api(CFFI): Add dc_contact_is_key_contact() (#6955)

We need this because it's not clear whether Android should switch to
JsonRPC for everything, because of concerns that JsonRPC might be a lot
slower than the CFFI (although we still need to measure that).

deltachat-ffi/deltachat.h

@@ -5285,6 +5285,20 @@ int             dc_contact_is_verified       (dc_contact_t* contact);
 int             dc_contact_is_bot            (dc_contact_t* contact);
 
 
+/**
+ * Returns whether contact is a key-contact,
+ * i.e. it is identified by the public key
+ * rather than the email address.
+ *
+ * If so, all messages to and from this contact are encrypted.
+ *
+ * @memberof dc_contact_t
+ * @param contact The contact object.
+ * @return 1 if the contact is a key-contact, 0 if it is an address-contact.
+ */
+int             dc_contact_is_key_contact    (dc_contact_t* contact);
+
+
 /**
  * Return the contact ID that verified a contact.
  *

deltachat-ffi/src/lib.rs

@@ -4303,6 +4303,15 @@ pub unsafe extern "C" fn dc_contact_is_bot(contact: *mut dc_contact_t) -> libc::
     (*contact).contact.is_bot() as libc::c_int
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn dc_contact_is_key_contact(contact: *mut dc_contact_t) -> libc::c_int {
+    if contact.is_null() {
+        eprintln!("ignoring careless call to dc_contact_is_key_contact()");
+        return 0;
+    }
+    (*contact).contact.is_key_contact() as libc::c_int
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn dc_contact_get_verifier_id(contact: *mut dc_contact_t) -> u32 {
     if contact.is_null() {