Field bug (ICS XP-K200L over USB): text printed, barcode + cut missing;
same bytes over TCP fine. sendRawUsb did ONE write() on an O_NONBLOCK
usblp fd and never checked bytesWritten — the kernel accepts only what
fits the printer's ~8 KB USB buffer and returns a short write, so the
tail of any job bigger than one buffer (the barcode mid-payload, the cut
at the end) was silently discarded. The regular-file test stand-in can't
short-write, which is why tests never caught it.
writeAllUsb now pushes 4 KB chunks until every byte is accepted,
continues after partial writes, retries EAGAIN/zero-byte with a short
pause, and fails at the deadline with an (N/M bytes) diagnostic. Driven
by fake-handle tests (short writes, EAGAIN interleave, wedged-printer
timeout, non-EAGAIN passthrough).
Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V
New concepts/printer-usb-transport.md (the seam, usblp char device,
reachability-only status, threat model). open-questions #14: confirm the
on-site printer is USB and bake the usblp + udev write-access rule into the
appliance image (provisioning, not app code; unverified on hardware). Updated
rongta-printer.md (USB transport note), index.md, log.md.
Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V
julian