fixed RESIZE-FILE for Cygwin (#198)

* docu: update example for IO_SOURCE
* removed getFilePathFromStream() from freopen call
* include Minix in selecting the Unix implementation

Fixes #189

csrc/stdio/pf_fileio_stdio.c

@@ -1,5 +1,6 @@
 /***************************************************************
-** File access routines based on ANSI C (no Unix stuff).
+** File access routines based on ANSI C
+**   (no more Unix stuff than strictly necessary).
 **
 ** This file is part of pForth
 **
@@ -25,32 +26,33 @@
 
 typedef int bool_t;
 
-/* Copy SIZE bytes from File FROM to File TO.  Return non-FALSE on error. */
-static bool_t CopyFile( FileStream *From, FileStream *To, long Size)
-{
-    bool_t Error = TRUE;
-    size_t Diff = Size;
-    size_t BufSize = 512;
-    char *Buffer = pfAllocMem( BufSize );
-    if( Buffer != 0 )
-    {
-        while( Diff > 0 )
-        {
-            size_t N = MIN( Diff, BufSize );
-            if( fread( Buffer, 1, N, From ) < N ) goto cleanup;
-            if( fwrite( Buffer, 1, N, To ) < N ) goto cleanup;
-            Diff -= N;
-        }
-        Error = FALSE;
+static bool_t TruncateFile( FileStream *File, long Newsize );  /* Shrink the file FILE to NEWSIZE.  Return non-FALSE on error. */
 
-cleanup:
-        pfFreeMem( Buffer );
-    }
-    return Error;
+#if defined( __CYGWIN__) || defined( __FreeBSD__) || defined(__NetBSD__)  || defined(__minix__) /* __unix__ */
+/*  Cygwin, FreeBSD, NetBSD and (Manjaro)Linux all define "__unix__", 
+      which might also be defined on incompatible platforms as well (so we do not use it).
+      Linux is excluded from the if statement in order to test the portable code on build.
+    This uses Unix specific APIs to work around problems with the portable implementation.
+*/
+
+#include<stdio.h>   /* fileno()  */
+#include<unistd.h>  /* ftruncate */
+
+static bool_t TruncateFile( FileStream *File, long Newsize )
+{
+	bool_t Error = TRUE;
+	int fd;
+	if(  -1  !=  ( fd = fileno(File) )  )
+	{
+		if( 0 == ftruncate(fd, Newsize) )
+			Error = FALSE;
+	}
+	return Error;
 }
 
-/* Shrink the file FILE to NEWSIZE.  Return non-FALSE on error.
- *
+#else   /* __unix__ */
+
+/*
  * There's no direct way to do this in ANSI C.  The closest thing we
  * have is freopen(3), which truncates a file to zero length if we use
  * "w+b" as mode argument.  So we do this:
@@ -64,39 +66,34 @@ static bool_t CopyFile( FileStream *From, FileStream *To, long Size)
  *
  * We call freopen with NULL as path argument, because we don't know
  * the actual file-name.  It seems that the trick with path=NULL is
- * not part of C89 but it's in C99. It does not work on NetBSD though.
- */
-
-#if defined(__NetBSD__) || defined(_NETBSD_SOURCE)
-/*  Tested on NetBSD 10.1.
-    "F_GETPATH" is not defined on Linux (Kernel 6.6.63), FreeBSD (13.2) or MSYS-Cygwin
-    (MSYS_NT-10.0-22631), so we restrict this function to NetBSD.
-    It might also work on "Mac OS X" but that needs to be verified.
+ * not part of C89 but it's in C99.
+ * It does not work on NetBSD and Cygwin though.
 */
 
-#include<fcntl.h>
-
-/* note: we do not malloc this, so we need not to free it after use! */
-static char getFilePathFromStreamData[PATH_MAX];
-
-static char* getFilePathFromStream( FileStream* File)
+/* Copy SIZE bytes from File FROM to File TO.  Return non-FALSE on error. */
+static bool_t CopyFile( FileStream *From, FileStream *To, long Size)
 {
-    char* result = NULL;
-    int fd;
-    if( (fd=fileno(File)) != -1 )
+    bool_t Error = TRUE;
+    size_t Diff = Size;
+    size_t BufSize = 512;
+    char *Buffer = pfAllocMem( BufSize );
+    if( Buffer != 0 )
     {
-        if( fcntl(fd, F_GETPATH, getFilePathFromStreamData) != -1 )
+        while( Diff > 0 )
         {
-            result = getFilePathFromStreamData;
+            size_t N = MIN( Diff, BufSize );
+            if( fread( Buffer, 1, N, From ) < N ) goto cleanup;
+            if( fwrite( Buffer, 1, N, To ) < N ) goto cleanup;
+            Diff -= N;
         }
+        Error = FALSE;
+
+cleanup:
+        pfFreeMem( Buffer );
     }
-    return result;
+    return Error;
 }
 
-#else
-static char* getFilePathFromStream( FileStream* File) { return NULL; }
-#endif  /* NetBSD */
-
 static bool_t TruncateFile( FileStream *File, long Newsize )
 {
     bool_t Error = TRUE;
@@ -107,7 +104,7 @@ static bool_t TruncateFile( FileStream *File, long Newsize )
         {
             if( CopyFile( File, TmpFile, Newsize )) goto cleanup;
             if( fseek( TmpFile, 0, SEEK_SET ) != 0 ) goto cleanup;
-            if( freopen( getFilePathFromStream(File), "w+b", File ) == NULL ) goto cleanup;
+            if( freopen( NULL, "w+b", File ) == NULL ) goto cleanup;
             if( CopyFile( TmpFile, File, Newsize )) goto cleanup;
             Error = FALSE;
 
@@ -118,6 +115,9 @@ static bool_t TruncateFile( FileStream *File, long Newsize )
     return Error;
 }
 
+#endif  /* __unix__ */
+
+
 /* Write DIFF 0 bytes to FILE. Return non-FALSE on error. */
 static bool_t ExtendFile( FileStream *File, size_t Diff )
 {