Fixes: #111: Fix token RegExp expression

fb2cal/facebook_browser.py

@@ -4,6 +4,7 @@
 import json
 
 from .logger import Logger
+from .utils import remove_anti_hijacking_protection
 
 class FacebookBrowser:
     def __init__(self):
@@ -84,7 +85,7 @@ def get_token(self):
             return self.__cached_token
 
         FACEBOOK_BIRTHDAY_EVENT_PAGE_URL = 'https://www.facebook.com/events/birthdays/' # token is present on this page
-        FACEBOOK_TOKEN_REGEXP_STRING = r'{\"token\":\"(.*?)\"'
+        FACEBOOK_TOKEN_REGEXP_STRING = r'\[\"DTSGInitialData\",\[],{\"token\":\"(.*?)\"'
         regexp = re.compile(FACEBOOK_TOKEN_REGEXP_STRING, re.MULTILINE)
 
         birthday_event_page = self.browser.get(FACEBOOK_BIRTHDAY_EVENT_PAGE_URL)
@@ -128,9 +129,19 @@ def query_graph_ql_birthday_comet_monthly(self, offset_month):
 
         response = self.browser.post(FACEBOOK_GRAPHQL_ENDPOINT, data=payload)
 
+        # Sanity failsafe, GraphQL relay endpoint will always return 200
         if response.status_code != 200:
             self.logger.debug(response.text)
             self.logger.error(f'Failed to get {FACEBOOK_GRAPHQL_API_REQ_FRIENDLY_NAME} response. Payload: {payload}. Status code: {response.status_code}.')
             raise SystemError
 
-        return response.json()
+        trimmed_response = remove_anti_hijacking_protection(response.text)
+        response_json = json.loads(trimmed_response)
+
+        # Validate for errors
+        if 'error' in response_json:
+            self.logger.debug(response.text)
+            self.logger.error(f'Failed to parse {FACEBOOK_GRAPHQL_API_REQ_FRIENDLY_NAME} response. Payload: {payload}. Error: {response_json["errorSummary"]} - {response_json["errorDescription"]}')
+            raise SystemError
+
+        return response_json

fb2cal/utils.py

@@ -4,3 +4,14 @@
 # This is needed in many cases as the vanity url may change over time
 def generate_facebook_profile_url_permalink(facebook_user: FacebookUser):
     return f'https://www.facebook.com/{facebook_user.id}'
+
+# Facebook prepends an infinite while loop to their API responses as anti hijacking protection
+# It must be stripped away before parsing a response as JSON
+def remove_anti_hijacking_protection(text: str):
+    return remove_prefix(text, "for (;;);")
+
+# Replace with str.removeprefix in Python 3.9+
+def remove_prefix(text, prefix):
+    if text.startswith(prefix):
+        return text[len(prefix):]
+    return text