Adding MODE command support

[fclairamb]

We're only accepting the "Stream" mode though. But at least it's official.

To address #451

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.73%. Comparing base (d2b3c25) to head (3880fc0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #460      +/-   ##
==========================================
+ Coverage   86.68%   86.73%   +0.04%     
==========================================
  Files          11       11              
  Lines        1720     1726       +6     
==========================================
+ Hits         1491     1497       +6     
  Misses        155      155              
  Partials       74       74              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[drakkan]

@fclairamb thank you. I also had this change locally

rom 06190249a0885db147cc63dba04d292e8043c181 Mon Sep 17 00:00:00 2001
From: Nicola Murino <[email protected]>
Date: Tue, 30 Apr 2024 19:19:08 +0200
Subject: [PATCH] add support for MODE type

---
 handle_misc.go | 13 +++++++++++++
 server.go      |  1 +
 2 files changed, 14 insertions(+)

diff --git a/handle_misc.go b/handle_misc.go
index 097b3014..a5a3dee4 100644
--- a/handle_misc.go
+++ b/handle_misc.go
@@ -284,6 +284,19 @@ func (c *clientHandler) handleTYPE(param string) error {
 	return nil
 }
 
+func (c *clientHandler) handleMODE(param string) error {
+	param = strings.ToUpper(param)
+	switch param {
+	case "S":
+		c.writeMessage(StatusOK, "Transfer mode set to 'S'")
+	case "B", "C", "Z":
+		c.writeMessage(StatusNotImplementedParam, "Unimplemented MODE type")
+	default:
+		c.writeMessage(StatusSyntaxErrorParameters, "Unrecognized MODE type")
+	}
+	return nil
+}
+
 func (c *clientHandler) handleQUIT(_ string) error {
 	c.transferWg.Wait()
 
diff --git a/server.go b/server.go
index 0c0c2612..25f0dd23 100644
--- a/server.go
+++ b/server.go
@@ -91,6 +91,7 @@ var commandsMap = map[string]*CommandDescription{ //nolint:gochecknoglobals
 	"EPSV": {Fn: (*clientHandler).handlePASV},
 	"PORT": {Fn: (*clientHandler).handlePORT},
 	"EPRT": {Fn: (*clientHandler).handlePORT},
+	"MODE": {Fn: (*clientHandler).handleMODE},
 }
 
 var specialAttentionCommands = []string{"ABOR", "STAT", "QUIT"} //nolint:gochecknoglobals

But I never wrote a test case and then forgot about it, sorry