[cache (rust)] Implement Pack and Default for restoration

src/cache/hint.rs

@@ -1,3 +1,5 @@
+use anyhow::Result;
+use byteorder::WriteBytesExt;
 use nom::IResult;
 use std::convert::TryInto;
 
@@ -26,4 +28,19 @@ impl Unpack for Hint {
     }
 }
 
+impl Pack for Hint {
+    fn pack<W: WriteBytesExt>(&self, data: &mut W) -> Result<()> {
+        for v in &self.hint {
+            data.write_u8(*v)?;
+        }
+        Ok(())
+    }
+}
+
+impl Default for Hint {
+    fn default() -> Self {
+        Hint { hint: [0; 4] }
+    }
+}
+
 //------------------------------------------

src/cache/mapping.rs

@@ -1,3 +1,5 @@
+use anyhow::Result;
+use byteorder::WriteBytesExt;
 use nom::number::complete::*;
 use nom::IResult;
 
@@ -51,4 +53,20 @@ impl Unpack for Mapping {
     }
 }
 
+impl Pack for Mapping {
+    fn pack<W: WriteBytesExt>(&self, data: &mut W) -> Result<()> {
+        let m: u64 = (self.oblock << 16) | self.flags as u64;
+        m.pack(data)
+    }
+}
+
+impl Default for Mapping {
+    fn default() -> Self {
+        Mapping {
+            oblock: 0,
+            flags: 0,
+        }
+    }
+}
+
 //------------------------------------------