On 10.09.2015 23:50, Evgeny Kotkov wrote: > Stefan Fuhrmann <stef...@apache.org> 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].
I've reviewed the JavaHL code again and it indeed appears that this is caused by the difference in implementations of apr_file_pipe_create_ex() on Windows and elsewhere. The bindings code itself is not platform-specific; see TunnelContext in subversion/bindings/javahl/native/OperationContext.cpp. Those pipes get wrapped into streams deep in the RA layer. One could argue that apr_file_pipe_create is broken since it doesn't set the appropriate flags on the input and output handles, but that doesn't really help make this particular instance in the bindings code work. -- Brane
