ConsoleLoggingHandler.cs

/// <summary>
/// <see cref="DelegatingHandler"/> that can be used to capture the actual outbound request and the returned
/// response. These are logged by default to the console but can also be routed to an action. This can be useful
/// for tests that use a <see cref="HttpClient"/> to call a fake service.
/// </summary>
/// <example>
/// new HttpClient(new LoggingDelegatingHandler(new HttpClientHandler()));
/// </example>
public class LoggingDelegatingHandler : DelegatingHandler
{
    private readonly Action<string> _loggerAction;

    /// <summary>
    /// Logs all requests and responses to the console.
    /// </summary>
    /// <param name="innerHandler"></param>
    public LoggingDelegatingHandler(HttpMessageHandler innerHandler)
        : this(innerHandler, Console.WriteLine) { }

    /// <summary>
    /// Logs all requests and responses to the supplied action.
    /// </summary>
    /// <param name="innerHandler"></param>
    /// <param name="loggerAction"></param>
    public LoggingDelegatingHandler(HttpMessageHandler innerHandler, Action<string> loggerAction)
        : base(innerHandler) => _loggerAction = loggerAction;

    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        await LogRequest( request );

        var response = await base.SendAsync(request, cancellationToken);

        await LogResponse( response );

        return response;
    }

    private async Task LogResponse( HttpResponseMessage response ) =>
        _loggerAction((await LogContent(StartLog(response), response.Content)).ToString());

    private async Task LogRequest( HttpRequestMessage request ) =>
        _loggerAction((await LogContent(StartLog(request), request.Content)).ToString());

    private StringBuilder StartLog(object obj) =>
        new StringBuilder(obj switch
        {
            HttpRequestMessage _ => "Request -> ",
            HttpResponseMessage _ => "Response -> "
        })
        .Append(obj).AppendLine();

    private async Task<StringBuilder> LogContent(StringBuilder stringBuilder, HttpContent content)
    {
        if( content != null )
        {
            stringBuilder.AppendLine( await content.ReadAsStringAsync() );
        }
        return stringBuilder;
    }
}