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# frozen_string_literal: true
module Gitlab
module Utils
# This class estimates the JSON blob byte size of a ruby object using as
# little allocations as possible.
# The estimation should be quite accurate when using simple objects.
#
# Example:
#
# Gitlab::Utils::JsonSizeEstimator.estimate(["a", { b: 12, c: nil }])
class JsonSizeEstimator
ARRAY_BRACKETS_SIZE = 2 # []
OBJECT_BRACKETS_SIZE = 2 # {}
DOUBLEQUOTE_SIZE = 2 # ""
COLON_SIZE = 1 # : character size from {"a": 1}
MINUS_SIGN_SIZE = 1 # - character size from -1
NULL_SIZE = 4 # null
class << self
# Returns: integer (number of bytes)
def estimate(object)
case object
when Hash
estimate_hash(object)
when Array
estimate_array(object)
when String
estimate_string(object)
when Integer
estimate_integer(object)
when Float
estimate_float(object)
when DateTime, Time
estimate_time(object)
when NilClass
NULL_SIZE
else
# might be incorrect, but #to_s is safe, #to_json might be disabled for some objects: User
estimate_string(object.to_s)
end
end
private
def estimate_hash(hash)
size = 0
item_count = 0
hash.each do |key, value|
item_count += 1
size += estimate(key.to_s) + COLON_SIZE + estimate(value)
end
size + OBJECT_BRACKETS_SIZE + comma_count(item_count)
end
def estimate_array(array)
size = 0
item_count = 0
array.each do |item|
item_count += 1
size += estimate(item)
end
size + ARRAY_BRACKETS_SIZE + comma_count(item_count)
end
def estimate_string(string)
string.bytesize + DOUBLEQUOTE_SIZE
end
def estimate_float(float)
float.to_s.bytesize
end
def estimate_integer(integer)
if integer > 0
integer_string_size(integer)
elsif integer < 0
integer_string_size(integer.abs) + MINUS_SIGN_SIZE
else # 0
1
end
end
def estimate_time(time)
time.to_json.size
end
def integer_string_size(integer)
Math.log10(integer).floor + 1
end
def comma_count(item_count)
item_count == 0 ? 0 : item_count - 1
end
end
end
end
end
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