Add set-binary-mode primitive to switch a standard stream to binary I/O.

 src/fileio.c: Include binary-io.h.
 (Fset_binary_mode): New function.
 (syms_of_fileio): Defsubr it.
 (syms_of_fileio) <Qstdin, Qstdout, Qstderr>: DEFSYM them.

 admin/unidata/unidata/uvs.el (uvs-print-table-ivd): Call set-binary-mode on
 stdout.

 doc/lispref/streams.texi (Input Functions): Document 'set-binary-mode'.
 (Output Functions): Cross-reference to documentation of
 'set-binary-mode'.

 etc/NEWS: Mention 'set-binary-mode'.

1 files changed, 24 insertions, 0 deletions

diff --git a/doc/lispref/streams.texi b/doc/lispref/streams.texi
index 5e4df009b73..e52a543110b 100644
--- a/doc/lispref/streams.texi
+++ b/doc/lispref/streams.texi
@@ -339,6 +339,25 @@ shared structures.  @xref{Circular Objects}.  Its default value is
 @code{t}.
 @end defvar
 
+@cindex binary I/O in batch mode
+When reading or writing from the standard input/output streams of the
+Emacs process in batch mode, it is sometimes required to make sure any
+arbitrary binary data will be read/written verbatim, and/or that no
+translation of newlines to or from CR-LF pairs are performed.  This
+issue does not exist on Posix hosts, only on MS-Windows and MS-DOS.
+The following function allows to control the I/O mode of any standard
+stream of the Emacs process.
+
+@defun set-binary-mode stream mode
+Switch @var{stream} into binary or text I/O mode.  If @var{mode} is
+non-@code{nil}, switch to binary mode, otherwise switch to text mode.
+The value of @var{stream} can be one of @code{stdin}, @code{stdout},
+or @code{stderr}.  This function flushes any pending output data of
+@var{stream} as a side effect, and returns the previous value of I/O
+mode for @var{stream}.  On Posix hosts, it always returns a
+non-@code{nil} value and does nothing except flushing pending output.
+@end defun
+
 @node Output Streams
 @section Output Streams
 @cindex stream (for printing)
@@ -686,6 +705,11 @@ This function outputs @var{object} to @var{stream}, just like
 indent and fill the object to make it more readable for humans.
 @end defun
 
+If you need to use binary I/O in batch mode, e.g., use the functions
+described in this section to write out arbitrary binary data or avoid
+conversion of newlines on non-Posix hosts, see @ref{Input Functions,
+set-binary-mode}.
+
 @node Output Variables
 @section Variables Affecting Output
 @cindex output-controlling variables