Add data section names and conversion to object file format

* Data section names are encoded in the object file format
* Objects can be converted into their file format layouts
* Add writing/reading test to make sure that an object converted to
  bytes and then back from bytes is equal to hopefully catch major
  object translations

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/vm/obj/assemble.rs

@@ -143,6 +143,7 @@ impl Assemble for DataSection {
         );
         asm.names.pop();
         Ok(obj::DataSection {
+            name: self.name.clone(),
             start,
             len: section_len,
             contents,

src/vm/obj/obj.rs

@@ -1,23 +1,34 @@
 use crate::vm::obj::error::{ParseError, Result};
-use byteorder::{ReadBytesExt, LE};
+use byteorder::{ReadBytesExt, WriteBytesExt, LE};
 use std::{
     collections::HashMap,
     convert::{TryFrom, TryInto},
     fmt::Debug,
-    io::{Cursor, Read},
+    io::{Cursor, Read, Write},
 };
 
 pub const MAGIC: u64 = 0xDEAD_BEA7_BA5E_BA11;
 pub const OBJ_VERSION: u32 = 0;
 const OBJECT_HEADER_LEN: usize = 16; // 8 + 4 + 4
 
-#[derive(Debug)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Object {
     pub version: u32,
     pub sections: Vec<Section>,
 }
 
 impl Object {
+    pub fn to_bytes(&self) -> Vec<u8> {
+        let mut cursor = Cursor::new(Vec::new());
+        cursor.write_u64::<LE>(MAGIC).unwrap();
+        cursor.write_u32::<LE>(OBJ_VERSION).unwrap();
+        cursor.write_u32::<LE>(self.sections.len() as u32).unwrap();
+        for section in self.sections.iter() {
+            cursor.write(&section.to_bytes()).unwrap();
+        }
+        cursor.into_inner()
+    }
+
     pub fn from_bytes(bytes: &[u8]) -> Result<Self> {
         let mut cursor = Cursor::new(bytes);
         let magic = cursor.read_u64::<LE>()?;
@@ -29,18 +40,23 @@ impl Object {
 
         let mut sections = Vec::new();
         for _ in 0..section_count {
-            let section = Section::from_bytes(&mut cursor)?;
+            let start = cursor.position() as usize;
+            let section = Section::from_bytes(&bytes[start..])?;
+            cursor.set_position((start + section.len()) as u64);
             sections.push(section);
         }
         Ok(Object { version, sections })
     }
 
     pub fn virtual_len(&self) -> usize {
-        self.sections.iter()
+        self.sections
+            .iter()
             .map(|s| match s {
-                Section::Data(DataSection { start, len, .. }) => { (start + len) as usize }
-                Section::Meta { .. } => { 0 }
-            }).max().unwrap_or(0)
+                Section::Data(DataSection { start, len, .. }) => (start + len) as usize,
+                Section::Meta { .. } => 0,
+            })
+            .max()
+            .unwrap_or(0)
     }
 }
 
@@ -69,6 +85,16 @@ macro_rules! section_kind {
                 }
             }
         }
+
+        impl From<SectionKind> for u8 {
+            fn from(other: SectionKind) -> Self {
+                match other {
+                    $(
+                        $enum_name::$name => $value,
+                    )*
+                }
+            }
+        }
     };
 }
 
@@ -79,20 +105,45 @@ section_kind! {
     }
 }
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub enum Section {
     Data(DataSection),
     Meta(MetaSection),
 }
 
 impl Section {
-    fn from_bytes(cursor: &mut Cursor<&[u8]>) -> Result<Self> {
+    pub fn len(&self) -> usize {
+        match self {
+            Section::Data(s) => { 1 + 8 + s.len() },
+            Section::Meta(s) => { 1 + 8 + s.len() },
+        }
+    }
+
+    pub fn to_bytes(&self) -> Vec<u8> {
+        let mut cursor = Cursor::new(Vec::new());
+        let bytes = match self {
+            Section::Data(s) => {
+                cursor.write_u8(SectionKind::Data.into()).unwrap();
+                s.to_bytes()
+            }
+            Section::Meta(s) => {
+                cursor.write_u8(SectionKind::Meta.into()).unwrap();
+                s.to_bytes()
+            },
+        };
+        cursor.write_u64::<LE>(bytes.len() as u64).unwrap();
+        cursor.write(&bytes).unwrap();
+        cursor.into_inner()
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Result<Self> {
+        let mut cursor = Cursor::new(bytes);
+        let kind: SectionKind = cursor.read_u8()?.try_into()?;
         let len = cursor.read_u64::<LE>()?;
         let start = cursor.position() as usize;
         let end = start + len as usize;
 
         let bytes = &cursor.get_ref()[start..end];
-        let kind: SectionKind = cursor.read_u8()?.try_into()?;
         match kind {
             SectionKind::Data => Ok(Section::Data(DataSection::from_bytes(bytes)?)),
             SectionKind::Meta => Ok(Section::Meta(MetaSection::from_bytes(bytes)?)),
@@ -100,20 +151,46 @@ impl Section {
     }
 }
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct DataSection {
+    pub name: String,
     pub start: u64,
     pub len: u64,
     pub contents: Vec<u8>,
 }
 
 impl DataSection {
+    pub fn len(&self) -> usize {
+        2 + self.name.as_bytes().len() + 8 + 8 + self.contents.len()
+    }
+
+    pub fn to_bytes(&self) -> Vec<u8> {
+        let mut cursor = Cursor::new(Vec::new());
+        assert!(self.name.len() < u16::max_value() as usize);
+        cursor.write_u16::<LE>(self.name.len() as u16).unwrap();
+        cursor.write(self.name.as_bytes()).unwrap();
+        cursor.write_u64::<LE>(self.start).unwrap();
+        cursor.write_u64::<LE>(self.len).unwrap();
+        cursor.write(&self.contents).unwrap();
+        cursor.into_inner()
+    }
+
     pub fn from_bytes(bytes: &[u8]) -> Result<Self> {
         let mut cursor = Cursor::new(bytes);
+
+        let name_len = cursor.read_u16::<LE>()? as usize;
+        let name_start = cursor.position() as usize;
+        let name_end = name_start + name_len;
+        let name_bytes = &bytes[name_start .. name_end];
+        let name_string = String::from_utf8(name_bytes.to_vec())?;
+        cursor.set_position(name_end as u64);
+
         let start = cursor.read_u64::<LE>()?;
         let len = cursor.read_u64::<LE>()?;
+
         let contents = &bytes[cursor.position() as usize..];
         Ok(DataSection {
+            name: name_string,
             start,
             len,
             contents: From::from(contents),
@@ -121,12 +198,20 @@ impl DataSection {
     }
 }
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct MetaSection {
     pub entries: HashMap<String, u64>,
 }
 
 impl MetaSection {
+    pub fn len(&self) -> usize {
+        todo!() // 8 + ...
+    }
+
+    pub fn to_bytes(&self) -> Vec<u8> {
+        todo!()
+    }
+
     pub fn from_bytes(bytes: &[u8]) -> Result<Self> {
         let mut cursor = Cursor::new(bytes);
         let entry_count = cursor.read_u64::<LE>()?;
@@ -145,3 +230,27 @@ impl MetaSection {
         Ok(MetaSection { entries })
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_to_from_bytes() {
+        let obj = Object {
+            version: OBJ_VERSION,
+            sections: vec![
+                Section::Data(DataSection {
+                    name: "data".to_string(),
+                    start: 0,
+                    len: 16,
+                    contents: vec!(0u8; 16),
+                }),
+            ],
+        };
+
+        let obj_bytes = obj.to_bytes();
+        let converted = Object::from_bytes(&obj_bytes).unwrap();
+        assert_eq!(obj, converted);
+    }
+}

src/vm/state.rs

@@ -26,6 +26,7 @@ impl State {
         for section in object.sections {
             match section {
                 Section::Data(DataSection {
+                    name: _,
                     start,
                     len,
                     contents,