From 2973852fbbd4f11a633dc4e4630e042f9169c998 Mon Sep 17 00:00:00 2001
From: Scott Kitterman <scott@kitterman.com>
Date: Sun, 3 Nov 2019 11:57:30 -0500
Subject: [PATCH]     - Add new DKIM.present function to allow applications to
 test if a DKIM       signature is present without doing validation (LP:
 #1851141)

---
 ChangeLog               |  2 ++
 dkim/__init__.py        |  5 +++++
 dkim/tests/test_dkim.py | 10 ++++++++++
 3 files changed, 17 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 5774634..cd4c3fc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,8 @@
 Version 1.0.0
     - Add support for RFC 8460 tlsrpt DKIM signature processing (LP: #1847020)
     - Add new timeout parameter to enable DNS lookup timeouts to be adjusted
+    - Add new DKIM.present function to allow applications to test if a DKIM
+      signature is present without doing validation (LP: #1851141)
     - Drop usage of pymilter Milter.dns in dnsplug since it doesn't support
       havine a timeout passed to it
 
diff --git a/dkim/__init__.py b/dkim/__init__.py
index e00908c..d3f1fb0 100644
--- a/dkim/__init__.py
+++ b/dkim/__init__.py
@@ -872,6 +872,11 @@ class DKIM(DomainSigner):
     self.signature_fields = dict(sigfields)
     return b'DKIM-Signature: ' + res
 
+  #: Checks if any DKIM signature is present
+  #: @return: True if there is one or more DKIM signatures present or False otherwise
+  def present(self):
+    return (len([(x,y) for x,y in self.headers if x.lower() == b"dkim-signature"]) > 0)
+
   #: Verify a DKIM signature.
   #: @type idx: int
   #: @param idx: which signature to verify.  The first (topmost) signature is 0.
diff --git a/dkim/tests/test_dkim.py b/dkim/tests/test_dkim.py
index 6b6f7b6..578c260 100644
--- a/dkim/tests/test_dkim.py
+++ b/dkim/tests/test_dkim.py
@@ -300,6 +300,16 @@ p=11qYAYKxCrfVS/7TyWQHOg7hcvPapiMlrwIaaPcHURo="""
                 res = dkim.verify(sig + self.message, dnsfunc=self.dnsfunc)
                 self.assertTrue(res)
 
+    def test_present(self):
+        # Test DKIM.present().
+        d = dkim.DKIM(self.message,signature_algorithm=b'rsa-sha256')
+        present = d.present()
+        self.assertFalse(present)
+        sig = d.sign(b"test", b"example.com", self.key)
+        signed = sig + self.message
+        d2 = dkim.DKIM(signed)
+        present = d2.present()
+        self.assertTrue(present)
 
     def test_badly_encoded_domain_fails(self):
         # Domains should be ASCII. Bad ASCII causes verification to fail.