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'
Related
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);
}
}
Looking at the different ways to upload a file in .NET, e.g. HttpPostedFile, and using a HttpHandler, I'm trying to understand how the process works in a bit more details.
Specifically how it writes the information to a file.
Say I have the following:
HttpPostedFile file = context.Request.Files[0];
file.SaveAs("c:\temp\file.zip");
The actual file does not get created until the full stream seems to be processed.
Similarly:
using (Stream output = File.OpenWrite("c:\temp\file.zip"))
using (Stream input = file.InputStream)
{
byte[] buffer = new byte[8192];
int bytesRead;
while ((bytesRead = input.Read(buffer, 0, buffer.Length)) > 0)
{
output.Write(buffer, 0, bytesRead);
}
}
I would have thought that this would "progressively" write the file as it reads the stream. Looking at the filesystem, it does not seems to do this at all. If I breakpoint inside the while, it does though.
What I'm trying to do, is have it so you upload a file (using a javascript uploader), and poll alongside, whereby the polling ajax request tries to get the fileinfo(file size) of the uploaded file every second. However, it always returns 0 until the upload is complete.
Vimeo seems to be able to do this type of functionality (for IE)?? Is this a .NET limitation, or is there a way to progressively write the file from the stream?
Two points:
First, in Windows, the displayed size of a file is not updated constantly. The file might indeed be growing continually, but the size only increases once.
Second (more likely in this case), the stream might not be flushing to the disk. You could force it to by adding output.Flush() after the call to output.Write(). You might not want to do that, though, since it will probably have a negative impact on performance.
Perhaps you could poll the Length property of the output stream directly, instead of going through the file system.
EDIT:
To make the Length property of the stream accessible to other threads, you could have a field in your class and update it with each read/write:
private long _uploadedByteCount;
void SomeMethod()
{
using (Stream output = File.OpenWrite("c:\temp\file.zip"))
using (Stream input = file.InputStream)
{
byte[] buffer = new byte[8192];
int bytesRead;
while ((bytesRead = input.Read(buffer, 0, buffer.Length)) > 0)
{
output.Write(buffer, 0, bytesRead);
Interlocked.Add(ref _uploadedByteCount, bytesRead);
}
}
}
public long GetUploadedByteCount()
{
return _uploadedByteCount;
}
Hi
Does anyone have workable sample code that copy files and support resuming them if there are the source has been disconnected?
In this example I am copying videos files. If the source is disconnected ie usb was unplugged, how can I support resuming them again? I have tried some code on stackoverflow, but after resuming, the video files seem to be corrupted. Is FileStream the best solution for video transfers/resume?
Any other pointers or tips are welcome.
private void CreateNewCopyTo(FileStream source, FileStream dest) {
int size = (source.CanSeek) ? Math.Min((int)(source.Length - source.Position), 0x2000) : 0x2000;
byte[] buffer = new byte[size];
int read;
long fileLength = source.Length;
while ((read = source.Read(buffer, 0, buffer.Length)) > 0) {
dest.Write(buffer, 0, read);
dest.Close();
dest = new FileStream(dest.Name, FileMode.Append, FileAccess.Write);
}
dest.Close();
}
private void ResumeCopyTo(FileStream source, FileStream dest) {
int size = (source.CanSeek) ? Math.Min((int)(source.Length - source.Position), 0x2000) : 0x2000;
byte[] buffer = new byte[size];
long TempPos = source.Position;
while (true) {
int read = source.Read(buffer, 0, buffer.Length);
if (read <= 0)
return;
dest.Write(buffer, 0, read);
dest.Close();
dest = new FileStream(dest.Name, FileMode.Append, FileAccess.Write);
}
}
Try to insert source.Seek(dest.Length, SeekOrigin.Begin); as first line in ResumeCopyTo method.
create a file that is the same size as the file your copying. And if the connection is broken write a "BookMark" into the file. Some arbitrary string at the end of the file that tells you where you left off.
Best to get a hash of the original file to determine if the file has changed since the last copy attempt. (if the file is different then you should check the data in the destination with the data in the source, perhaps with another hash of the data.)
The most important part tho is to seek in the source and the destination to the exact same point in both files. before the resume attempt.
You will want to make sure that your seek will give you the next byte in the source file. Not the same byte you left off at. Otherwise you will be left with your data having a single duplicate character. Which will corrupt the data.
(e.g. if the source file is 12345678901234567890 and your destination made it to 123456 , you dont want to resume at 6, you want to resume at 7. otherwise your destination would be 123456678901234567890)
Assuming that the file does not change in time, we can use the functions that you have written. However, they should be slightly modified and simplified to one function.
private void ResumeCopy(FileStream source, FileStream dest)
{
byte[] buffer = new byte[0x10000]; //use 64kB buffer
int read;
source.Seek(dest.Length, SeekOrigin.Begin);
while ((read = source.Read(buffer, 0, buffer.Length)) > 0)
{
dest.Write(buffer, 0, read);
dest.Flush();
}
}
We can create an additional function:
private void ResumeCopyTo(string sourceFilePath, string destFilePath)
{
FileStream input = new FileStream(sourceFilePath, FileMode.Open, FileAccess.Read);
FileStream output = new FileStream(destFilePath, FileMode.Append, FileAccess.Write);
ResumeCopy(input, output);
output.Close();
input.Close();
}
Ideas for a production environment:
add error handling
check whether the file has changed (use checksum)
opened the source file in exclusive mode
BTW:
In this way, I copied an 15 GB file in 9 hours via a network connection of really poor quality.
pretty much...i want to do something like this:
Stream Answer = WebResp.GetResponseStream();
Response.OutputStream = Answer;
Is this possible?
No, but you can of course copy the data, either synchronously or asynchronously.
Allocate a buffer (like 4kb in size or so)
Do a read, which will either return the number of bytes read or 0 if the end of the stream has been reached
If data was received, write the amount read and loop to the read
Like so:
using (Stream answer = webResp.GetResponseStream()) {
byte[] buffer = new byte[4096];
for (int read = answer.Read(buffer, 0, buffer.Length); read > 0; read = answer.Read(buffer, 0, buffer.Length)) {
Response.OutputStream.Write(buffer, 0, read);
}
}
This answer has a method CopyStream to copy data between streams (and also indicates the built-in way to do it in .NET 4).
You could do something like:
using (stream answer = WebResp.GetResponseStream())
{
CopyStream(answer, Response.OutputStream);
Response.Flush();
}