Stefan Fuhrmann <[email protected]> writes: + * Special files like STDIN will have no flags set at all. In that case, + * we can't filter and must allow any operation - which may then fail at + * the APR level further down the stack. + */ + apr_uint32_t flags = apr_file_flags_get(file); + svn_boolean_t supports_read = (flags == 0) || (flags & APR_READ); + svn_boolean_t supports_write = (flags == 0) || (flags & APR_WRITE);
Files corresponding to the standard I/O streams actually have the appropriate APR_READ / APR_WRITE flags set starting from APR 1.3 — see, for example, apr_file_open_flags_stderr() in [1]. Hence, the (flags == 0) check is going to return false for them. > Note that this check is not perfect for arbitrary APR file handles > (may enable more functions than the handle actually supports) but > works correctly for our STD* streams and the files opened through > our svn_io_* API. The actual problem, to my mind, is that relying on flags to determine if the file allows reading or writing, is fragile. There are examples of apr_file_t's that don't have the corresponding flags, but still allow reading and writing, and svn_stream_from_aprfile2() is going to break for them. One example would be apr_file_pipe_create() on Unix that sets APR_INHERIT flag on the created pipe [2]. Another example is creating a pipe on Windows that currently initializes flags to zero [3]. [1] https://svn.apache.org/repos/asf/apr/apr/branches/1.3.x/file_io/unix/open.c [2] https://svn.apache.org/repos/asf/apr/apr/trunk/file_io/unix/pipe.c [3] https://svn.apache.org/repos/asf/apr/apr/trunk/file_io/win32/pipe.c Regards, Evgeny Kotkov
