add provider db documentation url

default case for unwrapping
try fixing python linting

deltachat-ffi/deltachat.h

@@ -3663,22 +3663,24 @@ int             dc_contact_is_verified       (dc_contact_t* contact);
 
 /**
  * Get the provider json object for the given domain.
+ * For more documentation see https://docs.rs/deltachat-provider-database/
  *
  * @memberof dc_provider_t
  * @param domain The domain to get provider info for.
- * @return a provider json object as string.  If no provider info is found, an empty string will be returned.
+ * @return a provider json object as string. If no provider info is found, an empty string will be returned.
  */
 char*            dc_provider_json_from_domain           (const char* domain);
 
 
 /**
  * Get the provider json object for the given email address.
+ * For more documentation see https://docs.rs/deltachat-provider-database/
  *
  * The provider is extracted from the email address and it's information is returned.
  *
  * @memberof dc_provider_t
  * @param email The user's email address to extract the provider info form.
- * @return a provider json object as string.  If no provider info is found, an empty string will be returned.
+ * @return a provider json object as string. If no provider info is found, an empty string will be returned.
  */
 char*            dc_provider_json_from_email           (const char* email);
 

deltachat-ffi/src/providers.rs

@@ -11,7 +11,7 @@ pub unsafe extern "C" fn dc_provider_json_from_domain(
 ) -> *mut libc::c_char {
     let domain = to_string_lossy(domain);
     match deltachat_provider_database::get_provider_info(&domain) {
-        Some(provider) => serde_json::to_string(provider).unwrap().strdup(),
+        Some(provider) => serde_json::to_string(provider).unwrap_or("".to_owned()).strdup(),
         None => "".strdup(),
     }
 }
@@ -23,7 +23,7 @@ pub unsafe extern "C" fn dc_provider_json_from_email(
     let email = to_string_lossy(email);
     let domain = deltachat_provider_database::get_domain_from_email(&email);
     match deltachat_provider_database::get_provider_info(domain) {
-        Some(provider) => serde_json::to_string(provider).unwrap().strdup(),
+        Some(provider) => serde_json::to_string(provider).unwrap_or("".to_owned()).strdup(),
         None => "".strdup(),
     }
 }

python/src/deltachat/provider.py

@@ -1,9 +1,10 @@
 """Provider info class."""
 
-from .capi import ffi, lib
+from .capi import lib
 from .cutil import as_dc_charpointer, from_dc_charpointer
 import json
 
+
 class ProviderNotFoundError(Exception):
     """The provider information was not found."""
 
@@ -55,7 +56,7 @@ class Provider(object):
     def status(self):
         """The status of the provider information.
 
-        This is 
+        This is
         :attr:`"OK"`,
         :attr:`"PREPARATION"` or
         :attr:`"BROKEN"`.