nomsu/lib/file_hash.nom

#!/usr/bin/env nomsu -V6.14
#
    This file defines some actions for hashing files and looking up files by hash.
    
use "lib/os"
use "lib/base64"

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lua> "local \$use_sha1, \$hashlib = pcall(require, 'openssl.digest')"
test:
    assume (hash "hello world") == (hash "hello world")
    if ((hash "hello world") == (hash "goodbye")):
        fail ("
            Hash collision:
                (hash "hello world") = \(hash "hello world")
                (hash "goodbye") = \(hash "goodbye")
        ")
    
    assume
        (
            hash ("
                This is a really long string meant to stress test the hashing function and
                ensure that it's not overflowing with long inputs.
            ")
        ) != "inf"
    
    if ((hash "\000") == (hash "\000\000\000\000\000")):
        fail "Incorrect hashing of null strings"
    
    if $use_sha1:
        assume ((hash "hello world") == "Kq5sNclPz7QV2+lfQIuc6R7oRu0=")

if $use_sha1:
    externally (hash $) means:
        $hash = (=lua "\$hashlib.new('sha1'):final(\$)")
        return (base64 $hash)
..else:
    # TODO: remove warning?
    say ("
        \027[31;1mWARNING: OpenSSL module not found. Defaulting to a non-cryptographically secure \
        ..hash function.\027[0m
    ")
    
    externally (hash $) means:
        $bytes = ($, bytes)
        $hash = ($bytes.1 << 7)
        for $i in 2 to (size of $bytes):
            $hash = ((1000003 * $hash) ~ $bytes.$i)
        $hash = ($hash ~ (size of $bytes))
        return "\$hash"

externally (file with hash $hash) means:
    for $filename in (files for "."):
        $contents = (read file $filename)
        $file_hash = (hash $contents)
        if ($file_hash == $hash):
            return $filename

(hash of file $filename) parses as (hash (read file $filename))