remove network from dc_provider_new_from_email(), add an explicit function for network provider lookup (#3256)

CHANGELOG.md

@@ -6,6 +6,8 @@
 
 - replaced stock string `DC_STR_ONE_MOMENT` by `DC_STR_NOT_CONNECTED` #3222
 - add `dc_resend_msgs()` #3238
+- `dc_provider_new_from_email()` does no longer do an DNS lookup for checking custom domains,
+  this is done by `dc_provider_new_from_email_with_dns()` now #3256
 
 ### Fixes
 

deltachat-ffi/deltachat.h

@@ -4648,9 +4648,10 @@ int             dc_contact_is_verified       (dc_contact_t* contact);
 
 
 /**
- * Create a provider struct for the given e-mail address.
+ * Create a provider struct for the given e-mail address by local lookup.
  *
- * The provider is extracted from the e-mail address and it's information is returned.
+ * Lookup is done from the local database by extracting the domain from the e-mail address.
+ * Therefore the provider for custom domains cannot be identified.
  *
  * @memberof dc_provider_t
  * @param context The context object.
@@ -4662,6 +4663,23 @@ int             dc_contact_is_verified       (dc_contact_t* contact);
 dc_provider_t*  dc_provider_new_from_email            (const dc_context_t* context, const char* email);
 
 
+/**
+ * Create a provider struct for the given e-mail address by local and DNS lookup.
+ *
+ * First lookup is done from the local database as of dc_provider_new_from_email().
+ * If the first lookup fails, an additional DNS lookup is done,
+ * trying to figure out the provider belonging to custom domains.
+ *
+ * @memberof dc_provider_t
+ * @param context The context object.
+ * @param email The user's e-mail address to extract the provider info form.
+ * @return A dc_provider_t struct which can be used with the dc_provider_get_*
+ *     accessor functions. If no provider info is found, NULL will be
+ *     returned.
+ */
+dc_provider_t*  dc_provider_new_from_email_with_dns    (const dc_context_t* context, const char* email);
+
+
 /**
  * URL of the overview page.
  *

deltachat-ffi/src/lib.rs

@@ -3973,6 +3973,25 @@ pub unsafe extern "C" fn dc_provider_new_from_email(
     }
     let addr = to_string_lossy(addr);
 
+    let ctx = &*context;
+
+    match block_on(provider::get_provider_info(ctx, addr.as_str(), true)) {
+        Some(provider) => provider,
+        None => ptr::null_mut(),
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn dc_provider_new_from_email_with_dns(
+    context: *const dc_context_t,
+    addr: *const libc::c_char,
+) -> *const dc_provider_t {
+    if context.is_null() || addr.is_null() {
+        eprintln!("ignoring careless call to dc_provider_new_from_email_with_dns()");
+        return ptr::null();
+    }
+    let addr = to_string_lossy(addr);
+
     let ctx = &*context;
     let socks5_enabled = block_on(async move {
         ctx.get_config_bool(config::Config::Socks5Enabled)