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name : imds.py
 # Copyright (C) 2022 Microsoft Corporation.
#
# This file is part of cloud-init. See LICENSE file for license information.

import logging
from time import time
from typing import Dict, Optional, Type, Union

import requests

from cloudinit import util
from cloudinit.sources.helpers.azure import report_diagnostic_event
from cloudinit.url_helper import UrlError, readurl

LOG = logging.getLogger(__name__)

IMDS_URL = "http://169.254.169.254/metadata"


class ReadUrlRetryHandler:
    """Manager for readurl retry behavior using exception_callback().

    :param logging_backoff: Backoff to limit logging.
    :param max_connection_errors: Number of connection errors to retry on.
    :param retry_codes: Set of http codes to retry on.
    :param retry_deadline: Optional time()-based deadline to retry until.
    """

    def __init__(
        self,
        *,
        logging_backoff: float = 1.0,
        max_connection_errors: Optional[int] = None,
        retry_codes=(
            404,  # not found (yet)
            410,  # gone / unavailable (yet)
            429,  # rate-limited/throttled
            500,  # server error
        ),
        retry_deadline: Optional[float] = None,
    ) -> None:
        self.logging_backoff = logging_backoff
        self.max_connection_errors = max_connection_errors
        self.retry_codes = retry_codes
        self.retry_deadline = retry_deadline
        self._logging_threshold = 1.0
        self._request_count = 0
        self._last_error: Union[None, Type, int] = None

    def exception_callback(self, req_args, exception) -> bool:
        self._request_count += 1
        if not isinstance(exception, UrlError):
            report_diagnostic_event(
                "Polling IMDS failed with unexpected exception: %r"
                % (exception),
                logger_func=LOG.warning,
            )
            return False

        log = True
        if self.retry_deadline is not None and time() >= self.retry_deadline:
            retry = False
        else:
            retry = True

        # Check for connection errors which may occur early boot, but
        # are otherwise indicative that we are not connecting with the
        # primary NIC.
        if self.max_connection_errors is not None and isinstance(
            exception.cause, requests.ConnectionError
        ):
            self.max_connection_errors -= 1
            if self.max_connection_errors <= 0:
                retry = False
        elif (
            exception.code is not None
            and exception.code not in self.retry_codes
        ):
            retry = False

        if self._request_count >= self._logging_threshold:
            self._logging_threshold *= self.logging_backoff
        else:
            log = False

        # Always log if error does not match previous.
        if exception.code is not None:
            # This is an HTTP response with failing code, log if different.
            if self._last_error != exception.code:
                log = True
                self._last_error = exception.code
        elif (
            # No previous error to match against.
            self._last_error is None
            # Previous error is exception code (int).
            or not isinstance(self._last_error, type)
            # Previous error is different class.
            or not isinstance(exception.cause, self._last_error)
        ):
            log = True
            self._last_error = type(exception.cause)

        if log or not retry:
            report_diagnostic_event(
                "Polling IMDS failed attempt %d with exception: %r"
                % (self._request_count, exception),
                logger_func=LOG.warning,
            )
        return retry


def _fetch_url(
    url: str,
    *,
    retry_handler: ReadUrlRetryHandler,
    log_response: bool = True,
    timeout: int = 30,
) -> bytes:
    """Fetch URL from IMDS.

    :param url: url to fetch.
    :param log_response: log responses in readurl().
    :param retry_deadline: time()-based deadline to retry until.
    :param timeout: Read/connection timeout in seconds for readurl().

    :raises UrlError: on error fetching metadata.
    """
    try:
        response = readurl(
            url,
            exception_cb=retry_handler.exception_callback,
            headers={"Metadata": "true"},
            infinite=True,
            log_req_resp=log_response,
            timeout=timeout,
        )
    except UrlError as error:
        report_diagnostic_event(
            "Failed to fetch metadata from IMDS: %s" % error,
            logger_func=LOG.warning,
        )
        raise

    return response.contents


def _fetch_metadata(
    url: str,
    *,
    retry_handler: ReadUrlRetryHandler,
) -> Dict:
    """Fetch IMDS metadata.

    :param url: url to fetch.
    :param retry_deadline: time()-based deadline to retry until.

    :raises UrlError: on error fetching metadata.
    :raises ValueError: on error parsing metadata.
    """
    metadata = _fetch_url(url, retry_handler=retry_handler)

    try:
        return util.load_json(metadata.decode("utf-8"))
    except ValueError as error:
        report_diagnostic_event(
            "Failed to parse metadata from IMDS: %s" % error,
            logger_func=LOG.warning,
        )
        raise


def fetch_metadata_with_api_fallback(
    retry_deadline: float, max_connection_errors: Optional[int] = None
) -> Dict:
    """Fetch extended metadata, falling back to non-extended as required.

    :param retry_deadline: time()-based deadline to retry until.

    :raises UrlError: on error fetching metadata.
    :raises ValueError: on error parsing metadata.
    """
    retry_handler = ReadUrlRetryHandler(
        max_connection_errors=max_connection_errors,
        retry_deadline=retry_deadline,
    )
    try:
        url = IMDS_URL + "/instance?api-version=2021-08-01&extended=true"
        return _fetch_metadata(url, retry_handler=retry_handler)
    except UrlError as error:
        if error.code == 400:
            report_diagnostic_event(
                "Falling back to IMDS api-version: 2019-06-01",
                logger_func=LOG.warning,
            )
            retry_handler = ReadUrlRetryHandler(
                max_connection_errors=max_connection_errors,
                retry_deadline=retry_deadline,
            )
            url = IMDS_URL + "/instance?api-version=2019-06-01"
            return _fetch_metadata(url, retry_handler=retry_handler)
        raise


def fetch_reprovision_data() -> bytes:
    """Fetch extended metadata, falling back to non-extended as required.

    :raises UrlError: on error.
    """
    url = IMDS_URL + "/reprovisiondata?api-version=2019-06-01"

    handler = ReadUrlRetryHandler(
        logging_backoff=2.0,
        max_connection_errors=1,
        retry_codes=(
            404,
            410,
            429,
        ),
        retry_deadline=None,
    )
    response = readurl(
        url,
        exception_cb=handler.exception_callback,
        headers={"Metadata": "true"},
        infinite=True,
        log_req_resp=False,
        timeout=30,
    )

    report_diagnostic_event(
        f"Polled IMDS {handler._request_count+1} time(s)",
        logger_func=LOG.debug,
    )
    return response.contents
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