Here's my code for StreamReader in Xamarin Forms What I want is simply read a file and convert it into byte array but when I try this code I simply get this error that is Cannot convert from string to System.IO.Stream
using (var sr = new StreamReader(filename))
{
buffer = new byte[(int)sr.BaseStream.Length];
await sr.ReadAsync(buffer, 0, (int)sr.BaseStream.Length);
}
StreamReader operates upon an existing Stream. But you still need to open or create that underlying stream first by using the device operating system. The process of doing this is slightly different on each platform, and so you can't put that part of your code into the PCL project.
See the section of the documentation titled "Saving and Loading Files" here: https://developer.xamarin.com/guides/xamarin-forms/working-with/files/
One way to do it is by using xamarin dependency service and use FileStream to read the bytes
public byte[] ImageToBinary(string imagePath)
{
FileStream fileStream = new FileStream(imagePath, FileMode.Open, FileAccess.Read);
byte[] buffer = new byte[fileStream.Length];
fileStream.Read(buffer, 0, (int)fileStream.Length);
fileStream.Close();
return buffer;
}
Related
I want to clone the IRandomAccessStream. I tried the CloneStream() to clone the stream but it not supported. Is there any way to clone the random access stream.
Thanks,
Santhiya A
You can use the CopyTo method
https://learn.microsoft.com/en-us/dotnet/api/system.io.stream.copyto?view=netframework-4.7.2
You can try converting it to a byte[] and then clone the byte[] in to new IRandomAccessStream.
public async Task<IRandomAccessStream> CloneIRandomeAccessStream(IRandomAccessStream randomAccessStream)
{
var reader = new DataReader(randomAccessStream.GetInputStreamAt(0));
byte[] bytes = new byte[randomAccessStream.Size];
await reader.LoadAsync((uint)randomAccessStream.Size);
reader.ReadBytes(bytes);
MemoryStream stream = new MemoryStream(bytes.ToArray());
IRandomAccessStream ClonerandomAccessStream = stream.AsRandomAccessStream();
return ClonerandomAccessStream;
}
I am seeing the "Padding is invalid and cannot be removed" error when I call the method below to decrypt the string from a windows application. String was encrypted from an asp.net application. Both application references the same assembly. I am able encrypt and decrypt with out any problem from the asp.net application. Here is the main code where I do the encryption and decryption.
private static byte[] EncryptHelper(byte[] arrData, string Password, bool Encrypt)
{
//Create the SymetricAlgorithem object
SymmetricAlgorithm myAlg = new RijndaelManaged();
//define a salt value to derive the key.
byte[] salt = System.Text.Encoding.ASCII.GetBytes("hjkhj877ffasah");
//Instantiate Rfc2898DeriveBytes with the password and salt.
Rfc2898DeriveBytes key = new Rfc2898DeriveBytes(Password, salt);
myAlg.Key = key.GetBytes(myAlg.KeySize / 8);
myAlg.IV = key.GetBytes(myAlg.BlockSize / 8);
myAlg.Padding = PaddingMode.PKCS7;
//Create the ICryptoTransform Object
ICryptoTransform encrytptor = Encrypt ? myAlg.CreateEncryptor() : myAlg.CreateDecryptor();
//Create Memorystream to write the encrypted data
using (MemoryStream aStream = new MemoryStream())
{
//Create the CryptoStream Ojbect using the aStream object
using (CryptoStream encryptStream = new CryptoStream(aStream, encrytptor, CryptoStreamMode.Write))
{
//Write the contents to crypto stream
encryptStream.Write(arrData, 0, arrData.Length);
//Flush the cryptostream
encryptStream.FlushFinalBlock();
//Reposition the memorystream to write the contents to an array.
aStream.Position = 0;
}
aStream.Flush();
//Convert to an array and return
return aStream.ToArray();
}
}
This is the method I use to convert the plain text from/to byte array
private static byte[] GetBytes(string str)
{
byte[] bytes = new byte[str.Length * sizeof(char)];
System.Buffer.BlockCopy(str.ToCharArray(), 0, bytes, 0, bytes.Length);
return bytes;
}
private static string GetString(byte[] bytes)
{
char[] chars = new char[bytes.Length / sizeof(char)];
System.Buffer.BlockCopy(bytes, 0, chars, 0, bytes.Length);
return new string(chars);
}
For persist the cipher text to database I use Convert.ToBase64String() and Convert.FromBase64String. Is the problem is with the way I use Rfc2898DeriveBytes class?
Well I think it's important to mention that from a security perspective, you are going to have the same IV for every message with the same password, and a predictable IV is a really big no no.
After that point I kinda don't want to look at it more to see what's going wrong, there are a lot of really bad cut and paste C# encryption on stackoverflow, and they just sit there with no mechanism for update, no one looking at them again except for people finding them to cut and paste again.
Look at Modern Examples of Symmetric Authenticated Encryption of a string. c#.
I try to keep it up to date and reviewed.
I have the following method that writes a stream in a HttpResponse object.
public HttpResponse ShowPDF(Stream stream)
{
MemoryStream memoryStream = (MemoryStream) stream;
httpResponse.Clear();
httpResponse.Buffer = true;
httpResponse.ContentType = "application/pdf";
httpResponse.BinaryWrite(memoryStream.ToArray());
httpResponse.End();
return httpResponse;
}
In order to test it, I need to recover the processed stream.
Is there someway to read the stream from the httpResponse object?
I have two ideas... one to mock the HttpResponse, and the other is to simulate a web server.
1. Mocking HttpResponse
I wrote this before I knew which mocking framework you used. Here's how you could test your method using TypeMock.
This assumes that you pass your httpResponse variable to the method, changing the method as follows:
public void ShowPDF(Stream stream, HttpResponse httpResponse)
Of course you would change this to passing it to a property on your Page object instead, if it is a member of your Page class.
And here's an example of how you could test using a fake HttpResponse:
internal void TestPDF()
{
FileStream fileStream = new FileStream("C:\\deleteme\\The Mischievous Nerd's Guide to World Domination.pdf", FileMode.Open);
MemoryStream memoryStream = new MemoryStream();
try
{
memoryStream.SetLength(fileStream.Length);
fileStream.Read(memoryStream.GetBuffer(), 0, (int)fileStream.Length);
memoryStream.Flush();
fileStream.Close();
byte[] buffer = null;
var fakeHttpResponse = Isolate.Fake.Instance<HttpResponse>(Members.ReturnRecursiveFakes);
Isolate.WhenCalled(() => fakeHttpResponse.BinaryWrite(null)).DoInstead((context) => { buffer = (byte[])context.Parameters[0]; });
ShowPDF(memoryStream, fakeHttpResponse);
if (buffer == null)
throw new Exception("It didn't write!");
}
finally
{
memoryStream.Close();
}
}
2. Simulate a Web Server
Perhaps you can do this by simulating a web server. It might sound crazy, but it doesn't look like it's that much code. Here are a couple of links about running Web Forms outside of IIS.
Can I run a ASPX and grep the result without making HTTP request?
http://msdn.microsoft.com/en-us/magazine/cc163879.aspx
In the HttpApplication.BeginRequest event, how can I read the entire raw request body? When I try to read it the InputStream is of 0 length, leading me to believe it was probably already read by ASP.NET.
I've tried to read the InputStream like this:
using (StreamReader reader = new StreamReader(context.Request.InputStream))
{
string text = reader.ReadToEnd();
}
But all I get is an empty string. I've reset the position back to 0, but of course once the stream is read it's gone for good, so that didn't work. And finally, checking the length of the stream returns 0.
Edit: This is for POST requests.
The request object is not populated in the BeginRequest event. You need to access this object later in the event life cycle, for example Init, Load, or PreRender. Also, you might want to copy the input stream to a memory stream, so you can use seek:
protected void Page_Load(object sender, EventArgs e)
{
MemoryStream memstream = new MemoryStream();
Request.InputStream.CopyTo(memstream);
memstream.Position = 0;
using (StreamReader reader = new StreamReader(memstream))
{
string text = reader.ReadToEnd();
}
}
Pål's answer is correct, but it can be done much shorter as well:
string req_txt;
using (StreamReader reader = new StreamReader(HttpContext.Current.Request.InputStream))
{
req_txt = reader.ReadToEnd();
}
This is with .NET 4.6.
In ASP.NET Core 2:
using (var reader = new StreamReader(HttpContext.Request.Body)) {
var body = reader.ReadToEnd();
}
I had a similar requirement to get the raw content and struck the same issue. I found that calling Seek(0, SeekOrigin.Begin) solved the problem.
This is not a particularly good approach as it makes assumptions about how the underlying infrastructure operates, but it seems to work.
It is important to reset position of InputStream.
var memstream = new MemoryStream();
Request.InputStream.CopyTo(memstream);
Request.InputStream.Position = 0;
using (StreamReader reader = new StreamReader(memstream)) {
var text = reader.ReadToEnd();
Debug.WriteLine(text);
}
Here's what I ended up doing:
//Save the request content. (Unfortunately it can't be written to a stream directly.)
context.Request.SaveAs(filePath, false);
I am simply storing uploaded file into a binary field in SQL Server but I also need to allow users to download it with Asp.NET. How can I do that ?
Thanks in advance.
Here's a Microsoft Knowledge Base article on this.
How to retrieve the file from your database depends on the data access technology you use; I will just assume that you have some Byte array data containing the file (e.g. by filling a DataSet and accessing the field) and some string filename.
Response.Clear()
Response.ContentType = "application/octet-stream"
Response.AddHeader("Content-Disposition", "attachment;filename=""" & filename & """")
Response.BinaryWrite(data)
Response.End()
Put the above code in some download.aspx and link to this file. You probably want to pass some query string information to your download.aspx, so that your code knows which file to get from the database.
Read the data into a filestream object with the appropriate extension tacked on to it, and have the user download the resulting file.
You'll want to use the System.IO BinaryWriter object on the filestream to create the file...something like this:
FileStream fs = new FileStream("thisfile.bin", FileMode.Create);
binWriter= new BinaryWriter(fs);
binWriter.Write(varHoldingSqlRetrievedBinaryData);
Add a Generic Handler (.ashx) page to your web site. The ashx code body below demonstrates how to read an arbitrary stream (in this case a PNG file from disk) and write it out in the response:
using System;
using System.Web;
using System.IO;
namespace ASHXTest
{
public class GetLetter : IHttpHandler
{
public void ProcessRequest(HttpContext context)
{
// Get letter parameter from query string.
string fileName = context.Request.MapPath(string.Format("{0}.png",
context.Request.QueryString["letter"]));
// Load file from disk/database/ether.
FileStream stream = new FileStream(fileName, FileMode.Open,
FileAccess.Read);
byte[] buffer = new byte[stream.Length];
stream.Read(buffer, 0, buffer.Length);
stream.Close();
// Write response headers and content.
context.Response.ContentType = "image/png";
context.Response.OutputStream.Write(buffer, 0, buffer.Length);
}
public bool IsReusable
{
get
{
return false;
}
}
}
}
If desired, you can also set the Content-Disposition header as demonstrated in Heinzi's answer:
context.Response.AddHeader("Content-Disposition",
"attachment;filename=\"letter.png\"");