[whatwg] API for encoding/decoding ArrayBuffers into text

Jonas Sicking jonas at sicking.cc
Mon Mar 26 22:28:25 PDT 2012

On Mon, Mar 26, 2012 at 6:11 PM, Kenneth Russell <kbr at google.com> wrote:
> On Mon, Mar 26, 2012 at 5:33 PM, Jonas Sicking <jonas at sicking.cc> wrote:
>> On Mon, Mar 26, 2012 at 4:40 PM, Joshua Bell <jsbell at chromium.org> wrote:
>>>> * We lost the ability to decode from a arraybuffer and see how many
>>>> bytes were consumed before a null-terminator was hit. One not terribly
>>>> elegant solution would be to add a TextDecoder.decodeWithLength method
>>>> which return a DOMString+length tuple.
>>> Agreed, but of course see above - there was consensus earlier in the thread
>>> that searching for null terminators should be done outside the API,
>>> therefore the caller will have the length handy already. Yes, this would be
>>> a big flaw since decoding at tightly packed data structure (e.g. array of
>>> null terminated strings w/o length) would be impossible with just the
>>> nullTerminator flag.
>> Requiring callers to find the null character first, and then use that
>> will require one additional pass over the encoded binary data though.
>> Also, if we put the API for finding the null character on the Decoder
>> object it doesn't seem like we're creating an API which is easier to
>> use, just one that has moved some of the logic from the API to every
>> caller.
>> Though I guess the best solution would be to add methods to DataView
>> which allows consuming an ArrayBuffer up to a null terminated point
>> and returns the decoded string. Potentially such a method could take a
>> Decoder object as argument.
> The rationale for specifying the string encoding and decoding
> functionality outside the typed array specification is to keep the
> typed array spec small and easily implementable. The indexed property
> getters and setters on the typed array views, and methods on DataView,
> are designed to be implementable with a small amount of assembly code
> in JavaScript engines. I'd strongly prefer to continue to design the
> encoding/decoding functionality separately from the typed array views.

Is there a reason you couldn't keep the current set of functions on
DataView implemented using a small amount of assembly code, and let
the new functions fall back to slower C++ functions?

/ Jonas

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