JavaScriptServices/src/Microsoft.AspNetCore.SpaServices.Extensions/Proxying/ConditionalProxyMiddleware.cs

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Hosting;
using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

namespace Microsoft.AspNetCore.SpaServices.Extensions.Proxy
{
    // This duplicates and updates the proxying logic in SpaServices so that we can update
    // the project templates without waiting for 2.1 to ship. When 2.1 is ready to ship,
    // merge the additional proxying features (e.g., proxying websocket connections) back
    // into the SpaServices proxying code. It's all internal.
    internal class ConditionalProxyMiddleware
    {
        private readonly RequestDelegate _next;
        private readonly Task<Uri> _baseUriTask;
        private readonly string _pathPrefix;
        private readonly bool _pathPrefixIsRoot;
        private readonly HttpClient _httpClient;
        private readonly CancellationToken _applicationStoppingToken;

        public ConditionalProxyMiddleware(
            RequestDelegate next,
            string pathPrefix,
            TimeSpan requestTimeout,
            Task<Uri> baseUriTask,
            IApplicationLifetime applicationLifetime)
        {
            if (!pathPrefix.StartsWith("/"))
            {
                pathPrefix = "/" + pathPrefix;
            }

            _next = next;
            _pathPrefix = pathPrefix;
            _pathPrefixIsRoot = string.Equals(_pathPrefix, "/", StringComparison.Ordinal);
            _baseUriTask = baseUriTask;
            _httpClient = SpaProxy.CreateHttpClientForProxy(requestTimeout);
            _applicationStoppingToken = applicationLifetime.ApplicationStopping;
        }

        public async Task Invoke(HttpContext context)
        {
            if (context.Request.Path.StartsWithSegments(_pathPrefix) || _pathPrefixIsRoot)
            {
                var didProxyRequest = await SpaProxy.PerformProxyRequest(
                    context, _httpClient, _baseUriTask, _applicationStoppingToken, proxy404s: false);
                if (didProxyRequest)
                {
                    return;
                }
            }

            // Not a request we can proxy
            await _next.Invoke(context);
        }
    }
}