feat(server): usernames, IDs, and commands; sanitize names; richer join/leave messages

- Add go-nanoid to generate 6-char per-connection IDs; fallback to RemoteAddr
- Introduce sanitizeUsername with rules: [A-Za-z0-9_.-], spaces→_, trim ._-, max 12 chars
- Support /name <username> to change username with validation and broadcast [rename]
- Greet client with default username user_<id> and usage hint for /name
- Broadcast joins/leaves and messages including username and ID; exclude self on join
- Handle /quit to trigger unified leave flow; consistent leave announcement
- Comment/document broadcast struct, Hub, and startTCPServer
- Increase scanner buffer and add newline-delimited send in broadcaster

go.mod

@@ -14,6 +14,7 @@ require (
 	github.com/charmbracelet/x/term v0.2.1 // indirect
 	github.com/erikgeiser/coninput v0.0.0-20211004153227-1c3628e74d0f // indirect
 	github.com/lucasb-eyer/go-colorful v1.2.0 // indirect
+	github.com/matoous/go-nanoid/v2 v2.1.0 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/mattn/go-localereader v0.0.1 // indirect
 	github.com/mattn/go-runewidth v0.0.16 // indirect

go.sum

@@ -20,6 +20,8 @@ github.com/erikgeiser/coninput v0.0.0-20211004153227-1c3628e74d0f h1:Y/CXytFA4m6
 github.com/erikgeiser/coninput v0.0.0-20211004153227-1c3628e74d0f/go.mod h1:vw97MGsxSvLiUE2X8qFplwetxpGLQrlU1Q9AUEIzCaM=
 github.com/lucasb-eyer/go-colorful v1.2.0 h1:1nnpGOrhyZZuNyfu1QjKiUICQ74+3FNCN69Aj6K7nkY=
 github.com/lucasb-eyer/go-colorful v1.2.0/go.mod h1:R4dSotOR9KMtayYi1e77YzuveK+i7ruzyGqttikkLy0=
+github.com/matoous/go-nanoid/v2 v2.1.0 h1:P64+dmq21hhWdtvZfEAofnvJULaRR1Yib0+PnU669bE=
+github.com/matoous/go-nanoid/v2 v2.1.0/go.mod h1:KlbGNQ+FhrUNIHUxZdL63t7tl4LaPkZNpUULS8H4uVM=
 github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWEY=
 github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
 github.com/mattn/go-localereader v0.0.1 h1:ygSAOl7ZXTx4RdPYinUpg6W99U8jWvWi9Ye2JC/oIi4=

server.go

@@ -7,13 +7,18 @@ import (
 	"net"
 	"strings"
 	"sync"
+
+	gonanoid "github.com/matoous/go-nanoid/v2"
 )
 
+// broadcast represents a line to send to all connections with the ability
+// to exclude a single connection (e.g., exclude self on join).
 type broadcast struct {
 	text    string
 	exclude net.Conn
 }
 
+// Hub manages the set of connected clients and fan-out of messages.
 type Hub struct {
 	mu      sync.Mutex
 	conns   map[net.Conn]struct{}
@@ -51,6 +56,7 @@ func (h *Hub) Run() {
 				if msg.exclude != nil && c == msg.exclude {
 					continue
 				}
+				// Newline-delimited messages
 				fmt.Fprintln(c, msg.text)
 			}
 			h.mu.Unlock()
@@ -58,32 +64,105 @@ func (h *Hub) Run() {
 	}
 }
 
+// sanitizeUsername enforces server rules on allowed usernames.
+// - letters, digits, '_', '-', '.' allowed
+// - spaces converted to '_'
+// - trimmed of leading/trailing '.', '_' or '-'
+// - empty after sanitization is invalid
+// - max length limited
+func sanitizeUsername(s string) string {
+	s = strings.TrimSpace(s)
+	if s == "" {
+		return ""
+	}
+	const maxLen = 12
+	var out []rune
+	for _, r := range s {
+		switch {
+		case r >= 'a' && r <= 'z',
+			r >= 'A' && r <= 'Z',
+			r >= '0' && r <= '9',
+			r == '_', r == '-', r == '.':
+			out = append(out, r)
+		case r == ' ':
+			out = append(out, '_')
+		default:
+			// skip everything else
+		}
+		if len(out) >= maxLen {
+			break
+		}
+	}
+	res := strings.Trim(string(out), "._-")
+	return res
+}
+
 func handleConn(h *Hub, c net.Conn) {
 	defer func() { h.leaveCh <- c }()
 	h.joinCh <- c
 
-	name := c.RemoteAddr().String()
-	fmt.Fprintf(c, "Welcome %s\n", name)
-	h.msgCh <- broadcast{text: fmt.Sprintf("[join] %s", name), exclude: c}
+	// Generate per-connection ID
+	id, err := gonanoid.Generate("ABCDEF0123456789", 6)
+	if err != nil || id == "" {
+		// Fallback to remote addr if generation fails
+		id = c.RemoteAddr().String()
+	}
+
+	// Default username is server-controlled; not necessarily unique
+	defaultName := "user_" + strings.ToLower(id)
+	username := defaultName
+
+	// Greet client and instruct on setting username
+	fmt.Fprintf(c, "Welcome %s (%s)\n", username, id)
+	fmt.Fprintln(c, "Use /name <username> to set your username. Allowed: [A-Za-z0-9_.-] (spaces become _)")
+	// Announce join to others, exclude self
+	h.msgCh <- broadcast{text: fmt.Sprintf("[join] %s (%s)", username, id), exclude: c}
 
 	scanner := bufio.NewScanner(c)
+	// Allow reasonably large lines
 	scanner.Buffer(make([]byte, 0, 1024), 64*1024)
+
 	for scanner.Scan() {
 		line := strings.TrimSpace(scanner.Text())
 		if line == "" {
 			continue
 		}
+
+		// Commands
 		if line == "/quit" {
-			break
+			break // unified leave handling below
 		}
-		h.msgCh <- broadcast{text: fmt.Sprintf("%s: %s", name, line)}
+		if strings.HasPrefix(line, "/name ") {
+			desired := strings.TrimSpace(strings.TrimPrefix(line, "/name "))
+			newName := sanitizeUsername(desired)
+			if newName == "" {
+				fmt.Fprintln(c, "[error] invalid username")
+				continue
 			}
-	if err := scanner.Err(); err != nil {
-		log.Printf("read err from %s: %v", name, err)
+			if newName == username {
+				// No change
+				fmt.Fprintf(c, "[info] username unchanged: %s\n", username)
+				continue
 			}
-	h.msgCh <- broadcast{text: fmt.Sprintf("[leave] %s", name)}
+			old := username
+			username = newName
+			// Broadcast rename to everyone (including the renamer)
+			h.msgCh <- broadcast{text: fmt.Sprintf("[rename] %s (%s) -> %s", old, id, username)}
+			continue
 		}
 
+		// Regular chat message
+		h.msgCh <- broadcast{text: fmt.Sprintf("%s (%s): %s", username, id, line)}
+	}
+	if err := scanner.Err(); err != nil {
+		log.Printf("read err from %s (%s): %v", username, id, err)
+	}
+
+	// Single, consistent leave announcement
+	h.msgCh <- broadcast{text: fmt.Sprintf("[leave] %s (%s)", username, id)}
+}
+
+// startTCPServer starts a TCP chat server and never returns unless an error occurs.
 func startTCPServer(addr string) error {
 	ln, err := net.Listen("tcp", addr)
 	if err != nil {