为什么HttpWebResponse会丢失数据？

Posted 2021-04-21

在另一个问题中，当通过GetResponseStream（）从HttpWebResponse读取时，人们得到的数据不完整。

从嵌入式设备读取数据时我也遇到了这个问题，该设备应该向我发送1000个输入的配置，所有32个字节的头部和64个字节* 1000都会产生64032个字节的数据。

直接读取响应流只能为我提供前61个半输入的数据，从那里只有零。

版本a）不工作：

int headerSize = 32;
int inputSize = 64;
byte[] buffer = new byte[(inputSize*1000) + headerSize];

HttpWebResponse response = (HttpWebResponse)request.GetResponse();

using (Stream stream = response.GetResponseStream())
{
    if (stream != null)
    {
        stream.Seek(0, SeekOrigin.Begin);
        stream.Read(buffer, 0, buffer.Length);
    }
}

response.Close();
return buffer;

为了使问题可视化，我单独为每个输入配置打印了64个字节。它基本上由40个ascii字符和几个字节组成，表示布尔值和整数值。

版本A）输出：

1/1000 | 46656E7374657220576F686E656E2020202020202020202020202020202020202020202020202020000000000F0EB0AA00008100000001800000100090010020
2/1000 | 42574D20576F686E656E202020202020202020202020202020202020202020202020202020202020000000000F0EB0AA00008100000001800000100091010080
…
61/1000 | 53656E736F72203631202020202020202020202020202020202020202020202020202020202020200000000000000000000010003300000000001000C3010000
62/1000 | 53656E736F7220363220202020202020202020202020202020202020202020200000000000000000000000000000000000000000000000000000000000000000
63/1000 | 00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
…
999/1000 | 00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
1000/1000 | 00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

当我将ResponseStream复制到一个新的MemoryStream时，我可以完全读取所有1000个输入而没有任何损坏的字节。

版本B）完美工作：

（另见https://stackoverflow.com/a/22354617/6290907在第一种情况下解决了我的问题）

int headerSize = 32;
int inputSize = 64;
byte[] buffer = new byte[(inputSize*1000) + headerSize];

HttpWebResponse response = (HttpWebResponse)request.GetResponse();

using (Stream stream = response.GetResponseStream())
{
    if (stream != null)
    {
        MemoryStream memStream = new MemoryStream();
        stream.CopyTo(memStream);
        memStream.Flush();
        stream.Close();

        memStream.Seek(0, SeekOrigin.Begin);
        memStream.Read(buffer, 0, buffer.Length);

        memStream.Close();
    }
}

response.Close();
return buffer;

版本B）输出

1/1000 | 46656E7374657220576F686E656E2020202020202020202020202020202020202020202020202020000000000F0EB0AA00008100000001800000100090010020
2/1000 | 42574D20576F686E656E202020202020202020202020202020202020202020202020202020202020000000000F0EB0AA00008100000001800000100091010080
…
61/1000 | 53656E736F72203631202020202020202020202020202020202020202020202020202020202020200000000000000000000010003300000000001000C3010000
62/1000 | 53656E736F72203632202020202020202020202020202020202020202020202020202020202020200000000000000000000010003300000000001000C3010000
63/1000 | 53656E736F72203633202020202020202020202020202020202020202020202020202020202020200000000000000000000010003300000000001000C3010000
…
999/1000 | 53656E736F7220393939202020202020202020202020202020202020202020202020202020202020000000000000000000001000DA030000000010006A050000
1000/1000 | 53656E736F7220313030302020202020202020202020202020202020202020202020202020202020000000000000000000001000DB030000000010006B050000

从技术角度来看：为什么HttpWebResponse在直接访问时会丢失数据？我不仅希望它能够工作，而且我想了解为什么版本a失败而版本b成功，而两者都依赖于相同的数据源（response.GetResponseStream（））。在这种情况下，引擎盖下发生了什么？

感谢你付出的努力！

答案

检查int返回的Stream.Read，如docs所述：

如果当前没有多个字节可用，则这可能小于请求的字节数，如果已到达流的末尾，则可以小于零（0）。

我愿意打赌在第一次调用中只返回部分流。

如果你反复调用Stream.Read，你最终会获得所有字节。 http流的加载速度比代码运行的速度慢 - 在调用Read之前没有时间完成。

通过使用带有CopyTo的MemoryStream，调用将阻塞，直到读取整个流。包装在StreamReader中，然后调用ReadToEnd将获得相同的成功结果。