readdata.py: handle empty page ranges correctly

1 files changed, 10 insertions, 2 deletions

diff --git a/dexcom_reader/readdata.py b/dexcom_reader/readdata.py
index 5e2436b..e589b1a 100644
--- a/dexcom_reader/readdata.py
+++ b/dexcom_reader/readdata.py
@@ -241,7 +241,10 @@ class Dexcom(object):
     self.WriteCommand(constants.READ_DATABASE_PAGE_RANGE,
                       chr(record_type_index))
     packet = self.readpacket()
-    return struct.unpack('II', packet.data)
+    (a, b) = struct.unpack('II', packet.data)
+    if a == 2**32-1 or b == 2**32-1:
+        return None
+    return (a, b)
 
   def ReadDatabasePage(self, record_type, page):
     record_type_index = constants.RECORD_TYPES.index(record_type)
@@ -294,6 +297,8 @@ class Dexcom(object):
   def iter_records (self, record_type):
     assert record_type in constants.RECORD_TYPES
     page_range = self.ReadDatabasePageRange(record_type)
+    if page_range is None:
+      return
     start, end = page_range
     if start != end or not end:
       end += 1
@@ -302,11 +307,14 @@ class Dexcom(object):
       records.reverse( )
       for record in records:
         yield record
-  
+
   def ReadRecords(self, record_type, n=0):
     records = []
     assert record_type in constants.RECORD_TYPES
     page_range = self.ReadDatabasePageRange(record_type)
+    if page_range is None:
+      return records
+
     start, end = page_range
     if start != end or not end:
       end += 1