98 lines
3.4 KiB
C#
98 lines
3.4 KiB
C#
using Microsoft.Extensions.Logging;
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using Newtonsoft.Json;
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using Polly;
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using Polly.Wrap;
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using System;
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using System.Net.Http;
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using System.Threading.Tasks;
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namespace WebMVC.Services.Utilities
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{
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/// <summary>
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/// HttpClient wrapper that integrates Retry and Circuit
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/// breaker policies when calling to Api services.
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/// Currently is ONLY implemented for the ASP MVC
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/// and Xamarin App
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/// </summary>
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public class HttpApiClientWrapper : IHttpClient
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{
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private HttpClient _client;
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private PolicyWrap _policyWrapper;
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private ILogger _logger;
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public HttpClient Inst => _client;
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public HttpApiClientWrapper()
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{
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_client = new HttpClient();
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_logger = new LoggerFactory().CreateLogger(nameof(HttpApiClientWrapper));
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// Add Policies to be applied
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_policyWrapper = Policy.WrapAsync(
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CreateRetryPolicy(),
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CreateCircuitBreakerPolicy()
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);
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}
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private Policy CreateCircuitBreakerPolicy() =>
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Policy.Handle<HttpRequestException>()
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.CircuitBreakerAsync(
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// number of exceptions before breaking circuit
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5,
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// time circuit opened before retry
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TimeSpan.FromMinutes(1),
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(exception, duration) =>
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{
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// on circuit opened
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_logger.LogTrace("Circuit breaker opened");
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},
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() =>
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{
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// on circuit closed
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_logger.LogTrace("Circuit breaker reset");
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}
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);
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private Policy CreateRetryPolicy() =>
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Policy.Handle<HttpRequestException>()
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.WaitAndRetryAsync(
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// number of retries
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5,
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// exponential backofff
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retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)),
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// on retry
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(exception, timeSpan, retryCount, context) =>
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{
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_logger.LogTrace($"Retry {retryCount} " +
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$"of {context.PolicyKey} " +
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$"at {context.ExecutionKey}, " +
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$"due to: {exception}.");
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}
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);
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public Task<string> GetStringAsync(string uri) =>
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HttpInvoker(() =>
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_client.GetStringAsync(uri));
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public Task<HttpResponseMessage> PostAsync<T>(string uri, T item) =>
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// a new StringContent must be created for each retry
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// as it is disposed after each call
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HttpInvoker(() =>
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{
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var response = _client.PostAsync(uri, new StringContent(JsonConvert.SerializeObject(item), System.Text.Encoding.UTF8, "application/json"));
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// raise exception if not success response
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// needed for circuit breaker to track fails
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response.Result.EnsureSuccessStatusCode();
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return response;
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});
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public Task<HttpResponseMessage> DeleteAsync(string uri) =>
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HttpInvoker(() => _client.DeleteAsync(uri));
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private Task<T> HttpInvoker<T>(Func<Task<T>> action) =>
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// Executes the action applying all
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// the policies defined in the wrapper
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_policyWrapper.ExecuteAsync(() => action());
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}
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}
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