add get_enc_len to Decoder trait

src/fot/decoder.rs

@@ -5,6 +5,7 @@ use crate::fot::raw::Raw;
 pub trait Decoder: Sized {
     fn decode(raw: &Raw, offset: usize, size: usize) -> Result<Self>;
     fn encode(&self) -> Raw;
+    fn get_enc_len(&self) -> usize;
 }
 
 impl Decoder for String {
@@ -21,4 +22,8 @@ impl Decoder for String {
         str.push(0);
         Raw { offset: 0, size: str.len(), mem: str}
     }
+
+    fn get_enc_len(&self) -> usize {
+        self.len() + 1
+    }
 }

src/fot/tag.rs

@@ -8,12 +8,6 @@ pub struct Tag {
     pub version: String
 }
 
-impl Tag {
-    pub fn get_tag_len(&self) -> usize {
-        self.name.len() + 1 + self.version.len() + 1
-    }
-}
-
 impl Decoder for Tag {
     fn decode(raw: &Raw, offset: usize, size: usize) -> Result<Self> {
         let name = String::decode(raw, offset, size)?;
@@ -22,9 +16,13 @@ impl Decoder for Tag {
     }
 
     fn encode(&self) -> Raw {
-        Raw::join(0, self.get_tag_len(), &mut [
+        Raw::join(0, self.get_enc_len(), &mut [
             self.name.encode(),
             self.version.encode()
         ])
     }
+
+    fn get_enc_len(&self) -> usize {
+        self.name.get_enc_len() + self.version.get_enc_len()
+    }
 }

src/fot/world.rs

@@ -49,4 +49,8 @@ impl Decoder for World {
             Raw { offset: Self::WORLD_HDR_LEN, size: data.len(), mem: data}
         ])
     }
+
+    fn get_enc_len(&self) -> usize {
+        Self::WORLD_HDR_LEN + self.data.mem.len()
+    }
 }