# [RFC] HashContext as Object

- Thread: https://externals.io/message/97468
- Original archive: https://news-web.php.net/php.internals/97468
- Started by Sara Golemon on 2016-12-27T03:35:25+00:00
- Messages: 4
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## #97468 — Sara Golemon — 2016-12-27T03:35:25+00:00

URL: https://externals.io/message/97468#97468

I was trawling through Pull Requests and found #660 which I think is a
nice idea and deserves some attention.  It involves minor BC however,
so I've updated the patch and presented it for your discussing
pleasure.

https://wiki.php.net/rfc/hash-context.as-resource

-Sara

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## #97470 — Stanislav Malyshev — 2016-12-27T06:55:40+00:00

URL: https://externals.io/message/97468#97470 · In reply to: #97468

Hi!

> I was trawling through Pull Requests and found #660 which I think is a
> nice idea and deserves some attention.  It involves minor BC however,
> so I've updated the patch and presented it for your discussing
> pleasure.
> 
> https://wiki.php.net/rfc/hash-context.as-resource

The RFC looks good to me.

-- 
Stas Malyshev
smalyshev@gmail.com

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## #97492 — Sara Golemon — 2016-12-30T02:32:20+00:00

URL: https://externals.io/message/97468#97492

> I was trawling through Pull Requests and found #660 which I think is a
> nice idea and deserves some attention.  It involves minor BC however,
> so I've updated the patch and presented it for your discussing
> pleasure.
>
Specifically, I should say I'm eager to hear thoughts on the item
listed as an Open Issue.

That is: Currently `hash_final()` destroys the existing HashContext
resource immediately.  No hope of continuing or even just reissuing
the result.

I'm quite tempted atm, to go the "copy the context, finalize to get a
digest, then restoring to the saved context state".  For most use
cases of this API this is a slight overhead add since the context is
being duplicated then shortly thereafter discarded. (Bear in mind
though, that the hash_init->hash_update->hash_final API is the edge
case already compared to the all-in-one `hash()` and `hash_hmac()`
functions).

What doing this does offer, however, is a pathway to reasonable APIs
for streaming hash functions (see SHA3/Keccak Sponge Functions).  As a
minor side benefit, we also get an idempotent `hash_final()`. So even
though there's a VERY minor BC break involved, I think it's the right
thing to do.  If others agree, I'll update the diff to reflect.

-Sara

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## #97655 — Sara Golemon — 2017-01-10T08:23:42+00:00

URL: https://externals.io/message/97468#97655

> 
> > […]
> Specifically, I should say I'm eager to hear thoughts on the item
> listed as an Open Issue.
>
> That is: Currently `hash_final()` destroys the existing HashContext
> resource immediately.  No hope of continuing or even just reissuing
> the result.
>
> I'm quite tempted atm, to go the "copy the context, finalize to get a
> digest, then restoring to the saved context state".  For most use
> cases of this API this is a slight overhead add since the context is
> being duplicated then shortly thereafter discarded. (Bear in mind
> though, that the hash_init->hash_update->hash_final API is the edge
> case already compared to the all-in-one `hash()` and `hash_hmac()`
> functions).
>
> What doing this does offer, however, is a pathway to reasonable APIs
> for streaming hash functions (see SHA3/Keccak Sponge Functions).  As a
> minor side benefit, we also get an idempotent `hash_final()`. So even
> though there's a VERY minor BC break involved, I think it's the right
> thing to do.  If others agree, I'll update the diff to reflect.
>
Still looking for comments/feedback on Open Issue (above).  I've
implemented what it would look like as a stacked commit on the feature
branch: https://github.com/php/php-src/compare/master...sgolemon:pr-660
though I could easily squash before commit if it's voted in.

The downside of this is pretty obvious, a completely unnecessary
duplication in the majority of the use cases.  But the upside is that
HashContext actually behaves how you'd expect a normal object to
behave.  The idea of freezing an object on calling `hash_final()` (or
$hash->final(), eventually) makes me twitch a bit.

If I get no feedback at all, I'll just make it a secondary vote:  Do
it? "Yes", "No".  And if Yes, then:  "Keeping `freeze` behavior", or
"Include context-preservation."

FWIW, I think I'm actually favoring the idea of keeping the freeze
behavior of just the original implementation, and not including this
latest update.

-Sara