🥅 Return UnparsedData for unhandled response-data

Previously, unhandled `response-data` would attempt to parse to the end
of the string using `text`.  This would fail if the string contained
either literals or binary data.  The new `unparsed_response` approach
simply grabs all remaining bytes (except for the final CRLF).  Rather
than simply return string data, the response's data uses a new
`UnparsedData` struct, to unambiguously signal that the result may
change if a future release starts parsing the string.

The same approach has been copied over to `numeric_response`, allowing
unhandled numeric responses to be handled more robustly as well.

`IgnoredResponse` was converted to a subclass of `UntaggedResponse`, and
assigns any remaining unparsed text to an `UnparsedData` struct.  Other
than the subclass, it is now treated like any other unknown/unparsed
response type.  +NOOP+ still returns IgnoredResponse.

lib/net/imap/response_data.rb

@@ -55,17 +55,32 @@ class UntaggedResponse < Struct.new(:name, :data, :raw_data)
 
     # Net::IMAP::IgnoredResponse represents intentionally ignored responses.
     #
-    # This includes untagged response "NOOP" sent by eg. Zimbra to avoid some
-    # clients to close the connection.
+    # This includes untagged response "NOOP" sent by eg. Zimbra to avoid
+    # some clients to close the connection.
     #
     # It matches no IMAP standard.
-    #
-    class IgnoredResponse < Struct.new(:raw_data)
+    class IgnoredResponse < UntaggedResponse
+    end
+
+    # Net::IMAP::UnparsedData represents data for unknown or unhandled
+    # response types.  UnparsedData is an intentionally unstable API: where
+    # it is returned, future releases may return a different (incompatible)
+    # object without deprecation or warning.
+    class UnparsedData < Struct.new(:number, :unparsed_data)
       ##
-      # method: raw_data
-      # :call-seq: raw_data -> string
+      # method: number
+      # :call-seq: number -> integer
       #
-      # The raw response data.
+      # Returns a numeric response data prefix, when available.
+      #
+      # Many response types are prefixed with seqno or uid (for message
+      # data) or a message count (for mailbox data).
+
+      ##
+      # method: unparsed_data
+      # :call-seq: string -> string
+      #
+      # The unparsed data, not including #number or UntaggedResponse#name.
     end
 
     # Net::IMAP::TaggedResponse represents tagged responses.

lib/net/imap/response_parser.rb

@@ -476,13 +476,29 @@ def response_data
           when /\A(?:ENABLED)\z/ni
             return enable_data
           else
-            return text_response
+            return unparsed_response
           end
         else
           parse_error("unexpected token %s", token.symbol)
         end
       end
 
+      def unparsed_response(klass = UntaggedResponse)
+        num  = number?;          SP?
+        type = tagged_ext_label; SP?
+        text = remaining_unparsed
+        data = UnparsedData.new(num, text) if num || text
+        klass.new(type, data, @str)
+      end
+
+      # reads all the way up until CRLF
+      def remaining_unparsed
+        str = @str[@pos...-2] and @pos += str.bytesize
+        str&.empty? ? nil : str
+      end
+
+      def ignored_response; unparsed_response(IgnoredResponse) end
+
       # RFC3501 & RFC9051:
       #   response-tagged = tag SP resp-cond-state CRLF
       #
@@ -517,6 +533,10 @@ def numeric_response
           match(T_SPACE)
           data = FetchData.new(n, msg_att(n))
           return UntaggedResponse.new(name, data, @str)
+        else
+          klass = name == "NOOP" ? IgnoredResponse : UntaggedResponse
+          SP?; txt = remaining_unparsed
+          klass.new(name, UnparsedData.new(n, txt), @str)
         end
       end
 
@@ -976,20 +996,6 @@ def modseq_data
         return name, modseq
       end
 
-      def ignored_response
-        while lookahead.symbol != T_CRLF
-          shift_token
-        end
-        return IgnoredResponse.new(@str)
-      end
-
-      def text_response
-        token = match(T_ATOM)
-        name = token.value.upcase
-        match(T_SPACE)
-        return UntaggedResponse.new(name, text)
-      end
-
       def flags_response
         token = match(T_ATOM)
         name = token.value.upcase

test/net/imap/fixtures/response_parser/quirky_behaviors.yml

@@ -1,9 +1,23 @@
 ---
 :tests:
   test_invalid_noop_response_is_ignored:
-    :comment: |
-      This should probably use UntaggedResponse, perhaps with an
-      UnparsedResponseData object for its #data.
     :response: "* NOOP\r\n"
     :expected: !ruby/struct:Net::IMAP::IgnoredResponse
+      name: "NOOP"
       raw_data: "* NOOP\r\n"
+
+  test_invalid_noop_response_with_unparseable_data:
+    :response: "* NOOP froopy snood\r\n"
+    :expected: !ruby/struct:Net::IMAP::IgnoredResponse
+      name: "NOOP"
+      data: !ruby/struct:Net::IMAP::UnparsedData
+        unparsed_data: "froopy snood"
+      raw_data: "* NOOP froopy snood\r\n"
+
+  test_invalid_noop_response_with_numeric_prefix:
+    :response: "* 99 NOOP\r\n"
+    :expected: !ruby/struct:Net::IMAP::IgnoredResponse
+      name: "NOOP"
+      data: !ruby/struct:Net::IMAP::UnparsedData
+        number: 99
+      raw_data: "* 99 NOOP\r\n"