Added an e2e test harness with a fake R701 device

tests/mock/mod.rs emulates the device's TCP protocol (ping, get_name,
get_total_record_count, get_record_bytes), grounded in the reverse
engineering notes at
https://nicolabelluti.me/posts/2024/05/studying-a-communication-protocol/,
so tests/e2e.rs can exercise the real R701 client against it instead of
needing a physical reader. Starts with one test (connect + ping);
more scenarios (get_name, record streaming, error cases) to follow.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/e2e.rs

@@ -0,0 +1,14 @@
+//! End-to-end tests exercising R701's public API against the emulated
+//! device in `mock`.
+
+#![allow(clippy::unwrap_used)]
+
+mod mock;
+
+use r701::R701;
+
+#[tokio::test]
+async fn connects_and_pings_successfully() {
+    let addr = mock::spawn().await;
+    assert!(R701::connect(addr).await.is_ok());
+}

tests/mock/mod.rs

@@ -0,0 +1,144 @@
+//! Emulates an R701 device so `tests/e2e.rs` can exercise the real `R701`
+//! client against it, grounded in the protocol documented at
+//! <https://nicolabelluti.me/posts/2024/05/studying-a-communication-protocol/>.
+
+use chrono::{Datelike, Local, TimeZone, Timelike};
+use r701::{Clock, Record};
+use std::collections::HashMap;
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
+use tokio::net::TcpListener;
+
+/// The employee names the fake device reports
+fn fake_users() -> HashMap<u32, String> {
+    HashMap::from([(1, "mario".to_string())])
+}
+
+/// The attendance records the fake device reports
+fn fake_records() -> Vec<Record> {
+    vec![Record {
+        employee_id: 1,
+        clock: Clock::FirstIn,
+        datetime: Local
+            .with_ymd_and_hms(1970, 1, 1, 0, 0, 0)
+            .single()
+            .unwrap(),
+    }]
+}
+
+/// Starts a fake R701 device in the background and returns the address to
+/// connect to.
+pub async fn spawn() -> String {
+    let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
+    let addr = listener.local_addr().unwrap().to_string();
+
+    tokio::spawn(async move {
+        let (mut socket, _) = listener.accept().await.unwrap();
+
+        loop {
+            let mut request = [0u8; 16];
+            let Ok(bytes_read) = socket.read(&mut request).await else {
+                return;
+            };
+            if bytes_read == 0 {
+                return;
+            }
+
+            let response = if bytes_read < 16 {
+                vec![0xaa, 0x55, 0x01, 0, 0, 0, 0, 0, 0, 0]
+            } else if request[..2] != [0x55, 0xaa] {
+                continue;
+            } else {
+                let payload = &request[2..14];
+                match (payload[0], payload[1]) {
+                    (0x01, 0x80) => vec![0xaa, 0x55, 0x01, 0x01, 0, 0, 0, 0, 0, 0],
+                    (0x01, 0xc7) => get_name_response(payload),
+                    (0x01, 0xb4) => get_total_record_count_response(),
+                    (0x01, 0xa4) => get_record_bytes_response(payload),
+                    _ => vec![0xaa, 0x55, 0x01, 0, 0, 0, 0, 0, 0, 0],
+                }
+            };
+
+            if socket.write_all(&response).await.is_err() {
+                return;
+            }
+        }
+    });
+
+    addr
+}
+
+/// Builds the 34-byte get-name response: a 12-byte header (whether the
+/// employee was found), followed by their name (if found) null-padded to
+/// 10 bytes, followed by 12 don't-care bytes.
+fn get_name_response(payload: &[u8]) -> Vec<u8> {
+    let employee_id = u32::from_le_bytes(payload[2..6].try_into().unwrap());
+    let mut response = [0u8; 34];
+
+    if let Some(name) = fake_users().get(&employee_id) {
+        response[..12].clone_from_slice(&[0xaa, 0x55, 0x01, 0x01, 0, 0, 0, 0, 0, 0, 0x55, 0xaa]);
+        let name_bytes = name.as_bytes();
+        let len = name_bytes.len().min(10);
+        response[12..12 + len].clone_from_slice(&name_bytes[..len]);
+    } else {
+        response[..12].clone_from_slice(&[0xaa, 0x55, 0x01, 0, 0, 0, 0, 0, 0, 0, 0x55, 0xaa]);
+    }
+
+    response.to_vec()
+}
+
+/// Builds the 10-byte get-total-record-count response.
+#[allow(clippy::cast_possible_truncation)]
+fn get_total_record_count_response() -> Vec<u8> {
+    let count = fake_records().len() as u16;
+    let mut response = [0xaa, 0x55, 0x01, 0x01, 0, 0, 0, 0, 0, 0];
+    response[4..6].clone_from_slice(&count.to_le_bytes());
+    response.to_vec()
+}
+
+/// Builds the 1038-byte get-record-bytes response: a 12-byte header, the
+/// requested 1024-byte block of records (`ff`-padded past the last real
+/// one, since records don't align to 1024-byte block boundaries), and 2
+/// trailing bytes.
+fn get_record_bytes_response(payload: &[u8]) -> Vec<u8> {
+    let sequence_number = u16::from_le_bytes(payload[8..10].try_into().unwrap());
+    let all_bytes: Vec<u8> = fake_records().iter().flat_map(encode_record).collect();
+
+    let start = sequence_number as usize * 1024;
+    let mut block = [0xffu8; 1024];
+    let available = all_bytes.len().saturating_sub(start).min(1024);
+    block[..available].clone_from_slice(&all_bytes[start..start + available]);
+
+    let mut response = vec![0u8; 1038];
+    response[..12].clone_from_slice(&[0xaa, 0x55, 0x01, 0x01, 0, 0, 0, 0, 0, 0, 0x55, 0xaa]);
+    response[12..1036].clone_from_slice(&block);
+    response
+}
+
+/// Encodes a [`Record`] back into its 12-byte wire representation (the
+/// inverse of `Record`'s `TryFrom<&[u8]>`). The "unknown" bytes that
+/// `Record` doesn't decode are left as 0, since they only need to
+/// round-trip through our own parsing, not match a real device capture.
+fn encode_record(record: &Record) -> [u8; 12] {
+    let mut bytes = [0u8; 12];
+
+    let clock_bits: u8 = match record.clock {
+        Clock::FirstIn => 0,
+        Clock::FirstOut => 1,
+        Clock::SecondIn => 2,
+        Clock::SecondOut => 3,
+    };
+    bytes[1] = clock_bits << 6;
+
+    bytes[4..8].copy_from_slice(&record.employee_id.to_le_bytes());
+
+    #[allow(clippy::cast_sign_loss)]
+    let year = record.datetime.year() as u32 & 0x0fff;
+    let month = record.datetime.month() & 0x0f;
+    let day = record.datetime.day() & 0x1f;
+    let hour = record.datetime.hour() & 0x1f;
+    let minute = record.datetime.minute() & 0x3f;
+    let packed = year | (month << 12) | (day << 16) | (hour << 21) | (minute << 26);
+    bytes[8..12].copy_from_slice(&packed.to_le_bytes());
+
+    bytes
+}