func_odbc: Add SQL_ESC_BACKSLASHES dialplan function.

Some databases depending on their configuration using backslashes
for escaping. When combined with the use of ' this can result in
a broken func_odbc query.

This change adds a SQL_ESC_BACKSLASHES dialplan function which can
be used to escape the backslashes.

This is done as a dialplan function instead of being always done
as some databases do not require this, and always doing it would
result in incorrect data being put into the database.

ASTERISK-29838

Change-Id: I152bf34899b96ddb09cca3e767254d8d78f0c83d

configs/samples/func_odbc.conf.sample

@@ -36,6 +36,10 @@
 ; to use the dialplan function SQL_ESC() to escape the data prior to its
 ; inclusion in the SQL statement.
 ;
+; If you have data which may potentially contain backslashes, you may wish to
+; use the dialplan function SQL_ESC_BACKSLASHES() to escape the backslashes.
+; Note that not all databases may require escaping of the backslashes.
+;
 ;
 ; The following options are available in this configuration file:
 ;

doc/CHANGES-staging/func_odbc_esc_backslashes.txt

@@ -0,0 +1,7 @@
+Subject: func_odbc
+
+A SQL_ESC_BACKSLASHES dialplan function has been added which
+escapes backslashes. Usage of this is dependent on whether the
+database in use can use backslashes to escape ticks or not. If
+it can, then usage of this prevents a broken SQL query depending
+on how the SQL query is constructed.

funcs/func_odbc.c

@@ -96,6 +96,19 @@
 			<para>Example: SELECT foo FROM bar WHERE baz='${SQL_ESC(${ARG1})}'</para>
 		</description>
 	</function>
+	<function name="SQL_ESC_BACKSLASHES" language="en_US">
+		<synopsis>
+			Escapes backslashes for use in SQL statements.
+		</synopsis>
+		<syntax>
+			<parameter name="string" required="true" />
+		</syntax>
+		<description>
+			<para>Used in SQL templates to escape data which may contain backslashes
+			<literal>\</literal> which are otherwise used to escape data.</para>
+			<para>Example: SELECT foo FROM bar WHERE baz='${SQL_ESC(${SQL_ESC_BACKSLASHES(${ARG1})})}'</para>
+		</description>
+	</function>
  ***/
 
 static char *config = "func_odbc.conf";
@@ -1102,13 +1115,13 @@ end_acf_read:
 	return 0;
 }
 
-static int acf_escape(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
+static int acf_escape(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len, char character)
 {
 	char *out = buf;
 
 	for (; *data && out - buf < len; data++) {
-		if (*data == '\'') {
-			*out = '\'';
+		if (*data == character) {
+			*out = character;
 			out++;
 		}
 		*out++ = *data;
@@ -1118,9 +1131,25 @@ static int acf_escape(struct ast_channel *chan, const char *cmd, char *data, cha
 	return 0;
 }
 
+static int acf_escape_ticks(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
+{
+	return acf_escape(chan, cmd, data, buf, len, '\'');
+}
+
 static struct ast_custom_function escape_function = {
 	.name = "SQL_ESC",
-	.read = acf_escape,
+	.read = acf_escape_ticks,
+	.write = NULL,
+};
+
+static int acf_escape_backslashes(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
+{
+	return acf_escape(chan, cmd, data, buf, len, '\\');
+}
+
+static struct ast_custom_function escape_backslashes_function = {
+	.name = "SQL_ESC_BACKSLASHES",
+	.read = acf_escape_backslashes,
 	.write = NULL,
 };
 
@@ -1858,6 +1887,7 @@ static int load_module(void)
 
 	ast_config_destroy(cfg);
 	res |= ast_custom_function_register(&escape_function);
+	res |= ast_custom_function_register(&escape_backslashes_function);
 	ast_cli_register_multiple(cli_func_odbc, ARRAY_LEN(cli_func_odbc));
 
 	AST_RWLIST_UNLOCK(&queries);
@@ -1877,6 +1907,7 @@ static int unload_module(void)
 	}
 
 	res |= ast_custom_function_unregister(&escape_function);
+	res |= ast_custom_function_unregister(&escape_backslashes_function);
 	res |= ast_custom_function_unregister(&fetch_function);
 	res |= ast_unregister_application(app_odbcfinish);
 	ast_cli_unregister_multiple(cli_func_odbc, ARRAY_LEN(cli_func_odbc));