Where to find file information in a file?

Question

I plan to send and receive file with a microcontroller. I wrote up a simple protocol for both sender and receiver, but I have some trouble reconstructing the file back. I send the data in a stream of raw binary. However, I have not found the location of fileinfo (name, ext, size, etc.) in the file itself. Where is the fileinfo stored in the file? How does the OS know all these information if it isn't store in the file? (for eg name, extension, size, etc.)

Trivial question: Should I attach this file information with the protocol header? or should I just append it onto the file binary data?

Answer 1

You need to attach that information to your binary data yourself. If you have a binary stream, I suggest (it's easiest) you provide a fixed size header that contains all the file meta information. Then you append the file's content.

Why fixed size? Well, otherwise the receiver doesn't know where the file's content starts. You could also provide the header size in the first X bytes of the stream and then have a variable sized header. As you like it, but I prefer the fixed size solution.

Example for fixed size header:

<255 bytes file name><8 bytes file size><Content...>

Example for dynamically sized header:

<4 bytes length of file name><x bytes file name><8 bytes file size><Content...>

Let me stress that it is very important that you also transmit the size of the content in bytes, so that the receiver knows how many bytes to read! Packets may be fragmented, you know?

Answer 2

How does your self-made "protocol" work?

It is quite uncommon for files to store their own size, it is a responsibility of the underlying file system to keep track of that (name including extension, size, permissions, modification time, ...).

You can put the size information in the header, or if you are sure that a certain sequence of bytes is never sent as payload, you can use this as a termination sequence to tell the receiver to stop receiving.