mastodon/app/lib/signature_parser.rb

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# frozen_string_literal: true
class SignatureParser
class ParsingError < StandardError; end
# The syntax of this header is defined in:
# https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures-12#section-4
# See https://datatracker.ietf.org/doc/html/rfc7235#appendix-C
# and https://datatracker.ietf.org/doc/html/rfc7230#section-3.2.6
# In addition, ignore a `Signature ` string prefix that was added by old versions
# of `node-http-signatures`
class SignatureParamsParser < Parslet::Parser
rule(:token) { match("[0-9a-zA-Z!#$%&'*+.^_`|~-]").repeat(1).as(:token) }
rule(:quoted_string) { str('"') >> (qdtext | quoted_pair).repeat.as(:quoted_string) >> str('"') }
# qdtext and quoted_pair are not exactly according to spec but meh
rule(:qdtext) { match('[^\\\\"]') }
rule(:quoted_pair) { str('\\') >> any }
rule(:bws) { match('\s').repeat }
rule(:param) { (token.as(:key) >> bws >> str('=') >> bws >> (token | quoted_string).as(:value)).as(:param) }
rule(:comma) { bws >> str(',') >> bws }
# Old versions of node-http-signature add an incorrect "Signature " prefix to the header
rule(:buggy_prefix) { str('Signature ') }
rule(:params) { buggy_prefix.maybe >> (param >> (comma >> param).repeat).as(:params) }
root(:params)
end
class SignatureParamsTransformer < Parslet::Transform
rule(params: subtree(:param)) do
(param.is_a?(Array) ? param : [param]).each_with_object({}) { |(key, value), hash| hash[key] = value }
end
rule(param: { key: simple(:key), value: simple(:val) }) do
[key, val]
end
rule(quoted_string: simple(:string)) do
string.to_s
end
rule(token: simple(:string)) do
string.to_s
end
end
def self.parse(raw_signature)
tree = SignatureParamsParser.new.parse(raw_signature)
SignatureParamsTransformer.new.apply(tree)
rescue Parslet::ParseFailed
raise ParsingError
end
end