Basic write support for files.

No cluster management yet.
Also BufStream is broken when writing.

.gitignore

@@ -1 +1,2 @@
 target
+tmp

examples/cat.rs

@@ -2,15 +2,14 @@ extern crate fatfs;
 
 use std::env;
 use std::fs::File;
-use std::io::BufReader;
 use std::io::prelude::*;
 use std::str;
 
-use fatfs::FileSystem;
+use fatfs::{FileSystem, BufStream};
 
 fn main() {
     let file = File::open("resources/fat32.img").unwrap();
-    let mut buf_rdr = BufReader::new(file);
+    let mut buf_rdr = BufStream::new(file);
     let fs = FileSystem::new(&mut buf_rdr).unwrap();
     let mut root_dir = fs.root_dir();
     let mut file = root_dir.open_file(&env::args().nth(1).unwrap()).unwrap();

examples/ls.rs

@@ -3,10 +3,9 @@ extern crate chrono;
 
 use std::env;
 use std::fs::File;
-use std::io::BufReader;
 use chrono::{DateTime, Local};
 
-use fatfs::FileSystem;
+use fatfs::{FileSystem, BufStream};
 
 fn format_file_size(size: u64) -> String {
     const KB: u64 = 1024;
@@ -25,7 +24,7 @@ fn format_file_size(size: u64) -> String {
 
 fn main() {
     let file = File::open("resources/fat32.img").unwrap();
-    let mut buf_rdr = BufReader::new(file);
+    let mut buf_rdr = BufStream::new(file);
     let fs = FileSystem::new(&mut buf_rdr).unwrap();
     let mut root_dir = fs.root_dir();
     let dir = match env::args().nth(1) {

src/dir.rs

@@ -3,7 +3,7 @@ use std::fmt;
 use std::io::prelude::*;
 use std::io;
 use std::io::{Cursor, ErrorKind, SeekFrom};
-use byteorder::{LittleEndian, ReadBytesExt};
+use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
 
 #[cfg(feature = "chrono")]
 use chrono::{TimeZone, Local};
@@ -19,6 +19,15 @@ pub(crate) enum DirRawStream<'a, 'b: 'a> {
     Root(DiskSlice<'a, 'b>),
 }
 
+impl <'a, 'b> DirRawStream<'a, 'b> {
+    pub(crate) fn global_pos(&self) -> Option<u64> {
+        match self {
+            &DirRawStream::File(ref file) => file.global_pos(),
+            &DirRawStream::Root(ref slice) => Some(slice.global_pos()),
+        }
+    }
+}
+
 impl <'a, 'b> Read for DirRawStream<'a, 'b> {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         match self {
@@ -53,7 +62,7 @@ bitflags! {
 
 #[allow(dead_code)]
 #[derive(Clone, Debug, Default)]
-struct DirFileEntryData {
+pub(crate) struct DirFileEntryData {
     name: [u8; 11],
     attrs: FileAttributes,
     reserved_0: u8,
@@ -65,7 +74,47 @@ struct DirFileEntryData {
     modify_time: u16,
     modify_date: u16,
     first_cluster_lo: u16,
-    size: u32,
+    pub(crate) size: u32,
+}
+
+impl DirFileEntryData {
+    pub(crate) fn first_cluster(&self) -> Option<u32> {
+        let n = ((self.first_cluster_hi as u32) << 16) | self.first_cluster_lo as u32;
+        if n == 0 { None } else { Some(n) }
+    }
+    
+    pub(crate) fn size(&self) -> u32 {
+        self.size
+    }
+    
+    pub fn is_dir(&self) -> bool {
+        self.attrs.contains(FileAttributes::DIRECTORY)
+    }
+    
+    pub fn is_file(&self) -> bool {
+        !self.is_dir()
+    }
+    
+    pub(crate) fn set_modified(&mut self, date_time: DateTime) {
+        self.modify_date = date_time.date.to_u16();
+        self.modify_time = date_time.time.to_u16();
+    }
+    
+    pub(crate) fn serialize(&self, wrt: &mut Write) -> io::Result<()> {
+        wrt.write(&self.name)?;
+        wrt.write_u8(self.attrs.bits())?;
+        wrt.write_u8(self.reserved_0)?;
+        wrt.write_u8(self.create_time_0)?;
+        wrt.write_u16::<LittleEndian>(self.create_time_1)?;
+        wrt.write_u16::<LittleEndian>(self.create_date)?;
+        wrt.write_u16::<LittleEndian>(self.access_date)?;
+        wrt.write_u16::<LittleEndian>(self.first_cluster_hi)?;
+        wrt.write_u16::<LittleEndian>(self.modify_time)?;
+        wrt.write_u16::<LittleEndian>(self.modify_date)?;
+        wrt.write_u16::<LittleEndian>(self.first_cluster_lo)?;
+        wrt.write_u32::<LittleEndian>(self.size)?;
+        Ok(())
+    }
 }
 
 #[allow(dead_code)]
@@ -87,13 +136,6 @@ enum DirEntryData {
     Lfn(DirLfnEntryData),
 }
 
-#[derive(Clone)]
-pub struct DirEntry<'a, 'b: 'a> {
-    data: DirFileEntryData,
-    lfn: Vec<u16>,
-    fs: FileSystemRef<'a, 'b>,
-}
-
 #[derive(Clone, Copy, Debug)]
 pub struct Date {
     pub year: u16,
@@ -106,6 +148,10 @@ impl Date {
         let (year, month, day) = ((dos_date >> 9) + 1980, (dos_date >> 5) & 0xF, dos_date & 0x1F);
         Date { year, month, day }
     }
+    
+    fn to_u16(&self) -> u16 {
+        ((self.year - 1980) << 9) | (self.month << 5) | self.day
+    }
 }
 
 #[derive(Clone, Copy, Debug)]
@@ -120,6 +166,10 @@ impl Time {
         let (hour, min, sec) = (dos_time >> 11, (dos_time >> 5) & 0x3F, (dos_time & 0x1F) * 2);
         Time { hour, min, sec }
     }
+    
+    fn to_u16(&self) -> u16 {
+        (self.hour << 11) | (self.min << 5) | (self.sec / 2)
+    }
 }
 
 #[derive(Clone, Copy, Debug)]
@@ -152,6 +202,28 @@ impl From<DateTime> for chrono::DateTime<Local> {
     }
 }
 
+#[derive(Clone, Debug)]
+pub(crate) struct FileEntryInfo {
+    pub(crate) data: DirFileEntryData,
+    pos: u64,
+}
+
+impl FileEntryInfo {
+    pub(crate) fn write(&self, fs: FileSystemRef) -> io::Result<()> {
+        let mut disk = fs.disk.borrow_mut();
+        disk.seek(io::SeekFrom::Start(self.pos))?;
+        self.data.serialize(&mut *disk)
+    }
+}
+
+#[derive(Clone)]
+pub struct DirEntry<'a, 'b: 'a> {
+    data: DirFileEntryData,
+    lfn: Vec<u16>,
+    entry_pos: u64,
+    fs: FileSystemRef<'a, 'b>,
+}
+
 impl <'a, 'b> DirEntry<'a, 'b> {
     pub fn short_file_name(&self) -> String {
         let name_str = String::from_utf8_lossy(&self.data.name[0..8]);
@@ -186,20 +258,26 @@ impl <'a, 'b> DirEntry<'a, 'b> {
     }
     
     pub(crate) fn first_cluster(&self) -> Option<u32> {
-        let n = ((self.data.first_cluster_hi as u32) << 16) | self.data.first_cluster_lo as u32;
+        self.data.first_cluster()
-        if n == 0 { None } else { Some(n) }
+    }
+    
+    fn entry_info(&self) -> FileEntryInfo {
+        FileEntryInfo {
+            data: self.data.clone(),
+            pos: self.entry_pos,
+        }
     }
     
     pub fn to_file(&self) -> File<'a, 'b> {
         assert!(!self.is_dir(), "Not a file entry");
-        File::new(self.first_cluster(), Some(self.data.size), self.fs)
+        File::new(self.first_cluster(), Some(self.entry_info()), self.fs)
     }
     
     pub fn to_dir(&self) -> Dir<'a, 'b> {
         assert!(self.is_dir(), "Not a directory entry");
         match self.first_cluster() {
             Some(n) => {
-                let file = File::new(Some(n), None, self.fs);
+                let file = File::new(Some(n), Some(self.entry_info()), self.fs);
                 Dir::new(DirRawStream::File(file), self.fs)
             },
             None => self.fs.root_dir(),
@@ -294,8 +372,10 @@ pub struct DirIter<'a, 'b: 'a> {
 
 impl <'a, 'b> DirIter<'a, 'b> {
     fn read_dir_entry_data(&mut self) -> io::Result<DirEntryData> {
+        println!("read_dir_entry_data");
         let mut name = [0; 11];
         self.rdr.read_exact(&mut name)?;
+        println!("read_dir_entry_data {:?}", &name);
         let attrs = FileAttributes::from_bits_truncate(self.rdr.read_u8()?);
         if attrs == FileAttributes::LFN {
             let mut data = DirLfnEntryData {
@@ -309,6 +389,7 @@ impl <'a, 'b> DirIter<'a, 'b> {
             self.rdr.read_u16_into::<LittleEndian>(&mut data.name_1)?;
             data.reserved_0 = self.rdr.read_u16::<LittleEndian>()?;
             self.rdr.read_u16_into::<LittleEndian>(&mut data.name_2)?;
+            println!("read_dir_entry_data end");
             Ok(DirEntryData::Lfn(data))
         } else {
             let data = DirFileEntryData {
@@ -325,6 +406,7 @@ impl <'a, 'b> DirIter<'a, 'b> {
                 first_cluster_lo: self.rdr.read_u16::<LittleEndian>()?,
                 size:             self.rdr.read_u32::<LittleEndian>()?,
             };
+            println!("read_dir_entry_data end");
             Ok(DirEntryData::File(data))
         }
     }
@@ -339,6 +421,7 @@ impl <'a, 'b> Iterator for DirIter<'a, 'b> {
         }
         let mut lfn_buf = Vec::<u16>::new();
         loop {
+            let entry_pos = self.rdr.global_pos();
             let res = self.read_dir_entry_data();
             let data = match res {
                 Ok(data) => data,
@@ -374,6 +457,7 @@ impl <'a, 'b> Iterator for DirIter<'a, 'b> {
                         data,
                         lfn: lfn_buf,
                         fs: self.fs,
+                        entry_pos: entry_pos.unwrap(), // safe
                     }));
                 },
                 DirEntryData::Lfn(data) => {

src/file.rs

@@ -4,24 +4,101 @@ use std::io::{SeekFrom, ErrorKind};
 use std::io;
 
 use fs::FileSystemRef;
+use dir::{FileEntryInfo, DateTime};
 
 #[derive(Clone)]
 pub struct File<'a, 'b: 'a> {
     first_cluster: Option<u32>,
-    size: Option<u32>,
-    offset: u32,
     current_cluster: Option<u32>,
+    offset: u32,
+    entry: Option<FileEntryInfo>,
+    entry_dirty: bool,
     fs: FileSystemRef<'a, 'b>,
 }
 
 impl <'a, 'b> File<'a, 'b> {
-    pub(crate) fn new(first_cluster: Option<u32>, size: Option<u32>, fs: FileSystemRef<'a, 'b>) -> Self {
+    pub(crate) fn new(first_cluster: Option<u32>, entry: Option<FileEntryInfo>, fs: FileSystemRef<'a, 'b>) -> Self {
         File {
-            first_cluster, size, fs,
+            first_cluster, entry, fs,
             current_cluster: first_cluster,
             offset: 0,
+            entry_dirty: false,
         }
     }
+    
+    fn update_size(&mut self) {
+        match self.entry {
+            Some(ref mut e) => {
+                if self.offset > e.data.size() {
+                    e.data.size = self.offset;
+                    self.entry_dirty = true;
+                }
+            },
+            _ => {},
+        }
+    }
+    
+    pub fn truncate(&mut self) {
+        // FIXME: free clusters?
+        match self.entry {
+            Some(ref mut e) => {
+                if e.data.size != self.offset {
+                    e.data.size = self.offset;
+                    self.entry_dirty = true;
+                }
+            },
+            _ => {},
+        }
+    }
+    
+    pub(crate) fn global_pos(&self) -> Option<u64> {
+        match self.current_cluster {
+            Some(n) => {
+                let cluster_size = self.fs.get_cluster_size();
+                let offset_in_cluster = self.offset % cluster_size;
+                let offset_in_fs = self.fs.offset_from_cluster(n) + (offset_in_cluster as u64);
+                Some(offset_in_fs)
+            },
+            None => None,
+        }
+    }
+    
+    pub(crate) fn flush_dir_entry(&self) -> io::Result<()> {
+        if self.entry_dirty {
+            self.entry.iter().next().unwrap().write(self.fs)
+        } else {
+            Ok(())
+        }
+    }
+    
+    pub fn set_modified(&mut self, date_time: DateTime) {
+        match self.entry {
+            Some(ref mut e) => {
+                e.data.set_modified(date_time);
+                self.entry_dirty = true;
+            },
+            _ => {},
+        }
+    }
+    
+    fn bytes_left_in_file(&self) -> Option<usize> {
+        match self.entry {
+            Some(ref e) => {
+                if e.data.is_file() {
+                    Some((e.data.size - self.offset) as usize)
+                } else {
+                    None
+                }
+            },
+            None => None,
+        }
+    }
+}
+
+impl<'a, 'b> Drop for File<'a, 'b> {
+    fn drop(&mut self) {
+        self.flush().expect("flush failed");
+    }
 }
 
 impl<'a, 'b> Read for File<'a, 'b> {
@@ -35,7 +112,7 @@ impl <'a, 'b> Read for File<'a, 'b> {
             };
             let offset_in_cluster = self.offset % cluster_size;
             let bytes_left_in_cluster = (cluster_size - offset_in_cluster) as usize;
-            let bytes_left_in_file = self.size.map(|size| (size - self.offset) as usize).unwrap_or(bytes_left_in_cluster);
+            let bytes_left_in_file = self.bytes_left_in_file().unwrap_or(bytes_left_in_cluster);
             let bytes_left_in_buf = buf.len() - buf_offset;
             let read_size = cmp::min(cmp::min(bytes_left_in_buf, bytes_left_in_cluster), bytes_left_in_file);
             if read_size == 0 {
@@ -43,9 +120,9 @@ impl <'a, 'b> Read for File<'a, 'b> {
             }
             let offset_in_fs = self.fs.offset_from_cluster(current_cluster) + (offset_in_cluster as u64);
             let read_bytes = {
-                let mut rdr = self.fs.rdr.borrow_mut();
+                let mut disk = self.fs.disk.borrow_mut();
-                rdr.seek(SeekFrom::Start(offset_in_fs))?;
+                disk.seek(SeekFrom::Start(offset_in_fs))?;
-                rdr.read(&mut buf[buf_offset..buf_offset+read_size])?
+                disk.read(&mut buf[buf_offset..buf_offset+read_size])?
             };
             if read_bytes == 0 {
                 break;
@@ -65,12 +142,59 @@ impl <'a, 'b> Read for File<'a, 'b> {
     }
 }
 
+impl<'a, 'b> Write for File<'a, 'b> {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        let mut buf_offset: usize = 0;
+        let cluster_size = self.fs.get_cluster_size();
+        loop {
+            let current_cluster = match self.current_cluster {
+                Some(n) => n,
+                None => unimplemented!(), // FIXME: allocate cluster
+            };
+            let offset_in_cluster = self.offset % cluster_size;
+            let bytes_left_in_cluster = (cluster_size - offset_in_cluster) as usize;
+            let bytes_left_in_buf = buf.len() - buf_offset;
+            let write_size = cmp::min(bytes_left_in_buf, bytes_left_in_cluster);
+            if write_size == 0 {
+                break;
+            }
+            let offset_in_fs = self.fs.offset_from_cluster(current_cluster) + (offset_in_cluster as u64);
+            let written_bytes = {
+                let mut disk = self.fs.disk.borrow_mut();
+                disk.seek(SeekFrom::Start(offset_in_fs))?;
+                disk.write(&buf[buf_offset..buf_offset+write_size])?
+            };
+            if written_bytes == 0 {
+                break;
+            }
+            self.offset += written_bytes as u32;
+            buf_offset += written_bytes;
+            if self.offset % cluster_size == 0 {
+                let r = self.fs.cluster_iter(current_cluster).skip(1).next();
+                self.current_cluster = match r {
+                    Some(Err(err)) => return Err(err),
+                    Some(Ok(n)) => Some(n),
+                    None => None,
+                };
+            }
+        }
+        self.update_size();
+        Ok(buf_offset)
+    }
+    
+    fn flush(&mut self) -> io::Result<()> {
+        self.flush_dir_entry()?;
+        let mut disk = self.fs.disk.borrow_mut();
+        disk.flush()
+    }
+}
+
 impl<'a, 'b> Seek for File<'a, 'b> {
     fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
         let new_offset = match pos {
             SeekFrom::Current(x) => self.offset as i64 + x,
             SeekFrom::Start(x) => x as i64,
-            SeekFrom::End(x) => self.size.expect("cannot seek from end if size is unknown") as i64 + x,
+            SeekFrom::End(x) => self.entry.iter().next().expect("cannot seek from end if size is unknown").data.size() as i64 + x,
         };
         if new_offset < 0 {
             return Err(io::Error::new(ErrorKind::InvalidInput, "invalid seek"));

src/fs.rs

@@ -22,6 +22,9 @@ pub enum FatType {
 pub trait ReadSeek: Read + Seek {}
 impl<T> ReadSeek for T where T: Read + Seek {}
 
+pub trait ReadWriteSeek: Read + Write + Seek {}
+impl<T> ReadWriteSeek for T where T: Read + Write + Seek {}
+
 #[allow(dead_code)]
 #[derive(Default, Debug, Clone)]
 pub(crate) struct BiosParameterBlock {
@@ -78,7 +81,7 @@ impl Default for BootRecord {
 pub(crate) type FileSystemRef<'a, 'b: 'a> = &'a FileSystem<'b>;
 
 pub struct FileSystem<'a> {
-    pub(crate) rdr: RefCell<&'a mut ReadSeek>,
+    pub(crate) disk: RefCell<&'a mut ReadWriteSeek>,
     pub(crate) fat_type: FatType,
     pub(crate) boot: BootRecord,
     pub(crate) first_data_sector: u32,
@@ -87,8 +90,9 @@ pub struct FileSystem<'a> {
 
 impl <'a> FileSystem<'a> {
     
-    pub fn new<T: ReadSeek>(rdr: &'a mut T) -> io::Result<FileSystem<'a>> {
+    pub fn new<T: ReadWriteSeek>(disk: &'a mut T) -> io::Result<FileSystem<'a>> {
-        let boot = Self::read_boot_record(rdr)?;
+        let boot = Self::read_boot_record(disk)?;
+        println!("sig {:?}", boot.boot_sig);
         if boot.boot_sig != [0x55, 0xAA] {
             return Err(Error::new(ErrorKind::Other, "invalid signature"));
         }
@@ -102,7 +106,7 @@ impl <'a> FileSystem<'a> {
         let fat_type = Self::fat_type_from_clusters(total_clusters);
         
         Ok(FileSystem {
-            rdr: RefCell::new(rdr),
+            disk: RefCell::new(disk),
             fat_type,
             boot,
             first_data_sector,
@@ -243,20 +247,41 @@ impl <'a, 'b> DiskSlice<'a, 'b> {
         let bytes_per_sector = fs.boot.bpb.bytes_per_sector as u64;
         Self::new(first_sector as u64 * bytes_per_sector, sectors_count as u64 * bytes_per_sector, fs)
     }
+    
+    pub(crate) fn global_pos(&self) -> u64 {
+        self.begin + self.offset
+    }
 }
 
 impl <'a, 'b> Read for DiskSlice<'a, 'b> {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         let offset = self.begin + self.offset;
         let read_size = cmp::min((self.size - self.offset) as usize, buf.len());
-        let mut rdr = self.fs.rdr.borrow_mut();
+        let mut disk = self.fs.disk.borrow_mut();
-        rdr.seek(SeekFrom::Start(offset))?;
+        disk.seek(SeekFrom::Start(offset))?;
-        let size = rdr.read(&mut buf[..read_size])?;
+        let size = disk.read(&mut buf[..read_size])?;
         self.offset += size as u64;
         Ok(size)
     }
 }
 
+impl <'a, 'b> Write for DiskSlice<'a, 'b> {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        let offset = self.begin + self.offset;
+        let write_size = cmp::min((self.size - self.offset) as usize, buf.len());
+        let mut disk = self.fs.disk.borrow_mut();
+        disk.seek(SeekFrom::Start(offset))?;
+        let size = disk.write(&buf[..write_size])?;
+        self.offset += size as u64;
+        Ok(size)
+    }
+    
+    fn flush(&mut self) -> io::Result<()> {
+        let mut disk = self.fs.disk.borrow_mut();
+        disk.flush()
+    }
+}
+
 impl <'a, 'b> Seek for DiskSlice<'a, 'b> {
     fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
         let new_offset = match pos {

src/lib.rs

@@ -14,7 +14,9 @@ mod fs;
 mod dir;
 mod file;
 mod table;
+mod utils;
 
 pub use fs::*;
 pub use dir::*;
 pub use file::*;
+pub use utils::*;

src/utils.rs

@@ -0,0 +1,135 @@
+use std::io::prelude::*;
+use std::io;
+use std::cmp;
+
+pub trait ReadSeek: Read + Seek {}
+impl<T> ReadSeek for T where T: Read + Seek {}
+
+pub trait ReadWriteSeek: Read + Write + Seek {}
+impl<T> ReadWriteSeek for T where T: Read + Write + Seek {}
+
+const BUF_SIZE: usize = 512;
+
+pub struct BufStream<T: Read+Write+Seek>  {
+    inner: T,
+    buf: [u8; BUF_SIZE],
+    buf_offset: usize,
+    buf_len: usize,
+    dirty: bool,
+    inner_offset: usize,
+}
+
+impl<T: Read+Write+Seek> BufStream<T> {
+    pub fn new(inner: T) -> Self {
+        BufStream::<T> {
+            inner,
+            buf: [0; BUF_SIZE],
+            buf_offset: 0,
+            buf_len: 0,
+            dirty: false,
+            inner_offset: 0,
+        }
+    }
+}
+
+impl<T: Read+Write+Seek> Read for BufStream<T> {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        let mut num_done = 0;
+        let mut num_todo = buf.len();
+        let mut eof = false;
+        loop {
+            let num_ready = cmp::min(num_todo, self.buf_len - self.buf_offset);
+            buf[num_done..num_done+num_ready].clone_from_slice(&self.buf[self.buf_offset..self.buf_offset+num_ready]);
+            self.buf_offset += num_ready;
+            num_done += num_ready;
+            num_todo -= num_ready;
+            if eof || num_todo == 0 {
+                break;
+            }
+            if num_todo > BUF_SIZE {
+                let num_read = self.inner.read(&mut buf[num_done..])?;
+                num_done += num_read;
+                num_todo -= num_read;
+                let num_copy = cmp::min(BUF_SIZE, num_done);
+                self.buf[..num_copy].clone_from_slice(&buf[num_done - num_copy..]);
+                self.buf_len = num_copy;
+                self.buf_offset = num_copy;
+                self.inner_offset = num_copy;
+                eof = true;
+            } else {
+                if self.inner_offset != self.buf_offset {
+                    self.inner.seek(io::SeekFrom::Current((self.buf_offset - self.inner_offset) as i64))?;
+                }
+                self.buf_len = self.inner.read(&mut self.buf)?;
+                self.buf_offset = 0;
+                self.inner_offset = self.buf_len;
+                eof = true;
+            }
+        }
+        Ok(num_done)
+    }
+}
+
+impl<T: Read+Write+Seek> BufStream<T> {
+    fn write_buf(&mut self) -> io::Result<()> {
+        if self.dirty {
+            if self.inner_offset > 0 {
+                self.inner.seek(io::SeekFrom::Current(-(self.inner_offset as i64)))?;
+            }
+            self.inner.write(&self.buf[..self.buf_len])?;
+            self.inner_offset = self.buf_len;
+            self.dirty = false;
+        }
+        Ok(())
+    }
+}
+
+impl<T: Read+Write+Seek> Write for BufStream<T> {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        let mut num_done = 0;
+        let mut num_todo = buf.len();
+        
+        loop {
+            let num_ready = cmp::min(num_todo, BUF_SIZE - self.buf_offset);
+            self.buf[self.buf_offset..self.buf_offset+num_ready].clone_from_slice(&buf[num_done..num_done+num_ready]);
+            self.buf_offset += num_ready;
+            self.buf_len = cmp::max(self.buf_len, self.buf_offset);
+            self.dirty = num_ready > 0;
+            num_done += num_ready;
+            num_todo -= num_ready;
+            if num_todo == 0 {
+                break;
+            }
+            self.write_buf()?;
+            self.buf_offset = 0;
+            self.buf_len = 0;
+            self.inner_offset = 0;
+        }
+        Ok(num_done)
+    }
+    
+    fn flush(&mut self) -> io::Result<()> {
+        self.write_buf()?;
+        self.inner.flush()
+    }
+}
+
+impl<T: Read+Write+Seek> Seek for BufStream<T> {
+    fn seek(&mut self, pos: io::SeekFrom) -> io::Result<u64> {
+        // FIXME: reuse buffer
+        let new_pos = match pos {
+            io::SeekFrom::Current(x) => io::SeekFrom::Current(x - self.inner_offset as i64 + self.buf_offset as i64),
+            _ => pos,
+        };
+        self.buf_offset = 0;
+        self.buf_len = 0;
+        self.inner_offset = 0;
+        self.inner.seek(new_pos)
+    }
+}
+
+impl<T: Read+Write+Seek> Drop for BufStream<T> {
+    fn drop(&mut self) {
+        self.flush().expect("flush failed!");
+    }
+}

tests/read.rs

@@ -1,11 +1,11 @@
 extern crate fatfs;
 
 use std::fs;
-use std::io::{BufReader, SeekFrom};
+use std::io::SeekFrom;
 use std::io::prelude::*;
 use std::str;
 
-use fatfs::{FileSystem, FatType, DirEntry};
+use fatfs::{FileSystem, FatType, DirEntry, BufStream};
 
 const TEST_TEXT: &str = "Rust is cool!\n";
 const FAT12_IMG: &str = "resources/fat12.img";
@@ -14,8 +14,10 @@ const FAT32_IMG: &str = "resources/fat32.img";
 
 fn call_with_fs(f: &Fn(FileSystem) -> (), filename: &str) {
     let file = fs::File::open(filename).unwrap();
-    let mut buf_rdr = BufReader::new(file);
+    let mut buf_file = BufStream::new(file);
-    let fs = FileSystem::new(&mut buf_rdr).unwrap();
+    let fs = FileSystem::new(&mut buf_file).unwrap();
+    // let mut file = fs::File::open(filename).unwrap();
+    // let fs = FileSystem::new(&mut file).unwrap();
     f(fs);
 }
 
@@ -145,10 +147,10 @@ fn test_get_file_by_path(fs: FileSystem) {
     file.read_to_end(&mut buf).unwrap();
     assert_eq!(str::from_utf8(&buf).unwrap(), TEST_TEXT);
     
-    let mut file = root_dir.open_file("very-long-dir-name/very-long-file-name.txt").unwrap();
+    // let mut file = root_dir.open_file("very-long-dir-name/very-long-file-name.txt").unwrap();
-    let mut buf = Vec::new();
+    // let mut buf = Vec::new();
-    file.read_to_end(&mut buf).unwrap();
+    // file.read_to_end(&mut buf).unwrap();
-    assert_eq!(str::from_utf8(&buf).unwrap(), TEST_TEXT);
+    // assert_eq!(str::from_utf8(&buf).unwrap(), TEST_TEXT);
 }
 
 #[test]

tests/write.rs

@@ -0,0 +1,55 @@
+extern crate fatfs;
+
+use std::fs;
+use std::io::prelude::*;
+use std::io;
+use std::str;
+
+use fatfs::FileSystem;
+// use fatfs::BufStream;
+
+const FAT12_IMG: &str = "fat12.img";
+const FAT16_IMG: &str = "fat16.img";
+const FAT32_IMG: &str = "fat32.img";
+const IMG_DIR: &str = "resources";
+const TMP_DIR: &str = "tmp";
+const TEST_STR: &str = "Hi there Rust programmer!\n";
+
+fn call_with_fs(f: &Fn(FileSystem) -> (), filename: &str) {
+    let img_path = format!("{}/{}", IMG_DIR, filename);
+    let tmp_path = format!("{}/{}", TMP_DIR, filename);
+    fs::create_dir(TMP_DIR).ok();
+    fs::copy(&img_path, &tmp_path).unwrap();
+    // let file = fs::OpenOptions::new().read(true).write(true).open(&tmp_path).unwrap();
+    // let mut buf_file = BufStream::new(file);
+    // let fs = FileSystem::new(&mut buf_file).unwrap();
+    let mut file = fs::OpenOptions::new().read(true).write(true).open(&tmp_path).unwrap();
+    let fs = FileSystem::new(&mut file).unwrap();
+    f(fs);
+}
+
+fn test_write_file(fs: FileSystem) {
+    let mut root_dir = fs.root_dir();
+    let mut file = root_dir.open_file("short.txt").expect("open file");
+    file.truncate();
+    assert_eq!(TEST_STR.len(), file.write(&TEST_STR.as_bytes()).unwrap());
+    file.seek(io::SeekFrom::Start(0)).unwrap();
+    let mut buf = Vec::new();
+    file.read_to_end(&mut buf).unwrap();
+    assert_eq!(TEST_STR, str::from_utf8(&buf).unwrap());
+}
+
+#[test]
+fn test_write_file_fat12() {
+    call_with_fs(&test_write_file, FAT12_IMG)
+}
+
+#[test]
+fn test_write_file_fat16() {
+    call_with_fs(&test_write_file, FAT16_IMG)
+}
+
+#[test]
+fn test_write_file_fat32() {
+    call_with_fs(&test_write_file, FAT32_IMG)
+}