I got a file stream which has content read from a disk.
Stream input = new FileStream("filename");
This stream is to be passed to a third party library which after reading the stream, keeps the Stream's position pointer at the end of the file (as ususal).
My requirement is not to load the file from the desk everytime, instead I want to maintain MemoryStream, which will be used everytime.
public static void CopyStream(Stream input, Stream output)
{
byte[] buffer = new byte[32768];
int read;
while ((read = input.Read(buffer, 0, buffer.Length)) > 0)
{
output.Write(buffer, 0, read);
}
}
I have tried the above code. It works for the first very time to copy the input stream to output stream, but subsequent calls to CopyStream will not work as the source's Position will be at the end of the stream after the first call.
Are there other alternatives which copy the content of the source stream to another stream irrespective of the source stream's current Position.
And this code needs to run in thread safe manner in a multi threaded environment.
You can use .NET 4.0 Stream.CopyTo to copy your steam to a MemoryStream. The MemoryStream has a Position property you can use to move its postition to the beginning.
var ms = new MemoryStream();
using (Stream file = File.OpenRead(#"filename"))
{
file.CopyTo(ms);
}
ms.Position = 0;
To make a thread safe solution, you can copy the content to a byte array, and make a new MemoryStream wrapping the byte array for each thread that need access:
byte[] fileBytes = ms.ToArray();
var ms2 = new MemoryStream(fileBytes);
You should check the input stream's CanSeek property. If that returns false, you can only read it once anyway. If CanSeek returns true, you can set the position to zero and copy away.
if (input.CanSeek)
{
input.Position = 0;
}
You may also want to store the old position and restore it after copying.
ETA: Passing the same instance of a Stream around is not the safest thing to do. E.g. you can't be sure the Stream wasn't disposed when you get it back. I'd suggest to copy the FileStream to a MemoryStream in the beginning, but only store the byte content of the latter by calling ToArray(). When you need to pass a Stream somewhere, just create a new one each time with new MemoryStream(byte[]).
this code works fine. My question is what happens within the Net.ConnectionStream when i use the CopyTo() method?
System.Net.HttpWebRequest request
using (FileStream fileStream = new FileStream("C:\\myfile.txt")
{
using (Stream str = request.GetRequestStream())
{
fileStream.CopyTo(str);
}
}
More specific: What happens to the data?
1. write into the memory and upload then? (what's with big files?)
2. write into the network directly? (how does that work?)
Thanks for your answers
It creates a byte[] buffer and calls Read on the source and Write on the destination until the source doesn't have anymore data.
So when doing this with big files you don't need to be concerned about running out of memory because you'll only allocate as much as the buffer size, 81920 bytes by default.
Here's the actual implementation -
public void CopyTo(Stream destination)
{
// ... a bunch of argument validation stuff (omitted)
this.InternalCopyTo(destination, 81920);
}
private void InternalCopyTo(Stream destination, int bufferSize)
{
byte[] array = new byte[bufferSize];
int count;
while ((count = this.Read(array, 0, array.Length)) != 0)
{
destination.Write(array, 0, count);
}
}
I'm taking a Stream convert it to Image, process that image, then return a FileStream.
Is this a performance problem? If not, whats the optimized way to convert and return back a stream?
public FileStream ResizeImage(int h, int w, Stream stream)
{
var img = Image.FromStream(stream);
/* ..Processing.. */
//converting back to stream? is this right?
img.Save(stream, ImageFormat.Png);
return stream;
}
The situation in which this is running: User uploads image on my site (controller gives me a Stream, i resize this, then send this stream to rackspace (Rackspace takes a FileStream).
You basically want something like this, don't you:
public void Resize(Stream input, Stream output, int width, int height)
{
using (var image = Image.FromStream(input))
using (var bmp = new Bitmap(width, height))
using (var gr = Graphics.FromImage(bmp))
{
gr.CompositingQuality = CompositingQuality.HighSpeed;
gr.SmoothingMode = SmoothingMode.HighSpeed;
gr.InterpolationMode = InterpolationMode.HighQualityBicubic;
gr.DrawImage(image, new Rectangle(0, 0, width, height));
bmp.Save(output, ImageFormat.Png);
}
}
which will be used like this:
using (var input = File.OpenRead("input.jpg"))
using (var output = File.Create("output.png"))
{
Resize(input, output, 640, 480);
}
That looks as simple as it can be. You have to read the entire image contents to be able to process it and you have to write the result back.
FileStreams are the normal .NET way to handle files, so for normal purposes your approach is okay.
The only thing I don't understand is why you return the FileStream again - it is the same object as was passed by a parameter.
If you are doing a lot of images and only modify parts of the data, memory mapped files could improve performance. However it is a more advanced concept to use.
I am in process of sending the file along with HttpWebRequest. My file will be from FileUpload UI. Here I need to convert the File Upload to filestream to send the stream along with HttpWebRequest. How do I convert the FileUpload to a filestream?
Since FileUpload.PostedFile.InputStream gives me Stream, I used the following code to convert it to byte array
public static byte[] ReadFully(Stream input)
{
byte[] buffer = new byte[input.Length];
//byte[] buffer = new byte[16 * 1024];
using (MemoryStream ms = new MemoryStream())
{
int read;
while ((read = input.Read(buffer, 0, buffer.Length)) > 0)
{
ms.Write(buffer, 0, read);
}
return ms.ToArray();
}
}
Might be better to pipe the input stream directly to the output stream:
inputStream.CopyTo(outputStream);
This way, you are not caching the entire file in memory before re-transmission. For example, here is how you would write it to a FileStream:
FileUpload fu; // Get the FileUpload object.
using (FileStream fs = File.OpenWrite("file.dat"))
{
fu.PostedFile.InputStream.CopyTo(fs);
fs.Flush();
}
If you wanted to write it directly to another web request, you could do the following:
FileUpload fu; // Get the FileUpload object for the current connection here.
HttpWebRequest hr; // Set up your outgoing connection here.
using (Stream s = hr.GetRequestStream())
{
fu.PostedFile.InputStream.CopyTo(s);
s.Flush();
}
That will be more efficient, as you will be directly streaming the input file to the destination host, without first caching in memory or on disk.
You can't convert a FileUpload into a FileStream. You can, however, get a MemoryStream from that FileUpload's PostedFile property. You can then use that MemoryStream to fill your HttpWebRequest.
You can put a FileUpload file directly into a MemoryStream by using FileBytes (simplified answer from Tech Jerk)
using (MemoryStream ms = new MemoryStream(FileUpload1.FileBytes))
{
//do stuff
}
Or if you do not need a memoryStream
byte[] bin = FileUpload1.FileBytes;
What is the best way to copy the contents of one stream to another? Is there a standard utility method for this?
From .NET 4.5 on, there is the Stream.CopyToAsync method
input.CopyToAsync(output);
This will return a Task that can be continued on when completed, like so:
await input.CopyToAsync(output)
// Code from here on will be run in a continuation.
Note that depending on where the call to CopyToAsync is made, the code that follows may or may not continue on the same thread that called it.
The SynchronizationContext that was captured when calling await will determine what thread the continuation will be executed on.
Additionally, this call (and this is an implementation detail subject to change) still sequences reads and writes (it just doesn't waste a threads blocking on I/O completion).
From .NET 4.0 on, there's is the Stream.CopyTo method
input.CopyTo(output);
For .NET 3.5 and before
There isn't anything baked into the framework to assist with this; you have to copy the content manually, like so:
public static void CopyStream(Stream input, Stream output)
{
byte[] buffer = new byte[32768];
int read;
while ((read = input.Read(buffer, 0, buffer.Length)) > 0)
{
output.Write (buffer, 0, read);
}
}
Note 1: This method will allow you to report on progress (x bytes read so far ...)
Note 2: Why use a fixed buffer size and not input.Length? Because that Length may not be available! From the docs:
If a class derived from Stream does not support seeking, calls to Length, SetLength, Position, and Seek throw a NotSupportedException.
MemoryStream has .WriteTo(outstream);
and .NET 4.0 has .CopyTo on normal stream object.
.NET 4.0:
instream.CopyTo(outstream);
I use the following extension methods. They have optimized overloads for when one stream is a MemoryStream.
public static void CopyTo(this Stream src, Stream dest)
{
int size = (src.CanSeek) ? Math.Min((int)(src.Length - src.Position), 0x2000) : 0x2000;
byte[] buffer = new byte[size];
int n;
do
{
n = src.Read(buffer, 0, buffer.Length);
dest.Write(buffer, 0, n);
} while (n != 0);
}
public static void CopyTo(this MemoryStream src, Stream dest)
{
dest.Write(src.GetBuffer(), (int)src.Position, (int)(src.Length - src.Position));
}
public static void CopyTo(this Stream src, MemoryStream dest)
{
if (src.CanSeek)
{
int pos = (int)dest.Position;
int length = (int)(src.Length - src.Position) + pos;
dest.SetLength(length);
while(pos < length)
pos += src.Read(dest.GetBuffer(), pos, length - pos);
}
else
src.CopyTo((Stream)dest);
}
.NET Framework 4 introduce new "CopyTo" method of Stream Class of System.IO namespace. Using this method we can copy one stream to another stream of different stream class.
Here is example for this.
FileStream objFileStream = File.Open(Server.MapPath("TextFile.txt"), FileMode.Open);
Response.Write(string.Format("FileStream Content length: {0}", objFileStream.Length.ToString()));
MemoryStream objMemoryStream = new MemoryStream();
// Copy File Stream to Memory Stream using CopyTo method
objFileStream.CopyTo(objMemoryStream);
Response.Write("<br/><br/>");
Response.Write(string.Format("MemoryStream Content length: {0}", objMemoryStream.Length.ToString()));
Response.Write("<br/><br/>");
There is actually, a less heavy-handed way of doing a stream copy. Take note however, that this implies that you can store the entire file in memory. Don't try and use this if you are working with files that go into the hundreds of megabytes or more, without caution.
public static void CopySmallTextStream(Stream input, Stream output)
{
using (StreamReader reader = new StreamReader(input))
using (StreamWriter writer = new StreamWriter(output))
{
writer.Write(reader.ReadToEnd());
}
}
NOTE: There may also be some issues concerning binary data and character encodings.
The basic questions that differentiate implementations of "CopyStream" are:
size of the reading buffer
size of the writes
Can we use more than one thread (writing while we are reading).
The answers to these questions result in vastly different implementations of CopyStream and are dependent on what kind of streams you have and what you are trying to optimize. The "best" implementation would even need to know what specific hardware the streams were reading and writing to.
Unfortunately, there is no really simple solution. You can try something like that:
Stream s1, s2;
byte[] buffer = new byte[4096];
int bytesRead = 0;
while (bytesRead = s1.Read(buffer, 0, buffer.Length) > 0) s2.Write(buffer, 0, bytesRead);
s1.Close(); s2.Close();
But the problem with that that different implementation of the Stream class might behave differently if there is nothing to read. A stream reading a file from a local harddrive will probably block until the read operaition has read enough data from the disk to fill the buffer and only return less data if it reaches the end of file. On the other hand, a stream reading from the network might return less data even though there are more data left to be received.
Always check the documentation of the specific stream class you are using before using a generic solution.
There may be a way to do this more efficiently, depending on what kind of stream you're working with. If you can convert one or both of your streams to a MemoryStream, you can use the GetBuffer method to work directly with a byte array representing your data. This lets you use methods like Array.CopyTo, which abstract away all the issues raised by fryguybob. You can just trust .NET to know the optimal way to copy the data.
if you want a procdure to copy a stream to other the one that nick posted is fine but it is missing the position reset, it should be
public static void CopyStream(Stream input, Stream output)
{
byte[] buffer = new byte[32768];
long TempPos = input.Position;
while (true)
{
int read = input.Read (buffer, 0, buffer.Length);
if (read <= 0)
return;
output.Write (buffer, 0, read);
}
input.Position = TempPos;// or you make Position = 0 to set it at the start
}
but if it is in runtime not using a procedure you shpuld use memory stream
Stream output = new MemoryStream();
byte[] buffer = new byte[32768]; // or you specify the size you want of your buffer
long TempPos = input.Position;
while (true)
{
int read = input.Read (buffer, 0, buffer.Length);
if (read <= 0)
return;
output.Write (buffer, 0, read);
}
input.Position = TempPos;// or you make Position = 0 to set it at the start
Since none of the answers have covered an asynchronous way of copying from one stream to another, here is a pattern that I've successfully used in a port forwarding application to copy data from one network stream to another. It lacks exception handling to emphasize the pattern.
const int BUFFER_SIZE = 4096;
static byte[] bufferForRead = new byte[BUFFER_SIZE];
static byte[] bufferForWrite = new byte[BUFFER_SIZE];
static Stream sourceStream = new MemoryStream();
static Stream destinationStream = new MemoryStream();
static void Main(string[] args)
{
// Initial read from source stream
sourceStream.BeginRead(bufferForRead, 0, BUFFER_SIZE, BeginReadCallback, null);
}
private static void BeginReadCallback(IAsyncResult asyncRes)
{
// Finish reading from source stream
int bytesRead = sourceStream.EndRead(asyncRes);
// Make a copy of the buffer as we'll start another read immediately
Array.Copy(bufferForRead, 0, bufferForWrite, 0, bytesRead);
// Write copied buffer to destination stream
destinationStream.BeginWrite(bufferForWrite, 0, bytesRead, BeginWriteCallback, null);
// Start the next read (looks like async recursion I guess)
sourceStream.BeginRead(bufferForRead, 0, BUFFER_SIZE, BeginReadCallback, null);
}
private static void BeginWriteCallback(IAsyncResult asyncRes)
{
// Finish writing to destination stream
destinationStream.EndWrite(asyncRes);
}
For .NET 3.5 and before try :
MemoryStream1.WriteTo(MemoryStream2);
Easy and safe - make new stream from original source:
MemoryStream source = new MemoryStream(byteArray);
MemoryStream copy = new MemoryStream(byteArray);
The following code to solve the issue copy the Stream to MemoryStream using CopyTo
Stream stream = new MemoryStream();
//any function require input the stream. In mycase to save the PDF file as stream
document.Save(stream);
MemoryStream newMs = (MemoryStream)stream;
byte[] getByte = newMs.ToArray();
//Note - please dispose the stream in the finally block instead of inside using block as it will throw an error 'Access denied as the stream is closed'