✨ Add iscsi stringprep profile

This isn't used by IMAP at all, and never will be.  But once the generic
StringPrep algorithm is in place, this is trivial to add.  So it is
added for completeness and to test the stringprep code better.

lib/net/imap/stringprep.rb

@@ -9,6 +9,7 @@ class IMAP < Protocol
     # codepoint table defined in the RFC-3454 appendices is matched by a Regexp
     # defined in this module.
     module StringPrep
+      autoload :ISCSI,    File.expand_path("stringprep/iscsi",    __dir__)
       autoload :NamePrep, File.expand_path("stringprep/nameprep", __dir__)
       autoload :SASLprep, File.expand_path("stringprep/saslprep", __dir__)
       autoload :Tables,   File.expand_path("stringprep/tables",   __dir__)

lib/net/imap/stringprep/iscsi.rb

@@ -0,0 +1,115 @@
+# frozen_string_literal: true
+
+module Net
+  class IMAP
+    module StringPrep
+
+      # Defined in RFC3722[https://tools.ietf.org/html/rfc3722], the +iSCSI+
+      # profile of "Stringprep" is used to:
+      # >>>
+      #   prepare internationalized iSCSI names to increase the likelihood that
+      #   name input and comparison work in ways that make sense for typical
+      #   users throughout the world.
+      #
+      #   ...
+      #
+      #   The goal, then, is to generate iSCSI names that can be transcribed and
+      #   entered by users, and also compared byte-for-byte, with minimal
+      #   confusion.  To attain these goals, iSCSI names are generalized using a
+      #   normalized character set (converted to lower case or equivalent), with
+      #   no white space allowed, and very limited punctuation.
+      #
+      #   - The intended applicability of the profile: internationalized iSCSI
+      #     names.
+      #   - The character repertoire that is the input and output to
+      #     stringprep: Unicode 3.2, specified in section 3.
+      #   - The mappings used: specified in section 4.
+      #   - The Unicode normalization used: specified in section 5.
+      #   - The characters that are prohibited as output: specified in section 6.
+      #
+      #   This profile MUST be used with the iSCSI protocol.
+      module ISCSI
+
+        STRINGPREP_PROFILE = "iSCSI"
+
+        # From RFC3722[https://www.rfc-editor.org/rfc/rfc3722.html] §2
+        UNASSIGNED_TABLE = "A.1"
+
+        # From RFC3722[https://www.rfc-editor.org/rfc/rfc3722.html] §3
+        MAPPING_TABLES = %w[B.1 B.2].freeze
+
+        # From RFC3722[https://www.rfc-editor.org/rfc/rfc3722.html] §5
+        NORMALIZATION = :nfkc
+
+        # From RFC3722[https://www.rfc-editor.org/rfc/rfc3722.html] §6
+        PROHIBITED_TABLES = %w[C.1.1 C.1.2 C.2.1 C.2.2 C.3 C.4 C.5 C.6 C.7 C.8 C.9].freeze
+
+        # From RFC3722[https://www.rfc-editor.org/rfc/rfc3722.html] §6.1:
+        # >>>
+        #   6.1.  Inappropriate Characters from Common Input Mechanisms
+        #
+        #   u+3002 is used as if it were u+002e in many domain name input
+        #   mechanisms used by applications, particularly in Asia.  The character
+        #   u+3002 MUST NOT be used in an iSCSI name.
+        #
+        #      3002; ideographic full stop
+        INAPPROPRIATE_FROM_COMMON_INPUT_MECHANISMS = /\u{3002}/.freeze
+
+        # From RFC3722[https://www.rfc-editor.org/rfc/rfc3722.html] §6.2:
+        # >>>
+        #   6.2.  Currently-prohibited ASCII characters
+        #
+        #   Some of the ASCII characters that are currently prohibited in iSCSI
+        #   names by [RFC3721] are also used in protocol elements such as URIs.
+        #   Some examples are described in [RFC2396] and [RFC2732].  Note that
+        #   there are many other RFCs that define additional URI schemes.
+        #
+        #   The other characters in the range U+0000 to U+007F that are not
+        #   currently allowed are prohibited in iSCSI names to reserve them for
+        #   future use in protocol elements.  Note that the dash (U+002D), dot
+        #   (U+002E), and colon (U+003A) are not prohibited.
+        #
+        #   The following characters MUST NOT be used in iSCSI names:
+        #
+        #      0000-002C; [ASCII CONTROL CHARACTERS and SPACE through ,]
+        #      002F; [ASCII /]
+        #      003B-0040; [ASCII ; through @]
+        #      005B-0060; [ASCII [ through `]
+        #      007B-007F; [ASCII { through DEL]
+        PROHIBITED_ASCII = /[\x00-\x2c\x2f\x3b-\x40\x5b-\x60\x7B-\x7f]/.freeze
+
+        # From RFC3722[https://www.rfc-editor.org/rfc/rfc3722.html] §6.2:
+        #   In addition, this profile adds the following prohibitions.  The full
+        #   set of prohibited characters are those from the tables above plus
+        #   those listed individually below.
+        PROHIBITED_REGEXP = [
+          PROHIBITED_ASCII,
+          INAPPROPRIATE_FROM_COMMON_INPUT_MECHANISMS,
+        ]
+          .map(&:source).join
+          .then { /[#{_1}]/ }
+          .freeze
+
+        # From RFC3722[https://www.rfc-editor.org/rfc/rfc3722.html] §7
+        CHECK_BIDI = true
+
+        module_function
+
+        def stringprep_iscsi(string, **opts)
+          StringPrep.stringprep(
+            string,
+            unassigned:    UNASSIGNED_TABLE,
+            maps:          MAPPING_TABLES,
+            prohibited:    [*PROHIBITED_TABLES, PROHIBITED_REGEXP],
+            normalization: NORMALIZATION,
+            bidi:          CHECK_BIDI,
+            profile:       STRINGPREP_PROFILE,
+            **opts,
+          )
+        end
+
+      end
+
+    end
+  end
+end

test/net/imap/test_stringprep_profiles.rb

@@ -6,6 +6,7 @@
 class StringPrepProfilesTest < Test::Unit::TestCase
   include Net::IMAP::StringPrep
   include Net::IMAP::StringPrep::Trace
+  include Net::IMAP::StringPrep::ISCSI
 
   def test_trace_profile_prohibit_ctrl_chars
     assert_raise(ProhibitedCodepoint) {
@@ -22,4 +23,14 @@ def test_trace_profile_prohibit_tagging_chars
     }
   end
 
+  def test_iscsi_profile_case_maps
+    assert_equal "hêllω-woŗλd", stringprep_iscsi("HÊlLΩ-WoŖΛd")
+  end
+
+  def test_iscsi_profile_prohibit_ideographic_full_stop
+    assert_raise(ProhibitedCodepoint) {
+      stringprep_iscsi "hello\u{3002}world"
+    }
+  end
+
 end