增加UrlEncodedContent类型，提高HttpApiRequestMessage.AddFormFieldAsync性能

Author: xljiulang

WebApiClient/HttpApiRequestMessage.cs

@@ -145,69 +145,23 @@ public async Task AddFormFieldAsync(string name, string value)
         public async Task AddFormFieldAsync(IEnumerable<KeyValuePair<string, string>> keyValues)
         {
             this.EnsureNotGetOrHead();
+            this.EnsureMediaTypeEqual(UrlEncodedContent.MediaType);
 
             if (keyValues == null)
             {
                 return;
             }
 
-            var formBody = default(byte[]);
-            const string mediaType = "application/x-www-form-urlencoded";
-
-            if (this.Content != null)
+            var formContent = this.Content as UrlEncodedContent;
+            if (formContent == null)
             {
-                this.EnsureMediaTypeEqual(mediaType);
-                formBody = await this.Content.ReadAsByteArrayAsync();
-                this.Content.Dispose();
+                formContent = new UrlEncodedContent(this.Content);
             }
 
-            var bytesContent = MergeFields(formBody, keyValues);
-            var byteArrayContent = new ByteArrayContent(bytesContent);
-            byteArrayContent.Headers.ContentType = new MediaTypeHeaderValue(mediaType);
-            this.Content = byteArrayContent;
+            await formContent.AddFormFieldAsync(keyValues);
+            this.Content = formContent;
         }
 
-        /// <summary>
-        /// 合并内容
-        /// </summary>
-        /// <param name="formBody"></param>
-        /// <param name="keyValues"></param>
-        /// <returns></returns>
-        private static byte[] MergeFields(byte[] formBody, IEnumerable<KeyValuePair<string, string>> keyValues)
-        {
-            var encoding = Encoding.UTF8;
-            var kvs = from kv in keyValues select string.Format("{0}={1}", kv.Key, HttpUtility.UrlEncode(kv.Value, encoding));
-            var stringContent = string.Join("&", kvs);
-
-            if (formBody != null && formBody.Length > 0)
-            {
-                stringContent = "&" + stringContent;
-            }
-
-            var byteConent = encoding.GetBytes(stringContent);
-            return MergeBytes(formBody, byteConent);
-        }
-
-        /// <summary>
-        /// 合并字节组
-        /// </summary>
-        /// <param name="formBody"></param>
-        /// <param name="byteConent"></param>
-        /// <returns></returns>
-        private static byte[] MergeBytes(byte[] formBody, byte[] byteConent)
-        {
-            if (formBody == null || formBody.Length == 0 || byteConent == null)
-            {
-                return byteConent;
-            }
-
-            var bytes = new byte[formBody.Length + byteConent.Length];
-            formBody.CopyTo(bytes, 0);
-            byteConent.CopyTo(bytes, formBody.Length);
-            return bytes;
-        }
-
-
         /// <summary>
         /// 添加文件内容到已有的Content
         /// 要求content-type为multipart/form-data
@@ -353,10 +307,7 @@ private bool SetCookie(string cookieValues, bool useUrlEncode)
         /// <returns></returns>
         private MultipartContent CastOrCreateMultipartContent()
         {
-            if (this.Content != null)
-            {
-                this.EnsureMediaTypeEqual("multipart/form-data");
-            }
+            this.EnsureMediaTypeEqual("multipart/form-data");
 
             var httpContent = this.Content as MultipartContent;
             if (httpContent == null)
@@ -378,13 +329,12 @@ private MultipartContent CastOrCreateMultipartContent()
         /// <exception cref="NotSupportedException"></exception>
         private void EnsureMediaTypeEqual(string newMediaType)
         {
-            var contentType = this.Content.Headers.ContentType;
-            if (contentType == null)
+            var existsMediaType = this.Content?.Headers.ContentType?.MediaType;
+            if (string.IsNullOrEmpty(existsMediaType) == true)
             {
                 return;
             }
 
-            var existsMediaType = contentType.MediaType;
             if (string.Equals(existsMediaType, newMediaType, StringComparison.OrdinalIgnoreCase) == false)
             {
                 var message = string.Format("Content-Type必须保持为{0}", existsMediaType);

WebApiClient/Internal/UrlEncodedContent.cs

@@ -0,0 +1,128 @@
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Net;
+using System.Net.Http;
+using System.Net.Http.Headers;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace WebApiClient
+{
+    /// <summary>
+    /// 表示键值对表单内容
+    /// </summary>
+    class UrlEncodedContent : HttpContent
+    {
+        /// <summary>
+        /// 获取对应的ContentType
+        /// </summary>
+        public static string MediaType => "application/x-www-form-urlencoded";
+
+        /// <summary>
+        /// 用于保存表单内容
+        /// </summary>
+        private readonly MemoryStream stream = new MemoryStream();
+
+        /// <summary>
+        /// 键值对表单内容
+        /// </summary>
+        /// <param name="content">原始表单</param>
+        /// <param name="disposeContent">是否要释放原始表单</param>
+        public UrlEncodedContent(HttpContent content, bool disposeContent = true)
+        { 
+            if (content != null)
+            {
+                content.CopyToAsync(this.stream);
+                if (disposeContent == true)
+                {
+                    content.Dispose();
+                }
+            }
+            this.Headers.ContentType = new MediaTypeHeaderValue(MediaType);
+        }
+
+        /// <summary>
+        /// 添加字段到内存流
+        /// </summary>
+        /// <param name="keyValues">键值对</param>
+        /// <returns></returns>
+        public async Task AddFormFieldAsync(IEnumerable<KeyValuePair<string, string>> keyValues)
+        {
+            if (keyValues == null)
+            {
+                return;
+            }
+
+            var bytes = this.EncodedKeyValues(keyValues);
+            await this.stream.WriteAsync(bytes, 0, bytes.Length);
+        }
+
+        /// <summary>
+        /// 计算键值对的字节组
+        /// </summary>
+        /// <param name="keyValues">键值对</param>
+        /// <returns></returns>
+        private byte[] EncodedKeyValues(IEnumerable<KeyValuePair<string, string>> keyValues)
+        {
+            var encoding = Encoding.UTF8;
+            var parameters =
+                from kv in keyValues
+                let value = HttpUtility.UrlEncode(kv.Value, encoding)
+                select $"{kv.Key }={value}";
+
+            var parameterString = string.Join("&", parameters);
+            if (this.stream.Length > 0)
+            {
+                parameterString = "&" + parameterString;
+            }
+            return encoding.GetBytes(parameterString);
+        }
+
+        /// <summary>
+        /// 计算内容长度
+        /// </summary>
+        /// <param name="length"></param>
+        /// <returns></returns>
+        protected override bool TryComputeLength(out long length)
+        {
+            length = this.stream.Length;
+            return true;
+        }
+
+        /// <summary>
+        /// 创建只读流
+        /// </summary>
+        /// <returns></returns>
+        protected override Task<Stream> CreateContentReadStreamAsync()
+        {
+            var buffer = this.stream.ToArray();
+            var readStream = new MemoryStream(buffer, 0, buffer.Length, writable: false);
+            return Task.FromResult<Stream>(readStream);
+        }
+
+        /// <summary>
+        /// 序列化到目标流中
+        /// </summary>
+        /// <param name="stream">目标流</param>
+        /// <param name="context">上下文</param>
+        /// <returns></returns>
+        protected override async Task SerializeToStreamAsync(Stream stream, TransportContext context)
+        {
+            var position = this.stream.Position;
+            this.stream.Position = 0;
+            await this.stream.CopyToAsync(stream);
+            this.stream.Position = position;
+        }
+
+        /// <summary>
+        /// 释放资源
+        /// </summary>
+        /// <param name="disposing"></param>
+        protected override void Dispose(bool disposing)
+        {
+            this.stream.Dispose();
+            base.Dispose(disposing);
+        }
+    }
+}