[英]Using PushStreamContent to upload from an HTTPClient
我想从客户端计算机上将大量数据上传到Web服务器。 我跳到PushStreamContent,所以我可以直接写到流中,因为结果的大小各不相同,而且可能很大。
流程如下:
User runs query > Reader Ready Event Fires > Begin Upload
触发ready事件后,侦听器将其拾取并遍历结果集,以分段形式上传数据:
Console.WriteLine("Query ready, uploading");
byte[] buffer = new byte[1024], form = new byte[200];
int offset = 0, byteCount = 0;
StringBuilder rowBuilder = new StringBuilder();
string builderS;
var content = new PushStreamContent(async (stream, httpContent, transportContext) =>
//using (System.IO.Stream stream = new System.IO.FileStream("test.txt", System.IO.FileMode.OpenOrCreate))
{
int bytes = 0;
string boundary = createFormBoundary();
httpContent.Headers.Remove("Content-Type");
httpContent.Headers.TryAddWithoutValidation("Content-Type", "multipart/form-data; boundary=" + boundary);
await stream.WriteAsync(form, 0, form.Length);
form = System.Text.Encoding.UTF8.GetBytes(createFormElement(boundary, "file"));
await stream.WriteAsync(form, 0, form.Length);
await Task.Run(async () =>
{
foreach (var row in rows)
{
for (int i = 0; i < row.Length; i++)
{
rowBuilder.Append(row[i].Value);
if (i + 1 < row.Length)
rowBuilder.Append(',');
else
{
rowBuilder.Append("\r\n");
}
}
builderS = rowBuilder.ToString();
rowBuilder.Clear();
byteCount = System.Text.Encoding.UTF8.GetByteCount(builderS);
bytes += byteCount;
if (offset + byteCount > buffer.Length)
{
await stream.WriteAsync(buffer, 0, offset);
offset = 0;
if (byteCount > buffer.Length)
{
System.Diagnostics.Debug.WriteLine("Expanding buffer to {0} bytes", byteCount);
buffer = new byte[byteCount];
}
}
offset += System.Text.Encoding.UTF8.GetBytes(builderS, 0, builderS.Length, buffer, offset);
}
});
await stream.WriteAsync(buffer, 0, offset);
form = System.Text.Encoding.UTF8.GetBytes(boundary);
await stream.WriteAsync(form, 0, form.Length);
await stream.FlushAsync(); //pretty sure this does nothing
System.Diagnostics.Debug.WriteLine("Wrote {0}.{1} megabytes of data", bytes / 1000000, bytes % 1000000);
我认为如果我是服务器,上面的代码会很好用,只需添加stream.Close();
将完成它,但是由于我是这里的客户端,因此将导致错误( TaskCancelled
)。 我想等待读取也不会执行任何操作,因为除非我明确关闭流,否则PushStreamContent不会结束请求。 话虽如此,写入文件将产生我希望上传的文件,因此一切都能完美写入。
关于我在这里可以做什么的任何想法? 我可能完全滥用了PushStreamContent
但似乎这应该是一个合适的用例。
因此,该解决方案起初有点令人困惑,但它似乎很有意义,而且也许更重要的是,它可行:
using(var content = new MultipartFormDataContent())
{
var pushContent = new PushStreamContent(async (stream, httpContent, transportContext) =>
{
//do the stream writing stuff
stream.Close();
});
content.add(pushContent);
//post, put, etc. content here
}
之所以PushStreamContent
是因为传递给PushStreamContent
方法的流不是实际的请求流,而是由HttpClient
处理的流,就像将文件添加到请求流一样。 结果,关闭它表示HttpContent
这部分输入的结束,并允许请求完成。
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