1 files changed, 102 insertions, 1 deletions

diff --git a/resources/libraries/python/Constants.py b/resources/libraries/python/Constants.py
index e01536b5e6..86cbefeb9e 100644
--- a/resources/libraries/python/Constants.py
+++ b/resources/libraries/python/Constants.py
@@ -1,4 +1,4 @@
-# Copyright (c) 2019 Cisco and/or its affiliates.
+# Copyright (c) 2020 Cisco and/or its affiliates.
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at:
@@ -14,6 +14,104 @@
 """Constants used in CSIT."""
 
 
+import os
+
+
+def get_str_from_env(env_var_names, default_value):
+    """Attempt to read string from environment variable, return that or default.
+
+    If environment variable exists, but is empty (and default is not),
+    empty string is returned.
+
+    Several environment variable names are examined, as CSIT currently supports
+    a mix of naming conventions.
+    Here "several" means there are hard coded prefixes to try,
+    and env_var_names itself can be single name, or a list or a tuple of names.
+
+    :param env_var_names: Base names of environment variable to attempt to read.
+    :param default_value: Value to return if the env var does not exist.
+    :type env_var_names: str, or list of str, or tuple of str
+    :type default_value: str
+    :returns: The value read, or default value.
+    :rtype: str
+    """
+    prefixes = ("FDIO_CSIT_", "CSIT_", "")
+    if not isinstance(env_var_names, (list, tuple)):
+        env_var_names = [env_var_names]
+    for name in env_var_names:
+        for prefix in prefixes:
+            value = os.environ.get(prefix + name, None)
+            if value is not None:
+                return value
+    return default_value
+
+
+def get_int_from_env(env_var_names, default_value):
+    """Attempt to read int from environment variable, return that or default.
+
+    String value is read, default is returned also if conversion fails.
+
+    :param env_var_names: Base names of environment variable to attempt to read.
+    :param default_value: Value to return if read or conversion fails.
+    :type env_var_names: str, or list of str, or tuple of str
+    :type default_value: int
+    :returns: The value read, or default value.
+    :rtype: int
+    """
+    env_str = get_str_from_env(env_var_names, "")
+    try:
+        return int(env_str)
+    except ValueError:
+        return default_value
+
+
+def get_float_from_env(env_var_names, default_value):
+    """Attempt to read float from environment variable, return that or default.
+
+    String value is read, default is returned also if conversion fails.
+
+    :param env_var_names: Base names of environment variable to attempt to read.
+    :param default_value: Value to return if read or conversion fails.
+    :type env_var_names: str, or list of str, or tuple of str
+    :type default_value: float
+    :returns: The value read, or default value.
+    :rtype: float
+    """
+    env_str = get_str_from_env(env_var_names, "")
+    try:
+        return float(env_str)
+    except ValueError:
+        return default_value
+
+
+def get_pessimistic_bool_from_env(env_var_names):
+    """Attempt to read bool from environment variable, assume False by default.
+
+    Conversion is lenient and pessimistic, only few strings are considered true.
+
+    :param env_var_names: Base names of environment variable to attempt to read.
+    :type env_var_names: str, or list of str, or tuple of str
+    :returns: The value read, or False.
+    :rtype: bool
+    """
+    env_str = get_str_from_env(env_var_names, "").lower()
+    return bool(env_str in ("true", "yes", "y", "1"))
+
+
+def get_optimistic_bool_from_env(env_var_names):
+    """Attempt to read bool from environment variable, assume True by default.
+
+    Conversion is lenient and optimistic, only few strings are considered false.
+
+    :param env_var_names: Base names of environment variable to attempt to read.
+    :type env_var_names: str, or list of str, or tuple of str
+    :returns: The value read, or True.
+    :rtype: bool
+    """
+    env_str = get_str_from_env(env_var_names, "").lower()
+    return bool(env_str not in ("false", "no", "n", "0"))
+
+
 class Constants(object):
     """Constants used in CSIT.
 
@@ -109,6 +207,9 @@ class Constants(object):
     # Equivalent to ~0 used in vpp code
     BITWISE_NON_ZERO = 0xffffffff
 
+    # Global "kill switch" for CRC checking during runtime.
+    FAIL_ON_CRC_MISMATCH = get_pessimistic_bool_from_env("FAIL_ON_CRC_MISMATCH")
+
     # Mapping from NIC name to its bps limit.
     # TODO: Implement logic to lower limits to TG NIC or software. Or PCI.
     NIC_NAME_TO_LIMIT = {