I am referring to this article to understand file downloads using C#.
Code uses traditional method to read Stream like
((bytesSize = strResponse.Read(downBuffer, 0, downBuffer.Length)) > 0
How can I divide a file to be downloaded into multiple segments, so that I can download separate segments in parallel and merge them?
using (WebClient wcDownload = new WebClient())
{
try
{
// Create a request to the file we are downloading
webRequest = (HttpWebRequest)WebRequest.Create(txtUrl.Text);
// Set default authentication for retrieving the file
webRequest.Credentials = CredentialCache.DefaultCredentials;
// Retrieve the response from the server
webResponse = (HttpWebResponse)webRequest.GetResponse();
// Ask the server for the file size and store it
Int64 fileSize = webResponse.ContentLength;
// Open the URL for download
strResponse = wcDownload.OpenRead(txtUrl.Text);
// Create a new file stream where we will be saving the data (local drive)
strLocal = new FileStream(txtPath.Text, FileMode.Create, FileAccess.Write, FileShare.None);
// It will store the current number of bytes we retrieved from the server
int bytesSize = 0;
// A buffer for storing and writing the data retrieved from the server
byte[] downBuffer = new byte[2048];
// Loop through the buffer until the buffer is empty
while ((bytesSize = strResponse.Read(downBuffer, 0, downBuffer.Length)) > 0)
{
// Write the data from the buffer to the local hard drive
strLocal.Write(downBuffer, 0, bytesSize);
// Invoke the method that updates the form's label and progress bar
this.Invoke(new UpdateProgessCallback(this.UpdateProgress), new object[] { strLocal.Length, fileSize });
}
}
you need several threads to accomplish that.
first you start the first download thread, creating a webclient and getting the file size. then you can start several new thread, which add a download range header.
you need a logic which takes care about the downloaded parts, and creates new download parts when one finished.
http://msdn.microsoft.com/de-de/library/system.net.httpwebrequest.addrange.aspx
I noticed that the WebClient implementation has sometimes a strange behaviour, so I still recommend implementing an own HTTP client if you really want to write a "big" download program.
ps: thanks to user svick
Related
I am working on an ASP.NET framework 2.0 application. On a particular page I am providing a link to user. By clicking on this link a window opens with another aspx page. This page actually sends http request to a third-party url which points to a file(like - mirror urls to download file from cloud). The http response is sent back to user on the very first page using response.write from where user click the link.
Now, the problem I am facing is if the file size is low then it works fine. But, if the file is large (i.e., more than 1 GB), then my application waits until whole file is downloaded from the URL. I have tried using response.flush() to send chunk by chunk data to user, but still user is unable to use application because the worker process is busy getting streams of data from third party URL.
Is there any way by which large files can be downloaded asynchronously so that my pop-up window finishes its execution(download will be in progress) and also user can do other activities on application parallely.
Thanks,
Suvodeep
Use WebClient to read the remote file. Instead of downloading you can take the Stream from the WebClient. Put that in while() loop and push the bytes from the WebClient stream in the Response stream. On this way, you will be async downloading and uploading at the same time.
HttpRequest example:
private void WriteFileInDownloadDirectly()
{
//Create a stream for the file
Stream stream = null;
//This controls how many bytes to read at a time and send to the client
int bytesToRead = 10000;
// Buffer to read bytes in chunk size specified above
byte[] buffer = new byte[bytesToRead];
// The number of bytes read
try
{
//Create a WebRequest to get the file
HttpWebRequest fileReq = (HttpWebRequest)HttpWebRequest.Create("Remote File URL");
//Create a response for this request
HttpWebResponse fileResp = (HttpWebResponse)fileReq.GetResponse();
if (fileReq.ContentLength > 0)
fileResp.ContentLength = fileReq.ContentLength;
//Get the Stream returned from the response
stream = fileResp.GetResponseStream();
// prepare the response to the client. resp is the client Response
var resp = HttpContext.Current.Response;
//Indicate the type of data being sent
resp.ContentType = "application/octet-stream";
//Name the file
resp.AddHeader("Content-Disposition", $"attachment; filename=\"{ Path.GetFileName("Local File Path - can be fake") }\"");
resp.AddHeader("Content-Length", fileResp.ContentLength.ToString());
int length;
do
{
// Verify that the client is connected.
if (resp.IsClientConnected)
{
// Read data into the buffer.
length = stream.Read(buffer, 0, bytesToRead);
// and write it out to the response's output stream
resp.OutputStream.Write(buffer, 0, length);
// Flush the data
resp.Flush();
//Clear the buffer
buffer = new byte[bytesToRead];
}
else
{
// cancel the download if client has disconnected
length = -1;
}
} while (length > 0); //Repeat until no data is read
}
finally
{
if (stream != null)
{
//Close the input stream
stream.Close();
}
}
}
WebClient Stream reading:
using (WebClient client = new WebClient())
{
Stream largeFileStream = client.OpenRead("My Address");
}
I am experiencing some strange behaviour from my code which i am using to stream files to my clients.
I have a mssql server which acts as a filestore, with files that is accessed via an UNC path.
On my webserver i have some .net code running that handles streaming the files (in this case pictures and thumbnails) to my clients.
My code works, but i am experiencing a constant delay of ~12 sec on the initial file request. When i have made the initial request it is as the server wakes up and suddenly becomes responsive only to fall back to the same behaviour some time after.
At first i thought it was my code, but from what i can see on the server activity log there is no ressource intensive code going on. My theory is that at each call to the server the path must first be mounted and that is what causes the delay. It will then unmount some time after and will have to remount.
For reference i am posting my code (maybe i just cannot see the problem):
public async static Task StreamFileAsync(HttpContext context, FileInfo fileInfo)
{
//This controls how many bytes to read at a time and send to the client
int bytesToRead = 512 * 1024; // 512KB
// Buffer to read bytes in chunk size specified above
byte[] buffer = new Byte[bytesToRead];
// Clear the current response content/headers
context.Response.Clear();
context.Response.ClearHeaders();
//Indicate the type of data being sent
context.Response.ContentType = FileTools.GetMimeType(fileInfo.Extension);
//Name the file
context.Response.AddHeader("Content-Disposition", "filename=\"" + fileInfo.Name + "\"");
context.Response.AddHeader("Content-Length", fileInfo.Length.ToString());
// Open the file
using (var stream = fileInfo.OpenRead())
{
// The number of bytes read
int length;
do
{
// Verify that the client is connected
if (context.Response.IsClientConnected)
{
// Read data into the buffer
length = await stream.ReadAsync(buffer, 0, bytesToRead);
// and write it out to the response's output stream
await context.Response.OutputStream.WriteAsync(buffer, 0, length);
try
{
// Flush the data
context.Response.Flush();
}
catch (HttpException)
{
// Cancel the download if a HttpException happens
// (ie. the client has disconnected by we tried to send some data)
length = -1;
}
//Clear the buffer
buffer = new Byte[bytesToRead];
}
else
{
// Cancel the download if client has disconnected
length = -1;
}
} while (length > 0); //Repeat until no data is read
}
// Tell the response not to send any more content to the client
context.Response.SuppressContent = true;
// Tell the application to skip to the EndRequest event in the HTTP pipeline
context.ApplicationInstance.CompleteRequest();
}
If anyone could shed some light over this problem i would be very grateful!
How to download first 200 bytes of a file via HTTP protocol using C#?
I believed it could be done like this:
WebClient wc = new WebClient();
byte[] buffer = new byte[200];
using (var stream = wc.OpenRead(fileName))
{
stream.Read(buffer, 0, 200);
}
but when wc.OpenRead it called it downloads the whole file.
You need to set a Range Header on your WebClient before you invoke the OpenRead method.
See: http://msdn.microsoft.com/en-us/library/system.net.webclient.headers.aspx
I have written a procedure that will open a xls from a local disc, refresh the data in it and then save it again. This works fine.
The problem occurs when I replace the filename to point to a SharePoint site. It opens the file fine. Refreshes the file, but when it trys to save the file it throws an exception with the message "Cannot save as that name. Document was opened as read-only.".
If I try and save the file with a different filename then it works fine.
Does anybody know what I am missing? I think it must have somethoing to do with how I am opening the file. Is there another way that I can force the opening of the file in a read/write manner?
private static void RefreshExcelDocument(string filename)
{
var xls = new Microsoft.Office.Interop.Excel.Application();
xls.Visible = true;
xls.DisplayAlerts = false;
var workbook = xls.Workbooks.Open(Filename: filename, IgnoreReadOnlyRecommended: true, ReadOnly: false);
try
{
// Refresh the data from data connections
workbook.RefreshAll();
// Wait for the refresh occurs - *wish there was a better way than this.
System.Threading.Thread.Sleep(5000);
// Save the workbook back again
workbook.SaveAs(Filename: filename); // This is when the Exception is thrown
// Close the workbook
workbook.Close(SaveChanges: false);
}
catch (Exception ex)
{
//Exception message is "Cannot save as that name. Document was opened as read-only."
}
finally
{
xls.Application.Quit();
xls = null;
}
}
Many thanks in advance for suggestions.
Jonathan
Unfortunately you can't save directly to SharePoint using the Excel API. That's why the file is being opened as read only - it's not allowed.
The good news is that it is possible, but you have to submit the form via a web request. Even better news is that there is sample code on MSDN! In particular notice the PublishWorkbook method that sends a local copy of the Excel file to the server via a web request:
static void PublishWorkbook(string LocalPath, string SharePointPath)
{
WebResponse response = null;
try
{
// Create a PUT Web request to upload the file.
WebRequest request = WebRequest.Create(SharePointPath);
request.Credentials = CredentialCache.DefaultCredentials;
request.Method = "PUT";
// Allocate a 1K buffer to transfer the file contents.
// The buffer size can be adjusted as needed depending on
// the number and size of files being uploaded.
byte[] buffer = new byte[1024];
// Write the contents of the local file to the
// request stream.
using (Stream stream = request.GetRequestStream())
using (FileStream fsWorkbook = File.Open(LocalPath,
FileMode.Open, FileAccess.Read))
{
int i = fsWorkbook.Read(buffer, 0, buffer.Length);
while (i > 0)
{
stream.Write(buffer, 0, i);
i = fsWorkbook.Read(buffer, 0, buffer.Length);
}
}
// Make the PUT request.
response = request.GetResponse();
}
finally
{
response.Close();
}
}
The sample code describes a scenario for the 2007 versions of these products but other versions should behave in the same way.
What does the filename of a failed example looks like? Aren't documents used in SharePoint stored in the database? Or am I getting your problem wrong? Otherwise I could imagine that the file you are trying to store is write protected by the operation system and cannot be modified.
I have a monitoring system and I want to save a snapshot from a camera when alarm trigger.
I have tried many methods to do that…and it’s all working fine , stream snapshot from the camera then save it as a jpg in the pc…. picture (jpg format,1280*1024,140KB)..That’s fine
But my problem is in the application performance...
The app need about 20 ~30 seconds to read the steam, that’s not acceptable coz that method will be called every 2 second .I need to know what wrong with that code and how I can get it much faster than that. ?
Many thanks in advance
Code:
string sourceURL = "http://192.168.0.211/cgi-bin/cmd/encoder?SNAPSHOT";
byte[] buffer = new byte[200000];
int read, total = 0;
WebRequest req = (WebRequest)WebRequest.Create(sourceURL);
req.Credentials = new NetworkCredential("admin", "123456");
WebResponse resp = req.GetResponse();
Stream stream = resp.GetResponseStream();
while ((read = stream.Read(buffer, total, 1000)) != 0)
{
total += read;
}
Bitmap bmp = (Bitmap)Bitmap.FromStream(new MemoryStream(buffer, 0,total));
string path = JPGName.Text+".jpg";
bmp.Save(path);
I very much doubt that this code is the cause of the problem, at least for the first method call (but read further below).
Technically, you could produce the Bitmap without saving to a memory buffer first, or if you don't need to display the image as well, you can save the raw data without ever constructing a Bitmap, but that's not going to help in terms of multiple seconds improved performance. Have you checked how long it takes to download the image from that URL using a browser, wget, curl or whatever tool, because I suspect something is going on with the encoding source.
Something you should do is clean up your resources; close the stream properly. This can potentially cause the problem if you call this method regularly, because .NET will only open a few connections to the same host at any one point.
// Make sure the stream gets closed once we're done with it
using (Stream stream = resp.GetResponseStream())
{
// A larger buffer size would be benefitial, but it's not going
// to make a significant difference.
while ((read = stream.Read(buffer, total, 1000)) != 0)
{
total += read;
}
}
I cannot try the network behavior of the WebResponse stream, but you handle the stream twice (once in your loop and once with your memory stream).
I don't thing that's the whole problem but I'd give it a try:
string sourceURL = "http://192.168.0.211/cgi-bin/cmd/encoder?SNAPSHOT";
WebRequest req = (WebRequest)WebRequest.Create(sourceURL);
req.Credentials = new NetworkCredential("admin", "123456");
WebResponse resp = req.GetResponse();
Stream stream = resp.GetResponseStream();
Bitmap bmp = (Bitmap)Bitmap.FromStream(stream);
string path = JPGName.Text + ".jpg";
bmp.Save(path);
Try to read bigger pieces of data, than 1000 bytes per time. I can see no problem with, for example,
read = stream.Read(buffer, 0, buffer.Length);
Try this to download the file.
using(WebClient webClient = new WebClient())
{
webClient.DownloadFile("http://192.168.0.211/cgi-bin/cmd/encoder?SNAPSHOT", "c:\\Temp\myPic.jpg");
}
You can use a DateTime to put a unique stamp on the shot.