rest: Return error when header count is not integral

test/functional/interface_rest.py

@@ -279,6 +279,13 @@ class RESTTest (BitcoinTestFramework):
         json_obj = self.test_rest_request(f"/headers/5/{bb_hash}")
         assert_equal(len(json_obj), 5)  # now we should have 5 header objects
 
+        # Test number parsing
+        for num in ['5a', '-5', '0', '2001', '99999999999999999999999999999999999']:
+            assert_equal(
+                bytes(f'Header count out of range: {num}\r\n', 'ascii'),
+                self.test_rest_request(f"/headers/{num}/{bb_hash}", ret_type=RetType.BYTES, status=400),
+            )
+
         self.log.info("Test tx inclusion in the /mempool and /block URIs")
 
         # Make 3 tx and mine them on node 1