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, 16 insertions, 14 deletions

diff --git a/sourcecodes/modified_network.php b/sourcecodes/modified_network.php
index 9f38335c..3be0d69c 100644
--- a/sourcecodes/modified_network.php
+++ b/sourcecodes/modified_network.php
@@ -31,20 +31,22 @@ if($_POST["My_key"]!="")
 $filename = "/tmp/bnw/".$old_key."modify_edge.txt";
 
 $file = fopen($filename,'w');
-//fwrite($file,$json);
-fwrite($file,$nnodes);
-fwrite($file,"\n");
-fwrite($file,$node_labs);
-fwrite($file,"\n");
-fwrite($file,$nedges);
-fwrite($file,"\n");
-fwrite($file,$sources);
-fwrite($file,"\n");
-fwrite($file,$targets);
-fwrite($file,"\n");
-fwrite($file,$weights);
-fwrite($file,"\n");
-fclose($file);
+if ($file !== false) {
+  //fwrite($file,$json);
+  fwrite($file,$nnodes);
+  fwrite($file,"\n");
+  fwrite($file,$node_labs);
+  fwrite($file,"\n");
+  fwrite($file,$nedges);
+  fwrite($file,"\n");
+  fwrite($file,$sources);
+  fwrite($file,"\n");
+  fwrite($file,$targets);
+  fwrite($file,"\n");
+  fwrite($file,$weights);
+  fwrite($file,"\n");
+  fclose($file);
+}
 
 shell_exec('./run_scripts/run_mod_edges '.$old_key.' '.$keyval);