Made DirEntryReader return an Option when reading from bytes, instead of the caller checking for a specific error.

Improved documentation for `drv`.

dcb-io/src/drv.md

@@ -2,7 +2,11 @@
 
 # Layout
 
-The `.DRV` filesystem begins with the root directory.
-From there all other directories and files are situated, always sector (2048) aligned.
+The `.DRV` filesystem splits the file into sectors of `0x800` bytes, dedicating each one
+to either a file or directory.
+Both files and directories may only begin at the start of each sector, but may span various
+sectors.
 
-See the [`dir`] documentation for more information on the directory structure.
+The filesystem proper begins with a directory sector, called the 'root' directory.
+
+See the [`dir`] documentation for more information on how each directory works.

dcb-io/src/drv/dir.md

@@ -0,0 +1,12 @@
+# Directory
+
+# Layout
+
+Each directory is a contiguous array of [`entry`]'s.
+See it's module for details on each entry
+
+# Limitations
+
+Currently it is not known if directories must appear before files, but the original
+files all do this.
+The current implementations does _not_ ensure any order.

dcb-io/src/drv/dir.rs

@@ -1,4 +1,4 @@
-//! Directory
+#![doc(include = "dir.md")]
 
 // Modules
 pub mod entry;
@@ -58,10 +58,7 @@ impl DirReader {
 			}
 
 			// And parse it
-			match DirEntryReader::from_bytes(&entry_bytes) {
-				Err(entry::FromBytesError::InvalidKind(0)) => None,
-				res => Some(res.map_err(ReadEntryError::ParseEntry)),
-			}
+			DirEntryReader::from_bytes(&entry_bytes).map_err(ReadEntryError::ParseEntry).transpose()
 		});
 
 		Ok(iter)

dcb-io/src/drv/dir/entry.md

@@ -0,0 +1,19 @@
+# Directory entry
+
+# Layout
+
+Each directory entry has the following layout:
+
+| Offset | Size | Type         | Name                                                                   |
+| ------ | ---- | ------------ | ---------------------------------------------------------------------- |
+| 0x0    | 0x1  | `Kind`       | Entry kind, `0x0` for none, `0x1` for files and `0x80` for directories |
+| 0x1    | 0x3  | `[u8; 3]`    | (Files only) File extension                                            |
+| 0x4    | 0x4  | `u32`        | Entry sector position                                                  |
+| 0x8    | 0x4  | `u32`        | (Files only) File size in bytes                                        |
+| 0xc    | 0x4  | `u32`        | Entry date (seconds since epoch)                                       |
+| 0x10   | 0x10 | `[u8; 0x10]` | Entry name                                                             |
+
+# Limitations
+
+The max size for a file is `u32::MAX` bytes, but the filesystem itself can hold `2^43` bytes in total, as each
+directory and file position is done by sector.

dcb-io/src/drv/dir/entry.rs

@@ -1,4 +1,4 @@
-//! Directory entry
+#![doc(include = "entry.md")]
 
 // Modules
 pub mod error;
@@ -39,7 +39,7 @@ pub struct DirEntryReader {
 
 impl DirEntryReader {
 	/// Reads a directory entry reader from bytes
-	pub fn from_bytes(bytes: &[u8; 0x20]) -> Result<Self, FromBytesError> {
+	pub fn from_bytes(bytes: &[u8; 0x20]) -> Result<Option<Self>, FromBytesError> {
 		let bytes = array_split!(bytes,
 			kind      :  0x1,
 			extension : [0x3],
@@ -53,6 +53,7 @@ impl DirEntryReader {
 
 		// Check kind
 		let kind = match bytes.kind {
+			0x0 => return Ok(None),
 			0x1 => {
 				let mut extension = AsciiStrArr::from_bytes(bytes.extension).map_err(FromBytesError::Extension)?;
 				extension.trim_end(AsciiChar::Null);
@@ -79,7 +80,7 @@ impl DirEntryReader {
 		name.trim_end(AsciiChar::Null);
 		let date = NaiveDateTime::from_timestamp(i64::from(LittleEndian::read_u32(bytes.data)), 0);
 
-		Ok(Self { name, date, kind })
+		Ok(Some(Self { name, date, kind }))
 	}
 
 	/// Returns this entry's name