README_Customizations.md

Customizations

Customize HttpClient

You may want to customize your calls to the back end Apis.

You can customize the default HttpClient used by all the routes, to hit the backend Api.

    //Api gateway
    services.AddApiGateway(options =>
    {
        options.DefaultHttpClientConfigure = (sp, httpClient) => httpClient.DefaultRequestHeaders.Add("My header", "My header value");
    });

You can create the default HttpClient used by all the routes, to hit the backend Api.

Eg. below code adds Proxy info to a new HttpClient.

    var proxyHost = "http://localhost";
    var proxyPort = 80;
    var proxyUserName = "testUser";
    var proxyPassword = "testPwd";

    var proxy = new WebProxy
    {
        Address = new Uri($"http://{proxyHost}:{proxyPort}"),
        BypassProxyOnLocal = false,
        UseDefaultCredentials = false,

        // *** These creds are given to the proxy server, not the web server ***
        Credentials = new NetworkCredential(
            userName: proxyUserName,
            password: proxyPassword)
    };

    var httpClientHandler = new HttpClientHandler
    {
        Proxy = proxy
    };

    //Api gateway
    services.AddApiGateway(options =>
    {
        options.DefaultMyHttpClientHandler = () => httpClientHandler;
    });

Also, the library provides hooks to

• Customize the default HttpClient which each route uses to hit the backend Api.
• Use your own HttpClient for each route.

For eg.

These hooks are implemented in your Gateway API project (eg. WeatherService below).

    public class WeatherService : IWeatherService
    {
        /// <summary>
        /// If you want to customize the default HttpClient or
        /// use your own custom HttpClient or HttpContent 
        /// to hit the backend Api call, you can do this.
        /// </summary>
        /// <returns><see cref="HttpClientConfig"/></returns>
        public HttpClientConfig GetClientConfig()
        {
            return new HttpClientConfig()
            {
                //customize the default HttpClient. eg. add a header.
                CustomizeDefaultHttpClient = (httpClient, request) => httpClient.DefaultRequestHeaders.Add("My header", "My header value"), 
                //OR
                //your own custom HttpClient
                HttpClient = () => new HttpClient()
            };
        }
    }

Wire up the WeatherService for injection.

	services.AddTransient<IWeatherService, WeatherService>();

Then, they are hooked up to routes in the Api Orchestrator.

    public static class ApiOrchestration
    {
        public static void Create(IApiOrchestrator orchestrator, IApplicationBuilder app)
        {
            var serviceProvider = app.ApplicationServices;

            var weatherService = serviceProvider.GetService<IWeatherService>();

            var weatherApiClientConfig = weatherService.GetClientConfig();

            orchestrator.AddApi("weatherservice", "http://localhost:63969/")                                
                                //Get using customize default HttpClient or your own custom HttpClient
                                .AddRoute("types", GatewayVerb.GET, new RouteInfo { Path = "weatherforecast/types", ResponseType = typeof(string[]), HttpClientConfig = weatherApiClientConfig });        }
    }

Custom implementation

• Use your own custom implementation to hit the backend Api.

Create a Service (like WeatherService).

Add a method (like GetForecast) with the same method signature. See HttpRequest here.

In the method, put your custom implementation.

    public class WeatherService : IWeatherService
    {
        /// <summary>
        /// If you want to completely customize your backend Api call, you can do this
        /// </summary>
        /// <param name="apiInfo">The api info</param>
        /// <param name="request">The gateway's incoming request</param>
        /// <returns>The object to be returned</returns>
        public async Task<object> GetForecast(ApiInfo apiInfo, HttpRequest request)
        {
            //Create your own implementation to hit the backend.
        }
    }

Wire up the WeatherService for injection.

	services.AddTransient<IWeatherService, WeatherService>();

Create a Route in the ApiOrchestrator as shown below:

    public static class ApiOrchestration
    {
        public static void Create(IApiOrchestrator orchestrator, IApplicationBuilder app)
        {
            var serviceProvider = app.ApplicationServices;

            var weatherService = serviceProvider.GetService<IWeatherService>();

            orchestrator.AddApi("weatherservice", "http://localhost:63969/")                                
                                //Get using custom implementation
                                .AddRoute("forecast-custom", GatewayVerb.GET, weatherService.GetForecast);
        }
    }

Request aggregation

Your Api Gateway gets one incoming request.

Then, you can make multiple requests to back end, downstream Apis and aggregate their responses.

You can do this in a custom implementation.

Read more