commit e805caa483ba55e39ed32011873a7ceca425a200 Author: teor teor@torproject.org Date: Thu Aug 1 17:26:21 2019 +1000

script: Make getvar_conf() and opt() return more useful error messages

Part of 31305. --- updateFallbackDirs.py | 30 +++++++++++++++++++++++++----- 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/updateFallbackDirs.py b/updateFallbackDirs.py index 5c0e248..00e41f8 100755 --- a/updateFallbackDirs.py +++ b/updateFallbackDirs.py @@ -75,20 +75,40 @@ except ImportError:

def getenv_conf(var_name, default_val, type_fn): """Get var_name from the environment, using default_val if it is unset. - Cast the result using type_fn.""" - return type_fn(os.getenv(var_name, default_val)) + Cast the result using type_fn. If conversion fails, log an error and + exit.""" + try: + return type_fn(os.getenv(var_name, default_val)) + except ValueError as e: + # Log a useful message if conversion fails + logging.error('Could not cast env var "{}" using function "{}" and default "{}". ValueError: "{}"'.format(var_name, type_fn, default_val, e)) + sys.exit(1)

def opt(type_fn): """Higher-order function, which returns a function that converts a value - using type_fn, but returns None if the conversion fails.""" - def opt_type_fn(var_value): + using type_fn. The returned function handles some conversion failures. + See its description for details.""" + def opt_type_fn(var_value, default_val=None, var_name=None): """Converts its argument var_value using the type_fn passed to the outer function, and returns the result. - If the conversion fails, returns None.""" + If conversion fails, and var_value is None or the empty string, returns + None. + If conversion fails for any other values, throws a ValueError + exception, with an error string containing var_name, if present.""" try: return type_fn(var_value) + # Make type_fn(None) always return None for types that don't cast None except TypeError: return None + except ValueError as e: + # Make type_fn('') and type_fn(None) silently return None + if var_value == '' or var_value is None: + return None + else: + # Log a useful message if conversion fails, and throw the error to + # getenv_conf() + logging.error('Could not cast optional env var value "{}" using function "{}". ValueError: "{}"'.format(var_value, type_fn, e)) + raise e return opt_type_fn

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