操作指南：处理错误

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# Dict of known error codes: native errors.
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ERROR_STATUS_MAP = {
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    429: SlowDownError,
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    ...
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}
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# Dict of known error messages: native errros.
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ERROR_MESSAGE_MAP = {
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   "Channel Paused": ChannelPausedError,
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   "invalid_client": InvalidClientError,
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   "slow_down": SlowDownError,
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   ...
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}
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def _c2c_extract_error_message(response):
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    """
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    Gets the error message from an error payload. Returns `None` 
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    if an error payload is not found.
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    """
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    # Try to decode the payload, if it is not JSON return `None`
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    try:
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        payload = response.json() 
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    except JSONDecodeError:
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       return None
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    # Try the simple error schema first.
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    message = payload.get("error", default=None)
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    if message is not None:
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        return message
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    # Now try the detailed schema. Return None if we do not find one.
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    return payload.get("message", default=None)
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def _c2c_error_type_from_response(response):
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    """
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    Converts a bad HTTP response into an error.
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    """
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    error_message = _c2c_extract_error_message(response)
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    # try to do a lookup of the error type by message.
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    error_type = ERROR_MESSAGE_MAP.get(error_message, default=None) 
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    if error_type is not None:
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        return error_type()
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    # If not, try to do a lookup by error code.
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    error_type = ERROR_STATUS_MAP.get(response.status_code, default=None)
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    if error_type is not None:
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        return error_type()
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    # Otherwise we are going to return an `UnknownAPIError` to signal that we
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    # encoutnered an error from Frame.io's backend servers, but do not know the
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    # message and/or status code.
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    return UnknownAPIError(message=error_message)
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def raise_on_frameio_error(response, expected_status):
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    """
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    Raises a native error from an HTTP response if the response indicates an error
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    occured. Expected status should be the status we expect to get (200, 201, 204, 
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    etc).
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    """
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    # If the status code is less than `400`, then it is not an error status code.
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    if response.status < 400:
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        # Check that the status code is the one we expected, otherwise raise an
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        # error.
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        if response.status != expected_status:
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            raise UnexpectedStatusError(
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                expected=expected_status, received=response.status
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            )
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        return None
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    # Otherwise convert and raise a native error.
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    raise _c2c_error_type_from_response(response)

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delay = min(2 ** attempt / 2, 32.0)

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# List of errors we know are fatal and should not be retried.
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FATAL_ERRORS = (
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    ChannelPausedError,
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    DevicesDisabledError,
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    ...
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)
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# List of errors we know should be retried more than once.
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RETRY_ERRORS = (
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    TimeoutError,
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    NotFoundError,
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    SlowDownError,
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    UnknownAPIError,
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    ...
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)
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# List of errors that could be the result of Frame.io being unreachable.
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DISCONNECTED_ERRORS = (
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    TimeoutError,
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    HttpClientError,
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    ...
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)
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def retry_with_backoff(next_handler):
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    """
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    Middleware for retrying errors with exponential backoff.
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    """
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    def retry_handler(call, retry_count):
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        """
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        Handler for retrying c2c API calls with exponential backoff.
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        """
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        error = None
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        # We will retry the call 8 times here, totalling 63.5 seconds +- ~32 seconds.
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        for attempt in range(start=1, stop=retry_count + 1):
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            # If we are attempting to reach an endpoint that requires authorization
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            # we should wait unil we have valid authorization before attempting
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            # a call. We need to do this each time in case our access_token
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            # expires between attempts.
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            C2C.wait_for_authorized(call)
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            # Likewise, we should wait until we are connected to Frame.io to attempt
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            # a call if we are not calling `https://api.frame.io/health`
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            C2C.wait_for_connected(call)
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            try:
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                # Return the result on a success.
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                return next_handler(call)
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            except FATAL_ERRORS as error:
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                # If we hit an error we know is fatal, raise the error without
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                # retrying it.
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                raise error
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            except RETRY_ERRORS as error:
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                # If we hit an error we know we should retry many times, continue,
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                # but notify our client if we think we may have been disconnected.
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                if type(error) in DISCONNECTED_ERRORS:
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                    C2C.notify_disconnected()
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            except BaseException as error:
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                # Otherwise, do not retry the call more than once.
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                if attempt > 1:
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                    raise error
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            # The delay for the next attempt should be no more than 32 seconds.
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            # This algorithm will go: 0.5s, 1s, 2s, 4s, 8s, 16s, 32s, 32s, ...
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            delay = min(2 ** attempt / 2, 32.0)
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            # Add some randomness (jitter) to the delay (up to half the value of
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            # the delay in either direction).
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            delay += math.random(-delay, delay) / 2
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            # Wait between retries
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            sleep(delay)
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        # If we have exhausted all retries,
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        raise error
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    return retry_handler