From d1d4bc02ca1329a7d0d50cd8b5ba1ec9290c39fb Mon Sep 17 00:00:00 2001
From: Luke Else <mail@luke-else.co.uk>
Date: Sun, 9 Apr 2023 10:07:15 +0100
Subject: [PATCH] Added function to convert CIDR to subnet mask

---
 src/main.rs           |  2 +-
 src/networking/mod.rs | 62 ++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 60 insertions(+), 4 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 1a2a658..a28a8cb 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,5 +1,6 @@
 use std::{io};
 
+
 mod networking;
 
 #[allow(unused_variables, unused_mut, unused_assignments)]
@@ -22,6 +23,5 @@ fn main() {
 
         break;
     }
-
     println!("IP: {}, CIDR: {}", ip_and_cidr.0.to_string(), ip_and_cidr.1);
 }
diff --git a/src/networking/mod.rs b/src/networking/mod.rs
index d35a756..0497185 100644
--- a/src/networking/mod.rs
+++ b/src/networking/mod.rs
@@ -1,6 +1,8 @@
 use std::{str::FromStr};
 use ip::IpAddr;
 
+use self::ip::InvalidIPErr;
+
 pub mod ip;
 
 #[allow(unused)]
@@ -11,8 +13,52 @@ pub struct Network {
 }
 
 impl Network {
-//     pub fn generate_subnets(self) -> Vec<Network> {}
-//     fn get_net_id(self) -> u8 {}
+    // pub fn new(given_address: IpAddr, CIDR: u8) -> Network {
+    //     //Generate subnet Mask
+    // }
+        
+
+    #[allow(non_snake_case)]
+    /// Function that takes in a u8 CIDR and converts it to an IP address.
+    /// 
+    /// ```
+    /// let CIDR: u8 = 22
+    /// let subnet_mask: [u8; 4] = gen_subnet_mask(CIDR);
+    /// 
+    /// >> IpAddr::V4(255, 255, 252, 0)
+    /// ```
+    pub fn gen_subnet_mask(mut CIDR: u8) -> Result<IpAddr, InvalidIPErr> {
+        if CIDR > 32 {
+            return Err(InvalidIPErr)
+        }
+
+        let mut oct: [u8; 4] = [0; 4];
+
+        for octet in oct.iter_mut() {
+            *octet = if usize::from(CIDR) >= 8 {
+                CIDR -= 8;
+                u8::MAX
+            }else{
+                // Count the number of remaining 1s and convert to binary
+                let mut count: u8 = 0;
+                for i in ((8-CIDR)..8).rev() {
+                    count += u8::pow(2, u32::from(i));
+                }
+                CIDR = 0;
+                count
+            }
+        }
+
+        Ok(IpAddr::V4(oct[0], oct[1], oct[2], oct[3]))
+    }
+    //pub fn generate_subnets(self) -> Vec<Network> {}
+    //fn get_net_id(self) -> u8 {}
+}
+
+enum NetworkClassBits {
+    A = 8,
+    B = 16,
+    C = 24
 }
 
 /// Function that takes in a string reference and returns the result of splitting a string into 
@@ -44,7 +90,6 @@ pub fn ip_and_cidr_from_string(ip_and_cidr: &String) -> Result<(IpAddr, u8), ip:
                 Ok(cidr) => cidr
             }
         };
-        println!("CIDR: {:?}", cidr);
     }
     
     let ip_address: IpAddr = match IpAddr::from_str(&ip.trim()) {
@@ -69,4 +114,15 @@ mod tests {
         assert_eq!(result.0, IpAddr::V4(127, 0, 0, 1));
         assert_eq!(result.1, 8);
     }
+
+    #[test]
+    fn cidr_to_ip_test() {
+        use super::*;
+        
+        assert_eq!(Network::gen_subnet_mask(22).unwrap(), IpAddr::V4(255, 255, 252, 0));
+        assert_eq!(Network::gen_subnet_mask(24).unwrap(), IpAddr::V4(255, 255, 255, 0));
+        assert_eq!(Network::gen_subnet_mask(0).unwrap(), IpAddr::V4(0, 0, 0, 0));
+        assert_eq!(Network::gen_subnet_mask(4).unwrap(), IpAddr::V4(240, 0, 0, 0));
+        assert_eq!(Network::gen_subnet_mask(35).unwrap_err(), InvalidIPErr);
+    }
 }
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