Problem

When using HttpClient.PostAsJsonAsync() to call the GraphQL endpoint (EntityGraphQLEndpointRouteExtensions.MapGraphQL), the request fails with 400 Bad Request. This happens because PostAsJsonAsync:

• Sets Transfer-Encoding: chunked
• Does not set Content-Length

The current implementation in EntityGraphQLEndpointRouteExtensions.MapGraphQL<T>() rejects all requests where ContentLength == null or 0, making it incompatible with chunked transfers — despite chunked encoding being fully compliant with HTTP/1.1.

This behavior makes the GraphQL endpoint incompatible with a common usage of HTTP client libraries.

Fix

In MapGraphQL<TQueryType>, we now:

• Check for Transfer-Encoding: chunked
• If the request is chunked, we no longer reject it for having no Content-Length

This ensures the GraphQL endpoint accepts another valid type of HTTP/1.1 requests.

var isChunked = context.Request.Headers.TransferEncoding
    .Any(h => h is not null && h.Equals("chunked", StringComparison.OrdinalIgnoreCase));

if (!isChunked && (context.Request.ContentLength == null || context.Request.ContentLength == 0))
{
    context.Response.StatusCode = StatusCodes.Status400BadRequest;
    return;
}

Test Coverage

A new integration test using the existing CustomWebApplicationFactory infrastructure has been added. It runs the app over a real TCP socket (Kestrel) to confirm that:

• PostAsJsonAsync() sends a chunked request
• The endpoint accepts and successfully executes the GraphQL query

Note: the test must use communication over the wire, via CustomWebApplicationFactory, a Testcontainer, or any other way that's not pure in-memory, like with IClassFixture<WebApplicationFactory<Program>>. Otherwise, Content-Length is set. I've also tried to reproduce it with the .NET 10 Preview 4 feature "Use WebApplicationFactory with Kestrel for integration testing" but the test passed similar to the way it passes with IClassFixture<WebApplicationFactory<Program>>, so it wasn't a good way to reproduce it with that method:

    [Fact]
    public async Task GraphQl_Endpoint_Works_With_Kestrel()
    {
        using var factory = new WebApplicationFactory<Program>();

        factory.UseKestrel();     // <- new in .NET 10 preview
        factory.StartServer();    // <- new in .NET 10 preview

        using var client = factory.CreateClient();
        var resp = await client.PostAsJsonAsync("/graphql", new { query = "{ hello }" });
        resp.EnsureSuccessStatusCode();

        var json = await resp.Content.ReadAsStringAsync();
        Assert.Contains("\"hello\":\"world\"", json);

Result

• Fixes: chunked payloads being rejected with 400
• Supports: improved compliance with the GraphQL over HTTP spec
• Supports: PostAsJsonAsync