Re: [PATCH 01/10] t: add tool to translate hash-related values

On Mon, Jun 04, 2018 at 11:52:20PM +0000, brian m. carlson wrote:

The word "translate" is very generic and is (at least in my mind) strongly associated with i18n/l10n, so the name test_translate() may be confusing for readers. Perhaps test_oid_lookup() or test_oid_get() or even just test_oid()?

This is a very expensive lookup since it invokes a heavyweight command (perl, in this case) for *every* OID it needs to retrieve from the file. Windows users, especially, will likely not be happy about this. See below for an alternative.

This is less flexible than I had expected, allowing for only SHA1 and NewHash. When you had written about OID lookup table functionality in email previously, my impression was that the tables would allow values for arbitrary hash algorithms. Such flexibility would allow people to experiment with hash algorithms without having to once again retrofit the test suite machinery.

Here's what I had envisioned when reading your emails about OID lookup table functionality:

--- >8 ---
test_detect_hash () {
    test_hash_algo=...
}
    
test_oid_cache () {
    while read tag rest
    do
        case $tag in \#*) continue ;; esac

        for x in $rest
        do
            k=${x%:*}
            v=${x#*:}
            if test "$k" = $test_hash_algo
            then
                eval "test_oid_$tag=$v"
                break
            fi
        done
    done
}

test_oid () {
    if test $# -gt 1
    then
        test_oid_cache <<-EOF
        $*
        EOF
    fi
    eval "echo \$test_oid_$1"
}
--- >8 ---

test_detect_hash() would detect the hash algorithm and record it instead of having to determine it each time an OID needs to be "translated". It probably would be called by test-lib.sh.

test_oid_cache() reads a table of OID's and caches them so that subsequent look-ups are fast. It would be called (possibly multiple times) by any script needing to "translate" OID's. Each line of the table has form "tag algo:value ...". Lines starting with '#' are comments (as in your implementation). Since it reads stdin, it works equally well reading OID tables from files and here-docs, which provides extra flexibility for test authors. For instance:

    test_oid_cache <translate/hash-info

or:

    test_oid_cache <<-\EOF
    rawsz sha1:20 NewHash:32
    hexsz sha1:40 NewHash:64
    EOF

test_oid() does the actual OID lookup/translation. It looks up a pre-cached value or, for convenience (as per your implementation), can choose between values specified at invocation time. For example, the simple case:

    $(test_oid hexsz)

And, when specifying values from which to choose based upon hash algorithm:

    $(test_oid bored sha1:deadbeef NewHash:feedface)

A nice property of how this implementation caches values is that you don't need test_oid() for really simple cases. You can just access the variable directly. For instance: $test_oid_hexsz

Another nice property of how caching is implemented is that someone testing a new hash algorithm doesn't have edit the existing tables to tack the value for the new algorithm onto the end of each line. It works equally well to place those values in a new file or new here-doc or simply append new lines to existing files or here-docs. For instance, someone testing algorithm "NewShiny" can just add those lines without having to modify existing lines:

    test_oid_cache <<-\EOF
    rawsz sha1:20 NewHash:32
    hexsz sha1:40 NewHash:64
    # testing NewShiny algorithm
    rawsz: NewShiny:42
    hexsz: NewShiny:84
    EOF