src/cmd/cos_gpu_installer_v1/cos-gpu-installer-docker/get_metadata_value

#! /bin/bash
#
# Copyright 2020 Google LLC
#
# 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.
#
# Get a metadata value from the metadata server.
declare -r VARNAME=$1
declare -r MDS_PREFIX=http://metadata.google.internal/computeMetadata/v1
declare -r MDS_TRIES=${MDS_TRIES:-100}

function print_metadata_value() {
  local readonly tmpfile=$(mktemp)
  http_code=$(curl -f "${1}" -H "Metadata-Flavor: Google" -w "%{http_code}" \
    -s -o ${tmpfile} 2>/dev/null)
  local readonly return_code=$?
  # If the command completed successfully, print the metadata value to stdout.
  if [[ ${return_code} == 0 && ${http_code} == 200 ]]; then
    cat ${tmpfile}
  fi
  rm -f ${tmpfile}
  return ${return_code}
}

function print_metadata_value_if_exists() {
  local return_code=1
  local readonly url=$1
  print_metadata_value ${url}
  return_code=$?
  return ${return_code}
}

function get_metadata_value() {
  local readonly varname=$1
  # Print the instance metadata value.
  print_metadata_value_if_exists ${MDS_PREFIX}/instance/${varname}
  return_code=$?
  # If the instance doesn't have the value, try the project.
  if [[ ${return_code} != 0 ]]; then
    print_metadata_value_if_exists ${MDS_PREFIX}/project/${varname}
    return_code=$?
  fi
  return ${return_code}
}

function get_metadata_value_with_retries() {
  local return_code=1  # General error code.
  for ((count=0; count <= ${MDS_TRIES}; count++)); do
    get_metadata_value $VARNAME
    return_code=$?
    case $return_code in
      # No error.  We're done.
      0) exit ${return_code};;
      # Failed to resolve host or connect to host.  Retry.
      6|7) sleep 0.3; continue;;
      # A genuine error.  Exit.
      *) exit ${return_code};
    esac
  done
  # Exit with the last return code we got.
  exit ${return_code}
}

get_metadata_value_with_retries