From 82dee78837d1d21fa80271befa909efd86554567 Mon Sep 17 00:00:00 2001
From: Cyrille Bagard <nocbos@gmail.com>
Date: Thu, 12 Oct 2023 14:59:23 +0200
Subject: Show how to create a Python plugin for ROST.

---
 python-plugins/zipbomb/__init__.py |  2 ++
 python-plugins/zipbomb/plugin.py   | 71 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 73 insertions(+)
 create mode 100644 python-plugins/zipbomb/__init__.py
 create mode 100644 python-plugins/zipbomb/plugin.py

diff --git a/python-plugins/zipbomb/__init__.py b/python-plugins/zipbomb/__init__.py
new file mode 100644
index 0000000..a9d4527
--- /dev/null
+++ b/python-plugins/zipbomb/__init__.py
@@ -0,0 +1,2 @@
+
+from zipbomb.plugin import ZipBombChecker as AutoLoad
diff --git a/python-plugins/zipbomb/plugin.py b/python-plugins/zipbomb/plugin.py
new file mode 100644
index 0000000..be8c12f
--- /dev/null
+++ b/python-plugins/zipbomb/plugin.py
@@ -0,0 +1,71 @@
+
+import io
+import zipfile
+
+from pychrysalide.analysis.scan import ScanRegisteredItem
+from pychrysalide.analysis.scan.exprs import ScanLiteralExpression
+from pychrysalide.core import get_rost_root_namespace
+from pychrysalide.plugins import PluginModule
+
+
+class ZipBombKeyword(ScanRegisteredItem):
+    """Introduce a new keyword in the ROST grammar."""
+
+    _name = 'is_zip_bomb'
+
+
+    def _reduce(self, ctx, scope):
+
+        expr = None
+
+        try:
+
+            has_bomb = False
+
+            # compress < 10% plain => bomb
+            ZIP_BOMB_RATIO = 0.01
+
+            data = io.BytesIO(ctx.content.data)
+
+            zf = zipfile.ZipFile(data)
+
+            info = zf.infolist()
+
+            for i in info:
+
+                ratio = i.compress_size / i.file_size
+
+                has_bomb = ratio < ZIP_BOMB_RATIO
+
+                if has_bomb:
+                    break
+
+            expr = ScanLiteralExpression(has_bomb)
+
+        except:
+            pass
+
+        return expr
+
+
+class ZipBombChecker(PluginModule):
+    """Check for ZIP bombs."""
+
+    _name = 'ZipBombChecker'
+    _desc = 'Check if a ZIP archive may contain heavy files on extraction'
+    _version = '0.1'
+    _url = 'https://www.chrysalide.re/'
+
+    _actions = ( )
+
+
+    def __init__(self):
+        """Create a ZipBombChecker plugin instance."""
+
+        super().__init__()
+
+        ns = get_rost_root_namespace()
+
+        kw = ZipBombKeyword()
+
+        ns.register_item(kw)
-- 
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