Add a wrapper around vstr_add_fmt() to avoid having to link libcharon against libvstr

At least on Android the latter would be required.

src/libstrongswan/printf_hook.c

@@ -237,6 +237,21 @@ static inline Vstr_conf *get_vstr_conf()
 	return conf;
 }
 
+/**
+ * Described in header
+ */
+size_t vstr_print_in_hook(struct Vstr_base *base, size_t pos, const char *fmt,
+						  ...)
+{
+	va_list args;
+	int written;
+
+	va_start(args, fmt);
+	written = vstr_add_vfmt(base, pos, fmt, args);
+	va_end(args);
+	return written;
+}
+
 /**
  * Wrapper functions for printf and alike
  */

src/libstrongswan/printf_hook.h

@@ -61,7 +61,7 @@ struct printf_hook_data_t {
  * Helper macro to be used in printf hook callbacks.
  */
 #define print_in_hook(data, fmt, ...) ({\
-	int _written = fprintf(data->stream, fmt, ##__VA_ARGS__);\
+	ssize_t _written = fprintf(data->stream, fmt, ##__VA_ARGS__);\
 	if (_written < 0)\
 	{\
 		_written = 0;\
@@ -156,11 +156,25 @@ struct printf_hook_data_t {
 	size_t pos;
 };
 
+/**
+ * Wrapper around vstr_add_vfmt(), avoids having to link all users of
+ * print_in_hook() against libvstr.
+ *
+ * @param base		Vstr_string to add string to
+ * @param pos		position to write to
+ * @param fmt		format string
+ * @param ...		arguments
+ * @return			number of characters written
+ */
+size_t vstr_print_in_hook(struct Vstr_base *base, size_t pos, const char *fmt,
+						  ...);
+
 /**
  * Helper macro to be used in printf hook callbacks.
  */
 #define print_in_hook(data, fmt, ...) ({\
-	int _written =  vstr_add_fmt(data->base, data->pos, fmt, ##__VA_ARGS__);\
+	size_t _written; \
+	_written = vstr_print_in_hook(data->base, data->pos, fmt, ##__VA_ARGS__);\
 	data->pos += _written;\
 	_written;\
 })