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# frozen_string_literal: true
# Copyright (C) 2016-2023 MongoDB Inc.
#
# 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.
module Mongo
class Server
class AppMetadata
# Implements the metadata truncation logic described in the handshake
# spec.
#
# @api private
class Truncator
# @return [ BSON::Document ] the document being truncated.
attr_reader :document
# The max application metadata document byte size.
MAX_DOCUMENT_SIZE = 512
# Creates a new Truncator instance and tries enforcing the maximum
# document size on the given document.
#
# @param [ BSON::Document] document The document to (potentially)
# truncate.
#
# @note The document is modified in-place; if you wish to keep the
# original unchanged, you must deep-clone it prior to sending it to
# a truncator.
def initialize(document)
@document = document
try_truncate!
end
# The current size of the document, in bytes, as a serialized BSON
# document.
#
# @return [ Integer ] the size of the document
def size
@document.to_bson.to_s.length
end
# Whether the document fits within the required maximum document size.
#
# @return [ true | false ] if the document is okay or not.
def ok?
size <= MAX_DOCUMENT_SIZE
end
private
# How many extra bytes must be trimmed before the document may be
# considered #ok?.
#
# @return [ Integer ] how many bytes larger the document is than the
# maximum document size.
def excess
size - MAX_DOCUMENT_SIZE
end
# Attempt to truncate the document using the documented metadata
# priorities (see the handshake specification).
def try_truncate!
%i[ env_fields os_fields env platform ].each do |target|
break if ok?
send(:"try_truncate_#{target}!")
end
end
# Attempt to truncate or remove the {{:platform}} key from the
# document.
def try_truncate_platform!
@document.delete(:platform) unless try_truncate_string(@document[:platform])
end
# Attempt to truncate the keys in the {{:env}} subdocument.
def try_truncate_env_fields!
try_truncate_hash(@document[:env], reserved: %w[ name ])
end
# Attempt to truncate the keys in the {{:os}} subdocument.
def try_truncate_os_fields!
try_truncate_hash(@document[:os], reserved: %w[ type ])
end
# Remove the {{:env}} key from the document.
def try_truncate_env!
@document.delete(:env)
end
# A helper method for truncating a string (in-place) by whatever
# {{#excess}} is required.
#
# @param [ String ] string the string value to truncate.
#
# @note the parameter is modified in-place.
def try_truncate_string(string)
length = string&.length || 0
return false if excess > length
string[(length - excess)..-1] = ''
end
# A helper method for removing the keys of a Hash (in-place) until
# the document is the necessary size. The keys are considered in order
# (using the Hash's native key ordering), and each will be removed from
# the hash in turn, until the document is the necessary size.
#
# Any keys in the {{reserved}} list will be ignored.
#
# @param [ Hash | nil ] hash the Hash instance to consider.
# @param [ Array ] reserved the list of keys to ignore in the hash.
#
# @note the hash parameter is modified in-place.
def try_truncate_hash(hash, reserved: [])
return false unless hash
keys = hash.keys - reserved
keys.each do |key|
hash.delete(key)
return true if ok?
end
false
end
end
end
end
end
|
