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Don't assume USB device is configured when looking for endpoints #47

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Jan 2, 2024
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12 changes: 11 additions & 1 deletion src/Printers/Communication/UsbPrinterDeviceChannel.ts
Original file line number Diff line number Diff line change
Expand Up @@ -102,11 +102,21 @@ export class UsbPrinterDeviceChannel extends EventTarget implements IPrinterDevi
private async connect() {
const d = this.device;

// Any sane USB device should expose at least one configuration with one
// interface.
if (
d.configurations.length === 0 ||
d.configurations[0].interfaces.length === 0 ||
d.configurations[0].interfaces[0].alternates.length === 0
) {
throw new WebZlpError('USB printer did not expose any USB interfaces. Try power-cycling the printer. This is a hardware problem.');
}

// A standard Zebra printer will have two endpoints on one interface.
// One of them will be output, one of them will be input. They can be
// in a random order (or missing!) so we must enumerate them to find them.
let o: USBEndpoint, i: USBEndpoint;
for (const endpoint of d.configuration.interfaces[0].alternates[0].endpoints) {
for (const endpoint of d.configurations[0].interfaces[0].alternates[0].endpoints) {
if (endpoint.direction == 'out') {
o = endpoint;
} else if (endpoint.direction == 'in') {
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