feat: add lud-20 to LnurlPayMetaData (#52)

* feat: add lud-20 to LnurlPayMetaData

Author: dni

README.md

@@ -36,7 +36,7 @@ Check out the LUDS repository: [luds](https://github.com/lnurl/luds/)
 - [ ] LUD-17
 - [ ] LUD-18
 - [ ] LUD-19
-- [ ] LUD-20
+- [x] LUD-20
 - [ ] LUD-21
 
 

lnurl/types.py

@@ -240,7 +240,8 @@ def __get_url__(cls, address: str) -> Union[OnionUrl, ClearnetUrl, DebugUrl]:
 
 
 class LnurlPayMetadata(ReprMixin, str):
-    valid_metadata_mime_types = {"text/plain", "image/png;base64", "image/jpeg;base64"}
+    # LUD-20: Long payment description for pay protocol. "text/long-desc"
+    valid_metadata_mime_types = {"text/plain", "image/png;base64", "image/jpeg;base64", "text/long-desc"}
 
     __slots__ = ("_list",)
 
@@ -263,7 +264,11 @@ def __validate_metadata__(cls, json_str: str) -> List[Tuple[str, str]]:
         mime_types = [x[0] for x in clean_data]
         counts = {x: mime_types.count(x) for x in mime_types}
 
-        if not clean_data or "text/plain" not in mime_types or counts["text/plain"] > 1:
+        if (
+            not clean_data
+            or ("text/plain" not in mime_types and "text/long-desc" not in mime_types)
+            or counts["text/plain"] > 1
+        ):
             raise InvalidLnurlPayMetadata
 
         return clean_data