Intercepting responses

FromFolderDelegatingHandler.cs

using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Net.Http;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

internal class FromFolderDelegatingHandler : DelegatingHandler
{
    private readonly string folder;
    private readonly string captureFolder;

    private Dictionary<string, int> endpointsIncrement = new Dictionary<string, int>();

    public FromFolderDelegatingHandler(string folder, string captureFolder)
    {
        this.folder = folder;
        this.captureFolder = captureFolder;

        Directory.CreateDirectory(folder);
        Directory.CreateDirectory(captureFolder);
        foreach (var file in Directory.GetFiles(captureFolder))
        {
            File.Delete(file);
        }
    }

    protected async override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        var requestUri = request.RequestUri;
        var path = requestUri!.LocalPath;
        var method = request.Method;
        var baseName = method + "_" + path.Substring(1).Replace("/", "_");
        var fileToReturn = this.GetRequestFileName(this.folder, baseName);
        var fileToCapture = this.GetRequestFileName(this.captureFolder, baseName);

        if (request.Content != null)
        {
            var requestContent = await request.Content.ReadAsStringAsync(cancellationToken).ConfigureAwait(false);
            await File.WriteAllTextAsync(fileToCapture, requestContent, cancellationToken).ConfigureAwait(false);
        }
        else if (request.Method == HttpMethod.Post)
        {
            await File.WriteAllTextAsync(fileToCapture, string.Empty, cancellationToken).ConfigureAwait(false);
        }

        var content = await File.ReadAllTextAsync(fileToReturn, cancellationToken).ConfigureAwait(false);

        var responseContent = new StringContent(content, Encoding.UTF8, "application/json");
        var response = new HttpResponseMessage(HttpStatusCode.OK)
        {
            Content = responseContent,
        };
        return response;
    }

    private string GetRequestFileName(string folder, string baseName)
    {
        var basePath = Path.Combine(folder, baseName);
        var increment = this.GetEndpointIncrement(basePath);
        this.endpointsIncrement[basePath] = increment + 1;
        if (increment != 0)
        {
            basePath = basePath + "_" + increment;
        }

        return basePath + ".json";
    }

    private int GetEndpointIncrement(string key)
    {
        int increment = 0;
        this.endpointsIncrement.TryGetValue(key, out increment);
        if (increment == 0)
        {
            return 0;
        }

        return increment;
    }
}

sample.cs

var httpClient = new HttpClient(new FromFolderDelegatingHandler(responsesFolderApi, captureFolderApi)