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Viewing File: azure_metadata.rb

#
# Author:: Tim Smith (<tsmith@chef.io>)
# Copyright:: 2017-2020 Chef Software, Inc.
# License:: Apache License, Version 2.0
#
# 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
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

require "net/http" unless defined?(Net::HTTP)

module Ohai
  module Mixin
    #
    # This code parses the Azure Instance Metadata API to provide details
    # of the running instance.
    #
    # The code probes the instance metadata endpoint for
    # available versions, determines the most advanced version known to
    # work and executes the metadata retrieval using that version.
    #
    # If no compatible version is found, an empty hash is returned.
    #
    module AzureMetadata

      AZURE_METADATA_ADDR ||= "169.254.169.254".freeze

      # it's important that the newer versions are at the end of this array so we can skip sorting it
      AZURE_SUPPORTED_VERSIONS ||= %w{ 2017-04-02 2017-08-01 2017-12-01 2018-02-01 2018-04-02
                                   2018-10-01 2019-02-01 2019-03-11 2019-04-30 2019-06-01
                                   2019-06-04 2019-08-01 2019-08-15 2019-11-01 }.freeze

      def best_api_version
        @api_version ||= begin
          logger.trace("Mixin AzureMetadata: Fetching http://#{AZURE_METADATA_ADDR}/metadata/instance to determine the latest supported metadata release")
          response = http_get("/metadata/instance")
          if response.code == "404"
            logger.trace("Mixin AzureMetadata: Received HTTP 404 from metadata server while determining API version, assuming #{AZURE_SUPPORTED_VERSIONS.last}")
            return AZURE_SUPPORTED_VERSIONS.last
          elsif response.code != "400" # 400 is actually what we want
            raise "Mixin AzureMetadata: Unable to determine Azure metadata version (returned #{response.code} response)"
          end

          # azure returns a list of the 3 latest versions it supports
          versions = parse_json(response.body).fetch("newest-versions", [])
          versions.sort!

          until versions.empty? || AZURE_SUPPORTED_VERSIONS.include?(versions.last)
            pv = versions.pop
            logger.trace("Mixin AzureMetadata: Azure metadata version #{pv} is not present in the versions provided by the Azure Instance Metadata service")
          end

          if versions.empty?
            logger.debug "Mixin AzureMetadata: The short list of supported versions provided by Azure Instance Metadata service doesn't match any known versions to Ohai. Using the latest supported release known to Ohai instead: #{AZURE_SUPPORTED_VERSIONS.last}"
            return AZURE_SUPPORTED_VERSIONS.last
          end

          logger.trace("Mixin AzureMetadata: Latest supported Azure metadata version: #{versions.last}")
          versions.last
        end
      end

      # fetch the meta content with a timeout and the required header and a read timeout of 6s
      #
      # @param [String] the relative uri to fetch from the Azure Metadata Service URL
      #
      # @return [Net::HTTP]
      def http_get(uri)
        conn = Net::HTTP.start(AZURE_METADATA_ADDR)
        conn.read_timeout = 6
        conn.get(uri, { "Metadata" => "true" })
      end

      # parse JSON data from a String to a Hash
      #
      # @param [String] response_body json as string to parse
      #
      # @return [Hash]
      def parse_json(response_body)
        data = String(response_body)
        parser = FFI_Yajl::Parser.new
        parser.parse(data)
      rescue FFI_Yajl::ParseError
        logger.warn("Mixin AzureMetadata: Metadata response is NOT valid JSON")
        nil
      end

      def fetch_metadata(api_version = nil)
        metadata_url = "/metadata/instance?api-version=#{best_api_version}"
        logger.trace("Mixin AzureMetadata: Fetching metadata from host #{AZURE_METADATA_ADDR} at #{metadata_url}")
        response = http_get(metadata_url)
        if response.code == "200"
          parse_json(response.body)
        else
          logger.warn("Mixin AzureMetadata: Received response code #{response.code} requesting metadata")
          nil
        end
      end
    end
  end
end