Question

为什么我从WebClient流中读取时会丢失字节，如下所示？

const int chuckDim = 80;

System.Net.WebClient client = new System.Net.WebClient();
Stream stream = client.OpenRead("http://media-cdn.tripadvisor.com/media/photo-s/01/70/3e/a9/needed-backup-lol.jpg");
//Stream stream = client.OpenRead("file:///C:/Users/Tanganello/Downloads/needed-backup-lol.jpg");

//searching file length
WebHeaderCollection whc = client.ResponseHeaders;
int totalLength = (Int32.Parse(whc["Content-Length"]));
byte[] buffer = new byte[totalLength];

//reading and writing
FileStream filestream = new FileStream("C:\\Users\\Tanganello\\Downloads\\clone1.jpg", FileMode.Create, FileAccess.ReadWrite);
int accumulator = 0;
while (accumulator + chuckDim < totalLength) {
    stream.Read(buffer, accumulator, chuckDim);
    filestream.Write(buffer, accumulator, chuckDim);

    accumulator += chuckDim;
}
stream.Read(buffer, accumulator, totalLength - accumulator);
filestream.Write(buffer, accumulator, totalLength - accumulator);

stream.Close();
filestream.Flush();
filestream.Close();

这是第一个流我得到的： http://img839.imageshack.us/img839/830/clone1h.jpg

Answer 1

问题在于您忽略了Stream.Read Method的返回值：

计数的

从当前流中读取的最大字节数。

返回值

读入缓冲区的总字节数。这可以比请求的字节数

只需使用WebClient.DownloadFile Method：

，即可完全避免阅读和编写流的整个过程

using (var client = new WebClient())
{
    client.DownloadFile(
        "http://media-cdn.tripadvisor.com/media/photo-s/01/70/3e/a9/needed-backup-lol.jpg",
        "C:\\Users\\Tanganello\\Downloads\\clone1.jpg");
}

或者，如果您真的想要使用流，则可以使用Stream.CopyTo Method：

using (var client = new WebClient())
using (var stream = client.OpenRead("http://..."))
using (var file = File.OpenWrite("C:\\..."))
{
    stream.CopyTo(file);
}

如果你坚持自己真正复制字节，那么正确的方法如下：

using (var client = new WebClient())
using (var stream = client.OpenRead("http://..."))
using (var file = File.OpenWrite("C:\\..."))
{
    var buffer = new byte[512];
    int bytesReceived;
    while ((bytesReceived = stream.Read(buffer, 0, buffer.Length)) != 0)
    {
        file.Write(buffer, 0, bytesReceived);
    }
}

从WebClient流读取时缺少字节

1 个答案: