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Return BLOB stream without reading in memory

I have a blob storage
class Blob{
public Guid Id { get; set; }
public byte[] Content { get; set; }
}
I want to return stream of Content. For now I read whole data and return MemoryStream.
Current code
public async Task<Stream> GetOrNullAsync(BlobProviderGetArgs args)
{
var blob = await DatabaseBlobRepository.FindAsync(id);
if (blob == null)
{
return null;
}
return new MemoryStream(blob.Content);
}
As you see, firstly I read whole data then return MemoryStream.
It is not problem for small objects but consider that there is a 1gb Blob, it will be problem.
Is there any way to improve it like return Stream through EfCore?
Can you suggest best practises for this issue.

Read CSV from variable using CsvHelper (or similar library)

I've got a function that makes something equivalent to a web request, and it returns a formatted CSV. My goal is to now import this data into CsvHelper. However, I can't seem to get CSVParser to read from static text, only from a stream.
I could write the output to a file then read it back, but I feel that doesn't make much sense here.
I'm not tied down at all to CsvHelper, however I can't seem to find a CSV library that supports this behavior. How should I do this?
var csvString = functionThatReturnsCsv()
/* as string:
columnA,columnB
dataA,dataB
*/
// my goal
???.parse(csvString)

You can convert the string to a Stream in-memory and then use that as the source for your CSV reader:
public static Stream StringAsStream(string value)
{
return StringAsStream(value, System.Text.Encoding.UTF8);
}
public static Stream StringAsStream(string value, System.Text.Encoding encoding)
{
var bytes = encoding.GetBytes(value);
return new MemoryStream(bytes);
}
Usage:
using (var stream = StringAsStream("hello"))
{
// csv reading code here
}
or
using (var stream = StringAsStream("hello", Encoding.Ascii))
{
// csv reading code here
}
Try it online
Note If you are reading from a source that can return a Stream (like a web request), you should use that Stream rather than doing this.

You could use StringReader. The CsvReader constructor takes a TextReader argument rather than a Stream. If you did have a stream instead of a string, just replace StringReader with StreamReader.
public static void Main(string[] args)
{
using (var reader = new StringReader(FunctionThatReturnsCsv()))
using (var csv = new CsvReader(reader))
{
var results = csv.GetRecords<Foo>().ToList();
}
}
public static string FunctionThatReturnsCsv()
{
return "columnA,columnB\ndataA,dataB";
}
public class Foo
{
public string columnA { get; set; }
public string columnB { get; set; }
}

Is there a construct or pattern similar to C# `using` which will return an object?

I have a WCF message inspector which inspects requests and responses: Message. The inspector works fine. A Message object can only be read once so once you read it, you cannot simply propagate as WCF will complain that the message has been read. Therefore, I am creating a brand new copy of the message and propagating that.
I have designed a class that allows message reading and after the caller has read whatever they want, they need to call Close which will return a copy of the message. Here is the skeleton of my class:
using System.ServiceModel.Channels;
internal abstract class MessageReader
{
internal string ReadSomething(string id)
{
// Return string
}
internal string ReadSomethingElse(string id)
{
// Return string
}
internal Message Close()
{
// Create copy and return it.
}
}
Users of my class may forget to call Close() which is fine because WCF will yell at them. Right now I have documentation to let users know they need to call Close().
Here is the question
Is there a pattern, or something similar, to C#'s using construct but one which returns an object at the end? This will be really convenient because then users of my class can just use a construct like that and at the end it will return the copy of the message. Something like this:
UsingSomeConstruct(var reader = new MessageReader(ref originalMessage))
{
var a = reader.ReadSomething("something");
var b = reader.ReadSomethingElse("something");
// Do something with what was read
}
// At this point originalMessage will be the copy of the message and no longer the original message.
EDIT
I thought about hacking IDisposable to achieve this but I am NOT going to do it that way so looking for other ideas.

There is no such language construct of course.
What I could suggest is to use IDisposable for cleaning up, and add ref Message message argument to each ReadXXX method. I know it will not be so convenient for your users, but from the other side they cannot forget passing the parameter.
So the implementation would be something like this:
internal class MessageReader : IDisposable
{
private MessageBuffer buffer;
private Message message;
private void Release()
{
if (buffer == null) return;
buffer.Close();
buffer = null;
message = null;
}
protected void OnReadRequest(ref Message message)
{
if (message == null) throw new ArgumentNullException("message");
if (this.message == message) return;
Release();
this.buffer = message.CreateBufferedCopy(int.MaxValue);
message = this.message = buffer.CreateMessage();
}
public void Dispose()
{
Release();
}
internal string ReadSomething(ref Message message, string id)
{
OnReadRequest(ref message);
// Return string
}
internal string ReadSomethingElse(ref Message message, string id)
{
OnReadRequest(ref message);
// Return string
}
}
and the sample usage:
using (var reader = new MessageReader())
{
var a = reader.ReadSomething(ref originalMessage, "something");
var b = reader.ReadSomethingElse(ref originalMessage, "something");
// Do something with what was read
}
// At this point originalMessage will be the copy of the message and no longer the original message.

The way I'd do this is as follows:
public MessageReader: IDisposable
{
public static MessageReader Create(ref Message message)
{
var buffer = message.CreateBufferedCopy(/*whatever is fit*/);
try
{
var reader = new MessageReader(buffer);
message = buffer.CreateMessage();
return reader;
}
catch
{
buffer.Close();
throw;
}
}
private readonly MessageBuffer buffer;
private bool disposed;
private MessageReader(MessageBuffer buffer) { this.buffer = buffer; }
public void Dispose()
{
if (disposed)
return;
buffer.Close();
disposed = true;
}
public string Read(string id)
{
var newCopy = buffer.CreateMessage();
//work with new copy...
}
}
And you'd simply use it like this:
using (var reader = MessageReader.Create(ref message))
//message here is already an untouched copy with no need of user active
//intervention and is never touched again by the reader.
{
var a = reader.Read("something"); //reads copy
...
}
IMHO, this is as clean as it can be. Note that MessageReader implements IDisposable exclusively because it holds a reference to the disposable private MessageBuffer.

Thanks to all the help from #InBetween, #quetzalcoatl, and #Ivan Stoev. Upvoted your answers because it helped me arrive at the following.
In the constructor, I create a copy of the message and set the original message to the copy. Since the status of this message is Created WCF will be happy propogating it. I create another copy and use that for reading multiple times.
#Ivan said but what if the user does not ask for anything to be read then the copying was wasted work. That is a good point but in my case, this is an interceptor and all messages are intercepted to be read.
Here is the code I ended up with suggestions from all of you:
public class MessageReader : IDisposable {
private readonly Message message;
public MessageReader(ref Message originalMessage) {
using( var buffer = originalMessage.CreateBufferedCopy( int.MaxValue ) ) {
// Keep original message for reading
this.message = buffer.CreateMessage();
// Set original message to a copy of the original
originalMessage = buffer.CreateMessage();
}
}
public int ReadSomething(string id) {
// Read from this.message;
}
public int ReadSomethingElse(string id) {
// Read from this.message;
}
public void Close() {
this.Dispose();
}
public void Dispose() {
this.message.Close();
}
}
The caller can either use it in a using block or without it. The using block is used for good reasons and not as a hack.
public object AfterReceiveRequest(ref Message request, IClientChannel channel,
InstanceContext instanceContext) {
try {
using( var rdr = new MessageReader(ref request) ) {
var value= rdr.ReadSomething( someIdentifier );
return value;
}
}
catch( System.Exception ex ) {
throw CreateFault( ex, request );
}
}

Nope, there is no such construct. It is simply too specific to exist there out of the box. There are extension methods which often are very helpful, but you won't be able to use them on this ref Message parameter..
However, if you are willing to use ref at all, then why dont simply include all that logic it in Reader's constructor?
Here's an example, somewhat contrived, but it should show what I mean. Like others mentioned in comments, I also suggest implementing IDisposable on the Reader object instead of Close, so I included that already.
TL;DR: In example below, the most important thing is in Reader(ref msg) constructor which clones the message, copies the data, and replaces the original message with a safe-message class which can be read many times..
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
namespace Rextester
{
public class Program
{
public static void Main(string[] args)
{
// real-world variables, keep them typed as base Message
// to be able to silently replace them with different objects
Message original1;
Message original2;
// let's construct some one-time readable messages
{
var tmp1 = new OneTimeMessage();
tmp1.data["mom"] = "dad";
tmp1.data["cat"] = "dog";
original1 = tmp1;
var tmp2 = new OneTimeMessage();
tmp2.data["mom"] = "dad";
tmp2.data["cat"] = "dog";
original2 = tmp2;
}
// test1 - can't read twice
Console.WriteLine("test0A:" + original1.GetData("mom"));
//Console.WriteLine("test0B:" + original1.GetData("mom")); // fail
// test2 - can read twice with Reader's help
var backup1 = original2;
using(var rd1 = new Reader(ref original2))
{
Console.WriteLine("test1A:" + rd1.ReadSomething("mom"));
}
var backup2 = original2;
using(var rd2 = new Reader(ref original2))
{
Console.WriteLine("test1A:" + rd2.ReadSomething("mom"));
//^ ok - becase Reader replaced 'original2' with SafeMessage
}
// test3: Reader's ctor is intelligent
// so no more SafeMessages created during future usage
var backup3 = original2;
using(var rd3 = new Reader(ref original2))
{
}
var backup4 = original2;
using(var rd4 = new Reader(ref original2))
{
}
Console.WriteLine("checking for copies:" + (original2 == backup1));
Console.WriteLine("checking for copies:" + (original2 == backup2));
Console.WriteLine("checking for copies:" + (original2 == backup3));
Console.WriteLine("checking for copies:" + (original2 == backup4));
}
}
}
public abstract class Message
{
public abstract string GetData(string id);
}
public class OneTimeMessage : Message // this models your current one-time-readable message
{
public IDictionary<string, string> data = new Dictionary<string, string>();
public override string GetData(string id)
{
var tmp = data[id];
data.Remove(id);
// that's nonsense, but I want to show that you can't
// read the same thing twice from this object
return tmp;
}
}
public class SafeMessage : Message
{
public IDictionary<string, string> data;
public override String GetData(string id)
{
return data[id];
}
public SafeMessage(Message msg)
{
// read out the full msg's data and store it
// since this is example, we can do it in a pretty simple way
// in your code that will probably be more complex
this.data = new Dictionary<string,string>(((OneTimeMessage)msg).data);
}
}
public class Reader : IDisposable
{
private Message message;
public Reader(ref Message src)
{
src = src is SafeMessage ? src : new SafeMessage(src);
this.message = src;
}
public string ReadSomething(string id){ return message.GetData(id); }
public void Dispose(){ Close(); }
public void Close(){ message=null; Console.WriteLine("reader closed"); }
}
EDIT: improved example
using System;
using System.Collections.Generic;
using System.Linq;
using System.ServiceModel.Channels;
using System.Text.RegularExpressions;
using System.Xml;
namespace MyProgram
{
public class Program
{
public static void Main(string[] args)
{
// real-world variables, keep them typed as base Message
// to be able to silently replace them with different objects
Message original1;
Message original2;
// let's construct some one-time readable messages
{
original1 = new TheMessage("dad", "dog");
original2 = new TheMessage("dad", "dog");
}
// test1 - can't read twice
Console.WriteLine("test0A:" + original1.GetReaderAtBodyContents().ReadOuterXml());
// Console.WriteLine("test0B:" + original1.GetReaderAtBodyContents().ReadOuterXml()); // fail: InvalidOperationException - it was already read
// test2 - can read ONCE with Reader's help, but the message is replaced and is usable again
var backup1 = original2;
using (var rd1 = new ReaderOnce(ref original2))
{
Console.WriteLine("is message replaced after opening Reader:" + (original2 != backup1));
Console.WriteLine("test1A:" + rd1.ReadBodyXml());
// Console.WriteLine("test1B:" + rd1.ReadBodyXml()); // fail: InvalidOperationException - it was already read
}
// test3 - can read MANY TIMES with ReaderMany's help
// also note we use 'original2' again, which was already used above, so in fact ReaderOnce really works as well
var backup2 = original2;
using (var rd1 = new ReaderMany(ref original2))
{
Console.WriteLine("is message replaced after opening Reader:" + (original2 != backup2));
Console.WriteLine("test2A:" + rd1.ReadBodyXml());
Console.WriteLine("test2B:" + rd1.ReadBodyXml()); // ok
}
Console.WriteLine("Press enter to exit");
Console.ReadLine();
}
}
}
// solution1
public class ReaderOnce : IDisposable
{
private Message localCopy;
public ReaderOnce(ref Message src)
{
// create a WCF MessageBuffer to assist in copying messages
// btw. I suppose you should set some sane limit instead of that below
using (var tempBuffer = src.CreateBufferedCopy(int.MaxValue))
{
src = tempBuffer.CreateMessage(); // FIRST copy for outer use
localCopy = tempBuffer.CreateMessage(); // SECOND copy for internal use in the Reader
}
}
public void Dispose() { Close(); }
public void Close()
{
localCopy.Close(); // but that does NOT affect FIRST copy sent to outer scope outside reader
Console.WriteLine("reader closed");
}
public string ReadBodyXml() // careful: that's again ONE TIME readable
{
return localCopy.GetReaderAtBodyContents().ReadOuterXml();
}
}
// solution2
public class ReaderMany : IDisposable
{
private MessageBuffer localBuffer;
public ReaderMany(ref Message src)
{
localBuffer = src.CreateBufferedCopy(int.MaxValue);
src = localBuffer.CreateMessage(); // FIRST copy for outer use
}
public void Dispose() { Close(); }
public void Close()
{
localBuffer.Close();
Console.WriteLine("reader closed");
}
public string ReadBodyXml() // this is readable multiple times
{
using (var tmp = localBuffer.CreateMessage())
return tmp.GetReaderAtBodyContents().ReadOuterXml();
}
}
// let's fake some Message type to have something to test the Reader on
public class TheMessage : Message
{
public override MessageHeaders Headers => _mh;
public override MessageProperties Properties => _mp;
public override MessageVersion Version => _mv;
private MessageHeaders _mh;
private MessageProperties _mp;
private MessageVersion _mv;
private string data1;
private string data2;
// btw. below: surprise! XmlDictionaryWriter is in "System.Runtime.Serialization", not in "System.Xml"
protected override void OnWriteBodyContents(XmlDictionaryWriter writer)
{
writer.WriteStartElement("foo");
writer.WriteAttributeString("data1", data1);
writer.WriteAttributeString("data2", data2);
writer.WriteEndElement();
}
public TheMessage(string data1, string data2)
{
// remember, this class is just an example, you will work on your own messages you already have
_mv = MessageVersion.Soap12;
_mh = new MessageHeaders(_mv);
_mp = new MessageProperties();
// below: yeah, that's super-naive and wrong, but that's an example
this.data1 = data1;
this.data2 = data2;
}
}

There is no language construct in c# that does what you are asking. As stated in comments, you could abuse IDisposable and the language and use a using block to achieve what you want.
But, I fail see what you are gaining, you are just punting the problem; now users will need to remember to use usinginstead of Close. The latter is simple and clean, the former uses a very known language construct to do something different to what it was thought for, something that will potentially be very confusing.

Get file information from System.Web.HttpInputStream

I have code:
public Upload.UploadResponse Post(Upload.UploadRequest request)
{
Stream str = request.RequestStream; // RequestStream is System.Web.HttpInputStream
byte[] result;
using (var streamReader = new MemoryStream())
{
str.CopyTo(streamReader);
result = streamReader.ToArray();
}
return new Upload.UploadResponse() { Successed = 1 };
}
Is there any way to get file name ( with extension) from MemoryStream or stream or System.Web.HttpInputStream (part of Upload.UploadRequest request) without saving the file? I need to recognize the file without knowing what is sent to me. I've tried to cast it to FileStream but it was null. Service framework that I am using is service stack ServiceStack
edit: Maybe I need to send file info with request?
p.s sorry for my poor English any corrections are welcome
EDIT:
this is UploadClass that I am using for code above
public class Upload
{
[Route("/upload")]
public class UploadRequest : IRequiresRequestStream
{
public System.IO.Stream RequestStream { set; get; }
}
public class UploadResponse
{
public int Successed { set; get; }
}
}

You cannot extract file name from stream.
You need to add FileName property to your request.

Writing unittest to create a file and then delete that file

I have this method I created :
public static bool DeleteFile(FileInfo fileInfo)
{
try
{
fileInfo.Delete();
return true;
}
catch (Exception exception)
{
LogManager.LogError(exception);
return false;
}
}
Now I wrote the following unittest:
[TestMethod]
public void DeleteFileSuccessFul()
{
string fileName = "c:\\Temp\\UnitTest3.txt";
FileInfo fileInfo = new FileInfo(fileName);
File.Create(Path.Combine(fileName));
bool success = FileActions.DeleteFile(fileInfo);
Assert.IsTrue(success);
}
This test fails because the file is in use by a different proces.
The test fails on het bool success = FileActions.DeleteFile(fileInfo); because the file is in use by a different process.
How can I change my test so it works ?

You have to call Dispose method on the FileStream object returned by the File.Create method to release the handle to that file:
[TestMethod]
public void DeleteFileSuccessFul()
{
string fileName = "c:\\Temp\\UnitTest3.txt";
FileInfo fileInfo = new FileInfo(fileName);
using (File.Create(Path.Combine(fileName)))
{
}
bool success = FileActions.DeleteFile(fileInfo);
Assert.IsTrue(success);
}
UPDATE: using block provides a convenient syntax that ensures the Dispose method of an IDisposable object is get called after leaving the scope of the block even if an exception occurs. The equivalent to the above code could be re-written with try-finally block:
[TestMethod]
public void DeleteFileSuccessFul()
{
string fileName = "c:\\Temp\\UnitTest3.txt";
FileInfo fileInfo = new FileInfo(fileName);
FileStream fileStream = null;
try
{
fileStream = File.Create(Path.Combine(fileName));
}
finally
{
if (fileStream != null)
fileStream.Dispose();
}
bool success = FileActions.DeleteFile(fileInfo);
Assert.IsTrue(success);
}