pc+-file-reader: Fix handling of short files.

The code failed to return an error properly when fread() read past end of
file.

The function comment didn't properly reflect what the function actually
returned, so this commit also updates the comment.

Reported by John Darrington.

diff --git a/src/data/pc+-file-reader.c b/src/data/pc+-file-reader.c
index 0aa4587d38ca3ebe81fe2b3edd10f1edd2272be1..08e6470697361b871acecdd6d9174da670268e62 100644 (file)
--- a/src/data/pc+-file-reader.c
+++ b/src/data/pc+-file-reader.c
@@ -1,5 +1,5 @@
 /* PSPP - a program for statistical analysis.
-   Copyright (C) 1997-2000, 2006-2007, 2009-2014 Free Software Foundation, Inc.
+   Copyright (C) 1997-2000, 2006-2007, 2009-2015 Free Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -505,18 +505,20 @@ pcp_file_casereader_destroy (struct casereader *reader UNUSED, void *r_)
   pcp_close (&r->any_reader);
 }
 
-/* Returns true if FILE is an SPSS/PC+ system file,
-   false otherwise. */
+/* Detects whether FILE is an SPSS/PC+ system file.  Returns 1 if so, 0 if
+   not, and a negative errno value if there is an error reading FILE. */
 static int
 pcp_detect (FILE *file)
 {
   static const char signature[4] = "SPSS";
   char buf[sizeof signature];
 
-  if (fseek (file, 0x104, SEEK_SET)
-      || (fread (buf, sizeof buf, 1, file) != 1 && !feof (file)))
+  if (fseek (file, 0x104, SEEK_SET))
     return -errno;
 
+  if (fread (buf, sizeof buf, 1, file) != 1)
+    return ferror (file) ? -errno : 0;
+
   return !memcmp (buf, signature, sizeof buf);
 }
 \f