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

From: Eric Sunshine <sunshine@sunshineco.com>
Date: Jun 12, 2018, 07:29 UTC
Message-ID: <CAPig+cSEpCTg+rYQYNQ5wUz3PL+51dr7bQdn-2cOWgg2ScdXNA@mail.gmail.com>
In-Reply-To: <20180612010513.GH38834@genre.crustytoothpaste.net>

On Mon, Jun 11, 2018 at 9:05 PM, brian m. carlson <sandals@crustytoothpaste.net> wrote:

Show 9 quoted lines

> On Mon, Jun 11, 2018 at 03:47:43AM -0400, Eric Sunshine 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()?
>
> 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.

It was surprising to see it used for non-OID's (such as hash characteristics), but not hard to deal with.

One could also view this as a generic key/value cache (not specific to OID's) with overriding super-key (the hash algorithm, in this case), which would allow for more generic name than test_oid(), but we don't have to go there presently.

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>> 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.

Can you give examples of cases in which values will contain spaces? It wasn't obvious from this patch series that such a need would arise.

Are these values totally free-form? If not, some character (such as "_", "-", ".", etc.) could act as a stand-in for space. That shouldn't be too hard to handle.

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>> Here's what I had envisioned when reading your emails about OID lookup
>> table functionality:
>>
>> --- >8 ---
>> 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
>> }
>
> 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.

Is that just a general concern or do you have specific "weird" keys in mind?

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>> 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.

My original version of test_oid_cache() actually allowed for that by caching _all_ information from the tables rather than only values corresponding to $test_hash_algo. It looked like this:

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

        for x in $rest
        do
            eval "test_oid_${tag}_${x%:*}=${x#*:}"
        done
    done
}
--- >8 ---

The hash algorithm is incorporated into the cache variable name like this: "test_oid_hexsz_sha256"

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>> 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.

See above about possibly using a stand-in character for space.

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>> 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.

Indeed, this isn't a real selling point; I only just thought of it while composing the mail. Going through the API is more robust. (Although, see above how the revised test_oid_cache() incorporates the hash algorithm into the cache variable name.)