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'
I use the following code to return a byte array in HttpResponseMessage:
using (WebResponse response = (HttpWebResponse)request.GetResponse())
{
byte[] bytes = ReadFully(response.GetResponseStream());
......
}
public static byte[] ReadFully(Stream input)
{
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(); // This line throws OutOfMemory exception
}
}
An OutOfMemory exception is thrown in the last return ms.ToArray() statement.
I need to set the resulting byte[] as HttpResponseMessage.Content.
You should return the stream directly instead of reading it into memory first.
public HttpResponseMessage CreateMessage(Stream input)
{
HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK);
result.Content = new StreamContent(input);
return result;
}
Do not forget to set the appropriate headers etc.
Edit
... i need to write the byte array from the HttpResponseMessage into a file
Based on your last comment you changed your question and want to go the other way. Here is an example of writing to a file from a web response.
public void writetoFile(HttpWebResponse response)
{
var inStream = response.GetResponseStream();
using (var file = System.IO.File.OpenWrite("your file path here"))
{
inStream.CopyTo(file);
}
}
Igor posted the solution, and the correct way to deal with stream content. Use one of the MVC helper functions like File(stream,contentype) or classes like StreamContent to send the stream contents directly to the client, eg:
return File(myStream,myExcelContentTypeString);
or
return File(myStream,myExcelContentTypeString,"ReallyBigFile.xlsx");
The reason for the error, is that OOM can occur because memory is too fragmented to allocate a new object. A MemoryStream stores data in a buffer. When it exceeds the buffer limits, it allocates a new one with double the capacity and copies the old data. Copying 250MB of data like this is going to cause a lot of reallocations and thus a lot of memory fragmentation.
This can be avoided by specifying the desired capacity in the stream's constructor. This will allocate a large enough buffer immediatelly.
It's even better though to avoid caching this content though, by sending it to the browser directly.
I'm trying to get a byte[] array filled with request response, without any extra garbage data.
This is how I fetch the data:
using (Stream MyResponseStream = hwresponse.GetResponseStream())
{
byte[] MyBuffer = new byte[4096];
int BytesRead;
while (0 < (BytesRead = MyResponseStream.Read(MyBuffer, 0, MyBuffer.Length)))
{
ByteArrayToFile("request.txt", MyBuffer);
}
}
I use the function 'ByteArrayToFile' to see what data has been recieved.
public void ByteArrayToFile(string _FileName, byte[] _ByteArray)
{
System.IO.FileStream _FileStream = new System.IO.FileStream(_FileName, System.IO.FileMode.Append, System.IO.FileAccess.Write);
_FileStream.Write(_ByteArray, 0, _ByteArray.Length);
_FileStream.Close();
}
I get request written to the file, but a lot of 'null' characters are added at the end. How do I trim them? Since I'm going to need this to handle binary files, how can I safely trim out the endings and have just pure array of response? Thanks!
You need to utilise the value BytesRead, this will indicate exactly how many bytes were received:
public void ByteArrayToFile(string _FileName, byte[] _ByteArray, int _BytesRead)
{
using (var _FileStream = new FileStream(
_FileName, FileMode.Append, FileAccess.Write))
{
_FileStream.Write(_ByteArray, 0, _BytesRead);
}
}
Otherwise you're writing out an array of length X which has only been populated with Y number of elements, causing a number of 'unused' elements in the array to also be written out. There is also the possibility of stale data remaining in the buffer with a pass, meaning misinformation could also end up being written out with the next write.
You should also dispose of FileStream instances when done (although Close does this for a Stream, I'd recommend the consistency of calling Dispose in one of two ways: explicitly or as illustrated in the code above, implicitly using the using construct).
What is the best method to convert a Stream to a FileStream using C#.
The function I am working on has a Stream passed to it containing uploaded data, and I need to be able to perform stream.Read(), stream.Seek() methods which are methods of the FileStream type.
A simple cast does not work, so I'm asking here for help.
Read and Seek are methods on the Stream type, not just FileStream. It's just that not every stream supports them. (Personally I prefer using the Position property over calling Seek, but they boil down to the same thing.)
If you would prefer having the data in memory over dumping it to a file, why not just read it all into a MemoryStream? That supports seeking. For example:
public static MemoryStream CopyToMemory(Stream input)
{
// It won't matter if we throw an exception during this method;
// we don't *really* need to dispose of the MemoryStream, and the
// caller should dispose of the input stream
MemoryStream ret = new MemoryStream();
byte[] buffer = new byte[8192];
int bytesRead;
while ((bytesRead = input.Read(buffer, 0, buffer.Length)) > 0)
{
ret.Write(buffer, 0, bytesRead);
}
// Rewind ready for reading (typical scenario)
ret.Position = 0;
return ret;
}
Use:
using (Stream input = ...)
{
using (Stream memory = CopyToMemory(input))
{
// Seek around in memory to your heart's content
}
}
This is similar to using the Stream.CopyTo method introduced in .NET 4.
If you actually want to write to the file system, you could do something similar that first writes to the file then rewinds the stream... but then you'll need to take care of deleting it afterwards, to avoid littering your disk with files.
Can someone provide some light on how to do this? I can do this for regular text or byte array, but not sure how to approach for a pdf. do i stuff the pdf into a byte array first?
Use File.ReadAllBytes to load the PDF file, and then encode the byte array as normal using Convert.ToBase64String(bytes).
Byte[] fileBytes = File.ReadAllBytes(#"TestData\example.pdf");
var content = Convert.ToBase64String(fileBytes);
There is a way that you can do this in chunks so that you don't have to burn a ton of memory all at once.
.Net includes an encoder that can do the chunking, but it's in kind of a weird place. They put it in the System.Security.Cryptography namespace.
I have tested the example code below, and I get identical output using either my method or Andrew's method above.
Here's how it works: You fire up a class called a CryptoStream. This is kind of an adapter that plugs into another stream. You plug a class called CryptoTransform into the CryptoStream (which in turn is attached to your file/memory/network stream) and it performs data transformations on the data while it's being read from or written to the stream.
Normally, the transformation is encryption/decryption, but .net includes ToBase64 and FromBase64 transformations as well, so we won't be encrypting, just encoding.
Here's the code. I included a (maybe poorly named) implementation of Andrew's suggestion so that you can compare the output.
class Base64Encoder
{
public void Encode(string inFileName, string outFileName)
{
System.Security.Cryptography.ICryptoTransform transform = new System.Security.Cryptography.ToBase64Transform();
using(System.IO.FileStream inFile = System.IO.File.OpenRead(inFileName),
outFile = System.IO.File.Create(outFileName))
using (System.Security.Cryptography.CryptoStream cryptStream = new System.Security.Cryptography.CryptoStream(outFile, transform, System.Security.Cryptography.CryptoStreamMode.Write))
{
// I'm going to use a 4k buffer, tune this as needed
byte[] buffer = new byte[4096];
int bytesRead;
while ((bytesRead = inFile.Read(buffer, 0, buffer.Length)) > 0)
cryptStream.Write(buffer, 0, bytesRead);
cryptStream.FlushFinalBlock();
}
}
public void Decode(string inFileName, string outFileName)
{
System.Security.Cryptography.ICryptoTransform transform = new System.Security.Cryptography.FromBase64Transform();
using (System.IO.FileStream inFile = System.IO.File.OpenRead(inFileName),
outFile = System.IO.File.Create(outFileName))
using (System.Security.Cryptography.CryptoStream cryptStream = new System.Security.Cryptography.CryptoStream(inFile, transform, System.Security.Cryptography.CryptoStreamMode.Read))
{
byte[] buffer = new byte[4096];
int bytesRead;
while ((bytesRead = cryptStream.Read(buffer, 0, buffer.Length)) > 0)
outFile.Write(buffer, 0, bytesRead);
outFile.Flush();
}
}
// this version of Encode pulls everything into memory at once
// you can compare the output of my Encode method above to the output of this one
// the output should be identical, but the crytostream version
// will use way less memory on a large file than this version.
public void MemoryEncode(string inFileName, string outFileName)
{
byte[] bytes = System.IO.File.ReadAllBytes(inFileName);
System.IO.File.WriteAllText(outFileName, System.Convert.ToBase64String(bytes));
}
}
I am also playing around with where I attach the CryptoStream. In the Encode method,I am attaching it to the output (writing) stream, so when I instance the CryptoStream, I use its Write() method.
When I read, I'm attaching it to the input (reading) stream, so I use the read method on the CryptoStream. It doesn't really matter which stream I attach it to. I just have to pass the appropriate Read or Write enumeration member to the CryptoStream's constructor.