Modifying the default connectionedit

The client abstracts sending the request and creating a response behind IConnection and the default implementation uses

The reason for different implementations is that WebRequest and ServicePoint are not directly available on netstandard 1.3.

The Desktop CLR implementation using WebRequest is the most mature implementation, having been tried and trusted in production since the beginning of NEST. For this reason, we aren’t quite ready to it give up in favour of a HttpClient implementation across all CLR versions.

In addition to production usage, there are also a couple of important toggles that are easy to set against a ServicePoint that are not possible to set as yet on HttpClient.

Finally, another limitation is that HttpClient has no synchronous code paths, so supporting these means doing hacky async patches which definitely need time to bake.

So why would you ever want to pass your own IConnection? Let’s look at a couple of examples

Using InMemoryConnectionedit

InMemoryConnection is an in-built IConnection that makes it easy to write unit tests against. It can be configured to respond with default response bytes, HTTP status code and an exception when a call is made.

InMemoryConnection doesn’t actually send any requests or receive any responses from Elasticsearch; requests are still serialized and the request bytes can be obtained on the response if .DisableDirectStreaming is set to true on the request or globally

var connection = new InMemoryConnection();
var connectionPool = new SingleNodeConnectionPool(new Uri("http://localhost:9200"));
var settings = new ConnectionSettings(connectionPool, connection);
var client = new ElasticClient(settings);

Here we create a new ConnectionSettings by using the overload that takes a IConnectionPool and an IConnection. We pass it an InMemoryConnection which, using the default parameterless constructor, will return 200 for everything and never actually perform any IO.

Let’s see a more complex example

var response = new
{
    took = 1,
    timed_out = false,
    _shards = new
    {
        total = 2,
        successful = 2,
        failed = 0
    },
    hits = new
    {
        total = 25,
        max_score = 1.0,
        hits = Enumerable.Range(1, 25).Select(i => (object)new
        {
            _index = "project",
            _type = "project",
            _id = $"Project {i}",
            _score = 1.0,
            _source = new { name = $"Project {i}" }
        }).ToArray()
    }
};

var responseBytes = Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(response));
var connection = new InMemoryConnection(responseBytes, 200); 
var connectionPool = new SingleNodeConnectionPool(new Uri("http://localhost:9200"));
var settings = new ConnectionSettings(connectionPool, connection).DefaultIndex("project");
var client = new ElasticClient(settings);

var searchResponse = client.Search<Project>(s => s.MatchAll());

InMemoryConnection is configured to always return responseBytes along with a 200 HTTP status code

We can now assert that the searchResponse is valid and contains documents deserialized from our fixed InMemoryConnection response

searchResponse.IsValid.Should().BeTrue();
searchResponse.Documents.Count.Should().Be(25);

Changing HttpConnectionedit

There may be a need to change how the default HttpConnection works, for example, to add an X509 certificate to the request, change the maximum number of connections allowed to an endpoint, etc.

By deriving from HttpConnection, it is possible to change the behaviour of the connection. The following provides some examples

ServicePoint behaviouredit

If you are running on the Desktop CLR you can override specific properties for the current ServicePoint easily by overriding AlterServicePoint on an IConnection implementation deriving from HttpConnection

public class MyCustomHttpConnection : HttpConnection
{
    protected override void AlterServicePoint(ServicePoint requestServicePoint, RequestData requestData)
    {
        base.AlterServicePoint(requestServicePoint, requestData);
        requestServicePoint.ConnectionLimit = 10000;
        requestServicePoint.UseNagleAlgorithm = true;
    }
}

var connection = new MyCustomHttpConnection();
var connectionPool = new SingleNodeConnectionPool(new Uri("http://localhost:9200"));
var settings = new ConnectionSettings(connectionPool, connection);
var client = new ElasticClient(settings);

The Connection limit has been increased from the default 80 to much higher and nagling has been enabled, which is disabled by default in the client.

Note

The client reuses TCP connections through .NET’s internal connection pooling, so changing the connection limit to something really high should only be done with careful consideration and testing. It’s demonstrated here only as an example.

X.509 Certificatesedit

It is possible to add X509 certificates to each request from the client by overriding the CreateHttpWebRequest method in an IConnection implementation deriving from HttpConnection

public class X509CertificateHttpConnection : HttpConnection
{
    protected override HttpWebRequest CreateHttpWebRequest(RequestData requestData)
    {
        var request = base.CreateHttpWebRequest(requestData);
        request.ClientCertificates.Add(new X509Certificate("file_path_to_cert"));
        return request;
    }
}

As before, a new instance of the custom connection is passed to ConnectionSettings in order to use

var connection = new X509CertificateHttpConnection();
var connectionPool = new SingleNodeConnectionPool(new Uri("http://localhost:9200"));
var settings = new ConnectionSettings(connectionPool, connection);
var client = new ElasticClient(settings);

See Working with certificates for further details.