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.
Related
I'm working in C# on a program to list all course resources for a MOOC (e.g. Coursera). I don't want to download the content, just get a listing of all the resources (e.g. pdf, videos, text files, sample files, etc...) which are made available to the course.
My problem lies in parsing the html source (currently using HtmlAgilityPack) without downloading all the content.
For example, if you go to this intro video for a banking course on Coursera and check the source (F12 in Chrome for Developer Tools), you can see the page source. I can stop the video download which autoplays, but still see the source.
How can I get the source in C# without download all the content?
I've looked in the HttpWebRequest headers (problem: time out), and DownloadDataAsync with Cancel (problem: the Completed Result object is invalid when cancelling the async request). I've also tried various Loads from HtmlAgilityPack but with no success.
Time out:
HttpWebRequest postRequest = (HttpWebRequest)WebRequest.Create(url);
postRequest.Timeout = TIMEOUT * 1000000; //Really long
postRequest.Referer = "https://www.coursera.org";
if (headers != null)
{ //headers here }
//Deal with cookies
if (cookie != null)
{ cookieJar.Add(cookie); }
postRequest.CookieContainer = cookiejar;
postRequest.Method = "GET";
postRequest.AllowAutoRedirect = allowRedirect;
postRequest.ServicePoint.Expect100Continue = true;
HttpWebResponse postResponse = (HttpWebResponse)postRequest.GetResponse();
Any tips on how to proceed?
There are at least two ways to do what you're asking. The first is to use a range get. That is, specify the range of the file you want to read. You do that by calling AddRange on the HttpWebRequest. So if you want, say, the first 10 kilobytes of the file, you'd write:
request.AddRange(-10240);
Read carefully what the documentation says about the meaning of that parameter. If it's negative, it specifies the ending point of the range. There are also other overloads of AddRange that you might be interested in.
Not all servers support range gets, though. If that doesn't work, you'll have to do it another way.
What you can do is call GetResponse and then start reading data. Once you've read as much data as you want, you can stop reading and close the stream. I've modified your sample slightly to show what I mean.
string url = "https://www.coursera.org/course/money";
HttpWebRequest postRequest = (HttpWebRequest)WebRequest.Create(url);
postRequest.Method = "GET";
postRequest.AllowAutoRedirect = true; //allowRedirect;
postRequest.ServicePoint.Expect100Continue = true;
HttpWebResponse postResponse = (HttpWebResponse) postRequest.GetResponse();
int maxBytes = 1024*1024;
int totalBytesRead = 0;
var buffer = new byte[maxBytes];
using (var s = postResponse.GetResponseStream())
{
int bytesRead;
// read up to `maxBytes` bytes from the response
while (totalBytesRead < maxBytes && (bytesRead = s.Read(buffer, 0, maxBytes)) != 0)
{
// Here you can save the bytes read to a persistent buffer,
// or write them to a file.
Console.WriteLine("{0:N0} bytes read", bytesRead);
totalBytesRead += bytesRead;
}
}
Console.WriteLine("total bytes read = {0:N0}", totalBytesRead);
That said, I ran this sample and it downloaded about 6 kilobytes and stopped. I don't know why you're having trouble with timeouts or too much data.
Note that sometimes trying to close the stream before the entire response is read will cause the program to hang. I'm not sure why that happens at all, and I can't explain why it only happens sometimes. But you can solve it by calling request.Abort before closing the stream. That is:
using (var s = postResponse.GetResponseStream())
{
// do stuff here
// abort the request before continuing
postRequest.Abort();
}
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
Merged with How to free up memory after base64 convert.
Thanks for your great suggestions to an OOM (out of memory) problem I'm seeing in code intended to stream files for web services. [I hope it is OK to start another thread which provides a bit more detail.] From the suggestions, I shrunk the buffer size used to read from the file, and it looks like memory consumption is better, but I'm still seeing an OOM problem, and I'm seeing this problem with files sizes as small as 5MB. I potentially want to deal with files ten times larger.
My problem seems now to be with the use of TextWriter.
I create a request as follows [with a few edits to shrink the code]:
HttpWebRequest oRequest = (HttpWebRequest)WebRequest.Create(new Uri(strURL));
oRequest.Method = httpMethod;
oRequest.ContentType = "application/atom+xml";
oRequest.Headers["Authorization"] = getAuthHeader();
oRequest.ContentLength = strHead.Length + strTail.Length + longContentSize;
oRequest.SendChunked = true;
using (TextWriter tw = new StreamWriter(oRequest.GetRequestStream()))
{
tw.Write(strHead);
using (FileStream fileStream = new FileStream(strPath, FileMode.Open,
FileAccess.Read, System.IO.FileShare.ReadWrite))
{
StreamEncode(fileStream, tw);
}
tw.Write(strTail);
}
.....
Which calls into the routine:
public void StreamEncode(FileStream inputStream, TextWriter tw)
{
// For Base64 there are 4 bytes output for every 3 bytes of input
byte[] base64Block = new byte[9000];
int bytesRead = 0;
string base64String = null;
do
{
// read one block from the input stream
bytesRead = inputStream.Read(base64Block, 0, base64Block.Length);
// encode the base64 string
base64String = Convert.ToBase64String(base64Block, 0, bytesRead);
// write the string
tw.Write(base64String);
} while (bytesRead !=0 );
}
Should I use something other than TextWriter because of the potential large content? It seems very convenient for being able to create the whole payload of the request.
Is this totally the wrong approach? I want to be able to support very large files.
I download a file's parts (a picture), and then I want to save these parts into one file.
The problem is, that the first part is being downloaded and saved properly (I can see the part of that pricture). But, when the second part is saved (FileMode.Append) the picture seems to be broken.
Here's the code:
HttpWebRequest webRequest;
HttpWebResponse webResponse;
Stream responseStream;
long StartPosition, EndPosition;
if (File.Exists(LocalPath))
fileStream = new FileStream(LocalPath, FileMode.Append);
else fileStream = new FileStream(LocalPath, FileMode.Create);
webRequest = (HttpWebRequest)WebRequest.Create(FileURL);
webResponse = (HttpWebResponse)webRequest.GetResponse();
responseStream = webResponse.GetResponseStream();
StartPosition = 0; //download first 52062 bytes of the file
EndPosition = 52061;
webRequest.AddRange(StartPosition, EndPosition);
int SeekPosition = (int)StartPosition;
while ((bytesSize = responseStream.Read(Buffer, 0, Buffer.Length)) > 0)
{
lock (fileStream)
{
fileStream.Seek(SeekPosition, SeekOrigin.Begin);
fileStream.Write(Buffer,0, bytesSize);
}
//the Buffer.Length is 2048.
//When the bytes count to download is < 2048 then I decrease the Buffer.Length
//to prevent downloading more that 52062 bytes.
DownloadedBytesCount += bytesSize;
SeekPosition += bytesSize;
long TotalToDownload = EndPosition - StartPosition;
long bytesLeft = TotalToDownload - DownloadedBytesCount;
if (bytesLeft < Buffer.Length)
Buffer = new byte[bytesLeft];
}
WHen I want to download the second part of the file I set
StartPosition = 52062;
EndPosition = 104122;
and then there is a problem that I described above. Why the file is not appened properly ?
You don't need StartPosition, fileStream.Seek() and Buffer = new byte[bytesLeft];
Also the lock() shouldn't be necessary (if it is you've got a lot more troubles).
So remove all that because the chances are you got some of it wrong.
And if it then still doesn't work, edit the question and provide more information. There is quite a lot missing right now:
could you verify with the debugger if the download loop is executed at all.
how is the changeover to the 2nd range 52k - 104k performed
how long is the resulting file in the end?
does the file contain the first 52k bytes or the 2nd download?
etc
All of that matters and we shouldn't have to guess.
What i would try is to download the image some way that you know that it works and compare the byte result to check where the file gets broken and what is breaking it...
This code is wicked... sorry but you must start by deleting all the code and looking at your problem from the beginning. There are many better ways to accomplish what you want. Just take a look at some good solutions:
http://www.codeproject.com/KB/IP/MyDownloader.aspx
Here's the purpose of my console program: Make a web request > Save results from web request > Use QueryString to get next page from web request > Save those results > Use QueryString to get next page from web request, etc.
So here's some pseudocode for how I set the code up.
for (int i = 0; i < 3; i++)
{
strPageNo = Convert.ToString(i);
//creates the url I want, with incrementing pages
strURL = "http://www.website.com/results.aspx?page=" + strPageNo;
//makes the web request
wrGETURL = WebRequest.Create(strURL);
//gets the web page for me
objStream = wrGETURL.GetResponse().GetResponseStream();
//for reading web page
objReader = new StreamReader(objStream);
//--------
// -snip- code that saves it to file, etc.
//--------
objStream.Close();
objReader.Close();
//so the server doesn't get hammered
System.Threading.Thread.Sleep(1000);
}
Pretty simple, right? The problem is, even though it increments the page number to get a different web page, I'm getting the exact same results page each time the loop runs.
i IS incrementing correctly, and I can cut/paste the url strURL creates into a web browser and it works just fine.
I can manually type in &page=1, &page=2, &page=3, and it'll return the correct pages. Somehow putting the increment in there screws it up.
Does it have anything to do with sessions, or what? I make sure I close both the stream and the reader before it loops again...
Have you tried creating a new WebRequest object for each time during the loop, it could be the Create() method isn't adequately flushing out all of its old data.
Another thing to check is that the ResponseStream is adequately flushed out before the next loop iteration.
This code works fine for me:
var urls = new [] { "http://www.google.com", "http://www.yahoo.com", "http://www.live.com" };
foreach (var url in urls)
{
WebRequest request = WebRequest.Create(url);
using (Stream responseStream = request.GetResponse().GetResponseStream())
using (Stream outputStream = new FileStream("file" + DateTime.Now.Ticks.ToString(), FileMode.Create, FileAccess.Write, FileShare.None))
{
const int chunkSize = 1024;
byte[] buffer = new byte[chunkSize];
int bytesRead;
while ((bytesRead = responseStream.Read(buffer, 0, buffer.Length)) > 0)
{
byte[] actual = new byte[bytesRead];
Buffer.BlockCopy(buffer, 0, actual, 0, bytesRead);
outputStream.Write(actual, 0, actual.Length);
}
}
Thread.Sleep(1000);
}
Just a suggestion, try disposing the Stream, and the Reader. I've seen some weird cases where not disposing objects like these and using them in loops can yield some wacky results....
That URL doesn't quite make sense to me unless you are using MVC or something that can interpret the querystring correctly.
http://www.website.com/results.aspx&page=
should be:
http://www.website.com/results.aspx?page=
Some browsers will accept poorly formed URLs and render them fine. Others may not which may be the problem with your console app.
Here's my terrible, hack-ish, workaround solution:
Make another console app that calls THIS one, in which the first console app passes an argument at the end of strURL. It works, but I feel so dirty.