gpgmymail: remove all 'decoding' code

.gitignore

@@ -1,4 +1,9 @@
 venv/
+__pycache__/
 .idea/
-testing.py
+# misc testing scripts
+testing*.py
+# i have a symlink here so testing scripts can import gpgmymail
+# as python expects `import gpgmymail` to be importing `gpgmymail.py`
+gpgmymail.py
 

README.md

@@ -1,7 +1,14 @@
 # gpgmymail
 
-Takes an email from stdin and encrypts it using the recipient's PGP key,
+Takes an email from stdin and encrypts it to stdout using the recipient's PGP
-provided as an argument when calling the script.
+key, provided as an argument when calling the script.
+
+Leaves a `X-gpgmymail-Status` header on the email, which has the following
+statuses:
+
+* `entered` - the email has entered the encryption function, but not been
+              encrypted
+* `encrypted` - the encryption function has encrypted the email
 
 Written to be a Sieve filter to be used with `sieve_extprograms`. Can be used
 in a Sieve filter e.g.:
@@ -33,5 +40,6 @@ behaviour which is much better achieved with Sieve will be implemented, e.g.
 # Credits
 
 * Julian Klode for the [original code](https://github.com/julian-klode/ansible.jak-linux.org/blob/dovecot/roles/mailserver/files/usr/local/lib/dovecot-sieve-filters/gpgmymail)
-* revsuine for modifications to gpgmymail
+* revsuine for modifications to gpgmymail, mostly to make it work well with
+  Thunderbird
 

gpgmymail

@@ -24,6 +24,12 @@ works well for emails created with this tool. When encrypting, the tool
 preserves all headers in the original email in the encrypted part, and
 copies relevant headers to the output. When decrypting, any headers are
 ignored, and only the encrypted headers are restored.
+
+Emails exiting this script will have the 'X-gpgmymail-Status' header, which has
+the following options:
+
+- entered: the email has entered the encrypt() function
+- encrypted: the email has been encrypted
 """
 
 import argparse
@@ -40,13 +46,6 @@ import gnupg
 
 # constants
 DEFAULT_ENCODING='utf-8'  # default is latin-1 which fails w some unicode chars
-CTE_TO_ENCODER_DICT = {
-    "7bit": email.encoders.encode_7or8bit,
-    "8bit": email.encoders.encode_7or8bit,
-    "base64": email.encoders.encode_base64,
-    "quoted-printable": email.encoders.encode_quopri
-}
-DEFAULT_ENCODER = email.encoders.encode_7or8bit
 
 def is_message_encrypted(message: email.message.Message) -> bool:
     """Determines whether or not an email message is encrypted.
@@ -56,30 +55,34 @@ def is_message_encrypted(message: email.message.Message) -> bool:
 
     return message.get_content_subtype() == "encrypted"
 
-def get_encoder_from_msg(msg: email.message.Message) -> typing.Callable:
+def set_email_header(
+    message: email.message.Message,
+    name: str,
+    value: str
+) -> None:
     """
-    Return a suitable encoder function from email.encoders based on an input
+    Set the header of an email Message. Will either replace the first instance
-    message. If the input message has no Content-Transfer-Encoding header,
+    of the header, or if the header is not present, will add the header.
-    or there is no encoder function corresponding to the CTE header, a default
-    encoder will be returned.
 
-    :param msg: an unencrypted email Message
+    Note: Python passes objects as references, so there is no need for a return
-    :return: function from email.encoders, see
+    value.
-             https://docs.python.org/3/library/email.encoders.html
+
+    :param message: the Message object to be modified
+    :param name: the email header to set
+    :param value: the value to set the header to
     """
-    cte = msg.get("Content-Transfer-Encoding")
+    if message.get(name):
-    if cte:
+        message.replace_header(name, value)
-        encoder = CTE_TO_ENCODER_DICT.get(cte)
     else:
-        return DEFAULT_ENCODER
+        message.add_header(name, value)
-    return encoder if encoder else DEFAULT_ENCODER
 
 def encrypt(
         message: email.message.Message,
         recipients: typing.List[str],
         *,
         unconditionally_encrypt: bool = False,
-        encoding: str = DEFAULT_ENCODING
+        encoding: str = DEFAULT_ENCODING,
+        ignore_errors: bool = False,
     ) -> str:
     """Encrypt given message
 
@@ -89,14 +92,19 @@ def encrypt(
     False (default), will NOT encrypt if any of the following conditions are
     met:
     - The message is already encrypted
-
+    :param encoding: string for encoding to use for the gnupg.GPG object
     :return: The encrypted email as a string"""
+
+    # mark the email as having passed through us
+    set_email_header(message, 'X-gpgmymail-Status', 'entered')
     
+    # exclusion criteria:
     # some mail clients like Thunderbird don't like twice-encrypted emails,
     # so we return the message as-is if it's already encrypted
-    if is_message_encrypted(message) and not unconditionally_encrypt:
+    if not unconditionally_encrypt:
-        return message.as_string()
+        if is_message_encrypted(message):
-    
+            return message.as_string()
+
     gpg = gnupg.GPG()
     gpg.encoding = encoding
     encrypted_content = gpg.encrypt(message.as_string(), recipients, armor=True)
@@ -107,13 +115,13 @@ def encrypt(
     enc = email.mime.application.MIMEApplication(
         _data=str(encrypted_content).encode(),
         _subtype="octet-stream",
-        _encoder=get_encoder_from_msg(message)
+        _encoder=email.encoders.encode_7or8bit
     )
 
     control = email.mime.application.MIMEApplication(
         _data=b'Version: 1\n',
         _subtype='pgp-encrypted; name="msg.asc"',
-        _encoder=get_encoder_from_msg(message)
+        _encoder=email.encoders.encode_7or8bit
     )
     control['Content-Disposition'] = 'inline; filename="msg.asc"'
 
@@ -132,6 +140,9 @@ def encrypt(
         if key.lower() not in headers_not_to_override:
             encmsg[key] = value
 
+    # we have encrypted the email, set our gpgmymail header appropriately
+    set_email_header(encmsg, 'X-gpgmymail-Status', 'encrypted')
+
     return encmsg.as_string()
 
 def decrypt(message: email.message.Message, *, encoding: str = DEFAULT_ENCODING) -> str:
@@ -153,6 +164,8 @@ def main() -> None:
                         help="Encoding to use for the gnupg.GPG object")
     parser.add_argument('--unconditional', action="store_true",
                         help="Encrypt mail unconditionally. By default, mail is not encrypted if it is already encrypted.")
+    parser.add_argument('--ignore-errors', action="store_true",
+                        help="Ignore errors at certain error-prone points of the script.")
     parser.add_argument('recipient', nargs='*',
                         help="Key ID or email of keys to encrypt for")
     args = parser.parse_args()
@@ -165,7 +178,8 @@ def main() -> None:
             msg,
             args.recipient,
             unconditionally_encrypt=args.unconditional,
-            encoding=args.encoding
+            encoding=args.encoding,
+            ignore_errors=args.ignore_errors,
         ))
 
 if __name__ == '__main__':