.Net5下WebRequest、WebClient、HttpClient是否还存在使用争议？

　　WebRequest、WebClient、HttpClient 是C#中常用的三个Http请求的类，时不时也会有人发表对这三个类使用场景的总结，本人是HttpClient 一把梭，也没太关注它们的内部实现，最近比较闲就看了下它们内部实现到底有什么差别。

　　WebClient其实就是对WebRequest的二次封装，便于使用。所以主要看WebRequest和HttpClient之间的差别。WebRequest的默认实现是HttpWebRequest。我把其中关于今天主题关键的代码贴出来：

　　

public override WebResponse GetResponse()
        {
            try
            {
                _sendRequestCts = new CancellationTokenSource();
                return SendRequest(async: false).GetAwaiter().GetResult();
            }
            catch (Exception ex)
            {
                throw WebException.CreateCompatibleException(ex);
            }
        }

private async Task<WebResponse> SendRequest(bool async)
        {
            if (RequestSubmitted)
            {
                throw new InvalidOperationException(SR.net_reqsubmitted);
            }

            var request = new HttpRequestMessage(new HttpMethod(_originVerb), _requestUri);

            bool disposeRequired = false;
            HttpClient? client = null;
            try
            {
                client = GetCachedOrCreateHttpClient(async, out disposeRequired);
                if (_requestStream != null)
                {
                    ArraySegment<byte> bytes = _requestStream.GetBuffer();
                    request.Content = new ByteArrayContent(bytes.Array!, bytes.Offset, bytes.Count);
                }

                if (_hostUri != null)
                {
                    request.Headers.Host = Host;
                }

                // Copy the HttpWebRequest request headers from the WebHeaderCollection into HttpRequestMessage.Headers and
                // HttpRequestMessage.Content.Headers.
                foreach (string headerName in _webHeaderCollection)
                {
                    // The System.Net.Http APIs require HttpRequestMessage headers to be properly divided between the request headers
                    // collection and the request content headers collection for all well-known header names.  And custom headers
                    // are only allowed in the request headers collection and not in the request content headers collection.
                    if (IsWellKnownContentHeader(headerName))
                    {
                        if (request.Content == null)
                        {
                            // Create empty content so that we can send the entity-body header.
                            request.Content = new ByteArrayContent(Array.Empty<byte>());
                        }

                        request.Content.Headers.TryAddWithoutValidation(headerName, _webHeaderCollection[headerName!]);
                    }
                    else
                    {
                        request.Headers.TryAddWithoutValidation(headerName, _webHeaderCollection[headerName!]);
                    }
                }

                request.Headers.TransferEncodingChunked = SendChunked;

                if (KeepAlive)
                {
                    request.Headers.Connection.Add(HttpKnownHeaderNames.KeepAlive);
                }
                else
                {
                    request.Headers.ConnectionClose = true;
                }

                request.Version = ProtocolVersion;

                _sendRequestTask = async ?
                    client.SendAsync(request, _allowReadStreamBuffering ? HttpCompletionOption.ResponseContentRead : HttpCompletionOption.ResponseHeadersRead, _sendRequestCts!.Token) :
                    Task.FromResult(client.Send(request, _allowReadStreamBuffering ? HttpCompletionOption.ResponseContentRead : HttpCompletionOption.ResponseHeadersRead, _sendRequestCts!.Token));

                HttpResponseMessage responseMessage = await _sendRequestTask.ConfigureAwait(false);

                HttpWebResponse response = new HttpWebResponse(responseMessage, _requestUri, _cookieContainer);

                int maxSuccessStatusCode = AllowAutoRedirect ? 299 : 399;
                if ((int)response.StatusCode > maxSuccessStatusCode || (int)response.StatusCode < 200)
                {
                    throw new WebException(
                        SR.Format(SR.net_servererror, (int)response.StatusCode, response.StatusDescription),
                        null,
                        WebExceptionStatus.ProtocolError,
                        response);
                }

                return response;
            }
            finally
            {
                if (disposeRequired)
                {
                    client?.Dispose();
                }
            }
        }

 　　在SendRequest(bool async)方法中调用了一个方法GetCachedOrCreateHttpClient看到此处我一阵感慨，最终还是调用了HttpClient。到此也能粗显的看出来，三者在.Net5下，本质已经没有了区别，只是对外的表现形式不同而已，使用了时候不必太纠结内部实现优先不同，只关注自己喜欢怎么样的写法就行了。