Don't use dynamic allocation for FAT table wrapper.

FAT table still uses Box but its hardly avoidable when reading entire FAT into memory.

src/file.rs

@@ -4,6 +4,7 @@ use std::io::{SeekFrom, ErrorKind};
 use std::io;
 
 use fs::FatSharedStateRef;
+use table::FatNextCluster;
 
 
 pub struct FatFile<'a, 'b: 'a> {

src/fs.rs

@@ -8,7 +8,7 @@ use byteorder::{LittleEndian, ReadBytesExt};
 
 use file::FatFile;
 use dir::{FatDirReader, FatDir};
-use table::{FatTable, FatTable12, FatTable16, FatTable32};
+use table::FatTable;
 
 // FAT implementation based on:
 //   http://wiki.osdev.org/FAT
@@ -28,7 +28,7 @@ pub(crate) struct FatSharedState<'a> {
     pub(crate) boot: FatBootRecord,
     pub(crate) first_data_sector: u32,
     pub(crate) root_dir_sectors: u32,
-    pub(crate) table: Box<FatTable>,
+    pub(crate) table: FatTable,
 }
 
 impl <'a> FatSharedState<'a> {
@@ -128,12 +128,7 @@ impl <'a> FatFileSystem<'a> {
         let fat_offset = boot.bpb.reserved_sector_count * boot.bpb.bytes_per_sector;
         rdr.seek(SeekFrom::Start(fat_offset as u64))?;
         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 table = FatTable::from_read(rdr, fat_type, table_size_bytes as usize)?;
         
         let state = FatSharedState {
             rdr,

src/table.rs

@@ -1,78 +1,81 @@
 use std::io::prelude::*;
 use std::io;
 use byteorder::{LittleEndian, ReadBytesExt};
+use fs::FatType;
 
 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> {
+    pub fn new(data: Box<[T]>) -> Self {
+        Self {
             table: data,
         }
     }
 }
 
+pub(crate) type FatTable12 = FatTableData<u8>;
+pub(crate) type FatTable16 = FatTableData<u16>;
+pub(crate) type FatTable32 = FatTableData<u32>;
+
+pub(crate) enum FatTable {
+    Fat12(FatTable12),
+    Fat16(FatTable16),
+    Fat32(FatTable32),
+}
+
+impl FatTable {
+    pub fn from_read(rdr: &mut Read, fat_type: FatType, size: usize) -> io::Result<FatTable> {
+        let table = match fat_type {
+            FatType::Fat12 => FatTable::Fat12(FatTable12::from_read(rdr, size)?),
+            FatType::Fat16 => FatTable::Fat16(FatTable16::from_read(rdr, size)?),
+            FatType::Fat32 => FatTable::Fat32(FatTable32::from_read(rdr, size)?),
+            _ => panic!("TODO: exfat")
+        };
+        Ok(table)
+    }
+}
+
+pub(crate) trait FatNextCluster {
+    fn get_next_cluster(&self, cluster: u32) -> Option<u32>;
+}
+
+impl FatNextCluster for FatTable {
+    fn get_next_cluster(&self, cluster: u32) -> Option<u32> {
+        match *self {
+            FatTable::Fat12(ref fat) => fat.get_next_cluster(cluster),
+            FatTable::Fat16(ref fat) => fat.get_next_cluster(cluster),
+            FatTable::Fat32(ref fat) => fat.get_next_cluster(cluster),
+        }
+    }
+}
+
 impl FatTable12 {
-    pub fn read(rdr: &mut Read, size: usize) -> io::Result<Self> {
-        let mut fat = vec![0;size as usize];
+    pub fn from_read(rdr: &mut Read, size: usize) -> io::Result<Self> {
+        let mut fat = vec![0;size];
         rdr.read_exact(fat.as_mut())?;
-        Ok(FatTable12::new(fat.into_boxed_slice()))
+        Ok(Self::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()))
+    pub fn from_read(rdr: &mut Read, size: usize) -> io::Result<Self> {
+        let mut fat = vec![0;size/2];
+        rdr.read_u16_into::<LittleEndian>(fat.as_mut())?;
+        Ok(Self::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 fn from_read(rdr: &mut Read, size: usize) -> io::Result<Self> {
+        let mut fat = vec![0;size/4];
+        rdr.read_u32_into::<LittleEndian>(fat.as_mut())?;
+        Ok(Self::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 <= 1 || 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 <= 1 || val >= 0xFFF7 {
-            None
-        } else {
-            Some(val as u32)
-        }
-    }
-}
-
-impl FatTable for FatTable12 {
+impl FatNextCluster 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;
@@ -90,3 +93,25 @@ impl FatTable for FatTable12 {
         }
     }
 }
+
+impl FatNextCluster for FatTable16 {
+    fn get_next_cluster(&self, cluster: u32) -> Option<u32> {
+        let val = self.table[cluster as usize];
+        if val <= 1 || val >= 0xFFF7 {
+            None
+        } else {
+            Some(val as u32)
+        }
+    }
+}
+
+impl FatNextCluster for FatTable32 {
+    fn get_next_cluster(&self, cluster: u32) -> Option<u32> {
+        let val = self.table[cluster as usize] & 0x0FFFFFFF;
+        if val <= 1 || val >= 0x0FFFFFF7 {
+            None
+        } else {
+            Some(val)
+        }
+    }
+}