- Add new DKIM.present function to allow applications to test if a DKIM

signature is present without doing validation (LP: #1851141)

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.

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.