Print_server/JUNIOR_ENGINEER_TASKS.md

Junior Engineer Task List - Code Improvements

This document contains actionable tasks derived from the code analysis in plan.md. Complete tasks in priority order. After each fix, run:

dotnet build Inspectron.Epson.slnx
dotnet test EpsonTest/EpsonTest.csproj

---

CRITICAL PRIORITY (Fix First)

Task 1: Move API Key to Environment Variable

File: EpsonPrintService/config.json:4

Problem: API key stored in plaintext - security risk.

Steps:

1. Remove ApiKey from config.json
2. In EpsonPrintService/Program.cs, read from environment:

var apiKey = Environment.GetEnvironmentVariable("EPSON_API_KEY")
    ?? throw new InvalidOperationException("EPSON_API_KEY environment variable not set");

3. Update EpsonPrintServiceConfiguration class to accept apiKey via constructor or property
4. Add to systemd service file epson.service:

[Service]
Environment="EPSON_API_KEY=your-key-here"

5. Document the required environment variable in README

---

Task 2: Fix HttpClient Anti-Pattern

Files:

• EpsonPrintService/HeartbeatBackgroundTask.cs:24
• Inspectron.Epson/PrintServer/PrintServices/EpsonPrintService.cs:68

Problem: Creating new HttpClient per request causes socket exhaustion.

Steps:

1. In HeartbeatBackgroundTask.cs:

   • Change constructor to accept HttpClient as parameter
   • Remove _httpClient = new HttpClient(); line
   • Keep using _httpClient field

2. In Program.cs where HeartbeatBackgroundTask is created:

// Create ONE HttpClient instance for the app lifetime
var httpClient = new HttpClient();
var heartbeatTask = new HeartbeatBackgroundTask(httpClient, ...);

3. In EpsonPrintService.cs:68:
   • Add HttpClient _httpClient field to class
   • Inject via constructor
   • Replace using var httpClient = new HttpClient(); with _httpClient

---

Task 3: Add Graceful Shutdown

File: EpsonPrintService/Program.cs:51-82

Problem: PrintLoop and PrintServer never call StopAsync() - jobs lost on Ctrl+C.

Steps:

1. Store references to started services:

var printLoop = kernel.Get<PrintLoop>();
var printServer = kernel.Get<PrintServer>();

2. In the Console.CancelKeyPress handler (or before Environment.Exit):

Console.CancelKeyPress += async (sender, e) =>
{
    e.Cancel = true; // Prevent immediate exit
    Console.WriteLine("Shutting down gracefully...");

    await printLoop.StopAsync();
    await printServer.StopAsync();

    cts.Cancel();
};

3. Ensure PrintLoop and PrintServer have StopAsync() methods that properly clean up

---

Task 4: Add Null Check for PrinterId

File: Inspectron.Epson/PrintServer/PrintServices/EpsonPrintService.cs:35-44

Problem: GetPrinterIdAsync() can return null but .Value accessed without check.

Steps:

1. Find this code block:

var printerId = await epsonPrinter.GetPrinterIdAsync();
var printerAdapter = _wrapperPrinterFactory.CreatePrinterFromId(printerId.Value, ...);

2. Add null check:

var printerId = await epsonPrinter.GetPrinterIdAsync();
if (printerId == null || !printerId.HasValue)
{
    _logger.LogError("Failed to get printer ID from {PrinterIp}", printerIp);
    return false;
}
var printerAdapter = _wrapperPrinterFactory.CreatePrinterFromId(printerId.Value, ...);

---

Task 5: Fix Race Condition in PrintServer

File: Inspectron.Epson/Queue/PrintServer.cs:19-23

Problem: TOCTOU bug - two threads could create duplicate queues.

Steps:

1. Change dictionary type from Dictionary<string, PrinterQueue> to:

private readonly ConcurrentDictionary<string, PrinterQueue> _printerQueues = new();

2. Replace this pattern:

if (_printerQueues.ContainsKey(printerIp))
    return;
var queue = new PrinterQueue(...);
_printerQueues[printerIp] = queue;

With atomic operation:

var queue = _printerQueues.GetOrAdd(printerIp, ip =>
{
    var newQueue = new PrinterQueue(ip, _printService, _logger);
    newQueue.StartAsync(); // Start the queue
    Console.WriteLine($"Printer {ip} registered");
    return newQueue;
});

3. Add using System.Collections.Concurrent; at top of file

---

HIGH PRIORITY

Task 6: Add CancellationToken Support

File: Inspectron.Epson/EpsonPrinter.cs - Lines 52, 96, 129, 205, 335, 408, etc.

Problem: Async methods can't be cancelled by callers.

Steps:

1. Find all public async methods in EpsonPrinter.cs
2. Add optional parameter to each:

// Before:
public async Task<bool> ConnectAsync(string host, int port = 9100)

// After:
public async Task<bool> ConnectAsync(string host, int port = 9100, CancellationToken cancellationToken = default)

3. Pass cancellationToken to internal async calls:

await _stream.WriteAsync(data, cancellationToken);
await _stream.ReadAsync(buffer, cancellationToken);

4. Update interface IEpsonPrinter if one exists

---

Task 7: Add Exception Handling to Fire-and-Forget Tasks

Files:

• Inspectron.Epson/PrintServer/PrintLoop.cs:29
• EpsonPrintService/Program.cs:71-72

Problem: Unobserved exceptions crash the process.

Steps:

1. In PrintLoop.cs, replace:

_ = Task.Run(Loop);

With:

_ = Task.Run(async () =>
{
    try
    {
        await Loop();
    }
    catch (Exception ex)
    {
        _logger.LogError(ex, "PrintLoop crashed unexpectedly");
    }
});

2. In Program.cs, replace:

_ = discoveryTask.StartAsync(cts.Token);
_ = heartbeatTask.StartAsync(cts.Token);

With:

var discoveryRunning = Task.Run(async () =>
{
    try { await discoveryTask.StartAsync(cts.Token); }
    catch (Exception ex) { Console.WriteLine($"Discovery error: {ex.Message}"); }
});

var heartbeatRunning = Task.Run(async () =>
{
    try { await heartbeatTask.StartAsync(cts.Token); }
    catch (Exception ex) { Console.WriteLine($"Heartbeat error: {ex.Message}"); }
});

---

Task 8: Implement IDisposable for Resource Cleanup

Files:

• EpsonPrintService/HeartbeatBackgroundTask.cs
• Inspectron.Epson/Queue/PrinterQueue.cs:13-14
• Inspectron.Epson/EpsonPrinter.cs:757-761

Steps:

1. HeartbeatBackgroundTask.cs - Add IDisposable:

public class HeartbeatBackgroundTask : IDisposable
{
    private bool _disposed;

    public void Dispose()
    {
        if (_disposed) return;
        _httpClient?.Dispose();
        _disposed = true;
    }
}

2. PrinterQueue.cs - Add IDisposable:

public class PrinterQueue : IDisposable
{
    private bool _disposed;

    public void Dispose()
    {
        if (_disposed) return;
        _semaphore?.Dispose();
        _cts?.Dispose();
        _disposed = true;
    }
}

3. EpsonPrinter.cs - Fix DisposeAsync:

public async ValueTask DisposeAsync()
{
    Disconnect();
    GC.SuppressFinalize(this);
    await Task.CompletedTask;
}

---

Task 9: Replace .Wait() with await

File: Inspectron.Epson/Queue/PrintServer.cs:32

Problem: .Wait() can cause deadlocks.

Steps:

1. Find method containing:

queue.StopAsync().Wait();

2. Make the method async:

// Before:
public void StopQueue(string printerIp)

// After:
public async Task StopQueueAsync(string printerIp)

3. Replace .Wait() with await:

await queue.StopAsync();

4. Update all callers to use await StopQueueAsync()

---

Task 10: Add Configuration Validation at Startup

File: EpsonPrintService/Program.cs:20-21

Problem: No validation after deserializing config.

Steps:

1. After config deserialization, add validation:

var config = JsonSerializer.Deserialize<EpsonPrintServiceConfiguration>(configJson);

if (config == null)
    throw new InvalidOperationException("Failed to parse config.json");

if (string.IsNullOrEmpty(config.GroupId))
    throw new InvalidOperationException("GroupId is required in config.json");

if (string.IsNullOrEmpty(config.RestaurantId))
    throw new InvalidOperationException("RestaurantId is required in config.json");

if (config.PrinterConfigurations == null || config.PrinterConfigurations.Count == 0)
    Console.WriteLine("Warning: No printer configurations found");

---

MEDIUM PRIORITY

Task 11: Replace Console.WriteLine with ILogger

File: Inspectron.Epson/Queue/PrintServer.cs:25, 34, 64

Replace all Console.WriteLine() calls with proper logging:

// Before:
Console.WriteLine($"Printer {printerIp} registered");

// After:
_logger.LogInformation("Printer {PrinterIp} registered", printerIp);

---

Task 12: Fix Logger Factory Singleton

File: EpsonPrintService/Program.cs:33-40

Create factory once:

// Create once at startup
using var loggerFactory = LoggerFactory.Create(builder =>
{
    builder.AddConsole();
    builder.SetMinimumLevel(LogLevel.Debug);
});

// Bind as singleton for all injections
kernel.Bind<ILoggerFactory>().ToConstant(loggerFactory);
kernel.Bind(typeof(ILogger<>)).ToMethod(ctx =>
    loggerFactory.CreateLogger(ctx.Request.Service.GetGenericArguments()[0]));

---

Task 13: Extract Magic Numbers to Constants

File: Inspectron.Epson/Queue/PrinterQueue.cs:87-88

// Add at top of class:
private const int MaxRetryCount = 3;

// Replace:
if (job.RetryCount >= 3)
// With:
if (job.RetryCount >= MaxRetryCount)

---

Task 14: Fix Static Thread Safety

File: Inspectron.Epson/EpsonPrinter.cs:38-43

private static readonly object _initLock = new();
private static bool _initialized;

private static void RegisterCodepages()
{
    if (_initialized) return;

    lock (_initLock)
    {
        if (_initialized) return; // Double-check pattern
        Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
        _initialized = true;
    }
}

---

LOW PRIORITY

Task 15: Remove Commented-Out Code

• EpsonPrintService/Program.cs:27-28 - Delete old factory bindings
• Inspectron.Epson/PrintServer/Printers/TM-T30III.cs:25 - Delete dead code

Task 16: Resolve TODO Comments

File: Inspectron.Epson/Queue/PrintJob.cs:5

• Either change IP property to proper type or remove the TODO comment

Task 17: Remove Unused Serilog Packages

File: EpsonPrintService/EpsonPrintService.csproj:14-16

dotnet remove EpsonPrintService/EpsonPrintService.csproj package Serilog
dotnet remove EpsonPrintService/EpsonPrintService.csproj package Serilog.Extensions.Logging
dotnet remove EpsonPrintService/EpsonPrintService.csproj package Serilog.Sinks.Console

Task 18: Fix Inconsistent Logging Style

Change string interpolation to structured logging:

// Before:
_logger.LogWarning($"Printer {printerIp} not found");

// After:
_logger.LogWarning("Printer {PrinterIp} not found", printerIp);

---

Verification Checklist

After completing all tasks:

• dotnet build Inspectron.Epson.slnx - No errors
• dotnet test EpsonTest/EpsonTest.csproj - All tests pass
• Test printer connectivity manually
• Verify systemd service starts/stops cleanly
• Verify graceful shutdown with Ctrl+C
• Check no Console.WriteLine in library code (only logging)

---

Questions?

If you're unsure about any task:

1. Read the original issue in plan.md for more context
2. Look at existing patterns in the codebase
3. Ask a senior engineer before making architectural changes