add new method to UpdateMessage

src/packets/update.rs

@@ -7,7 +7,7 @@ use crate::path_attribute::{AsPath, Origin, PathAttribute};
 use crate::routing::Ipv4Network;
 use bytes::BytesMut;
 
-use super::header::Header;
+use super::header::{Header, MessageType};
 
 #[derive(PartialEq, Eq, Debug, Clone, Hash)]
 pub struct UpdateMessage {
@@ -25,7 +25,37 @@ impl UpdateMessage {
         network_layer_reachability_information: Vec<Ipv4Network>,
         withdrawn_routes: Vec<Ipv4Network>,
     ) -> Self {
-        todo!();
+        let path_attributes_length =
+            path_attributes.iter().map(|p| p.bytes_len()).sum::<usize>() as u16;
+
+        let network_layer_reachability_information_length = network_layer_reachability_information
+            .iter()
+            .map(|r| r.bytes_len())
+            .sum::<usize>() as u16;
+
+        let withdrawn_routes_length = withdrawn_routes
+            .iter()
+            .map(|w| w.bytes_len())
+            .sum::<usize>() as u16;
+
+        let header_minimum_length = 19u16;
+        let header = Header::new(
+            header_minimum_length
+                + path_attributes_length
+                + network_layer_reachability_information_length
+                + withdrawn_routes_length
+                + 4,
+            MessageType::Update,
+        );
+
+        Self {
+            header,
+            withdrawn_routes,
+            withdrawn_routes_length,
+            path_attributes,
+            path_attributes_length,
+            network_layer_reachability_information,
+        }
     }
 }
 

src/path_attribute.rs

@@ -23,3 +23,33 @@ pub enum AsPath {
     AsSequence(Vec<AutonomousSystemNumber>),
     AsSet(BTreeSet<AutonomousSystemNumber>),
 }
+
+impl PathAttribute {
+    pub fn bytes_len(&self) -> usize {
+        let path_attribute_value_length = match self {
+            PathAttribute::Origin(_) => 1,
+            PathAttribute::AsPath(a) => a.bytes_len(),
+            PathAttribute::NextHop(_) => 4,
+            PathAttribute::DontKnow(v) => v.len(),
+        };
+
+        let length = path_attribute_value_length + 2;
+
+        if path_attribute_value_length > 255 {
+            length + 2
+        } else {
+            length + 1
+        }
+    }
+}
+
+impl AsPath {
+    fn bytes_len(&self) -> usize {
+        let as_bytes_length = match self {
+            AsPath::AsSequence(as_sequence) => 2 * as_sequence.len(),
+            AsPath::AsSet(as_set) => 2 * as_set.len(),
+        };
+
+        2 + as_bytes_length
+    }
+}

src/routing.rs

@@ -49,6 +49,19 @@ impl FromStr for Ipv4Network {
     }
 }
 
+impl Ipv4Network {
+    pub fn bytes_len(&self) -> usize {
+        match self.prefix() {
+            0 => 1,
+            1..=8 => 2,
+            9..=16 => 3,
+            17..=24 => 4,
+            25..=32 => 5,
+            _ => panic!("Invalid prefix length: {:?}", self.prefix()),
+        }
+    }
+}
+
 impl LocRib {
     pub async fn new(config: &Config) -> Result<Self> {
         todo!();