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

["brian m. carlson" <sandals@crustytoothpaste.net>]

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On Mon, Jun 11, 2018 at 03:47:43AM -0400, Eric Sunshine wrote:
> On Mon, Jun 04, 2018 at 11:52:20PM +0000, brian m. carlson wrote:
> > Add a test function helper, test_translate, that will produce its first
> > argument if the hash in use is SHA-1 and the second if its argument is
> > NewHash.  Implement a mode that can read entries from a file as well for
> > reusability across tests.
> 
> 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()?

test_oid would be fine.  One note is that this doesn't always produce
OIDs; sometimes it will produce other values, but as long as you don't
think that's too confusing, I'm fine with it.

> 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.

I agree perl would be expensive if it were invoked frequently, but
excepting SHA1-prerequisite tests, this function is invoked 32 times in
the entire testsuite.

One of the reasons I chose perl was because we have a variety of cases
where we'll need spaces in values, and those tend to be complex in
shell.

> 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.

I wasn't thinking of that as a goal, but that would be a nice
improvement.

> 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"
> }

Using shell variables like this does have the downside that we're
restricted to only characters allowed in shell variables.  That was
something I was trying to avoid, but it certainly isn't fatal.

> 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.

We'll probably have to deal with multiple hashes in the future,
including for input and output, but this could probably be coerced to
handle that case.

> And, when specifying values from which to choose based upon hash
> algorithm:
> 
>     $(test_oid bored sha1:deadbeef NewHash:feedface)

This syntax won't exactly be usable, because we have to deal with spaces
in values.  It shouldn't be too much of a problem to just use
test_oid_cache at the top of the file, though.

> 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

Because we're going to need multiple hash support in the future, for
input, output, and on-disk, I feel like this is not a good direction for
us to go in the testsuite.  Internally, those variable names are likely
to change.

> 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:

That would be convenient.

I like a lot of things about your implementation.  This has been helpful
feedback; let me think about it some and reroll.
-- 
brian m. carlson: Houston, Texas, US
OpenPGP: https://keybase.io/bk2204

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