Add missing source file for decoder::ioslice

src/decoder/ioslice.rs

@@ -0,0 +1,76 @@
+use std::io::Error as IoError;
+use std::io::Read;
+use std::io::Seek;
+use std::io::SeekFrom;
+use std::rc::Rc;
+use std::sync::RwLock;
+
+pub struct IoSlice<R: Read + Seek> {
+    reader: Rc<RwLock<R>>,
+    pos: u64,
+    start: u64,
+    end: u64,
+}
+
+impl<R: Read + Seek> IoSlice<R> {
+    pub fn new(reader: Rc<RwLock<R>>, start: u64, end: u64) -> Self {
+        Self {
+            reader,
+            start,
+            end,
+            pos: start,
+        }
+    }
+}
+
+impl<R: Read + Seek> Read for IoSlice<R> {
+    fn read(&mut self, mut buffer: &mut [u8]) -> Result<usize, IoError> {
+        let mut reader = self.reader.write().unwrap();
+        reader.seek(SeekFrom::Start(self.pos))?;
+
+        let mut remaining = (self.end - self.pos) as usize;
+        if buffer.len() > remaining {
+            buffer = &mut buffer[..remaining];
+        }
+
+        let n = reader.read(buffer)?;
+        self.pos += n as u64;
+
+        Ok(n)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use std::io::Cursor;
+
+    #[test]
+    fn read() {
+        let data = b"ABCDEF";
+        let cursor = Cursor::new(&data);
+        let f = Rc::new(RwLock::new(cursor));
+
+        let mut s1 = IoSlice::new(f.clone(), 0, 2);
+        let mut s2 = IoSlice::new(f.clone(), 2, 4);
+        let mut s3 = IoSlice::new(f.clone(), 4, 6);
+
+        let mut x1 = String::new();
+        let mut x2 = String::new();
+        let mut x3 = String::new();
+
+        s2.read_to_string(&mut x2);
+        assert_eq!(x2, "CD");
+
+        s1.read_to_string(&mut x1);
+        assert_eq!(x1, "AB");
+
+        s3.read_to_string(&mut x3);
+        assert_eq!(x3, "EF");
+
+        x2.clear();
+        s2.read_to_string(&mut x2);
+        assert_eq!(x2, "");
+    }
+}