Mail::AddressList cannot parse CC header value

[carlhauck]

Here's how we're retrieving email objects from AWS S3 and then using the mail gem to parse them:

s3_object = Aws::S3::Client.new.get_object(bucket: bucket_name, key: s3_object_key)
mail = Mail.read_from_string(s3_object.body.read)

Here's an anonymized copy of a CC mail header we encountered this week:

#<Mail::Field 0x441b0 @name="Cc" @unparsed_value="Umi Anon <umi_anon@somecompany.com>, Allison Who\r\n\t<allison_who@somecompany.com>, \"gabby.where@other.com.\"\r\n\t<gabby.where@other.com.>" @charset="UTF-8" @field=#<Mail::UnstructuredField:0x00007f029fbbda48 @errors=[["Cc", "Umi Anon <umi_anon@somecompany.com>, Allison Who\r\n\t<allison_who@somecompany.com>, \"gabby.where@other.com.\"\r\n\t<gabby.where@other.com.>", #<Mail::Field::IncompleteParseError: Mail::AddressList can not parse |Umi Anon <umi_anon@somecompany.com>, Allison Who	<allison_who@somecompany.com>, "gabby.where@other.com."	<gabby.where@other.com.>|: Only able to parse up to "Umi Anon <umi_anon@somecompany.com>, Allison Who\t<allison_who@somecompany.com>, \"gabby.where@other.com.\"\t<gabby.where@other.com.">]], @name="Cc", @element=nil, @value="Umi Anon <umi_anon@somecompany.com>, Allison Who\r\n\t<allison_who@somecompany.com>, \"gabby.where@other.com.\"\r\n\t<gabby.where@other.com.>", @charset=#<Encoding:UTF-8>> @field_order_id=14>

As you can see, there's a Mail::Field::IncompleteParseError in the header itself, and we're ultimately receiving a string value from @mail.cc instead of an array of strings.

We were able to reproduce the error by mimicking some of the mail gem code:

class_name = Mail.const_get('CcField')
unfolded_anon = "Umi Anon <umi_anon@somecompany.com>, Allison Who\r\n\t<allison_who@somecompany.com>,
 \"gabby.where@other.com.\"\r\n\t<gabby.where@other.com.>".gsub(UNFOLD_WS, '\1')

class_name.parse(unfolded_anon, 'utf-8')
/usr/local/bundle/gems/mail-2.8.1/lib/mail/parsers/address_lists_parser.rb:33233:in `parse': Mail::AddressList can not parse |Umi Anon <umi_anon@somecompany.com>, Allison Who	<allison_who@somecompany.com>, "gabby.where@other.com."	<gabby.where@other.com.>|: Only able to parse up to "Umi Anon <umi_anon@somecompany.com>, Allison Who\t<allison_who@somecompany.com>, \"gabby.where@other.com.\"\t<gabby.where@other.com." (Mail::Field::IncompleteParseError)