Add a youtube URL sanitizer

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Samantaz Fox 2023-10-01 19:39:53 +02:00
parent e319c35f09
commit eb0f651812
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@ -0,0 +1,121 @@
require "uri"
module UrlSanitizer
extend self
ALLOWED_QUERY_PARAMS = {
channel: ["u", "user", "lb"],
playlist: ["list"],
search: ["q", "search_query", "sp"],
watch: [
"v", # Video ID
"list", "index", # Playlist-related
"playlist", # Unnamed playlist (id,id,id,...) (embed-only?)
"t", "time_continue", "start", "end", # Timestamp
"lc", # Highlighted comment (watch page only)
],
}
# Returns wether the given string is an ASCII word. This is the same as
# running the following regex in US-ASCII locale: /^[\w-]+$/
private def ascii_word?(str : String) : Bool
if str.bytesize == str.size
str.each_byte do |byte|
next if 'a'.ord <= byte <= 'z'.ord
next if 'A'.ord <= byte <= 'Z'.ord
next if '0'.ord <= byte <= '9'.ord
next if byte == '-'.ord || byte == '_'.ord
return false
end
return true
else
return false
end
end
# Return which kind of parameters are allowed based on the
# first path component (breadcrumb 0).
private def determine_allowed(path_root : String)
case path_root
when "watch", "w", "v", "embed", "e", "shorts", "clip"
return :watch
when .starts_with?("@"), "c", "channel", "user", "profile", "attribution_link"
return :channel
when "playlist", "mix"
return :playlist
when "results", "search"
return :search
else # hashtag, post, trending, brand URLs, etc..
return nil
end
end
# Create a new URI::Param containing only the allowed parameters
private def copy_params(unsafe_params : URI::Params, allowed_type) : URI::Params
new_params = URI::Params.new
ALLOWED_QUERY_PARAMS[allowed_type].each do |name|
if unsafe_params[name]?
# Only copy the last parameter, in case there is more than one
new_params[name] = unsafe_params.fetch_all(name)[-1]
end
end
return new_params
end
# Transform any user-supplied youtube URL into something we can trust
# and use across the code.
def process(str : String) : URI
# Because URI follows RFC3986 specifications, URL without a scheme
# will be parsed as a relative path. So we have to add a scheme ourselves.
str = "https://#{str}" if !str.starts_with?(/https?:\/\//)
unsafe_uri = URI.parse(str)
new_uri = URI.new(path: "/")
# Redirect to homepage for bogus URLs
return new_uri if (unsafe_uri.host.nil? || unsafe_uri.path.nil?)
breadcrumbs = unsafe_uri.path
.split('/', remove_empty: true)
.compact_map do |bc|
# Exclude attempts at path trasversal
next if bc == "." || bc == ".."
# Non-alnum characters are unlikely in a genuine URL
next if !ascii_word?(bc)
bc
end
# If nothing remains, it's either a legit URL to the homepage
# (who does that!?) or because we filtered some junk earlier.
return new_uri if breadcrumbs.empty?
# Replace the original query parameters with the sanitized ones
case unsafe_uri.host.not_nil!
when .ends_with?("youtube.com")
# Use our sanitized path (not forgetting the leading '/')
new_uri.path = "/#{breadcrumbs.join('/')}"
# Then determine which params are allowed, and copy them over
if allowed = determine_allowed(breadcrumbs[0])
new_uri.query_params = copy_params(unsafe_uri.query_params, allowed)
end
when "youtu.be"
# Always redirect to the watch page
new_uri.path = "/watch"
new_params = copy_params(unsafe_uri.query_params, :watch)
new_params["id"] = breadcrumbs[0]
new_uri.query_params = new_params
end
new_uri.host = nil # Safety measure
return new_uri
end
end