Add code to submodules

src/common.rs

@@ -0,0 +1,24 @@
+#[derive(Debug,Clone,PartialEq,Eq)]
+pub enum IpNetworkError {
+    InvalidAddr(String),
+    InvalidPrefix,
+    InvalidCidrFormat(String),
+}
+
+pub fn cidr_parts<'a>(cidr: &'a str) -> Result<(&'a str, &'a str), IpNetworkError> {
+    let parts = cidr.split('/').collect::<Vec<&str>>();
+    if parts.len() == 2 {
+        Ok((parts[0], parts[1]))
+    } else {
+        Err(IpNetworkError::InvalidCidrFormat(format!("CIDR must contain '/': {}", cidr)))
+    }
+}
+
+pub fn parse_prefix(prefix: &str, max: u8) -> Result<u8, IpNetworkError> {
+    let mask = try!(prefix.parse::<u8>().map_err(|_| IpNetworkError::InvalidPrefix));
+    if mask > max {
+        Err(IpNetworkError::InvalidPrefix)
+    } else {
+        Ok(mask)
+    }
+}