python: add cutil.from_optional_dc_charpointer()

`cutil.from_dc_charpointer()` is guaranteed to return `str`, while
`cutil.from_optional_dc_charpointer()` may return `None` if C function
returns `NULL`.

python/src/deltachat/account.py

@@ -8,7 +8,7 @@ import os
 from array import array
 from . import const
 from .capi import ffi, lib
-from .cutil import as_dc_charpointer, from_dc_charpointer, iter_array, DCLot
+from .cutil import as_dc_charpointer, from_dc_charpointer, from_optional_dc_charpointer, iter_array, DCLot
 from .chat import Chat
 from .message import Message
 from .contact import Contact
@@ -79,7 +79,7 @@ class Account(object):
             raise KeyError("{!r} not a valid config key, existing keys: {!r}".format(
                            name, self._configkeys))
 
-    def get_info(self):
+    def get_info(self) -> Dict[str, str]:
         """ return dictionary of built config parameters. """
         lines = from_dc_charpointer(lib.dc_get_info(self._dc_context))
         d = {}
@@ -135,7 +135,7 @@ class Account(object):
             valuebytes = ffi.NULL
         lib.dc_set_config(self._dc_context, namebytes, valuebytes)
 
-    def get_config(self, name: str):
+    def get_config(self, name: str) -> str:
         """ return unicode string value.
 
         :param name: configuration key to lookup (eg "addr" or "mail_pw")
@@ -200,11 +200,9 @@ class Account(object):
         """ return the latest backup file in a given directory.
         """
         res = lib.dc_imex_has_backup(self._dc_context, as_dc_charpointer(backupdir))
-        if res == ffi.NULL:
-            return None
-        return from_dc_charpointer(res)
+        return from_optional_dc_charpointer(res)
 
-    def get_blobdir(self) -> Optional[str]:
+    def get_blobdir(self) -> str:
         """ return the directory for files.
 
         All sent files are copied to this directory if necessary.
@@ -477,7 +475,7 @@ class Account(object):
     def imex(self, path, imex_cmd):
         lib.dc_imex(self._dc_context, imex_cmd, as_dc_charpointer(path), ffi.NULL)
 
-    def initiate_key_transfer(self):
+    def initiate_key_transfer(self) -> str:
         """return setup code after a Autocrypt setup message
         has been successfully sent to our own e-mail address ("self-sent message").
         If sending out was unsuccessful, a RuntimeError is raised.
@@ -488,7 +486,7 @@ class Account(object):
             raise RuntimeError("could not send out autocrypt setup message")
         return from_dc_charpointer(res)
 
-    def get_setup_contact_qr(self) -> Optional[str]:
+    def get_setup_contact_qr(self) -> str:
         """ get/create Setup-Contact QR Code as ascii-string.
 
         this string needs to be transferred to another DC account
@@ -584,7 +582,7 @@ class Account(object):
     def get_connectivity(self):
         return lib.dc_get_connectivity(self._dc_context)
 
-    def get_connectivity_html(self):
+    def get_connectivity_html(self) -> str:
         return from_dc_charpointer(lib.dc_get_connectivity_html(self._dc_context))
 
     def all_work_done(self):

python/src/deltachat/contact.py

@@ -1,10 +1,11 @@
 """ Contact object. """
 
 from . import props
-from .cutil import from_dc_charpointer
+from .cutil import from_dc_charpointer, from_optional_dc_charpointer
 from .capi import lib, ffi
 from .chat import Chat
 from . import const
+from typing import Optional
 
 
 class Contact(object):
@@ -35,12 +36,12 @@ class Contact(object):
         )
 
     @props.with_doc
-    def addr(self):
+    def addr(self) -> str:
         """ normalized e-mail address for this account. """
         return from_dc_charpointer(lib.dc_contact_get_addr(self._dc_contact))
 
     @props.with_doc
-    def name(self):
+    def name(self) -> str:
         """ display name for this contact. """
         return from_dc_charpointer(lib.dc_contact_get_display_name(self._dc_contact))
 
@@ -67,15 +68,13 @@ class Contact(object):
         """ Return True if the contact is verified. """
         return lib.dc_contact_is_verified(self._dc_contact)
 
-    def get_profile_image(self):
+    def get_profile_image(self) -> Optional[str]:
         """Get contact profile image.
 
         :returns: path to profile image, None if no profile image exists.
         """
         dc_res = lib.dc_contact_get_profile_image(self._dc_contact)
-        if dc_res == ffi.NULL:
-            return None
-        return from_dc_charpointer(dc_res)
+        return from_optional_dc_charpointer(dc_res)
 
     @property
     def status(self):

python/src/deltachat/cutil.py

@@ -19,7 +19,13 @@ def iter_array(dc_array_t, constructor: Callable[[int], T]) -> Generator[T, None
         yield constructor(lib.dc_array_get_id(dc_array_t, i))
 
 
-def from_dc_charpointer(obj) -> Optional[str]:
+def from_dc_charpointer(obj) -> str:
+    if obj != ffi.NULL:
+        return ffi.string(ffi.gc(obj, lib.dc_str_unref)).decode("utf8")
+    raise ValueError
+
+
+def from_optional_dc_charpointer(obj) -> Optional[str]:
     if obj != ffi.NULL:
         return ffi.string(ffi.gc(obj, lib.dc_str_unref)).decode("utf8")
     return None

python/src/deltachat/events.py

@@ -9,7 +9,7 @@ from .hookspec import account_hookimpl
 from contextlib import contextmanager
 from .capi import ffi, lib
 from .message import map_system_message
-from .cutil import from_dc_charpointer
+from .cutil import from_optional_dc_charpointer
 
 
 class FFIEvent:
@@ -235,7 +235,7 @@ class EventThread(threading.Thread):
             # function which provides us signature info of an event call
             evt_name = deltachat.get_dc_event_name(evt)
             if lib.dc_event_has_string_data(evt):
-                data2 = from_dc_charpointer(lib.dc_event_get_data2_str(event))
+                data2 = from_optional_dc_charpointer(lib.dc_event_get_data2_str(event))
             else:
                 data2 = lib.dc_event_get_data2_int(event)
 

python/src/deltachat/message.py

@@ -3,10 +3,11 @@
 import os
 import re
 from . import props
-from .cutil import from_dc_charpointer, as_dc_charpointer
+from .cutil import from_dc_charpointer, from_optional_dc_charpointer, as_dc_charpointer
 from .capi import lib, ffi
 from . import const
 from datetime import datetime, timezone
+from typing import Optional
 
 
 class Message(object):
@@ -75,7 +76,7 @@ class Message(object):
         return lib.dc_msg_get_id(self._dc_msg)
 
     @props.with_doc
-    def text(self):
+    def text(self) -> str:
         """unicode text of this messages (might be empty if not a text message). """
         return from_dc_charpointer(lib.dc_msg_get_text(self._dc_msg))
 
@@ -84,9 +85,9 @@ class Message(object):
         lib.dc_msg_set_text(self._dc_msg, as_dc_charpointer(text))
 
     @props.with_doc
-    def html(self):
+    def html(self) -> str:
         """html text of this messages (might be empty if not an html message). """
-        return from_dc_charpointer(
+        return from_optional_dc_charpointer(
             lib.dc_get_msg_html(self.account._dc_context, self.id)) or ""
 
     def has_html(self):
@@ -113,12 +114,13 @@ class Message(object):
         lib.dc_msg_set_file(self._dc_msg, as_dc_charpointer(path), mtype)
 
     @props.with_doc
-    def basename(self):
+    def basename(self) -> str:
         """basename of the attachment if it exists, otherwise empty string. """
+        # FIXME, it does not return basename
         return from_dc_charpointer(lib.dc_msg_get_filename(self._dc_msg))
 
     @props.with_doc
-    def filemime(self):
+    def filemime(self) -> str:
         """mime type of the file (if it exists)"""
         return from_dc_charpointer(lib.dc_msg_get_filemime(self._dc_msg))
 
@@ -130,7 +132,7 @@ class Message(object):
         """ return True if this message is a setup message. """
         return lib.dc_msg_is_setupmessage(self._dc_msg)
 
-    def get_setupcodebegin(self):
+    def get_setupcodebegin(self) -> str:
         """ return the first characters of a setup code in a setup message. """
         return from_dc_charpointer(lib.dc_msg_get_setupcodebegin(self._dc_msg))
 
@@ -146,7 +148,7 @@ class Message(object):
         """ return True if this message was forwarded. """
         return bool(lib.dc_msg_is_forwarded(self._dc_msg))
 
-    def get_message_info(self):
+    def get_message_info(self) -> str:
         """ Return informational text for a single message.
 
         The text is multiline and may contain eg. the raw text of the message.
@@ -203,11 +205,11 @@ class Message(object):
             return datetime.fromtimestamp(ts, timezone.utc)
 
     @property
-    def quoted_text(self):
+    def quoted_text(self) -> Optional[str]:
         """Text inside the quote
 
         :returns: Quoted text"""
-        return from_dc_charpointer(lib.dc_msg_get_quoted_text(self._dc_msg))
+        return from_optional_dc_charpointer(lib.dc_msg_get_quoted_text(self._dc_msg))
 
     @property
     def quote(self):
@@ -240,9 +242,9 @@ class Message(object):
             return email.message_from_string(s)
 
     @property
-    def error(self):
+    def error(self) -> Optional[str]:
         """Error message"""
-        return from_dc_charpointer(lib.dc_msg_get_error(self._dc_msg))
+        return from_optional_dc_charpointer(lib.dc_msg_get_error(self._dc_msg))
 
     @property
     def chat(self):
@@ -255,12 +257,12 @@ class Message(object):
         return Chat(self.account, chat_id)
 
     @props.with_doc
-    def override_sender_name(self):
+    def override_sender_name(self) -> Optional[str]:
         """the name that should be shown over the message instead of the contact display name.
 
         Usually used to impersonate someone else.
         """
-        return from_dc_charpointer(
+        return from_optional_dc_charpointer(
             lib.dc_msg_get_override_sender_name(self._dc_msg))
 
     def set_override_sender_name(self, name):

python/src/deltachat/provider.py

@@ -24,19 +24,19 @@ class Provider(object):
         self._provider = provider
 
     @property
-    def overview_page(self):
+    def overview_page(self) -> str:
         """URL to the overview page of the provider on providers.delta.chat."""
         return from_dc_charpointer(
             lib.dc_provider_get_overview_page(self._provider))
 
     @property
-    def get_before_login_hints(self):
+    def get_before_login_hints(self) -> str:
         """Should be shown to the user on login."""
         return from_dc_charpointer(
-            lib.dc_provider_get_before_login_hints(self._provider))
+            lib.dc_provider_get_before_login_hint(self._provider))
 
     @property
-    def status(self):
+    def status(self) -> int:
         """The status of the provider information.
 
         This is one of the