Fix detection of unseekable files for fseek() and ftello() with MSVC

Calling fseek() or ftello() on a handle to a non-seeking device such as
a pipe or a communications device is not supported.  Unfortunately,
MSVC's flavor of these routines, _fseeki64() and _ftelli64(), do not
return an error when given a pipe as handle.  Some of the logic of
pg_dump and restore relies on these routines to check if a handle is
seekable, causing failures when passing the contents of pg_dump to
pg_restore through a pipe, for example.

This commit introduces wrappers for fseeko() and ftello() on MSVC so as
any callers are able to properly detect the cases of non-seekable
handles.  This relies mainly on GetFileType(), sharing a bit of code
with the MSVC port for fstat().  The code in charge of getting a file
type is refactored into a new file called win32common.c, shared by
win32stat.c and the new win32fseek.c.  It includes the MSVC ports for
fseeko() and ftello().

Like 765f5df, this is backpatched down to 14, where the fstat()
implementation for MSVC is able to understand about files larger than
4GB in size.  Using a TAP test for that is proving to be tricky as
IPC::Run handles the pipes by itself, still I have been able to check
the fix manually.

Reported-by: Daniel Watzinger
Author: Juan José Santamaría Flecha, Michael Paquier
Discussion: https://postgr.es/m/CAC+AXB26a4EmxM2suXxPpJaGrqAdxracd7hskLg-zxtPB50h7A@mail.gmail.com
Backpatch-through: 14

configure

@@ -17287,6 +17287,12 @@ esac
  ;;
 esac
 
+  case " $LIBOBJS " in
+  *" win32common.$ac_objext "* ) ;;
+  *) LIBOBJS="$LIBOBJS win32common.$ac_objext"
+ ;;
+esac
+
   case " $LIBOBJS " in
   *" win32env.$ac_objext "* ) ;;
   *) LIBOBJS="$LIBOBJS win32env.$ac_objext"

configure.ac

@@ -2004,6 +2004,7 @@ if test "$PORTNAME" = "win32"; then
   AC_LIBOBJ(kill)
   AC_LIBOBJ(open)
   AC_LIBOBJ(system)
+  AC_LIBOBJ(win32common)
   AC_LIBOBJ(win32env)
   AC_LIBOBJ(win32error)
   AC_LIBOBJ(win32ntdll)

src/include/port/win32_port.h

@@ -201,15 +201,21 @@ struct itimerval
 
 int			setitimer(int which, const struct itimerval *value, struct itimerval *ovalue);
 
+/* Convenience wrapper for GetFileType() */
+extern DWORD pgwin32_get_file_type(HANDLE hFile);
+
 /*
  * WIN32 does not provide 64-bit off_t, but does provide the functions operating
- * with 64-bit offsets.
+ * with 64-bit offsets.  Also, fseek() might not give an error for unseekable
+ * streams, so harden that function with our version.
  */
 #define pgoff_t __int64
 
 #ifdef _MSC_VER
-#define fseeko(stream, offset, origin) _fseeki64(stream, offset, origin)
+extern int	_pgfseeko64(FILE *stream, pgoff_t offset, int origin);
-#define ftello(stream) _ftelli64(stream)
+extern pgoff_t _pgftello64(FILE *stream);
+#define fseeko(stream, offset, origin) _pgfseeko64(stream, offset, origin)
+#define ftello(stream) _pgftello64(stream)
 #else
 #ifndef fseeko
 #define fseeko(stream, offset, origin) fseeko64(stream, offset, origin)

src/port/win32common.c

@@ -0,0 +1,68 @@
+/*-------------------------------------------------------------------------
+ *
+ * win32common.c
+ *	  Common routines shared among the win32*.c ports.
+ *
+ * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/port/win32common.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifdef FRONTEND
+#include "postgres_fe.h"
+#else
+#include "postgres.h"
+#endif
+
+#ifdef WIN32
+
+/*
+ * pgwin32_get_file_type
+ *
+ * Convenience wrapper for GetFileType() with specific error handling for all the
+ * port implementations.  Returns the file type associated with a HANDLE.
+ *
+ * On error, sets errno with FILE_TYPE_UNKNOWN as file type.
+ */
+DWORD
+pgwin32_get_file_type(HANDLE hFile)
+{
+	DWORD		fileType = FILE_TYPE_UNKNOWN;
+	DWORD		lastError;
+
+	errno = 0;
+
+	/*
+	 * When stdin, stdout, and stderr aren't associated with a stream the
+	 * special value -2 is returned:
+	 * https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/get-osfhandle
+	 */
+	if (hFile == INVALID_HANDLE_VALUE || hFile == (HANDLE) -2)
+	{
+		errno = EINVAL;
+		return FILE_TYPE_UNKNOWN;
+	}
+
+	fileType = GetFileType(hFile);
+	lastError = GetLastError();
+
+	/*
+	 * Invoke GetLastError in order to distinguish between a "valid" return of
+	 * FILE_TYPE_UNKNOWN and its return due to a calling error.  In case of
+	 * success, GetLastError() returns NO_ERROR.
+	 */
+	if (fileType == FILE_TYPE_UNKNOWN && lastError != NO_ERROR)
+	{
+		_dosmaperr(lastError);
+		return FILE_TYPE_UNKNOWN;
+	}
+
+	return fileType;
+}
+
+#endif							/* WIN32 */

src/port/win32fseek.c

@@ -0,0 +1,75 @@
+/*-------------------------------------------------------------------------
+ *
+ * win32fseek.c
+ *	  Replacements for fseeko() and ftello().
+ *
+ * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/port/win32fseek.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifdef FRONTEND
+#include "postgres_fe.h"
+#else
+#include "postgres.h"
+#endif
+
+#if defined(WIN32) && defined(_MSC_VER)
+
+/*
+ * _pgfseeko64
+ *
+ * Calling fseek() on a handle to a non-seeking device such as a pipe or
+ * a communications device is not supported, and fseek() may not return
+ * an error.  This wrapper relies on the file type to check which cases
+ * are supported.
+ */
+int
+_pgfseeko64(FILE *stream, pgoff_t offset, int origin)
+{
+	DWORD		fileType;
+	HANDLE		hFile = (HANDLE) _get_osfhandle(_fileno(stream));
+
+	fileType = pgwin32_get_file_type(hFile);
+	if (errno != 0)
+		return -1;
+
+	if (fileType == FILE_TYPE_DISK)
+		return _fseeki64(stream, offset, origin);
+	else if (fileType == FILE_TYPE_CHAR || fileType == FILE_TYPE_PIPE)
+		errno = ESPIPE;
+	else
+		errno = EINVAL;
+
+	return -1;
+}
+
+/*
+ * _pgftello64
+ *
+ * Same as _pgfseeko64().
+ */
+pgoff_t
+_pgftello64(FILE *stream)
+{
+	DWORD		fileType;
+	HANDLE		hFile = (HANDLE) _get_osfhandle(_fileno(stream));
+
+	fileType = pgwin32_get_file_type(hFile);
+	if (errno != 0)
+		return -1;
+
+	if (fileType == FILE_TYPE_DISK)
+		return _ftelli64(stream);
+	else if (fileType == FILE_TYPE_CHAR || fileType == FILE_TYPE_PIPE)
+		errno = ESPIPE;
+	else
+		errno = EINVAL;
+
+	return -1;
+}
+
+#endif							/* defined(WIN32) && defined(_MSC_VER) */

src/port/win32stat.c

@@ -141,33 +141,17 @@ _pgfstat64(int fileno, struct stat *buf)
 {
 	HANDLE		hFile = (HANDLE) _get_osfhandle(fileno);
 	DWORD		fileType = FILE_TYPE_UNKNOWN;
-	DWORD		lastError;
 	unsigned short st_mode;
 
-	/*
+	if (buf == NULL)
-	 * When stdin, stdout, and stderr aren't associated with a stream the
-	 * special value -2 is returned:
-	 * https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/get-osfhandle
-	 */
-	if (hFile == INVALID_HANDLE_VALUE || hFile == (HANDLE) -2 || buf == NULL)
 	{
 		errno = EINVAL;
 		return -1;
 	}
 
-	fileType = GetFileType(hFile);
+	fileType = pgwin32_get_file_type(hFile);
-	lastError = GetLastError();
+	if (errno != 0)
-
-	/*
-	 * Invoke GetLastError in order to distinguish between a "valid" return of
-	 * FILE_TYPE_UNKNOWN and its return due to a calling error.  In case of
-	 * success, GetLastError returns NO_ERROR.
-	 */
-	if (fileType == FILE_TYPE_UNKNOWN && lastError != NO_ERROR)
-	{
-		_dosmaperr(lastError);
 		return -1;
-	}
 
 	switch (fileType)
 	{

src/tools/msvc/Mkvcbuild.pm

@@ -107,7 +107,7 @@ sub mkvcbuild
 	  pg_strong_random.c pgcheckdir.c pgmkdirp.c pgsleep.c pgstrcasecmp.c
 	  pqsignal.c mkdtemp.c qsort.c qsort_arg.c bsearch_arg.c quotes.c system.c
 	  strerror.c tar.c
-	  win32env.c win32error.c win32ntdll.c
+	  win32common.c win32env.c win32error.c win32fseek.c win32ntdll.c
 	  win32security.c win32setlocale.c win32stat.c);
 
 	push(@pgportfiles, 'strtof.c') if ($vsVersion < '14.00');