Impl some required functions

Still haven't fully "tied together the pieces of the puzzle".

Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "rust_network_status_rate"
+version = "0.1.0"

src/main.rs

@@ -1,3 +1,139 @@
+use std::fs::File;
+use std::io::{Read, Write};
+use std::ops::Sub;
+use std::thread::sleep;
+use std::time::{Duration, Instant};
+
+#[derive(Copy, Clone, Debug)]
+struct ByteState {
+    pub recv: u64,
+    pub send: u64,
+}
+
+impl Sub for ByteState {
+    type Output = ByteState;
+
+    fn sub(self, rhs: Self) -> Self::Output {
+        let mut result_byte_state = ByteState { recv: 0, send: 0 };
+
+        if self.recv >= rhs.recv {
+            result_byte_state.recv = self.recv - rhs.recv;
+        }
+        if self.send >= rhs.send {
+            result_byte_state.send = self.send - rhs.send;
+        }
+
+        result_byte_state
+    }
+}
+
+fn read_proc_net_dev(net_device: &str) -> Result<ByteState, String> {
+    let mut byte_state = ByteState { recv: 0, send: 0 };
+
+    let mut file_string = String::new();
+    {
+        let mut file = File::open("/proc/net/dev")
+            .map_err(|_| String::from("Failed to open \"/proc/net/dev\""))?;
+        file.read_to_string(&mut file_string)
+            .map_err(|_| String::from("Failed to read from \"/proc/net/dev\""))?;
+    }
+
+    for line in file_string.lines() {
+        if line.trim().starts_with(net_device) {
+            let mut count = 0u32;
+            for word in line.split(' ') {
+                if count == 1 {
+                    byte_state.recv = u64::from_str_radix(word, 10).map_err(|_| {
+                        String::from("Failed to parse recv bytes from \"/proc/net/dev\"")
+                    })?;
+                } else if count == 9 {
+                    byte_state.send = u64::from_str_radix(word, 10).map_err(|_| {
+                        String::from("Failed to parse send bytes from \"/proc/net/dev\"")
+                    })?;
+                    return Ok(byte_state);
+                }
+                count += 1;
+            }
+            return Err(String::from(
+                "Failed to parse from \"/proc/net/dev\", too few words?",
+            ));
+        }
+    }
+    Err(String::from(
+        "Failed to parse from \"/proc/net/dev\", missing device?",
+    ))
+}
+
+fn write_compare_state(
+    net_device: &str,
+    send_filename: &str,
+    recv_filename: &str,
+) -> Result<ByteState, String> {
+    let mut prev_byte_state = ByteState { send: 0, recv: 0 };
+
+    {
+        let mut temp_string: String = String::new();
+        let send_file_open_result = File::open(send_filename);
+        if let Ok(mut send_file) = send_file_open_result {
+            let read_result = send_file.read_to_string(&mut temp_string);
+            if read_result.is_ok() {
+                let int_parse_result = u64::from_str_radix(temp_string.trim(), 10);
+                if let Ok(i) = int_parse_result {
+                    prev_byte_state.send = i;
+                }
+            }
+        }
+    }
+    {
+        let mut temp_string: String = String::new();
+        let recv_file_open_result = File::open(recv_filename);
+        if let Ok(mut recv_file) = recv_file_open_result {
+            let read_result = recv_file.read_to_string(&mut temp_string);
+            if read_result.is_ok() {
+                let int_parse_result = u64::from_str_radix(temp_string.trim(), 10);
+                if let Ok(i) = int_parse_result {
+                    prev_byte_state.recv = i;
+                }
+            }
+        }
+    }
+
+    let byte_state = read_proc_net_dev(net_device)?;
+
+    {
+        let mut send_file = File::create(send_filename)
+            .map_err(|_| format!("Failed to create \"{}\"", send_filename))?;
+        send_file
+            .write_all(byte_state.send.to_string().as_bytes())
+            .map_err(|_| format!("Failed to write into \"{}\"", send_filename))?;
+    }
+
+    {
+        let mut recv_file = File::create(recv_filename)
+            .map_err(|_| format!("Failed to create \"{}\"", recv_filename))?;
+        recv_file
+            .write_all(byte_state.recv.to_string().as_bytes())
+            .map_err(|_| format!("Failed to write into \"{}\"", recv_filename))?;
+    }
+
+    Ok(byte_state - prev_byte_state)
+}
+
+fn timer_execute<F>(func: F, sleep_seconds: u64) -> Result<(), String>
+where
+    F: std::ops::Fn() -> Result<(), String>,
+{
+    let mut instant = Instant::now();
+    let mut duration: Duration;
+    loop {
+        func()?;
+        let newer_instant = Instant::now();
+        duration = Duration::from_secs(sleep_seconds) - (newer_instant - instant);
+        instant = newer_instant;
+        sleep(duration);
+    }
+}
+
 fn main() {
     println!("Hello, world!");
 }