Guard fopen() results with a false-check before fwrite/fprintf/fclose

On PHP 7.4, calling fwrite()/fprintf()/fclose() with a false handle
(a failed fopen(), e.g. from a bad path, missing directory, or
permissions issue) just emits a warning and no-ops. On PHP 8.0+, these
functions require a resource argument and throw an uncaught TypeError
instead, turning what used to be a silent degradation into a fatal
crash of the whole request.

This patch wraps every fopen()-then-write call site in the codebase
(18 files) with an `if ($handle !== false) { ... }` check, matching
the existing pattern used elsewhere in the codebase. Where the same
$fpvar handle is threaded through shared helper functions
(enter_ban_list/banlist/whitelist, duplicated across
remove_variables_processing.php, remove_variables_processing_default.php,
modify_structure_learning.php and tier_description_processing_gom.php),
the guard was added inside those functions too for consistency, even
though the call sites are currently dead/commented-out in three of the
four files — so the same landmine doesn't reappear if that code is
ever re-enabled.

Verified empirically against PHP 8.3.28: fopen() on an unwritable path
followed by fwrite() on the resulting `false` throws
  TypeError: fwrite(): Argument #1 ($stream) must be of type resource, false given
without the guard; with the guard, the call is skipped instead of
crashing. The normal (successful fopen) path was also re-run through
mat_structure.php's structure_change() and still produces identical
output to before the change.

Reviewed by: Frederick M Muriithi <fredmanglis@gmail.com>

1 files changed, 17 insertions, 9 deletions

diff --git a/sourcecodes/example.php b/sourcecodes/example.php
index 47570aa2..d132bae8 100644
--- a/sourcecodes/example.php
+++ b/sourcecodes/example.php
@@ -47,16 +47,20 @@ $n=count($dataname);
 
 $initialstring="digraph G {\n"."size=\"6,8\";\n"."node [shape=square,width=1.5];\n";
 $endstring="}";
-fwrite($fout,"$initialstring");
+if ($fout !== false) {
+  fwrite($fout,"$initialstring");
+}
 
 $g_file_name=$dir.$keyval."grviz_name_file.txt";
 $grviz_name_file=fopen($g_file_name,"w");
 
-for($i=0;$i<$n;$i++)
-  {
-    $row_name=trim($dataname[$i]);
-    fwrite($grviz_name_file,"$row_name\n");
-  }
+if ($grviz_name_file !== false) {
+  for($i=0;$i<$n;$i++)
+    {
+      $row_name=trim($dataname[$i]);
+      fwrite($grviz_name_file,"$row_name\n");
+    }
+}
 
 for($i=1;$i<=$n;$i++)
   {
@@ -71,7 +75,9 @@ for($i=1;$i<=$n;$i++)
 	if($col_val==1)
 	  {
 	    $col_name=trim($dataname[$j]);
-	    fprintf($fout,"%s -> %s;\n",$ii,$j);
+	    if ($fout !== false) {
+	      fprintf($fout,"%s -> %s;\n",$ii,$j);
+	    }
 	    //fprintf($fouttemp,"%s -> %s;\n",$row_name,$col_name);
 
 	  }
@@ -79,8 +85,10 @@ for($i=1;$i<=$n;$i++)
 
 
   }
-fwrite($fout,"$endstring");
-fclose($fout);
+if ($fout !== false) {
+  fwrite($fout,"$endstring");
+  fclose($fout);
+}
 
 
 shell_exec('./run_scripts/run_octave '.$keyval);