Modifying the default connection

The client abstracts sending the request and creating a response behind IConnection and the default implementation uses System.Net.Http.HttpClient.

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

Using InMemoryConnection

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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 = new { value = 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.ShouldBeValid();
searchResponse.Documents.Count.Should().Be(25);

Changing HttpConnection

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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

public class MyCustomHttpConnection : HttpConnection
{
    protected override HttpRequestMessage CreateRequestMessage(RequestData requestData)
    {
        var message = base.CreateRequestMessage(requestData);
        var header = string.Empty;
        message.Headers.Authorization = new AuthenticationHeaderValue("Negotiate", header);
        return message;
    }
}

public class KerberosConnection : HttpConnection
{
    protected override HttpRequestMessage CreateRequestMessage(RequestData requestData)
    {
        var message = base.CreateRequestMessage(requestData);
        var header = string.Empty;
        message.Headers.Authorization = new AuthenticationHeaderValue("Negotiate", header);
        return message;
    }
}

See Working with certificates for further details.

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