[serialize] adding short disconnect msg support

Signed-off-by: Jurek <git@jurek.io>

2 files changed, 37 insertions, 1 deletions

diff --git a/mqtt-format/src/v5/packets/disconnect.rs b/mqtt-format/src/v5/packets/disconnect.rs
index a03fa95..f8855e8 100644
--- a/mqtt-format/src/v5/packets/disconnect.rs
+++ b/mqtt-format/src/v5/packets/disconnect.rs
@@ -157,7 +157,34 @@ mod test {
             reason_code: DisconnectReasonCode::NormalDisconnection,
             properties: DisconnectProperties::new(),
         });
-
         assert_eq!(parsed, reference);
     }
+
+    #[test]
+    fn test_short_disconnect_encoding() {
+        let reference = MqttPacket::Disconnect(MDisconnect {
+            reason_code: DisconnectReasonCode::NormalDisconnection,
+            properties: DisconnectProperties::new(),
+        });
+        let mut writer = crate::v5::test::TestWriter { buffer: Vec::new() };
+        reference.write(&mut writer).unwrap();
+        let buf = [0xe0, 0x00];
+        assert_eq!(writer.buffer, buf);
+    }
+
+    #[test]
+    fn test_short_disconnect_long_encoding() {
+        let reference = MqttPacket::Disconnect(MDisconnect {
+            reason_code: DisconnectReasonCode::NormalDisconnection,
+            properties: DisconnectProperties {
+                session_expiry_interval: Some(SessionExpiryInterval(123)),
+                reason_string: None,
+                user_properties: None,
+                server_reference: None,
+            },
+        });
+        let mut writer = crate::v5::test::TestWriter { buffer: Vec::new() };
+        reference.write(&mut writer).unwrap();
+        assert!(writer.buffer.len() > 2, "the extra rule for short NormalDisconnect should not influence more complex disconnects");
+    }
 }
diff --git a/mqtt-format/src/v5/packets/mod.rs b/mqtt-format/src/v5/packets/mod.rs
index 9c7172a..55b39b8 100644
--- a/mqtt-format/src/v5/packets/mod.rs
+++ b/mqtt-format/src/v5/packets/mod.rs
@@ -29,6 +29,7 @@ use super::write::WResult;
 use super::write::WriteMqttPacket;
 use crate::v5::fixed_header::MFixedHeader;
 use crate::v5::packets::connack::MConnack;
+use crate::v5::packets::disconnect::{DisconnectProperties, DisconnectReasonCode};
 use crate::v5::MResult;
 
 pub mod auth;
@@ -162,6 +163,14 @@ impl<'i> MqttPacket<'i> {
                     packet_type: PacketType::Disconnect,
                 };
                 fixed_header.write(buffer)?;
+                // if reason code is NormalDisconnection AND properties are empty, we can skip writing the payload
+                if p.reason_code == DisconnectReasonCode::NormalDisconnection
+                    && p.properties == DisconnectProperties::new()
+                {
+                    // writing length of packet 0
+                    crate::v5::integers::write_variable_u32(buffer, 0)?;
+                    return Ok(());
+                }
                 crate::v5::integers::write_variable_u32(buffer, p.binary_size())?;
                 p.write(buffer)?;
             }