mxaccessgw/src/ZB.MOM.WW.MxGateway.Tests/Diagnostics/WorkerExecutableHealthCheckTests.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Diagnostics.HealthChecks;
using Microsoft.Extensions.Options;
using ZB.MOM.WW.Health;
using ZB.MOM.WW.MxGateway.Server;
using ZB.MOM.WW.MxGateway.Server.Configuration;
using ZB.MOM.WW.MxGateway.Server.Diagnostics;

namespace ZB.MOM.WW.MxGateway.Tests.Diagnostics;

/// <summary>Readiness coverage for the worker executable (#206).</summary>
public sealed class WorkerExecutableHealthCheckTests : IDisposable
{
    private readonly string _directory = Path.Combine(Path.GetTempPath(), $"mxgw-workercheck-{Guid.NewGuid():N}");

    /// <summary>Initializes a new instance of the <see cref="WorkerExecutableHealthCheckTests"/> class.</summary>
    public WorkerExecutableHealthCheckTests() => Directory.CreateDirectory(_directory);

    /// <inheritdoc />
    public void Dispose() => Directory.Delete(_directory, recursive: true);

    /// <summary>A present x86 worker image is healthy.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task Healthy_WhenWorkerExecutableIsLaunchable()
    {
        string path = WritePeStub(machine: 0x014c);

        HealthCheckResult result = await CheckAsync(path, WorkerArchitecture.X86);

        Assert.Equal(HealthStatus.Healthy, result.Status);
    }

    /// <summary>A missing worker executable is unhealthy and reports only the error code, never the path.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task Unhealthy_WhenWorkerExecutableIsMissing()
    {
        string path = Path.Combine(_directory, "missing", "ZB.MOM.WW.MxGateway.Worker.exe");

        HealthCheckResult result = await CheckAsync(path, WorkerArchitecture.X86);

        Assert.Equal(HealthStatus.Unhealthy, result.Status);
        Assert.Equal("ExecutableNotFound", result.Data["error_code"]);
        Assert.DoesNotContain(_directory, result.Description, StringComparison.OrdinalIgnoreCase);
    }

    /// <summary>A worker image of the wrong architecture is unhealthy, as the launcher would reject it.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task Unhealthy_WhenWorkerExecutableHasWrongArchitecture()
    {
        string path = WritePeStub(machine: 0x8664);

        HealthCheckResult result = await CheckAsync(path, WorkerArchitecture.X86);

        Assert.Equal(HealthStatus.Unhealthy, result.Status);
        Assert.Equal("InvalidExecutable", result.Data["error_code"]);
    }

    /// <summary>
    /// The gateway registers the check on the ready tier, and the session check stays on the active
    /// tier so zero sessions keeps readiness green.
    /// </summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task Build_RegistersWorkerExecutableCheckOnReadyTier()
    {
        await using WebApplication app = GatewayApplication.Build([]);
        HealthCheckServiceOptions options =
            app.Services.GetRequiredService<IOptions<HealthCheckServiceOptions>>().Value;

        HealthCheckRegistration worker = Assert.Single(options.Registrations, r => r.Name == "worker-executable");
        Assert.Contains(ZbHealthTags.Ready, worker.Tags);
        HealthCheckRegistration sessions = Assert.Single(options.Registrations, r => r.Name == "mxaccess-sessions");
        Assert.DoesNotContain(ZbHealthTags.Ready, sessions.Tags);
    }

    private static Task<HealthCheckResult> CheckAsync(string path, WorkerArchitecture architecture)
    {
        WorkerExecutableHealthCheck check = new(Options.Create(new GatewayOptions
        {
            Worker = new WorkerOptions
            {
                ExecutablePath = path,
                RequiredArchitecture = architecture,
            },
        }));
        return check.CheckHealthAsync(new HealthCheckContext());
    }

    private string WritePeStub(ushort machine)
    {
        string path = Path.Combine(_directory, "ZB.MOM.WW.MxGateway.Worker.exe");
        byte[] bytes = new byte[0x100];
        bytes[0] = (byte)'M';
        bytes[1] = (byte)'Z';
        BitConverter.GetBytes(0x80).CopyTo(bytes, 0x3c);
        bytes[0x80] = (byte)'P';
        bytes[0x81] = (byte)'E';
        BitConverter.GetBytes(machine).CopyTo(bytes, 0x84);
        File.WriteAllBytes(path, bytes);
        return path;
    }
}