Let's Talk HTTP in .NET Core

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Let's Talk HTTP in .NET Core

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 What we’ll cover • Why do we
need IHttpClientFactory? • How to use IHttpClientFactory • Outgoing middleware • Handling transient errors with Polly • Patterns and recommendations • Other HTTP improvements in .NET Core 2.1 • Coming in .NET Core 3.0 NOTE: I'm generally speaking about .NET Core today.

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 public class GitHubController : ControllerBase { [HttpGet]
public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { using (var client = new HttpClient()) { client.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json"); client.DefaultRequestHeaders.Add("User-Agent", "my-user-agent"); var url = "https://api.github.com/orgs/aspnet/repos"; var request = new HttpRequestMessage(HttpMethod.Get, url); var response = await _httpClient.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } } }

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 The Solution

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 What’s the solution?

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 public class Startup { public Startup(IConfiguration configuration)
{ Configuration = configuration; } public IConfiguration Configuration { get; } public void ConfigureServices(IServiceCollection services) { services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); } public void Configure(IApplicationBuilder app, IHostingEnvironment env) { app.UseMvc(); } }

{ Configuration = configuration; } public IConfiguration Configuration { get; } public void ConfigureServices(IServiceCollection services) { services.AddSingleton<HttpClient>(); services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); } public void Configure(IApplicationBuilder app, IHostingEnvironment env) { app.UseMvc(); } }

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 public class GitHubController : ControllerBase { [HttpGet]
public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { using (var client = new HttpClient()) { client.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json"); client.DefaultRequestHeaders.Add("User-Agent", "my-user-agent"); var url = "https://api.github.com/orgs/aspnet/repos"; var request = new HttpRequestMessage(HttpMethod.Get, url); var response = await client.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } } }

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 public class GitHubController : ControllerBase { private
readonly HttpClient _httpClient; public GitHubController(HttpClient httpClient) => _httpClient = httpClient; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { using (var client = new HttpClient()) { client.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json"); client.DefaultRequestHeaders.Add("User-Agent", "my-user-agent"); var url = "https://api.github.com/orgs/aspnet/repos"; var request = new HttpRequestMessage(HttpMethod.Get, url); var response = await client.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } } }

readonly HttpClient _httpClient; public GitHubController(HttpClient httpClient) => _httpClient = httpClient; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { client.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json"); client.DefaultRequestHeaders.Add("User-Agent", "my-user-agent"); var url = "https://api.github.com/orgs/aspnet/repos"; var request = new HttpRequestMessage(HttpMethod.Get, url); var response = await client.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } }

readonly HttpClient _httpClient; public GitHubController(HttpClient httpClient) => _httpClient = httpClient; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { var url = "https://api.github.com/orgs/aspnet/repos"; var request = new HttpRequestMessage(HttpMethod.Get, url); request.Headers.Add("Accept", "application/vnd.github.v3+json"); request.Headers.Add("User-Agent", "my-user-agent"); var response = await client.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } }

readonly HttpClient _httpClient; public GitHubController(HttpClient httpClient) => _httpClient = httpClient; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { var url = "https://api.github.com/orgs/aspnet/repos"; var request = new HttpRequestMessage(HttpMethod.Get, url); request.Headers.Add("Accept", "application/vnd.github.v3+json"); request.Headers.Add("User-Agent", "my-user-agent"); var response = await _httpClient.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } }

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 But…

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 IHttpClientFactory • Manages the lifetime of HttpMessageHandlers
• Provides a central location for naming and configuring logical HttpClients • Codifies the concept of outgoing middleware via delegating handlers • Integrates with Polly for transient-fault handling • Improved diagnostics and logging

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Converting Our Code

{ Configuration = configuration; } public IConfiguration Configuration { get; } public void ConfigureServices(IServiceCollection services) { services.AddSingleton<HttpClient>(); services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); } public void Configure(IApplicationBuilder app, IHostingEnvironment env) { app.UseMvc(); } }

{ Configuration = configuration; } public IConfiguration Configuration { get; } public void ConfigureServices(IServiceCollection services) { services.AddHttpClient(); services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); } public void Configure(IApplicationBuilder app, IHostingEnvironment env) { app.UseMvc(); } }

readonly HttpClient _httpClient; public GitHubController(HttpClient httpClient) => _httpClient = httpClient; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { var url = "https://api.github.com/orgs/aspnet/repos"; var request = new HttpRequestMessage(HttpMethod.Get, url); request.Headers.Add("Accept", "application/vnd.github.v3+json"); request.Headers.Add("User-Agent", "my-user-agent"); var response = await _httpClient.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } }

readonly IHttpClientFactory _factory; public GitHubController(IHttpClientFactory factory) => _factory = factory; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { var url = "https://api.github.com/orgs/aspnet/repos"; var request = new HttpRequestMessage(HttpMethod.Get, url); request.Headers.Add("Accept", "application/vnd.github.v3+json"); request.Headers.Add("User-Agent", "my-user-agent"); var response = await _httpClient.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } }

readonly IHttpClientFactory _factory; public GitHubController(IHttpClientFactory factory) => _factory = factory; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { var url = "https://api.github.com/orgs/aspnet/repos"; var request = new HttpRequestMessage(HttpMethod.Get, url); request.Headers.Add("Accept", "application/vnd.github.v3+json"); request.Headers.Add("User-Agent", "my-user-agent"); var httpClient = _factory.CreateClient(); var response = await httpClient.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } }

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Named Clients

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 public class Startup { ... public void
ConfigureServices(IServiceCollection services) { services.AddHttpClient(); services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); } public void Configure(IApplicationBuilder app, IHostingEnvironment env) { … } }

ConfigureServices(IServiceCollection services) { services.AddHttpClient("github", client => { client.BaseAddress = new Uri("https://api.github.com/"); client.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json"); client.DefaultRequestHeaders.Add("User-Agent", "my-user-agent"); }); services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); } public void Configure(IApplicationBuilder app, IHostingEnvironment env) { … } }

readonly IHttpClientFactory _factory; public GitHubController(IHttpClientFactory factory) => _factory = factory; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { var url = "https://api.github.com/orgs/aspnet/repos"; var request = new HttpRequestMessage(HttpMethod.Get, url); request.Headers.Add("Accept", "application/vnd.github.v3+json"); request.Headers.Add("User-Agent", "my-user-agent"); var httpClient = _factory.CreateClient(); var response = await httpClient.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } }

readonly IHttpClientFactory _factory; public GitHubController(IHttpClientFactory factory) => _factory = factory; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); request.Headers.Add("Accept", "application/vnd.github.v3+json"); request.Headers.Add("User-Agent", "my-user-agent"); var httpClient = _factory.CreateClient(); var response = await httpClient.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } }

readonly IHttpClientFactory _factory; public GitHubController(IHttpClientFactory factory) => _factory = factory; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); var httpClient = _factory.CreateClient(); var response = await httpClient.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } }

readonly IHttpClientFactory _factory; public GitHubController(IHttpClientFactory factory) => _factory = factory; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); var httpClient = _factory.CreateClient("github"); var response = await httpClient.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } }

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Typed Clients

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 public class GitHubClient : IGitHubClient { private
readonly HttpClient _httpClient; public GitHubClient(HttpClient client) { client.BaseAddress = new Uri("https://api.github.com/"); client.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json"); client.DefaultRequestHeaders.Add("User-Agent", "my_user_agent"); _httpClient = client; } public async Task<IEnumerable<GitHubRepo>> GetAspNetReposAsync() { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); var response = await _httpClient.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data); } }

ConfigureServices(IServiceCollection services) { services.AddHttpClient("github", client => { client.BaseAddress = new Uri("https://api.github.com/"); client.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json"); client.DefaultRequestHeaders.Add("User-Agent", "my-user-agent"); }); services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); } public void Configure(IApplicationBuilder app, IHostingEnvironment env) { … } }

ConfigureServices(IServiceCollection services) { services.AddHttpClient<IGitHubClient, GitHubClient>(); services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); } public void Configure(IApplicationBuilder app, IHostingEnvironment env) { … } }

readonly IHttpClientFactory _factory; public GitHubController(IHttpClientFactory factory) => _factory = factory; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); var httpClient = _factory.CreateClient("github"); var response = await httpClient.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } }

readonly IGitHubClient _gitHubClient; public GitHubController(IGitHubClient gitHubClient) => _gitHubClient = gitHubClient; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); var httpClient = _factory.CreateClient("github"); var response = await httpClient.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return Ok(JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data)); } }

readonly IGitHubClient _gitHubClient; public GitHubController(IGitHubClient gitHubClient) => _gitHubClient = gitHubClient; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { var data = await _gitHubClient.GetAspNetReposAsync(); return Ok(data); } }

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Outgoing "middleware" https://api.github.com Our Application HttpClient H
t t p R e q u e s t M e s s a g e H t t p R e s p o n s e M e s s a g e

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Outgoing "middleware" Outer Handler Middle Handler Inner
Handler HttpClientHandler SocketsHttpHandler https://api.github.com Our Application HttpClient H t t p R e q u e s t M e s s a g e H t t p R e s p o n s e M e s s a g e

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Delegating Handlers

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 public class StatusCodeMetricHandler : DelegatingHandler { private
readonly IMonitoringService _monitoringService; public StatusCodeMetricHandler(IMonitoringService monitoringService) => _monitoringService = monitoringService; protected override async Task<HttpResponseMessage> SendAsync( HttpRequestMessage request, CancellationToken ct) { // note: we could do things with the request before passing it along var response = await base.SendAsync(request, ct); _monitoringService.RecordStatusCodeMetric((int)response.StatusCode); return response; } }

ConfigureServices(IServiceCollection services) { services.AddHttpClient<IGitHubClient, GitHubClient>(); services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); } public void Configure(IApplicationBuilder app, IHostingEnvironment env) { … } }

ConfigureServices(IServiceCollection services) { services.AddTransient<IMonitoringService, MonitoringService>(); services.AddTransient<StatusCodeMetricHandler>(); services.AddHttpClient<IGitHubClient, GitHubClient>() .AddHttpMessageHandler<StatusCodeMetricHandler>(); services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); } public void Configure(IApplicationBuilder app, IHostingEnvironment env) { … } }

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Polly • Polly is a .NET resilience
and transient-fault-handling library • Integrates easily with IHttpClientFactory • Retry • Circuit-breaker • Timeout • Bulkhead isolation • Cache • Fallback • PolicyWrap

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Handling Transient Errors with Polly

ConfigureServices(IServiceCollection services) { services.AddTransient<IMonitoringService, MonitoringService>(); services.AddTransient<StatusCodeMetricHandler>(); services.AddHttpClient<IGitHubClient, GitHubClient>() .AddHttpMessageHandler<StatusCodeMetricHandler>(); services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); } public void Configure(IApplicationBuilder app, IHostingEnvironment env) { … } }

ConfigureServices(IServiceCollection services) { services.AddTransient<IMonitoringService, MonitoringService>(); services.AddTransient<StatusCodeMetricHandler>(); services.AddHttpClient<IGitHubClient, GitHubClient>() .AddTransientHttpErrorPolicy(builder => builder.WaitAndRetryAsync(3, retryCount => TimeSpan.FromSeconds(Math.Pow(2, retryCount)))) .AddHttpMessageHandler<StatusCodeMetricHandler>(); services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); } public void Configure(IApplicationBuilder app, IHostingEnvironment env) { … } }

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Taking care when handling response content

readonly HttpClient _httpClient; public GitHubClient(HttpClient client) { client.BaseAddress = new Uri("https://api.github.com/"); client.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json"); client.DefaultRequestHeaders.Add("User-Agent", "my_user_agent"); _httpClient = client; } public async Task<IEnumerable<GitHubRepo>> GetAspNetReposAsync() { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); var response = await _httpClient.SendAsync(request); var data = await response.Content.ReadAsStringAsync(); return JsonConvert.DeserializeObject<IEnumerable<GitHubRepo>>(data); } }

readonly HttpClient _httpClient; public GitHubClient(HttpClient client) { client.BaseAddress = new Uri("https://api.github.com/"); client.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json"); client.DefaultRequestHeaders.Add("User-Agent", "my_user_agent"); _httpClient = client; } public async Task<IEnumerable<GitHubRepo>> GetAspNetReposAsync() { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); var response = await _httpClient.SendAsync(request); return await response.Content.ReadAsAsync<IEnumerable<GitHubRepo>>(); } }

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Handling Errors

readonly HttpClient _httpClient; public GitHubClient(HttpClient client) { // hidden for brevity ... } public async Task<IEnumerable<GitHubRepo>> GetAspNetReposAsync() { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); var response = await _httpClient.SendAsync(request); return await response.Content.ReadAsAsync<IEnumerable<GitHubRepo>>(); } }

readonly HttpClient _httpClient; public GitHubClient(HttpClient client) { // hidden for brevity ... } public async Task<IEnumerable<GitHubRepo>> GetAspNetReposAsync() { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); var response = await _httpClient.SendAsync(request); response.EnsureSuccessStatusCode(); return await response.Content.ReadAsAsync<IEnumerable<GitHubRepo>>(); } }

readonly HttpClient _httpClient; public GitHubClient(HttpClient client) { // hidden for brevity ... } public async Task<IEnumerable<GitHubRepo>> GetAspNetReposAsync() { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); var response = await _httpClient.SendAsync(request); return response.IsSuccessStatusCode ? await response.Content.ReadAsAsync<IEnumerable<GitHubRepo>>() : Array.Empty<GitHubRepo>(); } }

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Handling Cancellation

readonly HttpClient _httpClient; public GitHubClient(HttpClient client) { // hidden for brevity ... } public async Task<IEnumerable<GitHubRepo>> GetAspNetReposAsync() { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); var response = await _httpClient.SendAsync(request); return response.IsSuccessStatusCode ? await response.Content.ReadAsAsync<IEnumerable<GitHubRepo>>() : Array.Empty<GitHubRepo>(); } }

readonly HttpClient _httpClient; public GitHubClient(HttpClient client) { // hidden for brevity ... } public async Task<IEnumerable<GitHubRepo>> GetAspNetReposAsync(CancellationToken ct = default) { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); var response = await _httpClient.SendAsync(request); return response.IsSuccessStatusCode ? await response.Content.ReadAsAsync<IEnumerable<GitHubRepo>>() : Array.Empty<GitHubRepo>(); } }

readonly HttpClient _httpClient; public GitHubClient(HttpClient client) { // hidden for brevity ... } public async Task<IEnumerable<GitHubRepo>> GetAspNetReposAsync(CancellationToken ct = default) { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); ct.ThrowIfCancellationRequested(); var response = await _httpClient.SendAsync(request); return response.IsSuccessStatusCode ? await response.Content.ReadAsAsync<IEnumerable<GitHubRepo>>() : Array.Empty<GitHubRepo>(); } }

readonly HttpClient _httpClient; public GitHubClient(HttpClient client) { // hidden for brevity ... } public async Task<IEnumerable<GitHubRepo>> GetAspNetReposAsync(CancellationToken ct = default) { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); ct.ThrowIfCancellationRequested(); var response = await _httpClient.SendAsync(request, ct); return response.IsSuccessStatusCode ? await response.Content.ReadAsAsync<IEnumerable<GitHubRepo>>() : Array.Empty<GitHubRepo>(); } }

readonly HttpClient _httpClient; public GitHubClient(HttpClient client) { // hidden for brevity ... } public async Task<IEnumerable<GitHubRepo>> GetAspNetReposAsync(CancellationToken ct = default) { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); ct.ThrowIfCancellationRequested(); var response = await _httpClient.SendAsync(request, ct); return response.IsSuccessStatusCode ? await response.Content.ReadAsAsync<IEnumerable<GitHubRepo>>(ct) : Array.Empty<GitHubRepo>(); } }

readonly IGitHubClient _gitHubClient; public GitHubController(IGitHubClient gitHubClient) => _gitHubClient = gitHubClient; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos() { var data = await _gitHubClient.GetAspNetReposAsync(); return Ok(data); } }

readonly IGitHubClient _gitHubClient; public GitHubController(IGitHubClient gitHubClient) => _gitHubClient = gitHubClient; [HttpGet] public async Task<ActionResult<IEnumerable<GitHubRepo>>> GetAspNetRepos(CancellationToken ct) { var data = await _gitHubClient.GetAspNetReposAsync(ct); return Ok(data); } }

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 When Should I Dispose? • HttpClient (using
IHttpClientFactory) – No effect • HttpClient (without IHttpClientFactory) – Generally never • HttpRequestMessage – Only has an effect if sending StreamContent. • HttpResponseMessage – Safest is always to dispose after handling response. No effect in most cases.

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 public class GitHubClient : IGitHubClient { //
ctor - hidden for brevity ... public async Task<IEnumerable<GitHubRepo>> GetAspNetReposAsync(CancellationToken ct = default) { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); ct.ThrowIfCancellationRequested(); var response = await _httpClient.SendAsync(request, ct); return response.IsSuccessStatusCode ? await response.Content.ReadAsAsync<IEnumerable<GitHubRepo>>(ct) : Array.Empty<GitHubRepo>(); } } }

ctor - hidden for brevity ... public async Task<IEnumerable<GitHubRepo>> GetAspNetReposAsync(CancellationToken ct = default) { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); ct.ThrowIfCancellationRequested(); var response = await _httpClient.SendAsync(request, ct); try { return response.IsSuccessStatusCode ? await response.Content.ReadAsAsync<IEnumerable<GitHubRepo>>(ct) : Array.Empty<GitHubRepo>(); } finally { response.Dispose(); } } }

ctor - hidden for brevity ... public async Task<IEnumerable<GitHubRepo>> GetAspNetReposAsync(CancellationToken ct = default) { var request = new HttpRequestMessage(HttpMethod.Get, "orgs/aspnet/repos"); ct.ThrowIfCancellationRequested(); var response = await _httpClient.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, ct); try { return response.IsSuccessStatusCode ? await response.Content.ReadAsAsync<IEnumerable<GitHubRepo>>(ct) : Array.Empty<GitHubRepo>(); } finally { response.Dispose(); } } }

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 SocketsHttpHandler • Sockets are the basis of
both outgoing and incoming networking communication • SocketsHttpHandler is a brand-new managed HttpMessageHandler and is the default implementation for HttpClient • Consistent behaviour across platforms and platform/dependency versions. Built on top of System.Net.Sockets • Elimination of platform dependencies on libcurl (for Linux) and WinHTTP (for Windows) – simplifies both development, deployment and servicing • Enabled by default in .NET Core 2.1+ (Does not support HTTP/2)

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Coming in .NET Core 3.0 • HTTP/2
is supported (primarily for gRPC scenarios) although not enabled by default • HttpClient now includes a Version property which applies to all messages sent via that client (HTTP/1.1 by default) • TLS 1.3 and OpenSSL 1.1.1 on Linux reduces connection times and improves security – Windows and macOS when OS support it

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 In Summary • Use IHttpClientFactory in .NET
Core 2.1+ • Use Polly for transient-fault handling • Beware content.ReadAsStringAsync and client.GetStringAsync • Expect and handle errors • Pass cancellation tokens • Go enjoy talking HTTP! ☺

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Thanks for listening! @stevejgordon www.stevejgordon.co.uk youtube.stevejgordon.co.uk https://app.pluralsight.com/profile/author/steve-gordon

@stevejgordon www.stevejgordon.co.uk https://bit.ly/letstalkhttp40 Resources 1. https://bit.ly/letstalkhttp40 2. https://www.stevejgordon.co.uk/httpclient-creation-and-disposal-internals-should-i-dispose-of- httpclient 3.
https://www.stevejgordon.co.uk/demystifying-httpclient-internals-httprequestmessage 4. https://www.stevejgordon.co.uk/demystifying-httpclient-internals-httpresponsemessage 5. https://aspnetmonsters.com/2016/08/2016-08-27-httpclientwrong/ 6. https://docs.microsoft.com/en-us/aspnet/core/fundamentals/http-requests?view=aspnetcore- 2.1 7. https://github.com/App-vNext/Polly

Let's Talk HTTP in .NET Core

Let's Talk HTTP in .NET Core

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