Question

抛出此错误

Bytes to be written to the stream exceed 
the Content-Length bytes size specified.

当我运行以下代码时：

var request = (HttpWebRequest)WebRequest.Create(url);
request.Method = "POST";
request.ContentType = "application/json";
request.ContentLength = Encoding.UTF8.GetByteCount(json);
using (var webStream = request.GetRequestStream())
using (var requestWriter = new StreamWriter(webStream, System.Text.Encoding.UTF8))
{
    requestWriter.Write(json);
}

我读过，当Method是HEAD或GET时可能会发生错误，但这里是POST。

知道那里有什么问题吗？

Answer 1

问题在于您首先要编写UTF-8 BOM，因为Encoding.UTF8默认情况下会这样做。简短而完整的例子：

using System;
using System.IO;
using System.Text;

class Test
{
    static void Main()
    {
        string text = "text";
        var encoding = Encoding.UTF8;
        Console.WriteLine(encoding.GetByteCount(text));
        using (var stream = new MemoryStream())
        {
            using (var writer = new StreamWriter(stream, encoding))
            {
                writer.Write(text);
            }
            Console.WriteLine(BitConverter.ToString(stream.ToArray()));
        }
    }
}

输出：

4
EF-BB-BF-74-65-78-74

最简单的解决方法是将前导码大小添加到内容长度或以使用没有BOM的编码：

Encoding utf8NoBom = new UTF8Encoding(false);

使用它代替Encoding.UTF8，一切都应该好。

REstful POST：要写入流的字节超过指定的Content-Length字节大小

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