[ruby/net-imap] Move UTF7 & datetime formatting to net/imap/data_encoding

Partially implements #10.

0d43c5e856

lib/net/imap/data_encoding.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+module Net
+  class IMAP < Protocol
+
+    # Decode a string from modified UTF-7 format to UTF-8.
+    #
+    # UTF-7 is a 7-bit encoding of Unicode [UTF7].  IMAP uses a
+    # slightly modified version of this to encode mailbox names
+    # containing non-ASCII characters; see [IMAP] section 5.1.3.
+    #
+    # Net::IMAP does _not_ automatically encode and decode
+    # mailbox names to and from UTF-7.
+    def self.decode_utf7(s)
+      return s.gsub(/&([^-]+)?-/n) {
+        if $1
+          ($1.tr(",", "/") + "===").unpack1("m").encode(Encoding::UTF_8, Encoding::UTF_16BE)
+        else
+          "&"
+        end
+      }
+    end
+
+    # Encode a string from UTF-8 format to modified UTF-7.
+    def self.encode_utf7(s)
+      return s.gsub(/(&)|[^\x20-\x7e]+/) {
+        if $1
+          "&-"
+        else
+          base64 = [$&.encode(Encoding::UTF_16BE)].pack("m0")
+          "&" + base64.delete("=").tr("/", ",") + "-"
+        end
+      }.force_encoding("ASCII-8BIT")
+    end
+
+    # Formats +time+ as an IMAP-style date.
+    def self.format_date(time)
+      return time.strftime('%d-%b-%Y')
+    end
+
+    # Formats +time+ as an IMAP-style date-time.
+    def self.format_datetime(time)
+      return time.strftime('%d-%b-%Y %H:%M %z')
+    end
+
+  end
+end