I've got a web app where I'm trying to validate that an uploaded file is .PDF. I can't use ContentType because if the user renames the file to have a ".PDF" extension, the browser reports the MIME type to be ".PDF" even if it isn't.
I understand that one way to "validate" that a file is a PDF file is to look at the first four bytes, which should always be "%PDF". How do I open and read the first four bytes of a file in VB.NET to see whether or not they are equal to "%PDF"?
After getting the file name I create a new filestream and load all the bytes from the FileStream into a byte array, now I need to get certain bytes and store them in fields like the second 4 bytes are the time the file was created. When storing these in the variables should I store them as bytes or as string/integers/etc.
Or have I done it completely wrong?
EDIT:Should I be doing this way instead of a filestream?
So i have one file, that has one header that tells me if the bytes are in little or big endian format.The content of the file after the file is something like this, one byte that indicates a new "section", then several bytes until the other "section". This bytes each one represent the number of the bytes that i need to read in the second section.
I'm trying to read 5 bytes from a file and then do something according to what has been read. This is my code (I'll explain in a bit what's wrong):[code...]
It reads the 5 bytes I added to the encrypted file, but I want the CryptoStream to start from the sixth value and then copy the original bytes into the decrypted file, but it gives me an error:
Padding is invalid and cannot be removed.That's why I'm trying to make it read from the sixth value and then continue copying normally, but I'm stuck.
I'm working on a project involving reading RFID tags, I've written the code and it reads the tags ok by using the recieved data handler and displaying the result in a listbox, the only problem is that the data displayed has a couple of unreadable characters at the start (I'm using ReadLine() command.)If I read the buffer byte by byte the data is all readable.How can I read and display the whole 16 Bytes in one go??
I am reading data from a socket (as bytes) and storing this data in a string. Then later i need to access specific bytes within the string and do some math with them. However the bytes that I read back from the string are not what I am expecting.
I want it to do is that you input a string, then you select an algorithm (Theres only going to be one RijnDael) then you input a key, then the Initialization Vector comes from "txtIV.text" then you select the key bytes and the block bytes from the numeric up/down, then you either encrypt or decrypt.
Ok i am having some issues designing a base-class to handle generics.Caveat is i need to restrict the type put in as a Numeric type, specifically Int16, Int32, or Int64 (Short or Long).I know you can do Of T as {Structure} but i dont want to select the key bytes and the block bytes from the numeric up/down.
I keep getting a ProtocolViolationException "Bytes to be written to the stream exceed the Content-Length bytes size specified." on the following code.I've tried setting Content-Length numerous ways with no success.
Dim url = "https://domain.com" Dim req As WebRequest = WebRequest.Create(url) req.Method = "POST" req.ContentType = "application/xml"
Does it read the entire message string sent by the client? I have a line to write to the stream later in the code and that does not seem to be sending anything back to the client, although the code around is excuting.
i = stream.Read(bytes, 0, bytes.Length) While (i <> 0) Try ' Translate data bytes to a ASCII string.
I need to be able to read bytes in Little Endian and in Big Endian as well. Is this possible to do in VB? I know that VB reads in Little Endian by default, but I also need to read in Big Endian.
I have tried this:
Dim i1 as Long Dim fs As New IO.FileStream(filename, IO.FileMode.Open) Dim br As New IO.BinaryReader(fs, System.Text.Encoding.BigEndianUnicode)
[code]....
This return the value "1616183296" when it is supposed to return "21856". I've opened the file up in Hex Workshop, and looking at it in Little Endian, I do get the value of "1616183296" and in Big Endian, I get the value of "21856".
I've been trying for a long time to create a sorted table of values in a particularly specific way, and I seem to be running into a wall in .NET's file operations. The premise is this - I'm creating a table of values which are being stored as [1 Byte][2 Bytes][3 Bytes]. The location within the file is a value that relates to these three stored values, and so I'm attempting to seek to a specific position in the file, write the 6 bytes into that position, and repeat. There are literally billions of these values, and the total file size is over 100 GB.
Now, I've tried multiple methods to do this, but every single time, it decides it needs to rewrite the ENTIRE FILE every time any change is made. This results in every one of these billions of iterations taking a good 15 minutes, making the task literally impossible. I'm using .NET 4, and I've attempted to use Text, Binary, and Random Access to get it not to rewrite the entire file every edit, but it simply will not obey.
So my question boils down to this: How do I edit specific bytes in a file without writing more than just those bytes? The entire file has been pre-created to the precise size required, and no bytes will be added or deleted in the process. I simply need to overwrite the bytes that already exist.
Probably missing something silly here, Her eis what my display looks like Sending image...(401303) I would prefer it displays as Sending image...(391 kb)
I've been using the following code to download a text file from the web. It only downloads the first 100,000 bytes of the file which is no good if the file is big. The size of the file I'm downloading can vary from day to day, so I need to be able to download a text file of any size.
Dim wr As HttpWebRequest = CType(WebRequest.Create("http://sooty.postalgroup.co.uk/tempmac/nat-import.txt"), HttpWebRequest) Dim ws As HttpWebResponse = CType(wr.GetResponse(), HttpWebResponse)
I have an old fashion Database with several random access files and I need to import the data to a new Sql Server dababase the data. There are tables with 6 Bytes floating numbers fields and we have no Number data type with that length in VB. I tried and tried and... and can't find. I found this code in the ERP folder, is AlphaBasic. It use an envoirement namend A-shell from Microsabio .
I am using the following code to write and empty (dummy) file to take up the remaining space on a device.RemSpace is a Public Variable declared as Long I have a function that gets the remaining space on the device and stores in the RemSpace variable (in bytes). I have tested with a msgbox to display the result of RemSpace, and it comes back correct (not 0). However, when the following code attempts to create the dummy file, the file is properly created but is only 0 bytes. What am I missing here?
I am not so good with buffers and arrays and I dont know how to continue from here:
[Code]...
My intention is to open an image file as bytes, Convert the bytes to a string, send bytes to server and server stores bytes in a database. Then I need to reverse the process and be able to convert the bytes to an image.
Well basicly i have a file from which i extract bytes and save them to a text file using this code :
Private Sub browse_Click(sender As System.Object, e As System.EventArgs) Handles browse.Click Dim oFile As System.IO.FileInfo
[Code]....
Everything works well, but I don't know how to recover this file using the extracted data from bytes ! I Know for example the first byte of that file is 39 But i just can't do :
dim mybytes() as byte mybytes(1)=39
You see what im talking about? I Want to recover those bytes from the same file I saved
I have a BIN file which I need to write a single byte to at the end and maintain the previous data. Here is an example.Viewed with a hex editor the file may have F0 FD 48 D3 C0 as the data. I want to be able to add to the end of it FF so that when I view it with the hex editor it is displayed as F0 FD 48 D3 C0 FF. I know how to open files for putting data but how can I take those characters and write them to the end of a file. I tried using the put function ( Put #FileNo, , MyStr) where MyStr = the characters in the textbox but it doesn't seem to work. Here is some code.
read each chunk of 256 bytes from a 32k file and then add the total value of each byte's decimal value. This will be some huge number which then needs to be converted to hex (Hex(number)and then truncate down to the LSB (I.E. 7F{4B}) and then convert the truncated byte (4B) back to a decimal (Num = Val("&H" & Num).
I am writing a CSV File from a Database. I am stuck in writing lines which become greater then 1024 bytes collectively. It write line terminator after 1024 bytes and thus adds the remaining string to new line which obviously results what I don't want. Is there any way so that I increase the line length limit to some reasonable amount of bytes?
Is there anyway to convert an image file bytes array into an array of the real RGB values of that image?
I don't really want to use GDI+ or the System.Drawing library, but simply apply a certain calculation/processing to every byte of the image file and get another array that contains the RGB values of every pixel in that image. I know it could be done as I know how to do it in a different programming language (Python) but not in Visual Basic.
