Added a method to store and get the previous IP.

src/main.rs

@@ -1,12 +1,35 @@
-use std::collections::HashMap;
 use std::fs::File;
 use std::io::prelude::*;
+use std::path::Path;
+use serde::{Serialize, Deserialize};
+
+const FILE_NAME: &'static str = "ddns_ip";
+
+#[derive(Deserialize)]
+struct IP {
+    origin: String,
+}
 
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
-    let ip = get_current_ip().await?;
+    let current_ip = get_current_ip().await?;
 
-    println!("{:#?}", ip);
+    let previous_ip = match check_previous_ip() {
+        Some(x) => x,
+        None => {
+            let mut file = File::create(FILE_NAME)?;
+            file.write_all(current_ip.as_ref())?;
+
+            String::new()
+        }
+    };
+
+    println!("Current IP: {}, Previous IP: {}", current_ip, previous_ip);
+
+    if current_ip.ne(&previous_ip) {
+        println!("Not equal!!!");
+        // TODO: GoDaddy connection.
+    }
 
     Ok(())
 }
@@ -14,8 +37,20 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
 async fn get_current_ip() -> Result<String, Box<dyn std::error::Error>> {
     let resp = reqwest::get("https://httpbin.org/ip")
         .await?
-        .json::<HashMap<String, String>>()
+        .json::<IP>()
         .await?;
 
-    Ok(resp.get("origin").unwrap().as_str().parse().unwrap())
+    Ok(resp.origin)
+}
+
+fn check_previous_ip() -> Option<String> {
+    if !Path::new(FILE_NAME).exists() {
+        return None;
+    }
+
+    let mut file = File::open(FILE_NAME).ok()?;
+    let mut contents = String::new();
+    file.read_to_string(&mut contents).expect("Error reading file");
+
+    return Some(contents);
 }