crystal-lang - 在 Crystal 中解析二进制格式

Question

给定一个二进制格式，其标题包括记录数和格式记录:
{ type : Int8, timestamp : UInt32, user_id : UInt64 }

0000 0004 0153 0927 d139 6747 c045 d991
2100 53d1 6287 4fd2 69fd 8e5f 0475 0153
f323 a72b 4984 a40b 8d54 db00 53a0 78d4
1db8 b1a6 4129 1651

我来自 Ruby，我有以下可行的解决方案，但我认为当它是结构化数据时，可能有一种更优雅或“ Crystal ”的方式来读取字节？

class User
  USER_TYPES = {
    0 => :admin,
    1 => :user,
  }
  property user_type : Symbol
  property timestamp : UInt32
  property user_id : UInt64

  def initialize(user_type : Int8, @timestamp : UInt32, @user_id : UInt64)
    @user_type = USER_TYPES[user_type]
  end
end

class Parser
  property users : Array(User)

  def initialize
    @users = [] of User
  end

  def parse(file_path : String)
    File.open(file_path) do |file|
      offset = 0
      count : UInt32 = seek_and_unpack(file, offset, UInt32)
      offset += 4

      (0..count).each do |i|
        user_type = seek_and_unpack(file, offset, Int8)
        timestamp = seek_and_unpack(file, offset + 1, UInt32)
        user_id = seek_and_unpack(file, offset + 5, UInt64)
        user = User.new(user_type, timestamp, user_id)
        @users << user
        offset += 13
      end
      @users
    end
  end

  private def seek_and_unpack(file : File, offset : Int32, read_type)
    file.seek(offset)
    file.read_bytes(read_type, IO::ByteFormat::BigEndian)
  end
end

puts Parser.new.parse("my_file.dat")
# [#<User:0x102805fe0 @user_type=:user, @timestamp=1393108945, @user_id=4136353673894269217>,
# #<User:0x102805fc0 @user_type=:admin, @timestamp=1406231175, @user_id=5751776211841778805>,
# #<User:0x102805fa0 @user_type=:user, @timestamp=1408443303, @user_id=3119170057034093787>,
# #<User:0x102805f80 @user_type=:admin, @timestamp=1403025620, @user_id=2141656950430570065>]

Answer 1

您可以摆脱搜索，因为 read_bytes已经在寻找 IO 并将解包操作包装在一个宏中以使其更具可读性:

class Parser
  property users

  @users = [] of User

  def parse(path)
    File.open(path) do |file|
      count = unpack(UInt32)

      count.times do
        @users << User.new(
          user_type: unpack(Int8),
          timestamp: unpack(UInt32),
          user_id: unpack(UInt64)
        )
      end
      @users
    end
  end

  macro unpack(type)
    file.read_bytes({{type}}, IO::ByteFormat::BigEndian)
  end
end