Implement a "schema guard" for `api` module

In order to catch errors related to assumed JSON schema, regroup all
JSON data access under a context manager that catch related errors:
- KeyError
- IndexError
- ValueError

src/delarte/api.py

@@ -3,13 +3,22 @@
 
 """Provide ArteTV JSON API utilities."""
 
+import contextlib
+
 from .error import UnexpectedAPIResponse, UnsupportedHLSProtocol
-from .model import ProgramMeta
 
 MIME_TYPE = "application/vnd.api+json; charset=utf-8"
 
 
-def _fetch_api_data(http_session, path, object_type):
+@contextlib.contextmanager
+def _schema_guard(*context):
+    try:
+        yield
+    except (KeyError, IndexError, ValueError) as e:
+        raise UnexpectedAPIResponse("SCHEMA", *context) from e
+
+
+def _fetch_api_object(http_session, path, object_type):
     # Fetch an API object.
     url = "https://api.arte.tv/api/player/v2/" + path
 
@@ -19,35 +28,43 @@ def _fetch_api_data(http_session, path, object_type):
     if (_ := r.headers["content-type"]) != MIME_TYPE:
         raise UnexpectedAPIResponse("MIME_TYPE", path, MIME_TYPE, _)
 
-    obj = r.json()["data"]
+    obj = r.json()
 
-    if (_ := obj["type"]) != object_type:
+    with _schema_guard(path):
+        data_type = obj["data"]["type"]
+        data_attributes = obj["data"]["attributes"]
+
+    if data_type != object_type:
         raise UnexpectedAPIResponse("OBJECT_TYPE", path, object_type, _)
 
-    return obj["attributes"]
+    return data_attributes
 
 
 def fetch_program_info(http_session, p_meta):
     """Fetch the given program metadata and indexes."""
-    obj = _fetch_api_data(
+    obj = _fetch_api_object(
         http_session, f"config/{p_meta.site}/{p_meta.id}", "ConfigPlayer"
     )
 
-    if (_ := obj["metadata"]["providerId"]) != p_meta.id:
+    with _schema_guard(p_meta.site, p_meta.id):
+        provider_id = obj["metadata"]["providerId"]
+        streams = [(s["protocol"], s["url"]) for s in obj["streams"]]
+
+    if provider_id != p_meta.id:
         raise UnexpectedAPIResponse(
             "PROGRAM_ID_MISMATCH",
             p_meta.site,
             p_meta.id,
-            _,
+            provider_id,
         )
 
     program_index_urls = set()
 
-    for s in obj["streams"]:
-        if (_ := s["protocol"]) != "HLS_NG":
-            raise UnsupportedHLSProtocol(p_meta.site, p_meta.id, _)
+    for protocol, program_index_url in streams:
+        if protocol != "HLS_NG":
+            raise UnsupportedHLSProtocol(p_meta.site, p_meta.id, protocol)
 
-        if (program_index_url := s["url"]) in program_index_urls:
+        if program_index_url in program_index_urls:
             raise UnexpectedAPIResponse(
                 "DUPLICATE_PROGRAM_INDEX_URL",
                 p_meta.site,

src/delarte/www.py

@@ -3,8 +3,8 @@
 
 """Provide ArteTV website utilities."""
 
+import contextlib
 import json
-from contextlib import contextmanager
 
 from .error import InvalidPage, PageNotFound, PageNotSupported
 from .model import ProgramMeta
@@ -12,12 +12,12 @@ from .model import ProgramMeta
 _DATA_MARK = '<script id="__NEXT_DATA__" type="application/json">'
 
 
-@contextmanager
+@contextlib.contextmanager
 def _schema_guard(*context):
     try:
         yield
     except (KeyError, IndexError, ValueError) as e:
-        raise InvalidPage("SCHEMA", *context, e)
+        raise InvalidPage("SCHEMA", *context) from e
 
 
 def _process_programs_page(page_value):
@@ -56,7 +56,6 @@ def fetch_program(http_session, url):
     # special handling of 404
     if r.status_code == 404:
         raise PageNotFound(url)
-
     # other network errors
     r.raise_for_status()