Allow passing an `IO` as the Base64.encode source

Fixes #14603

I haven't added decoding yet because I didn't have the code for that already written. This is a decent proof of concept, generating 100MB of binary data, writing it to a file on disk, then base64-encoding it as JSON to another file. It pauses before exiting so I could check how much RAM it's using and it only uses 2.1MB of RAM for all of this.

require "base64"
require "json"

# # Generate the giant binary file data
puts "Generating 100MB of binary data..."
File.open "foo.data", "w" do |f|
  (100 << 20).times do
    f.write_byte rand(UInt8)
  end
end

pp upload = FileUpload.new("output", Path["foo.data"])

puts "Writing JSON..."
File.open "output", "w" do |file|
  upload.to_json file
end

puts "Done."
# Pause before exiting to be able to check the amount of RAM used.
gets

struct FileUpload
  include JSON::Serializable

  getter filename : String
  @[JSON::Field(key: "data", converter: FileUpload::Base64Converter)]
  getter path : Path

  def initialize(@filename, @path)
  end

  module Base64Converter
    extend self

    # Output the file contents as base64 directly to the `JSON::Builder`'s `IO`
    def to_json(path : Path, json : JSON::Builder)
      File.open path do |file|
        json.string do |io|
          Base64.encode file, io
        end
      end
    end
  end
end

crystal-lang / crystal

Allow passing an `IO` as the Base64.encode source #14604