I want to convert an object of System.Byte[] which is actually a file, retrieved from the database, back to file and store the file in a folder. How can we convert it using ASP.Net with C# ?
It's right way:
byte[] b = YourByteArrayFromDb;
File.WriteAllBytes(MyFilePath, b);
Do something like:
byte[] b = YourByteArrayFromDb;
string s = System.Text.ASCIIEncoding.ASCII.GetString(b);
File.WriteAllText(MyFilePath, s);
Given that this is an ASP.Net application, you may run into permission issues writing to the file system. Place your code in a try/catch block and provide a reasonable error message or log entry if you can't write the file.
If your original file was not encoded in ASCII, you will need to adjust accordingly.
Related
My question is a bit similar to this one but it is with ASP.NET and my requirements are slightly different: Android append files to a zip file without having to re-write the entire zip file?
I need to insert data to a zip-file downloaded by users (not much 1KB of data at most, this is data for Adword off-line conversion actually). The zip-file is downloaded through an ASP.NET website. Because the zip file is already large enough (10's of MB) to avoid overloading the server, I need to insert these data without re-compressing everything. I can think of two ways to do this.
Way A: Find a zip-technology that lets embed a particular file in the ZIP file, this particular file being embedded uncompressed. Assuming there is no checksum, it'd be then easy to just override the bits of this un-compressed file with my specific data, in the zip file itself. If possible, this would have to be supported by all unzip tools (Windows integrated zip, winrar, 7zip...).
Way B: Append an extra file to the original ZIP file without having to recompress it! This extra file would have to be stored in an embedded folder in the ZIP file.
I looked a bit at SevenZipSharp which has an enumeration SevenZip.CompressionMode with values Create and Append that leads me to think that Way B could be implemented. DotNetZip seems also to work pretty well with Stream according to FAQ.
But if Way A could be possible I'd prefer it much since no extra zip library would be needed on the server side!
Ok, thanks to DotNetZip I am able to do what I want in a very resource efficient way:
using System.IO;
using Ionic.Zip;
class Program {
static void Main(string[] args) {
byte[] buffer;
using (var memoryStream = new MemoryStream()) {
using (var zip = new ZipFile(#"C:\temp\MylargeZipFile.zip")) {
// The file on which to override content in MylargeZipFile.zip
// has the path "Path\FileToUpdate.txt"
zip.UpdateEntry(#"Path\FileToUpdate.txt", #"Hello My New Content");
zip.Save(memoryStream);
}
buffer = memoryStream.ToArray();
}
// Here the buffer will be sent to httpResponse
// httpResponse.Clear();
// httpResponse.AddHeader("Content-Disposition", "attachment; filename=MylargeZipFile.zip");
// httpResponse.ContentType = "application/octe-t-stream";
// httpResponse.BinaryWrite(buffer);
// httpResponse.BufferOutput = true;
// Just to check it worked!
File.WriteAllBytes(#"C:\temp\Result.zip", buffer);
}
}
Long time lurker first time poster. Working with .Net / Linq for just a few years so I'm sure I'm missing something here. After countless hours of research I need help.
I based my code on a suggestion from https:http://damieng.com/blog/2010/01/11/linq-to-sql-tips-and-tricks-3
The following code currently saves a chosen file (pdf, doc, png, etc) which is stored in an sql database to the C:\temp. Works great. I want to take it one step further. Instead of saving it automatically to the c:\temp can I have the browser prompt so they can save it to their desired location.
{
var getFile = new myDataClass();
//retrieve attachment id from selected row
int attachmentId = Convert.ToInt32((this.gvAttachments.SelectedRow.Cells[1].Text));
//retrieve attachment information from dataclass (sql attachment table)
var results = from file in getFile.AttachmentsContents
where file.Attachment_Id == attachmentId
select file;
string writePath = #"c:\temp";
var myFile = results.First();
File.WriteAllBytes(Path.Combine(writePath, myFile.attach_Name), myFile.attach_Data.ToArray());
}
So instead of using File.WriteAllBytes can I instead take the data returned from my linq Query (myFile) and pass it into something that would prompt for the user to save the file instead?). Can this returned object be used with response.transmitfile? Thanks so much.
Just use the BinaryWrite(myFile.attach_Data.ToArray()) method to send the data since it is already in memory.
But first set headers appropriately, for example:
"Content-Disposition", "attachment; filename="+myFile.attach_Name
"Content-Type", "application/vnd.openxmlformats-officedocument.wordprocessingml.document"
Content-type guides the receiving system on how it should handle the file. Here are more MS Office content types. If they are known at the point the data is stored, the content-type should be stored, too.
Also, since the file content is the only data you want in the response, call Clear before and End after BinaryWrite.
I need a snippet to check file for validity (I'm allowing users to upload xml files). So I need to check whether uploaded file is XML.
The best I can think of is just check if extension is ".xml". What if its replaced?
You can try loading it like this and catch the exception:
XDocument xdoc = XDocument.Load("data.xml"));
Presumably, if they're uploading XML, then you're going to use it for something afterwards. In this case you should validate the XML against a Schema (XSD etc) so that you know you aren't going to hit unexpected values/layouts etc.
In Urlmon.dll, there's a function called FindMimeFromData.
From the documentation
MIME type detection, or "data
sniffing," refers to the process of
determining an appropriate MIME type
from binary data. The final result
depends on a combination of
server-supplied MIME type headers,
file extension, and/or the data
itself. Usually, only the first 256
bytes of data are significant.
So, read the first (up to) 256 bytes from the file and pass it to FindMimeFromData.
If you must validate the xml (assuming you want to validate the entire thing) you can use the XmlDocument class and catch an exception if it's not XML.
We have encountered this difference in file creation while using a HttpHandler Versus a Code Behind Aspx page.
We are reading a saved jpg/png picture as byte array from a 'Image' field in sql server database and create a physical file in the server.
Both the Aspx Page and Httphandler use the same code pasted below.
//Begin
int docID = Convert.ToInt32(Request.QueryString["DocID"]);
var docRow = documentDB.GetDocument(docID);
// Retrieve the physical directory path for the Uploads subdirectory
string destDir = Server.MapPath("../../Uploads").ToString() + "\\";
string strFileName = destDir + DateTime.Now.ToFileTime() + "_" + docRow.DocName.ToString();
FileStream fs = new FileStream(strFileName, FileMode.CreateNew, FileAccess.Write);
fs.Write(docRow.DocData, 0, docRow.DocData.Length);
fs.Flush();
fs.Close();
// End
After the file is created, it is viewable as a jpg/png Image only in Aspx Code Behind. While in case of HttpHandler it is not a valid Image.
Any ideas for this behavior/missing link/resolution steps will be helpful.
Thank you.
Finally isolating different steps the problem was identified to be the data being stored into Database Table.
The way to eliminate this issue was during upload of file, Create a physical file on the server local system. Read this file into a byte array and store into the Database Table. (Could be Encoding Issue)
I am creating an xml file. I need to check first if the file exists or not. If the file does not exist, create it and add the data cmg from a .cs file.
If the file exists, don't create the file just add the data cmg from a .cs file.
My code looks like this:
string filename="c:\\employee.xml";
XmlTextWriter tw=new XmlTextWriter(filename,null);//null represents
the Encoding Type//
tw.Formatting=Formatting.Indented; //for xml tags to be indented//
tw.WriteStartDocument(); //Indicates the starting of document (Required)//
tw.WriteStartElement("Employees");
tw.WriteStartElement("Employee","Genius");
tw.WriteStartElement("EmpID","1");
tw.WriteAttributeString("Name","krishnan");
tw.WriteElementString("Designation","Software Developer");
tw.WriteElementString("FullName","krishnan Lakshmipuram Narayanan");
tw.WriteEndElement();
tw.WriteEndElement();
tw.WriteEndDocument();
tw.Flush();
tw.Close();
so next time we add data to file we need to check if the file exits and add data to xml file
and as we have made empID as a primary key, if user tries to make duplicate entry we need to avoid
Is this possible to do?
if (!File.Exists(filename))
{
// create your file
}
or
if (File.Exists(filename))
{
File.Delete(filename);
}
// then create your file
File class is in System.IO namespace (add using System.IO; to your file)
You can't append records to an XML file, you have to read the file and then rewrite it.
So, just check if the file exists, and read the records from it. Then write the file including all previous records and the new record.
Have a look at the File.Exists method here
Testing for existance of a file before attempting to create it inherently is subject to a "things change after check" race condition. Who can guarantee you that your application isn't preempted and put to sleep for a moment after you checked, someone else creates/deletes that file, your app gets to run again and does exactly the opposite of what you intended ?
Windows (as well as all UN*X variants) supports file open/create modes that allow to perform that create-if-nonexistant/open-if-existant operation as a single call.
As far as .NET goes, this means for your task (create an XML file) you'd first create a System.IO.FileStream with the appropriate modes, see http://msdn.microsoft.com/en-us/library/system.io.filemode.aspx and then pass that stream to the XmlWriter constructor. That's safer than simply performing an "exists" check and hoping for the best.