I have a custom WebUploadTraceListener : TraceListener that I use to send HTTP (and eventually HTTPS) POST data to a web service that writes it to a database.
I have tested doing this with both WebClient and HttpWebRequest and empirically I'm seeing better performance with the latter.
Because of the one-way nature of the data, I don't care about the server response. But I found that if I don't handle the HttpWebResponse my code locks up on the third write. I think this is because of the DefaultConnectionLimit setting and the system not reusing the resource...
Per Jon Skeet
Note that you do need to dispose of the WebResponse returned by request.GetResponse - otherwise the underlying infrastructure won't know that you're actually done with it, and won't be able to reuse the connection.
HttpWebRequest httpRequest = (HttpWebRequest)WebRequest.Create(ServiceURI);
httpRequest.Method = "POST";
httpRequest.ContentType = "application/x-www-form-urlencoded";
try
{
using (Stream stream = httpRequest.GetRequestStream())
{
stream.Write(postBytes, 0, postBytes.Length);
}
using (HttpWebResponse response = (HttpWebResponse)httpRequest.GetResponse())
{
/// discard response
}
}
catch (Exception)
{
/// ...
}
I want to maximize the speed of sending the POST data and get back to the main program flow as quickly as possible. Because I'm tracing program flow, a synchronous write is preferable, but not mandatory as I can always add a POST field including a Tick count.
Is an HttpWebRequest and stream.Write the quickest method for doing this in .Net4.0 ?
Is there a cheaper way of discarding the unwanted response?
Attually, httpRequest.GetResponse only post the data to server and don't download anything to the client, except the information to tell client if the request is successfully processed by server.
You only get the respone data when you call GetResponseStream. If even the information about the success/error of the request you don't want to received, you don't have anyway to tell if server is success process the request or not.
So the answer is:
Yes, that is lowest level for managed code, unless you want mess up
with socket (which you shouldn't)
With HttpWebRequest, no. You almost don't get any data
you don't want.
Related
If we create a HttpWebRequest and get the ResponseStream from its response, then whether the data will get downloaded completely at once or, when we call the ReadBytes of the stream , then only the data will get download from the network and then reads the content?
Code sample which i want to refer is mentioned below:
var webRequest = HttpWebRequest.Create('url of a big file approx 700MB') as HttpWebRequest;
var webResponse = webRequest.GetResponse();
using (BinaryReader ns = new BinaryReader(webResponse.GetResponseStream()))
{
Thread.Sleep(60000); //Sleep for 60seconds, hope 700MB file get downloaded in 60 seconds
//At this point whether the response is totally downloaded or will not get downloaded at all
var buffer = ns.ReadBytes(bufferToRead);
//Or, in the above statement ReadBytes function is responsible for downloading the content from the internet.
}
GetResponseStream opens and returns a Stream object. The stream object is sourced from the underlying Socket. This Socket is sent data by the network adapter asynchronously. The data just arrives and is buffered. GetResponseStream will block execution until the first data arrives.
ReadByte pulls the data up from the socket layer to c#. This method will block execution until there is a byte avaliable.
Closing the stream prematurely will end the asynchronous transfer (closes the Socket, the sender will be notified of this as their connection will fail) and discard (flush) any buffered data that you have not used yet.
var webRequest = HttpWebRequest.Create('url of a big file approx 700MB') as HttpWebRequest;
Okay, we're set up ready to go. It's a bit different if you PUT or POST a stream of your own, but the differences are analogous.
var webResponse = webRequest.GetResponse();
When GetResponse() returns, it will at the very least have read all of the HTTP headers. It may well have read the headers of a redirect, and done another request to the URI it was redirected to. It's also possible that it's actually hitting a cache (either directly or because the webserver setnt 304 Not Modified) but by default the details of that are hidden from you.
There will likely be some more bytes in the socket's buffer.
using (BinaryReader ns = new BinaryReader(webResponse.GetResponseStream()))
{
At this point, we've got a stream representing the network stream.
Let's remove the Thread.Sleep() it does nothing except add a risk of the connection timing out. Even assuming it doesn't timeout while waiting, the connection will have "backed off" from sending bytes since you weren't reading them, so the effect will be to slow things even more than you did by adding a deliberate slow-down.
var buffer = ns.ReadBytes(bufferToRead);
At this point, either bufferToRead bytes have been read to create a byte[] or else fewer than bufferToRead because the total size of the stream was less than that, in which case buffer contains the entire stream. This will take as long as it takes.
}
At this point, because a successful HTTP GET was performed, the underlying web-access layer may cache the response (probably not if it's very large - the default assumption is that very large requests don't get repeated a lot and don't benefit from caching).
Error conditions will raise exceptions if they occur, and in that case no caching will ever be done (there is no point caching a buggy response).
There is no need to sleep, or otherwise "wait" on it.
It's worth considering the following variant that works at just a slightly lower level by manipulating the stream directly rather than through a reader:
using(var stm = webResponse.GetResponseStream())
{
We're going to work on the stream directly;
byte[] buffer = new byte[4096];
do
{
int read = stm.Read(buffer, 0, 4096);
This will return up to 4096 bytes. It may read less, because it has a chunk of bytes already available and it returns that many immediately. It will only return 0 bytes if it is at the end of the stream, so this gives us a balance between waiting and not waiting - it promises to wait long enough to get at least one byte, but whether or not it waits until it gets all 4096 bytes is up to the stream to choose whether it is more efficient to wait that long or return fewer bytes;
DoSomething(buffer, 0, read);
We work with the bytes we got.
} while(read != 0);
Read() only gives us zero bytes, if it's at the end of the stream.
}
And again, when the stream is disposed, the response may or may not be cached.
As you can see, even at the lowest level .NET gives us access to when using HttpWebResponse, there's no need to add code to wait on anything, as that is always done for us.
You can use asynchronous access to the stream to avoid waiting, but then the asynchronous mechanism still means you get the result when it's available.
To answer your question about when streaming starts, GetResponseStream() will start receiving data from the server. However, at some point the network buffers will become full and the server will stop sending data if you don't read off the buffers. For a detailed description of the tcp buffers, etc see here.
So your sleep of 60000 will not be helping you much as the network buffers along the way will fill up and data will stop arriving until you read it off. It is better to read it off and write it in chunks as you go.
More info on the workings of ResponseStream here.
If you are wondering about what buffer size to use, see here.
I'm calling a third party web API to update some of our data on their side. I've been submitting about five jobs in quick succession and, without fail, the first two requests are working properly. The last three however never update. The application seems to be indicating that the request is timing out, but I want to make sure that I'm not messing anything up on my side.
I'm calling the function below with an Action<string, Dictionary<string,object>> Delegate and I'm using BeginInvoke to call the API asynchronously. I don't really care about the response. Am I misunderstanding something about WebRequest.GetResponse() or is this a problem with the endpoint?
private void UpdateJobInfo(string jobId, Dictionary<string, object> updates)
{
var postData = GetJsonEncodedValues(updates);
var request = WebRequest.Create(string.Format(JobResultEndpoint, _username, jobId));
request.ContentType = "application/json; charset=utf-8";
request.Method = WebRequestMethods.Http.Put;
request.Headers[HttpRequestHeader.Authorization] = GetAuthenticationCredentials();
request.GetRequestStream().Write(Encoding.ASCII.GetBytes(postData), 0, Encoding.ASCII.GetBytes(postData).Length);
request.GetResponse();
}
You're not disposing of the response (or indeed the request stream, although that's a slightly different matter). That means you're leaving the connection to the server open until the finalizer happens to notice that the response can be finalized. The connections are pooled with (by default) two connections per URL. So your later requests are waiting for the earlier responses to be finalized before they can obtain a connection.
Better code:
// Is this definitely what you want? What about non-ASCII data?
byte[] binaryPostData = Encoding.ASCII.GetBytes(postData);
using (var requestStream = request.GetRequestStream())
{
requestStream.Write(binaryPostData, 0, binaryPostData.Length);
}
using (var response = request.GetResponse())
{
// We don't care about the response, but we have to fetch it
// and dispose it.
}
If the website isn't responding after one second or so, it's probably safe to assume that it's a bad link and that I should move on to my next link in a set of "possible links."
How do I tell the WebClient to stop attempting to download after some predetermined amount of time?
I suppose I could use a thread, but if it's taking longer than one second to download, that's ok. I just want to make sure that it's connecting with the site.
Perhaps I should modify the WebClient headers, but I don't see what I should modify.
Perhaps I should use some other class in the System.Net namespace?
If you use the System.Net.WebRequest class you can set the Timeout property to be short and handle timeout exceptions.
try{
var request = WebRequest.Create("http://www.contoso.com");
request.Timeout = 5000; //set the timeout to 5 seconds
request.Method = "GET";
var response = request.GetResponse();
}
catch(WebException webEx){
//there was an error, likely a timeout, try another link here
}
Can anyone point out the flaw in this code? I'm retrieving some HTML with TcpClient. NetworkStream.Read() never seems to finish when talking to an IIS server. If I go use the Fiddler proxy instead, it works fine, but when talking directly to the target server the .read() loop won't exit until the connection exceptions out with an error like "the remote server has closed the connection".
internal TcpClient Client { get; set; }
/// bunch of other code here...
try
{
NetworkStream ns = Client.GetStream();
StreamWriter sw = new StreamWriter(ns);
sw.Write(request);
sw.Flush();
byte[] buffer = new byte[1024];
int read=0;
try
{
while ((read = ns.Read(buffer, 0, buffer.Length)) > 0)
{
response.AppendFormat("{0}", Encoding.ASCII.GetString(buffer, 0, read));
}
}
catch //(SocketException se)
{
}
finally
{
Close();
}
Update
In the debugger, I can see the entire response coming through immediately and being appended to my StringBuilder (response). It just appears that the connection isn't being closed when the server is done sending the response, or my code isn't detecting it.
Conclusion
As has been said here, it's best to take advantage of the offerings of the protocol (in the case of HTTP, the Content-Length header) to determine when a transaction is complete. However, I've found that not all pages have content-length set. So, I'm now using a hybrid solution:
For ALL transactions, set the request's Connection header to "close", so that the server is discouraged from keeping the socket open. This improves the chances that the server will close the connection when it is through responding to your request.
If Content-Length is set, use it to determine when a request is complete.
Else, set the NetworkStream's RequestTimeout property to a large, but reasonable, value like 1 second. Then, loop on NetworkStream.Read() until either a) the timeout occurs, or b) you read fewer bytes than you asked for.
Thanks to everyone for their excellent and detailed responses.
Contrary to what the documentation for NetworkStream.Read implies, the stream obtained from a TcpClient does not simply return 0 for the number of bytes read when there is no data available - it blocks.
If you look at the documentation for TcpClient, you will see this line:
The TcpClient class provides simple methods for connecting, sending, and receiving stream data over a network in synchronous blocking mode.
Now my guess is that if your Read call is blocking, it's because the server has decided not to send any data back. This is probably because the initial request is not getting through properly.
My first suggestion would be to eliminate the StreamWriter as a possible cause (i.e. buffering/encoding nuances), and write directly to the stream using the NetworkStream.Write method. If that works, make sure that you're using the correct parameters for the StreamWriter.
My second suggestion would be not to depend on the result of a Read call to break the loop. The NetworkStream class has a DataAvailable property that is designed for this. The correct way to write a receive loop is:
NetworkStream netStream = client.GetStream();
int read = 0;
byte[] buffer = new byte[1024];
StringBuilder response = new StringBuilder();
do
{
read = netStream.Read(buffer, 0, buffer.Length);
response.Append(Encoding.ASCII.GetString(buffer, 0, read));
}
while (netStream.DataAvailable);
Read the response until you reach a double CRLF. What you now have is the Response headers.
Parse the headers to read the Content-Length header which will be the count of bytes left in the response.
Here is a regular expression that can catch the Content-Length header.
David's Updated Regex
Content-Length: (?<1>\d+)\r\n
Content-Length
Note
If the server does not properly set this header I would not use it.
Not sure if this is helpful or not but with HTTP 1.1 the underlying connection to the server might not be closed so maybe the stream doesn't get closed either? The idea being that you can reuse the connection to send a new request. I think you have to use the content-length. Alternatively use the WebClient or WebRequest classes instead.
I may be wrong, but it looks like your call to Write is writing (under the hood) to the stream ns (via StreamWriter). Later, you're reading from the same stream (ns). I don't quite understand why are you doing this?
Anyway, you may need to use Seek on the stream, to move to the location where you want to start reading. I'd guess that it seeks to the end after writing. But as I said, I'm not really sure if this is a useful answer!
Two Suggestions...
Have you tried using the DataAvailable property of NetworkStream? It should return true if there is data to be read from the stream.
while (ns.DataAvailable)
{
//Do stuff here
}
Another option would be to change the ReadTimeOut to a low value so you don't end up blocking for a long time. It can be done like this:
ns.ReadTimeOut=100;
As part of a suite of integration tests I am writing, I want to assert that my server behaves correctly when a client HTTP request terminates early, before all the response data has been sent.
Is it possible to create an HTTP request and terminate it after receiving just a few bytes of data in C#?
You don't have to read all bytes out fo the response. Just read as many bytes as you want and then return from your test.
You can do so more or less like this:
Stream myStream = resp.GetResponseStream();
myStream.Read(bufferArray, 0, 1); //read 1 byte into bufferArray
return;
You may find the documentation on WebReponse useful.
Just start the call asynchronously using, say a background worker, and then close the thread/channel.
I found a solution which works for me. I just close the response after getting it. This seems to leave me with the response headers, but closes the connection before the server is finished sending.
var response = request.getResponse();
response.Close();
// Assert that server has dealt with closed response correctly