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# frozen_string_literal: true
require 'openssl'
require 'uri'
module HTML
class Pipeline
# HTML Filter for replacing http image URLs with camo versions. See:
#
# https://github.com/atmos/camo
#
# All images provided in user content should be run through this
# filter so that http image sources do not cause mixed-content warnings
# in browser clients.
#
# Context options:
# :asset_proxy (required) - Base URL for constructed asset proxy URLs.
# :asset_proxy_secret_key (required) - The shared secret used to encode URLs.
# :asset_proxy_allowlist - Array of host Strings or Regexps to skip
# src rewriting.
#
# This filter does not write additional information to the context.
class CamoFilter < Filter
# Hijacks images in the markup provided, replacing them with URLs that
# go through the github asset proxy.
def call
return doc unless asset_proxy_enabled?
doc.search('img').each do |element|
original_src = element['src']
next unless original_src
begin
uri = URI.parse(original_src)
rescue Exception
next
end
next if uri.host.nil?
next if asset_host_allowed?(uri.host)
element['src'] = asset_proxy_url(original_src)
element['data-canonical-src'] = original_src
end
doc
end
# Implementation of validate hook.
# Errors should raise exceptions or use an existing validator.
def validate
needs :asset_proxy, :asset_proxy_secret_key
end
# The camouflaged URL for a given image URL.
def asset_proxy_url(url)
"#{asset_proxy_host}/#{asset_url_hash(url)}/#{hexencode(url)}"
end
# Private: calculate the HMAC digest for a image source URL.
def asset_url_hash(url)
OpenSSL::HMAC.hexdigest('sha1', asset_proxy_secret_key, url)
end
# Private: Return true if asset proxy filter should be enabled
def asset_proxy_enabled?
!context[:disable_asset_proxy]
end
# Private: the host to use for generated asset proxied URLs.
def asset_proxy_host
context[:asset_proxy]
end
def asset_proxy_secret_key
context[:asset_proxy_secret_key]
end
def asset_proxy_whitelist
warn "[DEPRECATION] 'asset_proxy_whitelist' is deprecated. Please use 'asset_proxy_allowlist' instead."
asset_proxy_allowlist
end
def asset_proxy_allowlist
context[:asset_proxy_allowlist] || context[:asset_proxy_whitelist] || []
end
def asset_host_whitelisted?(host)
warn "[DEPRECATION] 'asset_host_whitelisted?' is deprecated. Please use 'asset_host_allowed?' instead."
asset_host_allowed?(host)
end
def asset_host_allowed?(host)
asset_proxy_allowlist.any? do |test|
test.is_a?(String) ? host == test : test.match(host)
end
end
# Private: helper to hexencode a string. Each byte ends up encoded into
# two characters, zero padded value in the range [0-9a-f].
def hexencode(str)
str.unpack('H*').first
end
end
end
end
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