mail/lib/mail/field.rb

# frozen_string_literal: true
require 'mail/fields'
require 'mail/constants'

# encoding: utf-8
module Mail
  # Provides a single class to call to create a new structured or unstructured
  # field.  Works out per RFC what field of field it is being given and returns
  # the correct field of class back on new.
  #
  # ===Per RFC 2822
  #
  #  2.2. Header Fields
  #
  #     Header fields are lines composed of a field name, followed by a colon
  #     (":"), followed by a field body, and terminated by CRLF.  A field
  #     name MUST be composed of printable US-ASCII characters (i.e.,
  #     characters that have values between 33 and 126, inclusive), except
  #     colon.  A field body may be composed of any US-ASCII characters,
  #     except for CR and LF.  However, a field body may contain CRLF when
  #     used in header "folding" and  "unfolding" as described in section
  #     2.2.3.  All field bodies MUST conform to the syntax described in
  #     sections 3 and 4 of this standard.
  #
  class Field
    include Comparable

    STRUCTURED_FIELDS = %w[ bcc cc content-description content-disposition
                            content-id content-location content-transfer-encoding
                            content-type date from in-reply-to keywords message-id
                            mime-version received references reply-to
                            resent-bcc resent-cc resent-date resent-from
                            resent-message-id resent-sender resent-to
                            return-path sender to ]

    KNOWN_FIELDS = STRUCTURED_FIELDS + ['comments', 'subject']

    FIELDS_MAP = {
      "to" => ToField,
      "cc" => CcField,
      "bcc" => BccField,
      "message-id" => MessageIdField,
      "in-reply-to" => InReplyToField,
      "references" => ReferencesField,
      "subject" => SubjectField,
      "comments" => CommentsField,
      "keywords" => KeywordsField,
      "date" => DateField,
      "from" => FromField,
      "sender" => SenderField,
      "reply-to" => ReplyToField,
      "resent-date" => ResentDateField,
      "resent-from" => ResentFromField,
      "resent-sender" =>  ResentSenderField,
      "resent-to" => ResentToField,
      "resent-cc" => ResentCcField,
      "resent-bcc" => ResentBccField,
      "resent-message-id" => ResentMessageIdField,
      "return-path" => ReturnPathField,
      "received" => ReceivedField,
      "mime-version" => MimeVersionField,
      "content-transfer-encoding" => ContentTransferEncodingField,
      "content-description" => ContentDescriptionField,
      "content-disposition" => ContentDispositionField,
      "content-type" => ContentTypeField,
      "content-id" => ContentIdField,
      "content-location" => ContentLocationField,
    }

    FIELD_NAME_MAP = FIELDS_MAP.inject({}) do |map, (field, field_klass)|
      map.update(field => field_klass::NAME)
    end

    # Generic Field Exception
    class FieldError < StandardError
    end

    # Raised when a parsing error has occurred (ie, a StructuredField has tried
    # to parse a field that is invalid or improperly written)
    class ParseError < FieldError #:nodoc:
      attr_accessor :element, :value, :reason

      def initialize(element, value, reason)
        @element = element
        @value = to_utf8(value)
        @reason = to_utf8(reason)
        super("#{@element} can not parse |#{@value}|: #{@reason}")
      end

      private
        def to_utf8(text)
          if text.respond_to?(:force_encoding)
            text.dup.force_encoding(Encoding::UTF_8)
          else
            text
          end
        end
    end

    class NilParseError < ParseError #:nodoc:
      def initialize(element)
        super element, nil, 'nil is invalid'
      end
    end

    class IncompleteParseError < ParseError #:nodoc:
      def initialize(element, original_text, unparsed_index)
        parsed_text = to_utf8(original_text[0...unparsed_index])
        super element, original_text, "Only able to parse up to #{parsed_text.inspect}"
      end
    end

    # Raised when attempting to set a structured field's contents to an invalid syntax
    class SyntaxError < FieldError #:nodoc:
    end

    class << self
      # Parse a field from a raw header line:
      #
      #  Mail::Field.parse("field-name: field data")
      #  # => #<Mail::Field …>
      def parse(field, charset = 'utf-8')
        name, value = split(field)
        if name && value
          new name, value, charset
        end
      end

      def split(raw_field) #:nodoc:
        if raw_field.index(Constants::COLON)
          name, value = raw_field.split(Constants::COLON, 2)
          name.rstrip!
          if name =~ /\A#{Constants::FIELD_NAME}\z/
            [ name.rstrip, value.strip ]
          else
            Kernel.warn "WARNING: Ignoring unparsable header #{raw_field.inspect}: invalid header name syntax: #{name.inspect}"
            nil
          end
        else
          raw_field.strip
        end
      rescue => error
        warn "WARNING: Ignoring unparsable header #{raw_field.inspect}: #{error.class}: #{error.message}"
        nil
      end

      def field_class_for(name) #:nodoc:
        FIELDS_MAP[name.to_s.downcase]
      end
    end

    attr_reader :unparsed_value

    # Create a field by name and optional value:
    #
    #  Mail::Field.new("field-name", "value")
    #  # => #<Mail::Field …>
    #
    # Values that aren't strings or arrays are coerced to Strings with `#to_s`.
    #
    #  Mail::Field.new("field-name", 1234)
    #  # => #<Mail::Field …>
    #
    #  Mail::Field.new('content-type', ['text', 'plain', {:charset => 'UTF-8'}])
    #  # => #<Mail::Field …>
    def initialize(name, value = nil, charset = 'utf-8')
      case
      when name.index(Constants::COLON)
        raise ArgumentError, 'Passing an unparsed header field to Mail::Field.new is not supported in Mail 2.8.0+. Use Mail::Field.parse instead.'
      when Utilities.blank?(value)
        @name = name
        @unparsed_value = nil
        @charset = charset
      else
        @name = name
        @unparsed_value = value
        @charset = charset
      end
      @name = FIELD_NAME_MAP[@name.to_s.downcase] || @name
    end

    def field=(field)
      @field = field
    end

    def field
      @field ||= create_field(@name, @unparsed_value, @charset)
    end

    def name
      @name
    end

    def value
      field.value
    end

    def value=(val)
      @field = create_field(name, val, @charset)
    end

    def to_s
      field.to_s
    end

    def inspect
      "#<#{self.class.name} 0x#{(object_id * 2).to_s(16)} #{instance_variables.map do |ivar|
        "#{ivar}=#{instance_variable_get(ivar).inspect}"
      end.join(" ")}>"
    end

    def same(other)
      other.kind_of?(self.class) && Utilities.match_to_s(other.name, name)
    end

    def ==(other)
      same(other) && Utilities.match_to_s(other.value, value)
    end

    def responsible_for?(field_name)
      name.to_s.casecmp(field_name.to_s) == 0
    end

    def <=>(other)
      field_order_id <=> other.field_order_id
    end

    def field_order_id
      @field_order_id ||= FIELD_ORDER_LOOKUP.fetch(self.name.to_s.downcase, 100)
    end

    def method_missing(name, *args, &block)
      field.send(name, *args, &block)
    end

    def respond_to_missing?(method_name, include_private)
      field.respond_to?(method_name, include_private) || super
    end

    FIELD_ORDER_LOOKUP = Hash[%w[
      return-path received
      resent-date resent-from resent-sender resent-to
      resent-cc resent-bcc resent-message-id
      date from sender reply-to to cc bcc
      message-id in-reply-to references
      subject comments keywords
      mime-version content-type content-transfer-encoding
      content-location content-disposition content-description
    ].each_with_index.to_a]

    private

    def create_field(name, value, charset)
      parse_field(name, value, charset)
    rescue Mail::Field::ParseError => e
      field = Mail::UnstructuredField.new(name, value)
      field.errors << [name, value, e]
      field
    end

    def parse_field(name, value, charset)
      value = unfold(value) if value.is_a?(String)

      if klass = self.class.field_class_for(name)
        klass.parse(value, charset)
      else
        OptionalField.parse(name, value, charset)
      end
    end

    # 2.2.3. Long Header Fields
    #
    #  The process of moving from this folded multiple-line representation
    #  of a header field to its single line representation is called
    #  "unfolding". Unfolding is accomplished by simply removing any CRLF
    #  that is immediately followed by WSP.  Each header field should be
    #  treated in its unfolded form for further syntactic and semantic
    #  evaluation.
    def unfold(string)
      string.gsub(Constants::UNFOLD_WS, '\1')
    end
  end
end