Binary data exercise: how to tell if a file is a jpeg?

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Binary data exercise: how to tell if a file is a jpeg? // today I thought we would look at binary data, in the form of JPG images, and specifically see if we can write a program that will test whether or not a file is JPEG. We're looking at this in both C and Ruby, so you can see some of the pitfalls that you can run into with higher-level languages.

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Welcome! I post videos that help you learn to program and become a more confident software developer. I cover beginner-to-advanced systems topics ranging from network programming, threads, processes, operating systems, embedded systems and others. My goal is to help you get under-the-hood and better understand how computers work and how you can use them to become stronger students and more capable professional developers.

About me: I'm a computer scientist, electrical engineer, researcher, and teacher. I specialize in embedded systems, mobile computing, sensor networks, and the Internet of Things. I teach systems and networking courses at Clemson University, where I also lead the PERSIST research lab.

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[litlkaiser]

The read method in ruby has an option for encoding, e.g. f.read(3, encoding="UTF-8")

[suncrafterspielt]

Lets have a deep dive into the meta data

[NonTwinBrothers]

Definitely would be interested if more file format videos are to come :)

[zrodger]

"Strings are strings; bytes are bytes." That's the way it should always be! Good video.

[bolter]

Thank you for the example! Really a good intro to magic bytes 🙂 Maybe another nice video would be a simple jfif/exif low-level parser - just the big stuff - display the block type and size, could be useful for integrity check 🙂 most out-of-the-box libraries “fix” minor errors or ignore erroneous information when possible.

[valsk]

I love your vids... they helped me understand pointers :)

[unperrier]

Python3 doesn't have this problem: as you can read directly binary and get "bytes" objects.

[pseudopseudo]

a video on reading/writing bitmap data would be cool :)

[donaldmickunas]

Interesting. I’m taking a python course currently. This will make an interesting exercise in python. Thanks! 😀

[reverse_shell]

Yes for metadata and more file disassembly please!

[rexjuggler]

❤ This is one of my favorites! A real world example. Unix/Linux has "magic" built in, and I've edited /etc/magic by hand to add file types, but I do data migrations, so this indepth how-to is very helpful for building custom tools myself regardless of platform. It maybe a bit off the channel topic, but it might be useful for you to do a video on encoding - ASCII, UTF, ISO, EBCDIC - and maybe even add byte transmission like 7bit even parity, 8bit no parity...stuff like that. Working at the atomic level of data is very helpful to develop a better understanding of computers in general.

[samuelmartin]

I would love more videos on this topic!

[robertstrickland]

I would love to see some videos on binary file manipulation, especially something like writing your own encryption program.

[DelgardAlven]

feeling like home when somebody types things in C. Things are exactly what they are in 99%, and 1% stays just for rare machines’ unique memory conventions, and nothing else.

[andreisoceanu]

I love this way of questioning everything. Next: How to tell if a JPEG is a file.

[coolbrotherf]

That's pretty cool. I've never tried to do this before.

[minhajsixbyte]

basically an oddly specific version of "file" command/program

[gerdsfargen]

Could you check if it is not a real jpg but may have some hidden data within the file?

[raul_ribeiro_bonifacio]

Just found out about this channel. Nice content!

[eddaly]

Great video as usual, What is the proper way to exit a or with "return EXIT_FAILURE"...or use EXIT_SUCCESS...not sure when to use "return" or "exit" to end the program.