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开过车或者坐过车的都对限速是深恶痛绝吧，不过为了大家安全，忍一忍吧。系统究竟是如何判断车主是否超速那，本文主要介绍这个系统到底是如何设计的。本文基于微服务进行设计。
关于微服务，在微服务初探（0）和微服务-node.js中对微服务有简单的介绍。通过这篇文章，可以进一步了解微服务。
注：本文内容参考《Dapr For .NET developer》，专有名词保留英文原文，不做翻译。
Dapr
The Distributed Application Runtime (Dapr) provides APIs that simplify microservice connectivity. Whether your communication pattern is service to service invocation or pub/sub messaging, Dapr helps you write resilient and secured microservices.
Building blocks抽象了分布式应用能力的实现，service只需要和Building blocks进行交互即可。
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Dapr的现在和安装可参考Install the Dapr CLI。
限速设计
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这里面fine是罚单，罚款的意思。
VehicleState包括了车牌号，进入限速区域(Cameral)时间，退出限速区域(Cameral)时间。
public record struct VehicleState
{
public string LicenseNumber { get; init; }
public DateTime EntryTimestamp { get; init; }
public DateTime? ExitTimestamp { get; init; }
public VehicleState(string licenseNumber, DateTime entryTimestamp, DateTime? exitTimestamp = null)
{
this.LicenseNumber = licenseNumber;
this.EntryTimestamp = entryTimestamp;
this.ExitTimestamp = exitTimestamp;
}
}
据此就可以计算出平均时速，然后再与规定的时速进行比较，如果超过了，不好意思，您将收到一封邮件，也可以用短信等方式发送给车主。而车主的邮件信息通过VehicleRegistrationService来获取。
车辆信息的结构体定义如下：
public record struct VehicleInfo(string VehicleId, string Brand, string Model, string OwnerName, string OwnerEmail);
代码实现
windows平台下需要将start-maildev.ps1修改为，修改参考maildev/maildev。
docker run -d -p 4000:1080 -p 4025:1025 --name dtc-maildev maildev/maildev
-d: 后台运行容器，并返回容器ID；
(1) CameralSimulation.cs
模拟进入和退出代码：
// simulate entry
DateTime entryTimestamp = DateTime.Now;
var vehicleRegistered = new VehicleRegistered
{
Lane = _camNumber,
LicenseNumber = GenerateRandomLicenseNumber(),
Timestamp = entryTimestamp
};
await _trafficControlService.SendVehicleEntryAsync(vehicleRegistered);
Console.WriteLine($"Simulated ENTRY of vehicle with license-number {vehicleRegistered.LicenseNumber} in lane {vehicleRegistered.Lane}");
// simulate exit
TimeSpan exitDelay = TimeSpan.FromSeconds(_rnd.Next(_minExitDelayInS, _maxExitDelayInS) + _rnd.NextDouble());
Task.Delay(exitDelay).Wait();
vehicleRegistered.Timestamp = DateTime.Now;
vehicleRegistered.Lane = _rnd.Next(1, 4);
await _trafficControlService.SendVehicleExitAsync(vehicleRegistered);
Console.WriteLine($"Simulated EXIT of vehicle with license-number {vehicleRegistered.LicenseNumber} in lane {vehicleRegistered.Lane}");
跟踪 _trafficControlService.SendVehicleEntryAsync
public async Task SendVehicleEntryAsync(VehicleRegistered vehicleRegistered)
{
var eventJson = JsonSerializer.Serialize(vehicleRegistered);
var message = new MqttApplicationMessageBuilder()
.WithTopic("trafficcontrol/entrycam")
.WithPayload(Encoding.UTF8.GetBytes(eventJson))
.WithAtMostOnceQoS()
.Build();
await _client.PublishAsync(message, CancellationToken.None);
}
使用Input Binding来发布消息。可追踪到消息的订阅者是trafficcontrolservice。
（2）TrafficController.cs
[HttpPost("entrycam")]
public async Task<ActionResult> VehicleEntryAsync(VehicleRegistered msg)
{
try
{
// log entry
_logger.LogInformation($"ENTRY detected in lane {msg.Lane} at {msg.Timestamp.ToString("hh:mm:ss")} " +
$"of vehicle with license-number {msg.LicenseNumber}.");
// store vehicle state
var vehicleState = new VehicleState(msg.LicenseNumber, msg.Timestamp, null);
await _vehicleStateRepository.SaveVehicleStateAsync(vehicleState);
return Ok();
}
catch (Exception ex)
{
_logger.LogError(ex, "Error occurred while processing ENTRY");
return StatusCode(500);
}
}
跟踪_vehicleStateRepository.SaveVehicleStateAsync(vehicleState)
public async Task SaveVehicleStateAsync(VehicleState vehicleState)
{
await _daprClient.SaveStateAsync<VehicleState>(
DAPR_STORE_NAME, vehicleState.LicenseNumber, vehicleState);
}
使用state management building block来保存VehicleState。
同理可知退出时会调用trafficcontrolservice的VehicleExitAsync：
[HttpPost("exitcam")]
public async Task<ActionResult> VehicleExitAsync(VehicleRegistered msg, [FromServices] DaprClient daprClient)
{
try
{
// get vehicle state
var state = await _vehicleStateRepository.GetVehicleStateAsync(msg.LicenseNumber);
if (state == default(VehicleState))
{
return NotFound();
}
// log exit
_logger.LogInformation($"EXIT detected in lane {msg.Lane} at {msg.Timestamp.ToString("hh:mm:ss")} " +
$"of vehicle with license-number {msg.LicenseNumber}.");
// update state
var exitState = state.Value with { ExitTimestamp = msg.Timestamp };
await _vehicleStateRepository.SaveVehicleStateAsync(exitState);
// handle possible speeding violation
int violation = _speedingViolationCalculator.DetermineSpeedingViolationInKmh(exitState.EntryTimestamp, exitState.ExitTimestamp.Value);
if (violation > 0)
{
_logger.LogInformation($"Speeding violation detected ({violation} KMh) of vehicle" +
$"with license-number {state.Value.LicenseNumber}.");
var speedingViolation = new SpeedingViolation
{
VehicleId = msg.LicenseNumber,
RoadId = _roadId,
ViolationInKmh = violation,
Timestamp = msg.Timestamp
};
// publish speedingviolation (Dapr publish / subscribe)
await daprClient.PublishEventAsync("pubsub", "speedingviolations", speedingViolation);
}
return Ok();
}
catch (Exception ex)
{
_logger.LogError(ex, "Error occurred while processing EXIT");
return StatusCode(500);
}
}
如果存在超速的话会调用：
await daprClient.PublishEventAsync("pubsub", "speedingviolations", speedingViolation)
根据配置文件
apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
name: pubsub
namespace: dapr-trafficcontrol
spec:
type: pubsub.rabbitmq
version: v1
metadata:
- name: host
value: "amqp://localhost:5672"
- name: durable
value: "false"
- name: deletedWhenUnused
value: "false"
- name: autoAck
value: "false"
- name: reconnectWait
value: "0"
- name: concurrency
value: parallel
scopes:
- trafficcontrolservice
- finecollectionservice
可追踪到消息的订阅者是finecollectionservice。
（3）FineCollectionService
[Topic("pubsub", "speedingviolations")]
[Route("collectfine")]
[HttpPost()]
public async Task<ActionResult> CollectFine(SpeedingViolation speedingViolation, [FromServices] DaprClient daprClient)
{
decimal fine = _fineCalculator.CalculateFine(_fineCalculatorLicenseKey!, speedingViolation.ViolationInKmh);
// get owner info (Dapr service invocation)
var vehicleInfo = _vehicleRegistrationService.GetVehicleInfo(speedingViolation.VehicleId).Result;
// log fine
string fineString = fine == 0 ? "tbd by the prosecutor" : $"{fine} Euro";
_logger.LogInformation($"Sent speeding ticket to {vehicleInfo.OwnerName}. " +
$"Road: {speedingViolation.RoadId}, Licensenumber: {speedingViolation.VehicleId}, " +
$"Vehicle: {vehicleInfo.Brand} {vehicleInfo.Model}, " +
$"Violation: {speedingViolation.ViolationInKmh} Km/h, Fine: {fineString}, " +
$"On: {speedingViolation.Timestamp.ToString("dd-MM-yyyy")} " +
$"at {speedingViolation.Timestamp.ToString("hh:mm:ss")}.");
// send fine by email (Dapr output binding)
var body = EmailUtils.CreateEmailBody(speedingViolation, vehicleInfo, fineString);
var metadata = new Dictionary<string, string>
{
["emailFrom"] = "noreply@cfca.gov",
["emailTo"] = vehicleInfo.OwnerEmail,
["subject"] = $"Speeding violation on the {speedingViolation.RoadId}"
};
await daprClient.InvokeBindingAsync("sendmail", "create", body, metadata);
return Ok();
}
其中vehicleInfo 的值是通过service invocation调用VehicleRegistrationService获取的。
最后通过Output Binding来发送邮件:
await daprClient.InvokeBindingAsync("sendmail", "create", body, metadata);
运行
- start-all.ps1
- dapr run --app-id vehicleregistrationservice --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 --config ../dapr/config/config.yaml --components-path ../dapr/components dotnet run
- dapr run --app-id finecollectionservice --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 --config ../dapr/config/config.yaml --components-path ../dapr/components dotnet run
- dapr run --app-id trafficcontrolservice --app-port 6000 --dapr-http-port 3600 --dapr-grpc-port 60000 --config ../dapr/config/config.yaml --components-path ../dapr/components dotnet run
- cd Simulation && dotnet run
最终结果：
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车辆的进入退出信息都会实时捕获到，如果有超速信息，会通过邮件发送。
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写在最后
可视化版本
cd .\VisualSimulation\ && dotnet run
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视频可参见： https://live.csdn.net/v/238245
rabbitmq管理界面
默认账号密码都是guest。
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公众号
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