rshasum consumes a lot of RAM and crashes on large files

[shlomif]

Hi!

When running your program like this, go's RAM consumption balloons out of
control:

mkdir -p temp-zero
cat /dev/zero | head -c 4000000000 > temp-zero/zero.bin
go run ~/Download/unpack/file/rshasum/sum.go -a 512 temp-zero

Seems like you are reading the whole files into RAM . Note that sha checksums
can be calculated incrementally by using fixed size segments. This is the
approach taken by this quick bash script I wrote:

find . -type f -follow | (LC_ALL=C sort) | xargs -d '\n' sha256sum | tee >(a="`sha256sum -`"; sleep 0.05; echo "$a")

Please fix it.