[sane-devel] Byte ordering

[Ralph Little]

Hi,
Thanks, I will check that out.

Cheers,
Ralph

On Wed, Jun 4, 2025 at 9:25 AM m. allan noah <kitno455 at gmail.com> wrote:

> A quote from fujitsu.c that seems relevant:
>
> *
>  * @@ Section 5 - SANE cleanup functions
>  */
> /*
>  * Cancels a scan.
>  *
>  * It has been said on the mailing list that sane_cancel is a bit of a
>  * misnomer because it is routinely called to signal the end of a
>  * batch - quoting David Mosberger-Tang:
>  *
>  * > In other words, the idea is to have sane_start() be called, and
>  * > collect as many images as the frontend wants (which could in turn
>  * > consist of multiple frames each as indicated by frame-type) and
>  * > when the frontend is done, it should call sane_cancel().
>  * > Sometimes it's better to think of sane_cancel() as "sane_stop()"
>  * > but that name would have had some misleading connotations as
>  * > well, that's why we stuck with "cancel".
>  *
>  * The current consensus regarding duplex and ADF scans seems to be
>  * the following call sequence: sane_start; sane_read (repeat until
>  * EOF); sane_start; sane_read...  and then call sane_cancel if the
>  * batch is at an end. I.e. do not call sane_cancel during the run but
>  * as soon as you get a SANE_STATUS_NO_DOCS.
>  *
>  * From the SANE spec:
>  * This function is used to immediately or as quickly as possible
>  * cancel the currently pending operation of the device represented by
>  * handle h.  This function can be called at any time (as long as
>  * handle h is a valid handle) but usually affects long-running
>  * operations only (such as image is acquisition). It is safe to call
>  * this function asynchronously (e.g., from within a signal handler).
>  * It is important to note that completion of this operaton does not
>  * imply that the currently pending operation has been cancelled. It
>  * only guarantees that cancellation has been initiated. Cancellation
>  * completes only when the cancelled call returns (typically with a
>  * status value of SANE_STATUS_CANCELLED).  Since the SANE API does
>  * not require any other operations to be re-entrant, this implies
>  * that a frontend must not call any other operation until the
>  * cancelled operation has returned.
>  */
>
>
> On Wed, Jun 4, 2025 at 12:06 PM Ralph Little <skelband at gmail.com> wrote:
>
>> Hi,
>> BTW, just on that note, something that has bothered me is that the SANE
>> API specification doesn't make the ADF multi-page scanning process super
>> clear in terms of result codes, sequence etc. I will perhaps also review
>> that section to see if additional detail could be added to make it more
>> concrete.
>>
>> Any changes I propose, I will offer them up here for review before
>> updating the document.
>>
>> Cheers,
>> Ralph
>>
>> On Wed, Jun 4, 2025 at 9:02 AM Ralph Little <skelband at gmail.com> wrote:
>>
>>> Hi,
>>> OK, I will draft something up for the standard.
>>>
>>> If there is anything else to update the standard with, perhaps people
>>> could let me know.
>>> Just to be clear, I am not changing the interface with this update, just
>>> adding come clarification, so if anybody feels that there is anything else
>>> unclear in the standard, they should possibly raise it now.
>>>
>>> I will add address this on the weekend.
>>>
>>> Cheers,
>>> Ralph
>>>
>>> On Wed, Jun 4, 2025 at 8:57 AM m. allan noah <kitno455 at gmail.com> wrote:
>>>
>>>> Makes sense to me.
>>>>
>>>> On Wed, Jun 4, 2025 at 10:12 AM Ralph Little <skelband at gmail.com>
>>>> wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> On Tue, Jun 3, 2025 at 11:36 PM <sane-devel at symme.link> wrote:
>>>>>
>>>>>> On Tue, Jun 03, 2025 at 10:00:45PM -0700, Ralph Little wrote:
>>>>>> > On Tue, Jun 3, 2025 at 9:54 PM James Ring <sjr at jdns.org> wrote:
>>>>>> > > On Tue, Jun 3, 2025 at 9:46 PM Ralph Little <skelband at gmail.com>
>>>>>> wrote:
>>>>>> > >> Someone has asked the question about byte order in multi-byte
>>>>>> image data
>>>>>> > >> that we might get from a SANE backend.
>>>>>>
>>>>>> Hi, it's me, I had the question.
>>>>>>
>>>>>> > >> It is not enough to assume the local machine byte order since we
>>>>>> may get
>>>>>> > >> data through the net backend from a remote machine with a
>>>>>> different byte
>>>>>> > >> order.
>>>>>>
>>>>>> The `net` backend explicitly swaps to local machine byte order:
>>>>>>
>>>>>> https://gitlab.com/sane-project/backends/-/blob/master/backend/net.c?ref_type=heads#L2356-2362
>>>>>>
>>>>>> So, it does seem like the de facto standard is that backends produce
>>>>>> data in local machine byte order.
>>>>>>
>>>>>> (The protocol documentation reinforces this as a standard:
>>>>>>
>>>>>
>>>>> Agreed. Perhaps this is something we should add to the SANE API
>>>>> specification?
>>>>> Allan, do you concur?
>>>>>
>>>>> Cheers,
>>>>> Ralph
>>>>>
>>>>
>>>>
>>>> --
>>>> "well, I stand up next to a mountain- and I chop it down with the edge
>>>> of my hand"
>>>>
>>>
>
> --
> "well, I stand up next to a mountain- and I chop it down with the edge of
> my hand"
>
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