ApiGateway/Program.cs

@@ -32,6 +32,8 @@ app.UseAuthorization();
 
 app.MapControllers();
 
+app.UseWebSockets();
+
 await app.UseOcelot();
 
 app.Run();

ApiGateway/ocelot.json

@@ -127,6 +127,20 @@
           "Port": 7229
         }
       ]
+    },
+
+    {
+      "UpstreamPathTemplate": "/gateway/ws",
+      "UpstreamHttpMethod": [ "Get", "Post" ],
+      "DownstreamPathTemplate": "/ws",
+      "DownstreamScheme": "wss",
+      "DownstreamHostAndPorts": [
+        {
+          "Host": "localhost",
+          "Port": 7229
+        }
+      ],
+      "UseWebSockets": true
     }
   ]
 }

README.md

@@ -8,7 +8,7 @@
 
 ### Concept
 
-This application attempts to modelize a cat café, with cafés (called "bars" here), cats, and customers. The cats can go "meow".
+This application attempts to modelize a cat café, with cafés (called "bars" here), cats, and customers.
 
 ### API REST
 
@@ -18,8 +18,21 @@ We used an ASP .NET Web API, with a Swagger configuration to visualize the inter
 
 ### WebSocket
 
-...
+A websocket was set up to notify clients (who subscribe to it) whenever a Cat is `POST`ed. 
+
+Clients need to subscribe by typing the following code in the console of their browser, in developer mode :
 
+```js
+new WebSocket("wss://localhost:5003/gateway/ws").onmessage = function (event) {
+  if (event.data === "entity-created") {
+    alert("A new entity was created!");
+  }
+};
+```
+*Note*: 
+- while the app uses port `7229` in our default config, **you should use port `5003` anyway** to subscribe to our WebSocket through our *API Gateway*
+- `"entity-created"` is a hard-coded event ID and should not be changed.
+- you are free to change the content of the `Alert` itself, of course
 ### API Gateway
 
 An [Ocelot](https://ocelot.readthedocs.io/en/latest/) API Gateway manages the whole system.
@@ -54,12 +67,21 @@ Overall, the architecture may be summed up like so:
 #### Routes
 The Gateway routes offer access to the REST API in a similar way as the REST API itself, with a small transformation: there is a new port, and the word "gateway" replaces "api". The REST API's Swagger UI will give you all the information required about those routes.
 
-| REST(old) | Gateway(current) |
+| REST(old) | Gateway(current) | 
 |--|--|
-| `.../7229/api/...` | `.../5003/gateway/...` |
 | `GET` on `https://localhost/7229/api/cats` | `GET` on `https://localhost/5003/gateway/cats` |
 | `POST` on `https://localhost/7229/api/bars/{id}` | `GET` on `https://localhost/5003/gateway/bars/{id}` |
- 
+
+...and for the websocket:
+- old :
+```js
+new WebSocket("wss://localhost:7229/ws").onmessage = function (event) {...};
+```
+
+- new : 
+```js
+new WebSocket("wss://localhost:5003/gateway/ws").onmessage = function (event) {...};
+```
 
 #### Caching
 The gateway uses caching to ensure that the entire list of customers is only queried from the database once every 10 seconds. The rest of the time, clients sending `GET`-all requests get served the contents of a cache. 

Tests/Controllers/CatsControllerTest.cs

@@ -18,7 +18,7 @@ using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using FluentAssertions;
-
+using cat_cafe.WeSo;
 
 namespace cat_cafe.Controllers.Tests
 {
@@ -64,7 +64,7 @@ namespace cat_cafe.Controllers.Tests
         {
             mapper = mapperConf.CreateMapper();
             context = new CatCafeContext(options);
-            controller = new CatsController(context, mapper, logger);
+            controller = new CatsController(context, mapper, logger, new WebSocketHandler(new List<System.Net.WebSockets.WebSocket>()));
             aliceDto = mapper.Map<CatDto>(alice);
             bobDto = mapper.Map<CatDto>(bob);
         }

cat_cafe/ApiGateway.csproj

@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>net6.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Ocelot" Version="18.0.0" />
+    <PackageReference Include="Ocelot.Cache.CacheManager" Version="18.0.0" />
+    <PackageReference Include="Swashbuckle.AspNetCore" Version="6.5.0" />
+  </ItemGroup>
+
+</Project>

cat_cafe/Controllers/CatsController.cs

@@ -12,6 +12,7 @@ using cat_cafe.Dto;
 using Serilog;
 using Newtonsoft.Json;
 using Microsoft.Extensions.Logging.Abstractions;
+using cat_cafe.WeSo;
 
 namespace cat_cafe.Controllers
 {
@@ -22,12 +23,19 @@ namespace cat_cafe.Controllers
         private readonly CatCafeContext _context;
         private readonly IMapper _mapper;
         private readonly ILogger<CatsController> _logger;
-
+        private readonly WebSocketHandler _webSocketHandler;
-        public CatsController(CatCafeContext context, IMapper mapper, ILogger<CatsController> logger)
+
+        public CatsController(
+            CatCafeContext context, 
+            IMapper mapper, 
+            ILogger<CatsController> logger,
+            WebSocketHandler webSocketHandler
+            )
         {
             _mapper = mapper;
             _context = context;
             _logger = logger;
+            _webSocketHandler = webSocketHandler;
         }
 
         // GET: api/Cats
@@ -94,6 +102,8 @@ namespace cat_cafe.Controllers
             _context.Cats.Add(cat);
             await _context.SaveChangesAsync();
 
+            await _webSocketHandler.BroadcastMessageAsync("entity-created");
+
             return CreatedAtAction("GetCat", new { id = catDto.Id }, _mapper.Map<CatDto>(cat));
         }
 

cat_cafe/Program.cs

@@ -2,13 +2,19 @@ using Microsoft.EntityFrameworkCore;
 using cat_cafe.Repositories;
 using Serilog;
 using Serilog.Sinks.File;
+using System.Net.WebSockets;
+using cat_cafe.WeSo;
 
 var builder = WebApplication.CreateBuilder(args);
 
 Log.Logger = new LoggerConfiguration().MinimumLevel.Information().WriteTo.File("log.txt").CreateLogger();
 
+List<WebSocket> _sockets = new();
+
 // Add services to the container.
 
+builder.Services.AddSingleton<List<WebSocket>>(x => _sockets);
+builder.Services.AddSingleton<WebSocketHandler>();
 builder.Services.AddControllers();
 builder.Services.AddDbContext<CatCafeContext>(opt => opt.UseInMemoryDatabase("CatCafe"));
 builder.Services.AddEndpointsApiExplorer();
@@ -33,6 +39,40 @@ app.UseAuthorization();
 
 app.MapControllers();
 
+app.UseWebSockets();
+
+
+app.Use(async (context, next) =>
+{
+    if (context.Request.Path == "/ws")
+    {
+        if (context.WebSockets.IsWebSocketRequest)
+        {
+            WebSocket webSocket = await context.WebSockets.AcceptWebSocketAsync();
+
+            _sockets.Add(webSocket);
+
+            var buffer = new byte[1024 * 4];
+            WebSocketReceiveResult result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
+            while (!result.CloseStatus.HasValue)
+            {
+                await webSocket.SendAsync(new ArraySegment<byte>(buffer, 0, result.Count), result.MessageType, result.EndOfMessage, CancellationToken.None);
+
+                result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
+            }
+            await webSocket.CloseAsync(result.CloseStatus.Value, result.CloseStatusDescription, CancellationToken.None);
+        }
+        else
+        {
+            context.Response.StatusCode = 400;
+        }
+    }
+    else
+    {
+        await next();
+    }
+});
+
 Log.Information("program start");
 
 app.Run();

cat_cafe/WeSo/WebSocketHandler.cs

@@ -0,0 +1,28 @@
+using System.Net.WebSockets;
+using System.Text;
+
+namespace cat_cafe.WeSo
+{
+    public class WebSocketHandler
+    {
+        private readonly List<WebSocket> _sockets;
+
+        public WebSocketHandler(List<WebSocket> sockets)
+        {
+            _sockets = sockets;
+        }
+
+        public async Task BroadcastMessageAsync(string message)
+        {
+            var buffer = Encoding.UTF8.GetBytes(message);
+            foreach (var socket in _sockets)
+            {
+                if (socket.State == WebSocketState.Open)
+                {
+                    await socket.SendAsync(new ArraySegment<byte>(buffer), WebSocketMessageType.Text, true, CancellationToken.None);
+                }
+            }
+        }
+    }
+
+}

cat_cafe/cat_cafe.csproj

@@ -7,6 +7,7 @@
 	</PropertyGroup>
 
 	<ItemGroup>
+		<PackageReference Include="Microsoft.AspNetCore.WebSockets" Version="2.2.1" />
 		<PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="7.0.1" />
 		<PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="6.0.12" />
 		<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="6.0.12" />