx_variables(void)
 	ast_unregister_application("Set");
 	ast_unregister_application("MSet");
 	pbx_builtin_clear_globals();
+	AST_TEST_UNREGISTER(test_variable_substrings);
 }
 
 int load_pbx_variables(void)
@@ -1316,6 +1388,7 @@ int load_pbx_variables(void)
 	res |= ast_register_application2("Set", pbx_builtin_setvar, NULL, NULL, NULL);
 	res |= ast_register_application2("MSet", pbx_builtin_setvar_multiple, NULL, NULL, NULL);
 	ast_register_cleanup(unload_pbx_variables);
+	AST_TEST_REGISTER(test_variable_substrings);
 
 	return res;
 }