RDGen

A terminal program for generating reproducible random data for testing based on a provided seed.

Why?

For thash, I needed a way to generate reproducible random data for testing. A condition for this was that the seed will always reproduce the same data. So, I created RDGen.

Installation

You can install this with cargo.

cargo install rdgen

Currently it's only available on crates.io with cargo. If it gets popular enough, I'll happily upload it elsewhere.

How it works

This program simply takes the given seed, and recursively hashes it and creates an infinitely long string. The hashing algorithm chosen is blake2b, because it's secure and fast.

Usage

Run rdgen --help, to see all available options.

The seed is passed through stdin. The output of the data is written to stdout (in binary). You can process it by either piping it to a file, or some other program (see the examples below).

For platforms that don't have commands like cat to pass a file through stdin, you can use the -f command line argument to specify the file that contains the seed, instead of using stdin. If no -f is specified, stdin will be used.

Examples

• Say you want to generate 100 bytes of data, based on the seed "abc":

$ echo -n "abc" | rdgen -l100 | xxd -p -c 0
ba80a53f981c4d0d6a2797b69f12f6e94c212f14685ac4b74b12bb6fdbffa2d17d87c5392aab792dc252d5de4533cc9518d38aa8dbf1925ab92386edd400992366cb547665e462bbdd51d9b6ce1221116e9cfc6711c78d8798158349d12fa8ca513efb14

which will result in 100 bytes of binary data written out.

Notice that we use -n with echo to avoid adding a new line at the end.

Notice also that we also pipe the result to xxd -p -c 0, because otherwise the result will be printed to terminal using stdout. Since the result is binary, it will be nonsensical and unreadable.

• Though you can put that data into a binary file

$ echo -n "abc" | rdgen -l100 > random-data.bin

• If you want to pipe data written by hand, you can use xxd -r -p as well, then pipe it to rdgen

$ echo -n "deadbeef" | xxd -r -p | rdgen -l100 | xxd -p -c 0

this will decode deadbeef hex data into binary, then pipe it to rdgen as seed.

Happy testing!