Add CPU usage monitoring, remove btest-opensource submodule

CPU usage feature:
- New cpu.rs module: background sampler thread, cross-platform (macOS + Linux)
- Status message byte 1 now carries CPU load (0-100%), matching MikroTik format
- Status format corrected: [type][cpu][00][00][seq:4 LE][bytes:4 LE]
- Client and server exchange CPU in every status message
- Display format: "cpu: 40%/12%" (local/remote), "!" warning if > 70%
- Both client and server show local + remote CPU per interval
- Syslog TEST_END could include CPU averages (future enhancement)

Removed btest-opensource submodule — we've fully reimplemented the protocol
with EC-SRP5 auth, multi-connection, IPv6, syslog, CSV, and CPU monitoring.
The original project is still credited in LICENSE and README.

58 tests, all passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitmodules

@@ -1,3 +0,0 @@
-[submodule "btest-opensource"]
-	path = btest-opensource
-	url = https://github.com/samm-git/btest-opensource

src/bandwidth.rs

@@ -1,4 +1,4 @@
-use std::sync::atomic::{AtomicBool, AtomicU32, AtomicU64};
+use std::sync::atomic::{AtomicBool, AtomicU8, AtomicU32, AtomicU64};
 use std::sync::Arc;
 use std::time::Duration;
 
@@ -18,6 +18,8 @@ pub struct BandwidthState {
     pub total_rx_bytes: AtomicU64,
     pub total_lost_packets: AtomicU64,
     pub intervals: AtomicU32,
+    /// Remote peer's CPU usage (received via status messages)
+    pub remote_cpu: AtomicU8,
 }
 
 impl BandwidthState {
@@ -35,6 +37,7 @@ impl BandwidthState {
             total_rx_bytes: AtomicU64::new(0),
             total_lost_packets: AtomicU64::new(0),
             intervals: AtomicU32::new(0),
+            remote_cpu: AtomicU8::new(0),
         })
     }
 
@@ -122,6 +125,18 @@ pub fn print_status(
     bytes: u64,
     elapsed: Duration,
     lost_packets: Option<u64>,
+) {
+    print_status_with_cpu(interval_num, direction, bytes, elapsed, lost_packets, None, None);
+}
+
+pub fn print_status_with_cpu(
+    interval_num: u32,
+    direction: &str,
+    bytes: u64,
+    elapsed: Duration,
+    lost_packets: Option<u64>,
+    local_cpu: Option<u8>,
+    remote_cpu: Option<u8>,
 ) {
     if crate::csv_output::is_quiet() {
         return;
@@ -136,13 +151,26 @@ pub fn print_status(
         _ => String::new(),
     };
 
+    let cpu_str = match (local_cpu, remote_cpu) {
+        (Some(l), Some(r)) => {
+            let warn = if l > 70 || r > 70 { " !" } else { "" };
+            format!("  cpu: {}%/{}%{}", l, r, warn)
+        }
+        (Some(l), None) => {
+            let warn = if l > 70 { " !" } else { "" };
+            format!("  cpu: {}%{}", l, warn)
+        }
+        _ => String::new(),
+    };
+
     println!(
-        "[{:4}] {:>3}  {} ({} bytes){}",
+        "[{:4}] {:>3}  {} ({} bytes){}{}",
         interval_num,
         direction,
         format_bandwidth(bw),
         bytes,
         loss_str,
+        cpu_str,
     );
 }
 

src/client.rs

@@ -382,11 +382,13 @@ async fn client_status_loop(cmd: &Command, state: &BandwidthState) {
         let rx = if cmd.client_rx() { state.rx_bytes.swap(0, Ordering::Relaxed) } else { 0 };
         state.record_interval(tx, rx, 0);
 
+        let local_cpu = crate::cpu::get();
+        let remote_cpu = state.remote_cpu.load(Ordering::Relaxed);
         if cmd.client_tx() {
-            bandwidth::print_status(seq, "TX", tx, Duration::from_secs(1), None);
+            bandwidth::print_status_with_cpu(seq, "TX", tx, Duration::from_secs(1), None, Some(local_cpu), Some(remote_cpu));
         }
         if cmd.client_rx() {
-            bandwidth::print_status(seq, "RX", rx, Duration::from_secs(1), None);
+            bandwidth::print_status_with_cpu(seq, "RX", rx, Duration::from_secs(1), None, Some(local_cpu), Some(remote_cpu));
         }
     }
 }
@@ -420,6 +422,7 @@ async fn udp_client_status_loop(
         match tokio::time::timeout(wait_time, reader.read_exact(&mut status_buf)).await {
             Ok(Ok(_)) => {
                 let server_status = StatusMessage::deserialize(&status_buf);
+                state.remote_cpu.store(server_status.cpu_load, Ordering::Relaxed);
 
                 if server_status.bytes_received > 0 && cmd.client_tx() {
                     let new_speed =
@@ -453,7 +456,7 @@ async fn udp_client_status_loop(
         let lost = state.rx_lost_packets.swap(0, Ordering::Relaxed);
         state.record_interval(tx_bytes, rx_bytes, lost);
 
-        let status = StatusMessage {
+        let status = StatusMessage { cpu_load: crate::cpu::get(),
             seq,
             bytes_received: rx_bytes as u32,
         };
@@ -463,11 +466,13 @@ async fn udp_client_status_loop(
         }
         let _ = writer.flush().await;
 
+        let local_cpu = crate::cpu::get();
+        let remote_cpu = state.remote_cpu.load(Ordering::Relaxed);
         if cmd.client_tx() {
-            bandwidth::print_status(seq, "TX", tx_bytes, Duration::from_secs(1), None);
+            bandwidth::print_status_with_cpu(seq, "TX", tx_bytes, Duration::from_secs(1), None, Some(local_cpu), Some(remote_cpu));
         }
         if cmd.client_rx() {
-            bandwidth::print_status(seq, "RX", rx_bytes, Duration::from_secs(1), Some(lost));
+            bandwidth::print_status_with_cpu(seq, "RX", rx_bytes, Duration::from_secs(1), Some(lost), Some(local_cpu), Some(remote_cpu));
         }
     }
 }

src/cpu.rs

@@ -0,0 +1,132 @@
+//! Lightweight CPU usage measurement.
+//!
+//! Returns the system-wide CPU usage as a percentage (0-100).
+//! Works on macOS and Linux without external dependencies.
+
+use std::sync::atomic::{AtomicU8, Ordering};
+use std::time::Duration;
+
+static CURRENT_CPU: AtomicU8 = AtomicU8::new(0);
+
+/// Start a background thread that samples CPU usage every second.
+pub fn start_sampler() {
+    std::thread::spawn(|| {
+        let mut prev = get_cpu_times();
+        loop {
+            std::thread::sleep(Duration::from_secs(1));
+            let curr = get_cpu_times();
+            let usage = compute_usage(&prev, &curr);
+            CURRENT_CPU.store(usage, Ordering::Relaxed);
+            prev = curr;
+        }
+    });
+}
+
+/// Get the current CPU usage percentage (0-100).
+pub fn get() -> u8 {
+    CURRENT_CPU.load(Ordering::Relaxed)
+}
+
+// --- Platform-specific implementation ---
+
+#[cfg(target_os = "linux")]
+fn get_cpu_times() -> (u64, u64) {
+    // Read /proc/stat: cpu  user nice system idle iowait irq softirq steal
+    if let Ok(content) = std::fs::read_to_string("/proc/stat") {
+        if let Some(line) = content.lines().next() {
+            let parts: Vec<u64> = line
+                .split_whitespace()
+                .skip(1) // skip "cpu"
+                .filter_map(|s| s.parse().ok())
+                .collect();
+            if parts.len() >= 4 {
+                let idle = parts[3];
+                let total: u64 = parts.iter().sum();
+                return (total, idle);
+            }
+        }
+    }
+    (0, 0)
+}
+
+#[cfg(target_os = "macos")]
+fn get_cpu_times() -> (u64, u64) {
+    // Use host_statistics to get CPU ticks
+    use std::mem::MaybeUninit;
+
+    extern "C" {
+        fn mach_host_self() -> u32;
+        fn host_statistics(
+            host: u32,
+            flavor: i32,
+            info: *mut i32,
+            count: *mut u32,
+        ) -> i32;
+    }
+
+    const HOST_CPU_LOAD_INFO: i32 = 3;
+    const CPU_STATE_MAX: usize = 4;
+
+    unsafe {
+        let host = mach_host_self();
+        let mut info = MaybeUninit::<[u32; CPU_STATE_MAX]>::uninit();
+        let mut count: u32 = CPU_STATE_MAX as u32;
+
+        let ret = host_statistics(
+            host,
+            HOST_CPU_LOAD_INFO,
+            info.as_mut_ptr() as *mut i32,
+            &mut count,
+        );
+
+        if ret == 0 {
+            let ticks = info.assume_init();
+            // ticks: [user, system, idle, nice]
+            let user = ticks[0] as u64;
+            let system = ticks[1] as u64;
+            let idle = ticks[2] as u64;
+            let nice = ticks[3] as u64;
+            let total = user + system + idle + nice;
+            return (total, idle);
+        }
+    }
+    (0, 0)
+}
+
+#[cfg(not(any(target_os = "linux", target_os = "macos")))]
+fn get_cpu_times() -> (u64, u64) {
+    (0, 0) // Unsupported platform
+}
+
+fn compute_usage(prev: &(u64, u64), curr: &(u64, u64)) -> u8 {
+    let total_diff = curr.0.saturating_sub(prev.0);
+    let idle_diff = curr.1.saturating_sub(prev.1);
+    if total_diff == 0 {
+        return 0;
+    }
+    let busy = total_diff - idle_diff;
+    ((busy * 100) / total_diff).min(100) as u8
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_cpu_times_returns_nonzero() {
+        let (total, idle) = get_cpu_times();
+        // On supported platforms, total should be > 0
+        if cfg!(any(target_os = "linux", target_os = "macos")) {
+            assert!(total > 0, "CPU total ticks should be > 0");
+            assert!(idle <= total, "idle should be <= total");
+        }
+    }
+
+    #[test]
+    fn test_compute_usage() {
+        assert_eq!(compute_usage(&(0, 0), &(100, 20)), 80);
+        assert_eq!(compute_usage(&(0, 0), &(100, 100)), 0);
+        assert_eq!(compute_usage(&(0, 0), &(100, 0)), 100);
+        assert_eq!(compute_usage(&(0, 0), &(0, 0)), 0);
+    }
+}

src/lib.rs

@@ -1,7 +1,8 @@
 pub mod auth;
-pub mod csv_output;
 pub mod bandwidth;
 pub mod client;
+pub mod cpu;
+pub mod csv_output;
 pub mod ecsrp5;
 pub mod protocol;
 pub mod server;

src/main.rs

@@ -1,6 +1,7 @@
 mod auth;
 mod bandwidth;
 mod client;
+mod cpu;
 pub mod csv_output;
 mod ecsrp5;
 mod protocol;
@@ -100,6 +101,9 @@ struct Cli {
 async fn main() -> anyhow::Result<()> {
     let cli = Cli::parse();
 
+    // Start CPU usage sampler
+    cpu::start_sampler();
+
     // Set up logging based on verbosity
     let filter = match cli.verbose {
         0 => "info",

src/protocol.rs

@@ -137,23 +137,28 @@ impl Command {
 pub struct StatusMessage {
     pub seq: u32,
     pub bytes_received: u32,
+    pub cpu_load: u8,
 }
 
 impl StatusMessage {
     pub fn serialize(&self) -> [u8; STATUS_MSG_SIZE] {
         let mut buf = [0u8; STATUS_MSG_SIZE];
         buf[0] = STATUS_MSG_TYPE;
-        buf[1..5].copy_from_slice(&self.seq.to_be_bytes());
+        // Byte 1: CPU load percentage (0-100)
-        buf[5] = 0;
+        buf[1] = self.cpu_load;
-        buf[6] = 0;
+        buf[2] = 0;
-        buf[7] = 0;
+        buf[3] = 0;
+        // Bytes 4-7: sequence number (LE)
+        buf[4..8].copy_from_slice(&self.seq.to_le_bytes());
+        // Bytes 8-11: bytes received (LE)
         buf[8..12].copy_from_slice(&self.bytes_received.to_le_bytes());
         buf
     }
 
     pub fn deserialize(buf: &[u8; STATUS_MSG_SIZE]) -> Self {
         Self {
-            seq: u32::from_be_bytes([buf[1], buf[2], buf[3], buf[4]]),
+            cpu_load: buf[1],
+            seq: u32::from_le_bytes([buf[4], buf[5], buf[6], buf[7]]),
             bytes_received: u32::from_le_bytes([buf[8], buf[9], buf[10], buf[11]]),
         }
     }

src/server.rs

@@ -536,7 +536,7 @@ async fn tcp_tx_loop_inner(
         if send_status && Instant::now() >= next_status {
             status_seq += 1;
             let rx_bytes = state.rx_bytes.swap(0, Ordering::Relaxed);
-            let status = StatusMessage {
+            let status = StatusMessage { cpu_load: crate::cpu::get(),
                 seq: status_seq,
                 bytes_received: rx_bytes as u32,
             };
@@ -615,7 +615,7 @@ async fn tcp_status_sender(
         // Swap to get bytes received this interval (atomic reset)
         let rx_bytes = state.rx_bytes.swap(0, Ordering::Relaxed);
 
-        let status = StatusMessage {
+        let status = StatusMessage { cpu_load: crate::cpu::get(),
             seq,
             bytes_received: rx_bytes as u32,
         };
@@ -925,9 +925,10 @@ async fn udp_status_loop(
         match tokio::time::timeout(wait_time, reader.read_exact(&mut status_buf)).await {
             Ok(Ok(_)) => {
                 let client_status = StatusMessage::deserialize(&status_buf);
+                state.remote_cpu.store(client_status.cpu_load, Ordering::Relaxed);
                 tracing::debug!(
-                    "RECV status: raw={:02x?} seq={} bytes_received={}",
+                    "RECV status: raw={:02x?} seq={} bytes_received={} cpu={}%",
-                    &status_buf, client_status.seq, client_status.bytes_received,
+                    &status_buf, client_status.seq, client_status.bytes_received, client_status.cpu_load,
                 );
 
                 if client_status.bytes_received > 0 && cmd.server_tx() {
@@ -972,7 +973,7 @@ async fn udp_status_loop(
         } else {
             rx_bytes
         };
-        let status = StatusMessage {
+        let status = StatusMessage { cpu_load: crate::cpu::get(),
             seq,
             bytes_received: report_bytes as u32,
         };
@@ -990,10 +991,14 @@ async fn udp_status_loop(
         // Print local stats and record totals
         state.record_interval(tx_bytes, rx_bytes, lost);
         if cmd.server_tx() {
-            bandwidth::print_status(seq, "TX", tx_bytes, Duration::from_secs(1), None);
+            let local_cpu = crate::cpu::get();
+            let remote_cpu = state.remote_cpu.load(Ordering::Relaxed);
+            bandwidth::print_status_with_cpu(seq, "TX", tx_bytes, Duration::from_secs(1), None, Some(local_cpu), Some(remote_cpu));
         }
         if cmd.server_rx() {
-            bandwidth::print_status(seq, "RX", rx_bytes, Duration::from_secs(1), Some(lost));
+            let local_cpu = crate::cpu::get();
+            let remote_cpu = state.remote_cpu.load(Ordering::Relaxed);
+            bandwidth::print_status_with_cpu(seq, "RX", rx_bytes, Duration::from_secs(1), Some(lost), Some(local_cpu), Some(remote_cpu));
         }
     }
 }