Give an Examples of Asynch Middleware?
Asynchronous middleware in ASP.NET Core allows for non-blocking operations during request processing. This is especially useful for operations that involve I/O-bound tasks, such as querying a database, calling external services, or performing network operations.
Here are a few examples of asynchronous middleware to illustrate how you can implement and use them:
1. Asynchronous Logging Middleware
This middleware logs the request and response times asynchronously. It's useful for monitoring and debugging request processing times.
Example: Asynchronous Logging Middleware
public class AsyncLoggingMiddleware
{
private readonly RequestDelegate _next;
private readonly ILogger<AsyncLoggingMiddleware> _logger;
public AsyncLoggingMiddleware(RequestDelegate next, ILogger<AsyncLoggingMiddleware> logger)
{
_next = next;
_logger = logger;
}
public async Task InvokeAsync(HttpContext context)
{
var startTime = DateTime.UtcNow;
// Log request details
_logger.LogInformation("Request started: {Method} {Url}", context.Request.Method, context.Request.Path);
// Call the next middleware in the pipeline
await _next(context);
var endTime = DateTime.UtcNow;
var duration = endTime - startTime;
// Log response details
_logger.LogInformation("Request finished: {Method} {Url} with status code {StatusCode} in {Duration}ms",
context.Request.Method,
context.Request.Path,
context.Response.StatusCode,
duration.TotalMilliseconds);
}
}Usage
Add this middleware to your pipeline in Startup.cs:
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
app.UseMiddleware<AsyncLoggingMiddleware>();
// Other middleware
}2. Asynchronous Cache Middleware
This middleware checks if a cached version of the response exists and serves it asynchronously. If not, it processes the request and caches the response.
Example: Asynchronous Cache Middleware
public class AsyncCacheMiddleware
{
private readonly RequestDelegate _next;
private readonly IMemoryCache _cache;
public AsyncCacheMiddleware(RequestDelegate next, IMemoryCache cache)
{
_next = next;
_cache = cache;
}
public async Task InvokeAsync(HttpContext context)
{
var cacheKey = context.Request.Path.ToString();
if (_cache.TryGetValue(cacheKey, out var cachedResponse))
{
// Serve cached response
context.Response.ContentType = "application/json";
await context.Response.WriteAsync((string)cachedResponse);
return;
}
// Capture the original body stream
var originalBodyStream = context.Response.Body;
// Create a new memory stream to hold the response
using (var memoryStream = new MemoryStream())
{
context.Response.Body = memoryStream;
// Call the next middleware
await _next(context);
// Reset the stream position to the beginning
memoryStream.Seek(0, SeekOrigin.Begin);
// Read the response from the memory stream
var responseBody = await new StreamReader(memoryStream).ReadToEndAsync();
// Cache the response
_cache.Set(cacheKey, responseBody, TimeSpan.FromMinutes(5));
// Write the response to the original body stream
memoryStream.Seek(0, SeekOrigin.Begin);
await memoryStream.CopyToAsync(originalBodyStream);
}
}
}Usage
Configure caching services and add the middleware in Startup.cs:
public void ConfigureServices(IServiceCollection services)
{
services.AddMemoryCache();
// Other services
}
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
app.UseMiddleware<AsyncCacheMiddleware>();
// Other middleware
}3. Asynchronous External API Call Middleware
This middleware makes an asynchronous call to an external API and includes the API response in the HTTP response.
Example: Asynchronous External API Call Middleware
public class ExternalApiMiddleware
{
private readonly RequestDelegate _next;
private readonly HttpClient _httpClient;
public ExternalApiMiddleware(RequestDelegate next, HttpClient httpClient)
{
_next = next;
_httpClient = httpClient;
}
public async Task InvokeAsync(HttpContext context)
{
if (context.Request.Path.StartsWithSegments("/api/data"))
{
var apiResponse = await _httpClient.GetStringAsync("https://api.example.com/data");
context.Response.ContentType = "application/json";
await context.Response.WriteAsync(apiResponse);
return;
}
await _next(context);
}
}Usage
Configure HttpClient and add the middleware in Startup.cs:
public void ConfigureServices(IServiceCollection services)
{
services.AddHttpClient();
// Other services
}
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
app.UseMiddleware<ExternalApiMiddleware>();
// Other middleware
}4. Asynchronous Authentication Middleware
This middleware performs asynchronous authentication checks, for example, querying a user database.
Example: Asynchronous Authentication Middleware
public class AsyncAuthenticationMiddleware
{
private readonly RequestDelegate _next;
private readonly IUserService _userService;
public AsyncAuthenticationMiddleware(RequestDelegate next, IUserService userService)
{
_next = next;
_userService = userService;
}
public async Task InvokeAsync(HttpContext context)
{
var token = context.Request.Headers["Authorization"].ToString();
if (string.IsNullOrEmpty(token))
{
context.Response.StatusCode = StatusCodes.Status401Unauthorized;
await context.Response.WriteAsync("Unauthorized");
return;
}
var user = await _userService.AuthenticateAsync(token);
if (user == null)
{
context.Response.StatusCode = StatusCodes.Status401Unauthorized;
await context.Response.WriteAsync("Unauthorized");
return;
}
// Attach user information to the context
context.Items["User"] = user;
await _next(context);
}
}Usage
Configure IUserService and add the middleware in Startup.cs:
public void ConfigureServices(IServiceCollection services)
{
services.AddScoped<IUserService, UserService>();
// Other services
}
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
app.UseMiddleware<AsyncAuthenticationMiddleware>();
// Other middleware
}These examples demonstrate how to implement asynchronous middleware to handle various scenarios in ASP.NET Core. Each example highlights the use of await to perform non-blocking operations, which can improve the efficiency and responsiveness of your application.