fix: postfix socketmap protocol

internal/kcpolicy/socketmap.go

@@ -4,8 +4,10 @@ import (
 	"bufio"
 	"context"
 	"fmt"
+	"io"
 	"net"
 	"os"
+	"strconv"
 	"strings"
 )
 
@@ -37,49 +39,104 @@ func RunSocketmap(ctx context.Context, cfg *Config, db *AliasDB) error {
 	}
 }
 
-// Socketmap protocol: "mapname key\n" -> "OK value\n" or "NOTFOUND\n" or "TEMP\n"
+// Postfix socketmap framing: "<len>:<payload>,"
 func handleSocketmapConn(conn net.Conn, cfg *Config, db *AliasDB) {
 	defer conn.Close()
 	r := bufio.NewReader(conn)
 
 	for {
-		line, err := r.ReadString('\n')
+		payload, err := readSocketmapFrame(r)
 		if err != nil {
+			// normal close
 			return
 		}
-		line = strings.TrimSpace(line)
-		if line == "" {
+
+		payload = strings.TrimSpace(payload)
+		if payload == "" {
+			_ = writeSocketmapFrame(conn, "NOTFOUND")
 			continue
 		}
-		parts := strings.SplitN(line, " ", 2)
+
+		parts := strings.SplitN(payload, " ", 2)
 		if len(parts) != 2 {
-			fmt.Fprint(conn, "TEMP\n")
+			_ = writeSocketmapFrame(conn, "TEMP")
 			continue
 		}
+
 		mapName := parts[0]
 		key := strings.ToLower(strings.TrimSpace(parts[1]))
 
 		if mapName != "alias" {
-			fmt.Fprint(conn, "NOTFOUND\n")
+			_ = writeSocketmapFrame(conn, "NOTFOUND")
 			continue
 		}
 
 		// Only handle our domain
-		if !strings.HasSuffix(key, "@"+strings.ToLower(cfg.Policy.Domain)) {
-			fmt.Fprint(conn, "NOTFOUND\n")
+		domain := strings.ToLower(cfg.Policy.Domain)
+		if !strings.HasSuffix(key, "@"+domain) {
+			_ = writeSocketmapFrame(conn, "NOTFOUND")
 			continue
 		}
 
 		username, ok, err := db.AliasOwner(key)
 		if err != nil {
-			fmt.Fprint(conn, "TEMP\n")
+			_ = writeSocketmapFrame(conn, "TEMP")
 			continue
 		}
 		if !ok {
-			fmt.Fprint(conn, "NOTFOUND\n")
+			_ = writeSocketmapFrame(conn, "NOTFOUND")
 			continue
 		}
-		// rewrite alias -> primary rcpt (username@domain)
-		fmt.Fprintf(conn, "OK %s@%s\n", username, strings.ToLower(cfg.Policy.Domain))
+
+		// rewrite alias -> username@domain
+		_ = writeSocketmapFrame(conn, fmt.Sprintf("OK %s@%s", username, domain))
 	}
 }
+
+func readSocketmapFrame(r *bufio.Reader) (string, error) {
+	// read decimal length until ':'
+	var lenBuf strings.Builder
+	for {
+		b, err := r.ReadByte()
+		if err != nil {
+			return "", err
+		}
+		if b == ':' {
+			break
+		}
+		if b < '0' || b > '9' {
+			return "", io.ErrUnexpectedEOF
+		}
+		lenBuf.WriteByte(b)
+		if lenBuf.Len() > 10 {
+			return "", io.ErrUnexpectedEOF
+		}
+	}
+
+	n, err := strconv.Atoi(lenBuf.String())
+	if err != nil || n < 0 || n > 1024*1024 {
+		return "", io.ErrUnexpectedEOF
+	}
+
+	buf := make([]byte, n)
+	if _, err := io.ReadFull(r, buf); err != nil {
+		return "", err
+	}
+
+	// expect trailing comma
+	b, err := r.ReadByte()
+	if err != nil {
+		return "", err
+	}
+	if b != ',' {
+		return "", io.ErrUnexpectedEOF
+	}
+
+	return string(buf), nil
+}
+
+func writeSocketmapFrame(w io.Writer, payload string) error {
+	// "<len>:<payload>,"
+	_, err := fmt.Fprintf(w, "%d:%s,", len(payload), payload)
+	return err
+}