Rework read_sized_string(): truncate null bytes

src/error.rs

@@ -23,6 +23,7 @@
 //! Error type for NRGrip.
 
 use std::error::Error;
+use std::ffi;
 use std::fmt;
 use std::io;
 
@@ -30,6 +31,7 @@ use std::io;
 #[derive(Debug)]
 pub enum NrgError {
     Io(io::Error),
+    String(ffi::IntoStringError),
     NrgFormat,
     NrgFormatV1,
     NrgChunkId,
@@ -43,6 +45,7 @@ impl fmt::Display for NrgError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
             NrgError::Io(ref err) => err.fmt(f),
+            NrgError::String(ref err) => err.fmt(f),
             NrgError::NrgFormat => write!(f, "NRG format unknown."),
             NrgError::NrgFormatV1 => write!(f, "NRG v1 format is not handled."),
             NrgError::NrgChunkId => write!(f, "NRG chunk ID unknown."),
@@ -58,6 +61,7 @@ impl Error for NrgError {
     fn description(&self) -> &str {
         match *self {
             NrgError::Io(ref err) => err.description(),
+            NrgError::String(ref err) => err.description(),
             NrgError::NrgFormat => "NRG format",
             NrgError::NrgFormatV1 => "NRG format v1",
             NrgError::NrgChunkId => "NRG chunk ID",
@@ -71,6 +75,7 @@ impl Error for NrgError {
     fn cause(&self) -> Option<&Error> {
         match *self {
             NrgError::Io(ref err) => Some(err),
+            NrgError::String(ref err) => Some(err),
             NrgError::NrgFormat => None,
             NrgError::NrgFormatV1 => None,
             NrgError::NrgChunkId => None,
@@ -87,3 +92,9 @@ impl From<io::Error> for NrgError {
         NrgError::Io(err)
     }
 }
+
+impl From<ffi::IntoStringError> for NrgError {
+    fn from(err: ffi::IntoStringError) -> NrgError {
+        NrgError::String(err)
+    }
+}

src/metadata/mod.rs

@@ -139,7 +139,7 @@ fn read_nrg_chunks(fd: &mut File, nm: &mut NrgMetadata) -> Result<(), NrgError>
 
 
 /// Reads an NRG chunk ID (i.e. a 4-byte string) from `fd`.
-fn read_nrg_chunk_id(fd: &File) -> Result<String, NrgError> {
+fn read_nrg_chunk_id(fd: &mut File) -> Result<String, NrgError> {
     read_sized_string(fd, 4)
 }
 

src/metadata/readers.rs

@@ -22,6 +22,7 @@
 
 //! Miscellaneous functions to read fixed-size data from a file.
 
+use std::ffi::CString;
 use std::fs::File;
 use std::io::Read;
 use std::mem;
@@ -29,12 +30,28 @@ use std::mem;
 use ::error::NrgError;
 
 
-/// Reads a String of size `size` from `fd`.
-pub fn read_sized_string(fd: &File, size: u64) -> Result<String, NrgError> {
-    let mut handle = fd.take(size);
-    let mut string = String::new();
-    try!(handle.read_to_string(&mut string));
-    Ok(string)
+/// Reads a String of `size` bytes from `fd`.
+///
+/// The string will be truncated at the first null byte encountered; therefore,
+/// its length may be less than `size` characters.
+pub fn read_sized_string(fd: &mut File, size: usize)
+                         -> Result<String, NrgError> {
+    // Read size bytes
+    let mut bytes = vec!(0u8; size);
+    try!(fd.read_exact(&mut bytes));
+
+    // Truncate the vector at the first null byte
+    let mut i: usize = 0;
+    for b in bytes.iter() {
+        if *b == 0 { break; }
+        i += 1;
+    }
+    bytes.truncate(i);
+
+    let cstring = CString::new(bytes)
+        .expect("This Vec wasn't supposed to contain any null byte!");
+
+    cstring.into_string().map_err(NrgError::String)
 }