Inject printer faults

Real printers fail, and the code that drives them needs to handle it. The lab can push a printer into specific fault states on demand, flipping both sides at once: the CUPS queue state on the print server, and the SNMP device OIDs that the print-snmp sidecar serves.

Inject a fault

make print-fault STATE=toner-low Q=GH12-pLab    # SNMP toner OID drops, error bit set
make print-fault STATE=rejecting Q=GH12-pLab    # CUPS queue refuses jobs
make print-fault STATE=offline                   # all queues down
make print-fault STATE=clear Q=GH12-pLab        # reset one queue to healthy

The states

State	Layer	Effect
toner-low	SNMP only	Toner OID drops, error bit set; the queue stays up
paper-out	SNMP only	Paper-input status reports empty; the queue stays up
offline	CUPS + SNMP	The queue goes down
paused	CUPS	The queue is paused (holds jobs)
rejecting	CUPS	The queue refuses new jobs at submission
clear	CUPS + SNMP	Reset to healthy

toner-low and paper-out are physical conditions, so they reflect only in SNMP; the queue keeps accepting jobs. The other states change the CUPS queue itself.

How it crosses both layers

make print-fault writes a state file into a shared ./print-fault-state/ directory that the print-snmp sidecar polls, and it runs cupsdisable / cupsreject on the print server. That is why a single command can make the device report low toner and the queue refuse jobs, the way a real printer would behave when something is wrong.

SNMP faults are for the simulated devices only

print-snmp models a handful of representative printers, not all 77. SNMP fault states only reflect for those representative devices. CUPS-side states (offline, paused, rejecting) apply to any real queue.

Prove an error path end to end

make test-fault-path

This injects rejecting, proves a submitted job is refused, then clears the state and proves the same queue prints again. That before-and-after is the evidence your error handling has something real to react to.

Inspect the device side

make snmp-walk DEV=bmh12-plab     # hrPrinterStatus + toner level for one device
make ipp-validate                 # ipptool Get-Printer-Attributes conformance

Both exec into the sidecars, which matters: the host-networked DC is the macvlan parent and cannot reach macvlan children, so query from inside the sidecar rather than from the host.