NET 5 使用HttpClient和HttpWebRequest

HttpWebRequest

這是.NET創建者最初開發用於使用HTTP請求的標准類。HttpWebRequest是老版本.net下常用的，較為底層且復雜，訪問速度及並發也不甚理想，但是使用HttpWebRequest可以讓開發者控制請求/響應流程的各個方面，如 timeouts, cookies, headers, protocols。另一個好處是HttpWebRequest類不會阻塞UI線程。例如，當您從響應很慢的API服務器下載大文件時，您的應用程序的UI不會停止響應。通常和WebResponse一起使用，一個發送請求，一個獲取數據。另外HttpWebRequest庫已經過時，不適合業務中直接使用，他更適用於框架內部操作。

/// <summary>
        /// HttpWebRequest請求網頁示例
        /// </summary>
        /// <param name="args"></param>
        static void Main(string[] args)
        {
            HttpWebRequest httpWebRequest = null;
            HttpWebResponse httpWebResponse = null;
            Stream responseStream = null;
            string url = "https://www.cnblogs.com/";
            try
            {
                httpWebRequest = (HttpWebRequest)HttpWebRequest.Create(url);

                //cookie,cookie一般用來驗證登錄或是跟蹤使用
                httpWebRequest.CookieContainer = new CookieContainer();
                httpWebRequest.CookieContainer.Add(new Cookie() { Name = "test", Value = "test1",Domain="www.cnblogs.com" });

                //來源頁面
                httpWebRequest.Referer = url;

                //比較重要的UserAgent
                httpWebRequest.UserAgent = "Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0 Gecko/20100101 Firefox/52.0";

                //請求方法，有GET,POPST,PUT等
                httpWebRequest.Method = "GET";

                //如果上傳文件，是要設置 GetRequestStream
                //httpWebRequest.GetRequestStream

                try
                {
                    httpWebResponse = (HttpWebResponse)httpWebRequest.GetResponse();
                }
                catch (System.Net.WebException we)
                {
                    ///這個說明服務器返回了信息了，不過是非200,301,302這樣正常的狀態碼
                    if (we.Response != null)
                    {
                        httpWebResponse = (HttpWebResponse)we.Response;
                    }
                }

                ///得到返回的stream,如果請求的是一個文件或圖片，可以直接使用或保存
                responseStream = httpWebResponse.GetResponseStream();

                ///使用utf8方式讀取數據流
                StreamReader streamReader = new StreamReader(responseStream, Encoding.UTF8);

                ///這里是一次性讀取，對於超大的stream，要不斷讀取並保存
                string html = streamReader.ReadToEnd();
                streamReader.Close();
                responseStream.Close();
                Console.WriteLine(html.Length);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            finally
            {
                if (httpWebRequest != null) httpWebRequest.Abort();
                if (httpWebResponse != null) httpWebResponse.Close();
                if (responseStream != null) responseStream.Close();
            }
        }

HttpClient

HttpClient提供強大的功能，提供了異步支持，可以輕松配合async await 實現異步請求，使用HttpClient，在並發量不大的情況，一般沒有任何問題；但是在並發量一上去，如果使用不當，會造成很嚴重的堵塞的情況。

平時我們在使用HttpClient的時候，會將HttpClient包裹在using內部進行聲明和初始化，

using(var httpClient = new HttpClient())
{
    //other codes
}

在高並發的情況下，連接來不及釋放，socket被耗盡，耗盡之后就會出現喜聞樂見的一個錯誤：

Unable to connect to the remote serverSystem.Net.Sockets.SocketException: Only one usage of each socket address (protocol/network address/port) is normally permitted.

那么如何處理這個問題？“復用HttpClient”即可

• HttpClientFacotry很高效，可以最大程度上節省系統socket。（“JUST USE IT AND FXXK SHUT UP”:P）
• Factory，顧名思義HttpClientFactory就是HttpClient的工廠，內部已經幫我們處理好了對HttpClient的管理，不需要我們人工進行對象釋放，同時，支持自定義請求頭，支持DNS更新等等等

從微軟源碼分析，HttpClient繼承自HttpMessageInvoker，而HttpMessageInvoker實質就是HttpClientHandler。

HttpClientFactory 創建的HttpClient，也即是HttpClientHandler，只是這些個HttpClient被放到了“池子”中，工廠每次在create的時候會自動判斷是新建還是復用。(默認生命周期為2min)

還理解不了的話，可以參考Task和Thread的關系

解決方案如下：

IHttpClientFactory

一、可以參考微軟官方提供的方法：https://docs.microsoft.com/zh-cn/aspnet/core/fundamentals/http-requests?view=aspnetcore-3.1

https://docs.microsoft.com/zh-cn/aspnet/core/fundamentals/http-requests?view=aspnetcore-5.0

二、我的解決方案是根據官方提供的方法，選擇一種最適合項目的寫法進行改造。

1、nuget添加包Microsoft.AspNetCore.Http；

2、startup里ConfigureServices方法添加代碼：

services.AddHttpClient();

or

public void ConfigureServices(IServiceCollection services)
        {
            //other codes
            
            services.AddHttpClient("client_1",config=>  //這里指定的name=client_1，可以方便我們后期服用該實例 比如已經填寫url和header
            {
                config.BaseAddress= new Uri("http://client_1.com");
                config.DefaultRequestHeaders.Add("header_1","header_1");            });

            services.AddHttpClient();

            //other codes
            services.AddMvc().AddFluentValidation();
        }

3、可以使用依賴項注入 (DI) 來請求 IHttpClientFactory。 以下代碼使用 IHttpClientFactory 來創建 HttpClient 實例：（官方demo）

public class BasicUsageModel : PageModel
{
    private readonly IHttpClientFactory _clientFactory;

    public IEnumerable<GitHubBranch> Branches { get; private set; }

    public bool GetBranchesError { get; private set; }

    public BasicUsageModel(IHttpClientFactory clientFactory)
    {
        _clientFactory = clientFactory;
    }

    public async Task OnGet()
    {
        var request = new HttpRequestMessage(HttpMethod.Get,
            "https://api.github.com/repos/aspnet/AspNetCore.Docs/branches");
        request.Headers.Add("Accept", "application/vnd.github.v3+json");
        request.Headers.Add("User-Agent", "HttpClientFactory-Sample");

        var client = _clientFactory.CreateClient();

        var response = await client.SendAsync(request);

        if (response.IsSuccessStatusCode)
        {
            using var responseStream = await response.Content.ReadAsStreamAsync();
            Branches = await JsonSerializer.DeserializeAsync
                <IEnumerable<GitHubBranch>>(responseStream);
        }
        else
        {
            GetBranchesError = true;
            Branches = Array.Empty<GitHubBranch>();
        }
    }
}

在實際使用中，我們經常會用NewtonJson序列化，給一個簡單的Demo:

string api_domain = _config.GetSection("OuterApi:open-api").Value;
                string api_url = $"{api_domain}/common-service/api/basic?code={code}";
                var request = new HttpRequestMessage(HttpMethod.Get, api_url);
                request.Headers.Add("Accept", "application/vnd.github.v3+json");


                var client = _clientFactory.CreateClient();

                var response = await client.SendAsync(request);

                Result<List<OpenApiDictModel>> apiRet = new Result<List<OpenApiDictModel>>();
                if (response.IsSuccessStatusCode)
                {
                    string responseStr = await response.Content.ReadAsStringAsync();
                    apiRet = JsonConvert.DeserializeObject<Result<List<OpenApiDictModel>>>(responseStr);
                }

 IHttpClientFactory幫助類

using ICSharpCode.SharpZipLib.GZip;
using Jareds.Common.Logger;
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.IO;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;

namespace ZYS.MessageCenter.Facade.Common
{
    /// <summary>
    /// http 請求服務
    /// </summary>
    public interface IHttpClientHelper
    {
        /// <summary>
        /// 使用post返回異步請求直接返回對象
        /// </summary>
        /// <typeparam name="T">返回對象類型</typeparam>
        /// <typeparam name="T2">請求對象類型</typeparam>
        /// <param name="url">請求鏈接</param>
        /// <param name="obj">請求對象數據</param>
        /// <param name="header">請求頭</param>
        /// <param name="postFrom">表單提交 注* postFrom不為null 代表表單提交, 為null標識驚悚格式請求</param>
        /// <param name="gzip">是否壓縮</param>
        /// <returns>請求返回的目標對象</returns>
        Task<T> PostObjectAsync<T, T2>(string url, T2 obj, Dictionary<string, string> header = null, Dictionary<string, string> postFrom = null, bool gzip = false);
        /// <summary>
        /// 使用Get返回異步請求直接返回對象
        /// </summary>
        /// <typeparam name="T">請求對象類型</typeparam>
        /// <param name="url">請求鏈接</param>
        /// <returns>返回請求的對象</returns>
        Task<T> GetObjectAsync<T>(string url);
    }

    /// <summary>
    /// http 請求服務
    /// </summary>
    public class HttpClientHelper : IHttpClientHelper
    {
        private readonly IHttpClientFactory _httpClientFactory;
        /// <summary>
        /// 構造函數
        /// </summary>
        /// <param name="httpClientFactory"></param>
        public HttpClientHelper(IHttpClientFactory httpClientFactory)
        {
            _httpClientFactory = httpClientFactory;
        }
        #region http 請求方式
        /// <summary>
        /// 使用post方法異步請求 
        /// </summary>
        /// <param name="url">目標鏈接</param>
        /// <param name="posData">發送的參數JSON字符串</param>
        /// <param name="header">請求頭</param>
        /// <param name="posFrom">表單提交格式</param>
        /// <param name="gzip">是否壓縮</param>
        /// <returns>返回的字符串</returns>
        public async Task<string> PostAsync(string url, string posData, Dictionary<string, string> header = null, Dictionary<string, string> posFrom = null, bool gzip = false)
        {

            //從工廠獲取請求對象
            var client = _httpClientFactory.CreateClient();
            //消息狀態
            string responseBody = string.Empty;
            //存在則是表單提交信息
            if (posFrom != null)
            {
                var formData = new MultipartFormDataContent();
                foreach (var item in posFrom)
                {
                    formData.Add(new StringContent(item.Value), item.Key);
                }
                //提交信息
                var result = await client.PostAsync(url, formData);
                if (!result.IsSuccessStatusCode)
                {
                    Log.Error("請求出錯");
                    return null;
                }
                //獲取消息狀態
                responseBody = await result.Content.ReadAsStringAsync();
            }
            else
            {
                HttpContent content = new StringContent(posData);
                if (header != null)
                {
                    client.DefaultRequestHeaders.Clear();
                    foreach (var item in header)
                    {
                        client.DefaultRequestHeaders.Add(item.Key, item.Value);
                    }
                }
                content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
                HttpResponseMessage response = await client.PostAsync(url, content);
                if (!response.IsSuccessStatusCode)
                {
                    Log.Error("請求出錯");
                    return null;
                }

                //response.EnsureSuccessStatusCode();
                if (gzip)
                {
                    GZipInputStream inputStream = new GZipInputStream(await response.Content.ReadAsStreamAsync());
                    responseBody = new StreamReader(inputStream).ReadToEnd();
                }
                else
                {
                    responseBody = await response.Content.ReadAsStringAsync();

                }
            }

            return responseBody;

        }

        /// <summary>
        /// 使用get方法異步請求
        /// </summary>
        /// <param name="url">目標鏈接</param>
        /// <param name="header"></param>
        /// <param name="Gzip"></param>
        /// <returns>返回的字符串</returns>
        public async Task<string> GetAsync(string url, Dictionary<string, string> header = null, bool Gzip = false)
        {
            var client = _httpClientFactory.CreateClient();
            //HttpClient client = new HttpClient(new HttpClientHandler() { UseCookies = false });
            if (header != null)
            {
                client.DefaultRequestHeaders.Clear();
                foreach (var item in header)
                {
                    client.DefaultRequestHeaders.Add(item.Key, item.Value);
                }
            }
            HttpResponseMessage response = await client.GetAsync(url);
            if (!response.IsSuccessStatusCode)
            {
                Log.Error("請求出錯");
                return null;
            }

            //response.EnsureSuccessStatusCode();//用來拋異常
            string responseBody = "";
            if (Gzip)
            {
                GZipInputStream inputStream = new GZipInputStream(await response.Content.ReadAsStreamAsync());
                responseBody = new StreamReader(inputStream).ReadToEnd();
            }
            else
            {
                responseBody = await response.Content.ReadAsStringAsync();

            }
            return responseBody;
        }

        /// <summary>
        /// 使用post返回異步請求直接返回對象
        /// </summary>
        /// <typeparam name="T">返回對象類型</typeparam>
        /// <typeparam name="T2">請求對象類型</typeparam>
        /// <param name="url">請求鏈接</param>
        /// <param name="obj">請求對象數據</param>
        /// <param name="header">請求頭</param>
        /// <param name="postFrom">表單提交 表單提交 注* postFrom不為null 代表表單提交, 為null標識驚悚格式請求</param>
        /// <param name="gzip">是否壓縮</param>
        /// <returns>請求返回的目標對象</returns>
        public async Task<T> PostObjectAsync<T, T2>(string url, T2 obj, Dictionary<string, string> header = null, Dictionary<string, string> postFrom = null, bool gzip = false)
        {
            String json = JsonConvert.SerializeObject(obj);
            string responseBody = await PostAsync(url, json, header, postFrom, gzip); //請求當前賬戶的信息
            if (responseBody is null)
            {
                return default(T);
            }
            return JsonConvert.DeserializeObject<T>(responseBody);//把收到的字符串序列化
        }

        /// <summary>
        /// 使用Get返回異步請求直接返回對象
        /// </summary>
        /// <typeparam name="T">請求對象類型</typeparam>
        /// <param name="url">請求鏈接</param>
        /// <returns>返回請求的對象</returns>
        public async Task<T> GetObjectAsync<T>(string url)
        {
            string responseBody = await GetAsync(url); //請求當前賬戶的信息
            if (responseBody is null)
            {
                return default(T);
            }
            return JsonConvert.DeserializeObject<T>(responseBody);//把收到的字符串序列化
        }

        #endregion

    }
}