Brother MFC-9370CDW doesn't support two-sided scanning via. sane-airscan

[bkloppenborg]

My Brother MFC-9370CDW has a single-pass two-sided scanner in it. Under brscan4, the printer scans double-sided, but with sane-airscan I only get the front side.

Looking through the source code, I think this is because the printer reports that it does NOT have a duplexer (which is true since it is a single-pass double-sided scanner) yet sane-airscan's WDS implementation expects a duplexer to be present to configure the relevant double-sided features? Either that, or the long-name sane that include duplex capabilities are not being reported correctly.

For the later item, if I run simple-scan in debug mode using the brscan4 interface instead of airscan, I get the following modes:

[+22.46s] DEBUG: scanner.vala:1002: sane_get_option_descriptor (4)
[+22.46s] DEBUG: scanner.vala:795: Option 4: name='source' title='Scan source' type=string size=64 values=["FlatBed", "Automatic Document Feeder(left aligned)", "Automatic Document Feeder(left aligned,Duplex)", "Automatic Document Feeder(centrally aligned)", "Automatic Document Feeder(centrally aligned,Duplex)"] cap=soft-select,soft-detect
[+22.46s] DEBUG: scanner.vala:798:   Description: Selects the scan source (such as a document-feeder).
[+15.20s] DEBUG: scanner.vala:1002: sane_get_option_descriptor (5)

Yet when I run with sane-airscan I only get two modes, neither of which support duplex:

[+15.20s] DEBUG: scanner.vala:1002: sane_get_option_descriptor (4)
[+15.20s] DEBUG: scanner.vala:795: Option 4: name='source' title='Scan source' type=string size=8 values=["Flatbed", "ADF"] cap=soft-select,soft-detect
[+15.20s] DEBUG: scanner.vala:798:   Description: Selects the scan source (such as a document-feeder).
[+15.20s] DEBUG: scanner.vala:1002: sane_get_option_descriptor (5)

Airscan trace logs are attached. Thank you for your excellent work maintaining sane-airscan!

simple-scan-Brother-MFC-9340CDW.log