[sane-devel] ADF support in SANE API

[Rolf Bensch]

Hi Alexander,

What is the difference between sane-airscan and Sane's escl backend? I'm
a little bit confused about that.

Cheers,
Rolf


Am 29.06.20 um 01:09 schrieb Alexander Pevzner:
> Hi Jürgen,
>
> I'm the author of sane-airscan, the eSCL/WSD backend for SANE
> (https://github.com/alexpevzner/sane-airscan)
>
> At some point, your AirSane was one of my knowledge sources to learn
> the eSCL protocol :-)
>
>> I’m trying to incorporate ADF support into a SANE frontend that I
>> have written
>> (github.com/SimulPiscator/AirSane).
>> The frontend is a web server that needs to report or announce the
>> scanner’s status to its clients.
>> Without an ADF, scanner status is just idle vs busy, and any error
>> state is only temporary.
>> With an ADF, the "ADF empty" state prevents scanning but needs to be
>> monitored such that
>> a client can know it may initiate a scan when it switches to "ADF
>> loaded".
>
> It would be enough, if in a case of empty ADF,
> ScanJobs will fail with, say, HTTP 409 status, and subsequent
> ScannerStatus will return the reason of this failure.
>
> Hardware scanners are not very accurate in reporting current ADF
> status, and actually all behave the slightly different way.
>
> My backend even doesn't bother to request ScannerStatus until ScanJobs
> or NextDocument fails.
>
>> So my question is: What can I do in order to monitor ADF status? Call
>> sane_start() after setting an empty
>> scan region, so the scan is done at the first call to sane_read()?
>> This is obviously not an option, as in the
>> case of a loaded feeder this would consume the first original rather
>> than just read ADF status.
>> Cancel the scan immediately after sane_start() using sane_cancel()? I
>> have no idea whether this is possible.
>
> There are actually no such API that will return ADF status before
> actual scan attempt.
>
> BTW, some hardware scanners scan all pages loaded into ADF when
> ScanJobs command is issues and requires multiple NextDocument to
> gather all scanned pages, while others scan only one page.
>