Add value module

src/value.rs

@@ -0,0 +1,38 @@
+use std::fmt;
+use std::str::FromStr;
+use trackable::error::ErrorKindExt;
+
+use {Error, ErrorKind, Result};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct ByteRange {
+    pub length: usize,
+    pub start: Option<usize>,
+}
+impl fmt::Display for ByteRange {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.length)?;
+        if let Some(x) = self.start {
+            write!(f, "@{}", x)?;
+        }
+        Ok(())
+    }
+}
+impl FromStr for ByteRange {
+    type Err = Error;
+    fn from_str(s: &str) -> Result<Self> {
+        let mut tokens = s.splitn(2, '@');
+        let length = tokens.next().expect("Never fails");
+        let start = if let Some(start) = tokens.next() {
+            Some(track!(
+                start.parse().map_err(|e| ErrorKind::InvalidInput.cause(e))
+            )?)
+        } else {
+            None
+        };
+        Ok(ByteRange {
+            length: track!(length.parse().map_err(|e| ErrorKind::InvalidInput.cause(e)))?,
+            start,
+        })
+    }
+}