.net的 http 请求 利用单例减少创建销毁的资源开销 提高利用率

using System; using System.Collections.Concurrent; using System.Collections.Generic; using System.Net; using System.Net.Http; using System.Net.Http.Headers; using System.Text; using System.Threading.Tasks;  namespace TencentCloud.Common.Http {     public class HttpConnection     {         private class HttpClientHolder         {             private static readonly ConcurrentDictionary<string, HttpClientHolder> httpclients = new ConcurrentDictionary<string, HttpClientHolder>();              public static HttpClient GetClient(string proxy)             {                 string key = string.IsNullOrEmpty(proxy) ? "" : proxy;                 HttpClientHolder result = httpclients.GetOrAdd(key, (k) =>                 {                     return new HttpClientHolder(k);                 });                 TimeSpan timeSpan = DateTime.Now - result.createTime;                  // 每5分钟创建一个新的连接，放弃旧连接，避免DNS刷新问题。                 while (timeSpan.TotalSeconds > 300)                 {                     ICollection<KeyValuePair<string, HttpClientHolder>> kv = httpclients;                     kv.Remove(new KeyValuePair<string, HttpClientHolder>(key, result));                     result = httpclients.GetOrAdd(key, (k) =>                     {                         return new HttpClientHolder(k);                     });                     timeSpan = DateTime.Now - result.createTime;                 }                 return result.client;             }              public readonly HttpClient client;              public readonly DateTime createTime;              public HttpClientHolder(string proxy)             {                 string p = string.IsNullOrEmpty(proxy) ? "" : proxy;                 if (p == "")                 {                     this.client = new HttpClient();                 }                 else                 {                     var httpClientHandler = new HttpClientHandler                     {                         Proxy = new WebProxy(proxy),                     };                      this.client = new HttpClient(handler: httpClientHandler, disposeHandler: true);                 }                 this.client.Timeout = TimeSpan.FromSeconds(60);                 this.createTime = DateTime.Now;             }         }          private readonly HttpClient http;          private readonly string baseUrl;          private readonly string proxy;          private readonly int timeout;          public HttpConnection(string baseUrl, int timeout, string proxy, HttpClient http)         {             this.proxy = string.IsNullOrEmpty(proxy) ? "" : proxy;             this.timeout = timeout;             this.baseUrl = baseUrl;             if (http != null)             {                 this.http = http;             }             else             {                 this.http = HttpClientHolder.GetClient(this.proxy);             }         }          private static string AppendQuery(StringBuilder builder, Dictionary<string, string> param)         {             foreach (KeyValuePair<string, string> kvp in param)             {                 builder.Append($"{WebUtility.UrlEncode(kvp.Key)}={WebUtility.UrlEncode(kvp.Value)}&");             }             return builder.ToString().TrimEnd('&');         }          public async Task<HttpResponseMessage> GetRequestAsync(string url, Dictionary<string, string> param)         {             StringBuilder urlBuilder = new StringBuilder($"{baseUrl.TrimEnd('/')}{url}?");             string fullurl = AppendQuery(urlBuilder, param);             string payload = "";             Dictionary<string, string> headers = new Dictionary<string, string>();             return await this.Send(HttpMethod.Get, fullurl, payload, headers);         }          public async Task<HttpResponseMessage> GetRequestAsync(string path, string queryString, Dictionary<string, string> headers)         {             string fullurl = $"{this.baseUrl.TrimEnd('/')}{path}?{queryString}";             string payload = "";             return await this.Send(HttpMethod.Get, fullurl, payload, headers);         }          public async Task<HttpResponseMessage> PostRequestAsync(string path, string payload, Dictionary<string, string> headers)         {             string fullurl = $"{baseUrl.TrimEnd('/')}{path}";             return await this.Send(HttpMethod.Post, fullurl, payload, headers);         }          public async Task<HttpResponseMessage> PostRequestAsync(string url, Dictionary<string, string> param)         {             string fullurl = $"{this.baseUrl.TrimEnd('/')}{url}?";             StringBuilder payloadBuilder = new StringBuilder();             string payload = AppendQuery(payloadBuilder, param);             Dictionary<string, string> headers = new Dictionary<string, string>();             headers["Content-Type"] = "application/x-www-form-urlencoded";             return await this.Send(HttpMethod.Post, fullurl, payload, headers);         }          private async Task<HttpResponseMessage> Send(HttpMethod method, string url, string payload, Dictionary<string, string> headers)         {             using (var cts = new System.Threading.CancellationTokenSource(timeout * 1000))             {                 using (var msg = new HttpRequestMessage(method, url))                 {                     foreach (KeyValuePair<string, string> kvp in headers)                     {                         if (kvp.Key.Equals("Content-Type"))                         {                             msg.Content = new StringContent(payload, Encoding.UTF8, kvp.Value);                         }                         else if (kvp.Key.Equals("Host"))                         {                             msg.Headers.Host = kvp.Value;                         }                         else if (kvp.Key.Equals("Authorization"))                         {                             msg.Headers.Authorization = new AuthenticationHeaderValue("TC3-HMAC-SHA256", kvp.Value.Substring("TC3-HMAC-SHA256".Length));                         }                         else                         {                             msg.Headers.Add(kvp.Key, kvp.Value);                         }                     }                     return await http.SendAsync(msg, cts.Token);                 }             }         }     } }