Implement HELP command

README.md

@@ -45,7 +45,7 @@
   - :x: `LIST DISTRIB.PATS`
 - :construction: Information Commands
   - :heavy_check_mark: `DATE`
-  - :x: `HELP`
+  - :heavy_check_mark: `HELP`
   - :heavy_check_mark: `NEWGROUPS`
   - :x: `NEWNEWS`
 

internal/protocol/constants.go

@@ -60,6 +60,7 @@ const (
 	CommandHead         = "HEAD"
 	CommandBody         = "BODY"
 	CommandStat         = "STAT"
+	CommandHelp         = "HELP"
 )
 
 const (

internal/server/handler.go

@@ -40,6 +40,7 @@ func NewHandler(b backend.StorageBackend, serverDomain string) *Handler {
 		protocol.CommandHead:         h.handleArticle,
 		protocol.CommandBody:         h.handleArticle,
 		protocol.CommandStat:         h.handleArticle,
+		protocol.CommandHelp:         h.handleHelp,
 	}
 	h.serverDomain = serverDomain
 	return h
@@ -512,6 +513,49 @@ func (h *Handler) handleArticle(s *Session, command string, arguments []string,
 	return nil
 }
 
+func (h *Handler) handleHelp(s *Session, command string, arguments []string, id uint) error {
+	s.tconn.StartResponse(id)
+	defer s.tconn.EndResponse(id)
+
+	help :=
+		"  ARTICLE [message-ID|number]\r\n" +
+			"  BODY [message-ID|number]\r\n" +
+			"  CAPABILITIES [keyword]\r\n" +
+			"  DATE\r\n" +
+			"  GROUP newsgroup\r\n" +
+			"  HEAD [message-ID|number]\r\n" +
+			"  HELP\r\n" +
+			"  LAST\r\n" +
+			"  LIST [ACTIVE [wildmat]|NEWSGROUPS [wildmat]]\r\n" +
+			"  LISTGROUP [newsgroup [range]]\r\n" +
+			"  MODE READER\r\n" +
+			"  NEWGROUPS [yy]yymmdd hhmmss [GMT]\r\n" +
+			"  NEXT\r\n" +
+			"  POST\r\n" +
+			"  QUIT\r\n" +
+			"  STAT [message-ID|number]\r\n"
+
+	dw := s.tconn.DotWriter()
+	w := bufio.NewWriter(dw)
+
+	_, err := w.Write([]byte(protocol.NNTPResponse{Code: 100, Message: "Legal commands"}.String() + protocol.CRLF))
+	if err != nil {
+		return err
+	}
+
+	_, err = w.Write([]byte(help))
+	if err != nil {
+		return err
+	}
+
+	err = w.Flush()
+	if err != nil {
+		return err
+	}
+
+	return dw.Close()
+}
+
 func (h *Handler) Handle(s *Session, message string, id uint) error {
 	splittedMessage := strings.Split(message, " ")
 	for i, v := range splittedMessage {