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# frozen_string_literal: true
# Ensure that uploaded files are what they say they are for security and
# handling purposes. The checks are not 100% reliable so we err on the side of
# caution and allow by default, and deny when we're confident of a fail state.
#
# Include this concern, then call `check_upload_type` to check all
# uploads. Attach a `mime_type` or `extensions` parameter to only check
# specific upload types. Both parameters will be normalized to a MIME type and
# checked against the inferred MIME type of the upload content and filename
# extension.
#
# class YourUploader
# include UploadTypeCheck::Concern
# check_upload_type mime_types: ['image/png', /image\/jpe?g/]
#
# # or...
#
# check_upload_type extensions: ['png', 'jpg', 'jpeg']
# end
#
# The mime_types parameter can accept `NilClass`, `String`, `Regexp`,
# `Array[String, Regexp]`. This matches the CarrierWave `extension_whitelist`
# and `content_type_whitelist` family of behavior.
#
# The extensions parameter can accept `NilClass`, `String`, `Array[String]`.
module UploadTypeCheck
module Concern
extend ActiveSupport::Concern
class_methods do
def check_upload_type(mime_types: nil, extensions: nil)
define_method :check_upload_type_callback do |file|
magic_file = MagicFile.new(file.to_file)
# Map file extensions back to mime types.
if extensions
mime_types = Array(mime_types) +
Array(extensions).map { |e| MimeMagic::EXTENSIONS[e] }
end
if mime_types.nil? || magic_file.matches_mime_types?(mime_types)
check_content_matches_extension!(magic_file)
end
end
before :cache, :check_upload_type_callback
end
end
def check_content_matches_extension!(magic_file)
return if magic_file.ambiguous_type?
if magic_file.magic_type != magic_file.ext_type
raise CarrierWave::IntegrityError, 'Content type does not match file extension'
end
end
end
# Convenience class to wrap MagicMime objects.
class MagicFile
attr_reader :file
def initialize(file)
@file = file
end
def magic_type
@magic_type ||= MimeMagic.by_magic(file)
end
def ext_type
@ext_type ||= MimeMagic.by_path(file.path)
end
def magic_type_type
magic_type&.type
end
def ext_type_type
ext_type&.type
end
def matches_mime_types?(mime_types)
Array(mime_types).any? do |mt|
magic_type_type =~ /\A#{mt}\z/ || ext_type_type =~ /\A#{mt}\z/
end
end
# - Both types unknown or text/plain.
# - Ambiguous magic type with text extension. Plain text file.
# - Text magic type with ambiguous extension. TeX file missing extension.
def ambiguous_type?
(ext_type.to_s.blank? && magic_type.to_s.blank?) ||
(magic_type.to_s.blank? && ext_type_type == 'text/plain') ||
(ext_type.to_s.blank? && magic_type_type == 'text/plain')
end
end
end
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