From 3933a29078a33e196d8ff05ffe0f8427729d87c1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rafa=C5=82=20Harabie=C5=84?= <rafalh1992@o2.pl>
Date: Sat, 23 Sep 2017 14:16:02 +0200
Subject: [PATCH] Implemented basic FAT table support.

---
 src/fs.rs    | 13 ++++++++
 src/lib.rs   |  1 +
 src/table.rs | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 106 insertions(+)
 create mode 100644 src/table.rs

diff --git a/src/fs.rs b/src/fs.rs
index ebe78d4..2e5af17 100644
--- a/src/fs.rs
+++ b/src/fs.rs
@@ -5,6 +5,7 @@ use std::str;
 use byteorder::{LittleEndian, ReadBytesExt};
 
 use file::FatFile;
+use table::{FatTable, FatTable12, FatTable16, FatTable32};
 
 // FAT implementation based on:
 //   http://wiki.osdev.org/FAT
@@ -23,6 +24,7 @@ pub struct FatFileSystem<T: Read+Seek> {
     first_fat_sector: u32,
     pub(crate) first_data_sector: u32,
     pub(crate) root_dir_sectors: u32,
+    pub(crate) table: Box<FatTable>,
 }
 
 #[allow(dead_code)]
@@ -118,6 +120,16 @@ impl<T: Read+Seek> FatFileSystem<T> {
             println!("fat_type_label {}", fat_type_label_str);
         }
         
+        // FIXME: other versions
+        
+        let table_size_bytes = table_size * boot.bpb.bytes_per_sector as u32;
+        let table: Box<FatTable> = match fat_type {
+            FatType::Fat12 => Box::new(FatTable12::read(rdr, table_size_bytes as usize)?),
+            FatType::Fat16 => Box::new(FatTable16::read(rdr, table_size_bytes as usize)?),
+            FatType::Fat32 => Box::new(FatTable32::read(rdr, table_size_bytes as usize)?),
+            _ => panic!("TODO: exfat")
+        };
+        
         let fs = FatFileSystem {
             rdr: rdr,
             fat_type: fat_type,
@@ -125,6 +137,7 @@ impl<T: Read+Seek> FatFileSystem<T> {
             first_data_sector: first_data_sector,
             first_fat_sector: first_fat_sector,
             root_dir_sectors: root_dir_sectors as u32,
+            table: table,
         };
         
         Ok(fs)
diff --git a/src/lib.rs b/src/lib.rs
index c4a0b21..14d2320 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -10,6 +10,7 @@ extern crate bitflags;
 pub mod fs;
 pub mod dir;
 pub mod file;
+pub mod table;
 
 pub use fs::*;
 pub use dir::*;
diff --git a/src/table.rs b/src/table.rs
new file mode 100644
index 0000000..ec7a016
--- /dev/null
+++ b/src/table.rs
@@ -0,0 +1,92 @@
+use std::io::prelude::*;
+use std::io;
+use byteorder::{LittleEndian, ReadBytesExt};
+
+pub(crate) struct FatTableData<T> {
+    table: Box<[T]>,
+}
+
+pub(crate) type FatTable32 = FatTableData<u32>;
+pub(crate) type FatTable16 = FatTableData<u16>;
+pub(crate) type FatTable12 = FatTableData<u8>;
+
+impl <T> FatTableData<T> {
+    pub fn new(data: Box<[T]>) -> FatTableData<T> {
+        FatTableData::<T> {
+            table: data,
+        }
+    }
+}
+
+impl FatTable12 {
+    pub fn read(rdr: &mut Read, size: usize) -> io::Result<Self> {
+        let mut fat = vec![0;size as usize];
+        rdr.read_exact(fat.as_mut())?;
+        Ok(FatTable12::new(fat.into_boxed_slice()))
+    }
+}
+
+impl FatTable16 {
+    pub fn read(rdr: &mut Read, size: usize) -> io::Result<Self> {
+        let mut fat = Vec::with_capacity(size/2);
+        for _ in 0..size/2 {
+            fat.push(rdr.read_u16::<LittleEndian>()?);
+        }
+        Ok(FatTable16::new(fat.into_boxed_slice()))
+    }
+}
+
+impl FatTable32 {
+    pub fn read(rdr: &mut Read, size: usize) -> io::Result<Self> {
+        let mut fat = Vec::with_capacity(size/4);
+        for _ in 0..size/4 {
+            fat.push(rdr.read_u32::<LittleEndian>()?);
+        }
+        Ok(FatTable32::new(fat.into_boxed_slice()))
+    }
+}
+
+pub trait FatTable {
+    fn get_next_cluster(&self, cluster: u32) -> Option<u32>;
+}
+
+impl FatTable for FatTable32 {
+    fn get_next_cluster(&self, cluster: u32) -> Option<u32> {
+        let val = self.table[cluster as usize] & 0x0FFFFFFF;
+        if val >= 0x0FFFFFF7 {
+            None
+        } else {
+            Some(val)
+        }
+    }
+}
+
+impl FatTable for FatTable16 {
+    fn get_next_cluster(&self, cluster: u32) -> Option<u32> {
+        let val = self.table[cluster as usize];
+        if val >= 0xFFF7 {
+            None
+        } else {
+            Some(val as u32)
+        }
+    }
+}
+
+impl FatTable for FatTable12 {
+    fn get_next_cluster(&self, cluster: u32) -> Option<u32> {
+        let fat_offset = cluster + (cluster / 2);
+        let val1 = self.table[fat_offset as usize] as u16;
+        let val2 = self.table[(fat_offset + 1) as usize] as u16;
+         
+        let val = if cluster & 1 == 1 {
+            (val1 >> 4) | (val2 << 4)
+        } else {
+            val1 | (val2 & 0x0F)
+        };
+        if val >= 0xFF7 {
+            None
+        } else {
+            Some(val as u32)
+        }
+    }
+}