Вот алгоритм в ruby ...
require 'digest'
# PART_SIZE should match the chosen part size of the multipart upload
# Set here as 10MB
PART_SIZE = 1024*1024*10
class File
def each_part(part_size = PART_SIZE)
yield read(part_size) until eof?
end
end
file = File.new('')
hashes = []
file.each_part do |part|
hashes << Digest::MD5.hexdigest(part)
end
multipart_hash = Digest::MD5.hexdigest([hashes.join].pack('H*'))
multipart_etag = "#{multipart_hash}-#{hashes.count}"
Благодаря Shortest Hex2Bin в Ruby и Multipart Загружает на S3 ...