Implement basic USB setup in the cups printer detector. Factor out

chrome/browser/chromeos/printing/usb_util.cc

Index: chrome/browser/chromeos/printing/usb_util.cc
diff --git a/chrome/browser/chromeos/printing/usb_util.cc b/chrome/browser/chromeos/printing/usb_util.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c8c3a4fe801715543fa1204785087001ec0ba5be
--- /dev/null
+++ b/chrome/browser/chromeos/printing/usb_util.cc
@@ -0,0 +1,106 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/chromeos/printing/usb_util.h"
+
+#include <ctype.h>
+#include <stdint.h>
+#include <vector>
+
+#include "device/usb/usb_device_filter.h"
+#include "ui/base/l10n/l10n_util.h"
+
+namespace chromeos {
+namespace {
+
+// Base class used for printer USB interfaces
+// (https://www.usb.org/developers/defined_class).
+constexpr uint8_t kPrinterInterfaceClass = 7;
+
+// Escape URI strings the same way cups does it, so we end up with a URI cups
+// recognizes.  Cups hex-encodes '%', ' ', and anything with the MSB set, and

[skau, 2017/03/11 00:00:34]

Out of curiosity, how'd you find out it encodes characters with the MSB set? 
What encoding does this assume?

[Carlson, 2017/03/11 01:19:17]

By inspecting the cups source code.  Ultimately it's http_copy_encode() in
cups/http-support.c that performs this function.

As for encoding, you mean, like unicode?  It's ASCII all the way down in CUPS, I
think.

[skau, 2017/03/13 21:56:25]

Thanks.  It looks like they allow any ASCII character except for spaces.  Can
you say that we encode values outside the ASCII range (i.e. >127) rather than
where the MSB is set?  I do remember that ASCII is 128 characters. I don't
remember what the decimal representation of 0x80 is (even if I should).

On an unrelated note, I wouldn't expect /BEL to be a valid character in a
printer name.

[Carlson, 2017/03/15 00:31:15]

I agree that the escaping choice is...weird.

Updated comment.

+// lets everything else through unchanged.
+std::string CupsURIEscape(const std::string& in) {
+  static const char kHexDigits[] = "0123456789ABCDEF";
+  std::vector<char> buf;
+  buf.reserve(in.size());
+  for (char c : in) {
+    if (c == ' ' || c == '%' || (c & 0x80)) {
+      buf.push_back('%');
+      buf.push_back(kHexDigits[(c >> 4) & 0xf]);
+      buf.push_back(kHexDigits[c & 0xf]);
+    } else {
+      buf.push_back(c);
+    }
+  }
+  return std::string(buf.data(), buf.size());
+}
+
+}  // namespace
+
+bool UsbDeviceIsPrinter(scoped_refptr<device::UsbDevice> usb_device) {
+  device::UsbDeviceFilter printer_filter;
+  printer_filter.interface_class = kPrinterInterfaceClass;
+  return printer_filter.Matches(usb_device);
+}
+
+std::string UsbPrinterDeviceDetailsAsString(const device::UsbDevice& device) {
+  return base::StringPrintf(
+      " guid:                %s\n"
+      " usb version:         %d\n"
+      " device class:        %d\n"
+      " device subclass:     %d\n"
+      " device protocol:     %d\n"
+      " vendor id:           %04x\n"
+      " product id:          %04x\n"
+      " device version:      %d\n"
+      " manufacturer string: %s\n"
+      " product string:      %s\n"
+      " serial number:       %s",
+      device.guid().c_str(), device.usb_version(), device.device_class(),
+      device.device_subclass(), device.device_protocol(), device.vendor_id(),
+      device.product_id(), device.device_version(),
+      base::UTF16ToUTF8(device.manufacturer_string()).c_str(),
+      base::UTF16ToUTF8(device.product_string()).c_str(),
+      base::UTF16ToUTF8(device.serial_number()).c_str());
+}
+
+// Attempt to gather all the information we need to work with this printer by
+// querying the USB device.  This should only be called using devices we believe
+// are printers, not arbitrary USB devices, as we may get weird partial results
+// from arbitrary devices.
+//
+bool UsbDeviceToPrinter(const device::UsbDevice& device,
+                        chromeos::Printer* printer) {
+  // Preflight all required fields and log errors if we find something wrong.
+  if (device.vendor_id() == 0 || device.product_id() == 0 ||
+      device.manufacturer_string().empty() || device.product_string().empty()) {
+    LOG(ERROR) << "Failed to convert USB device to printer.  Fields were:\n"
+               << UsbPrinterDeviceDetailsAsString(device);
+    return false;
+  }
+
+  printer->set_manufacturer(base::UTF16ToUTF8(device.manufacturer_string()));
+  printer->set_model(base::UTF16ToUTF8(device.product_string()));
+  printer->set_display_name(base::StringPrintf("%s %s (USB)",
+                                               printer->manufacturer().c_str(),
+                                               printer->model().c_str()));
+  printer->set_description(printer->display_name());
+
+  // Note that serial may, for some devices, be empty or bogus (all zeros, non
+  // unique, or otherwise not really a serial number), but having a non-unique
+  // or empty serial field in the URI still lets us print, it just means we
+  // don't have a way to uniquely identify a printer if there are multiple ones
+  // plugged in with the same VID/PID, so we may print to the *wrong* printer.
+  // There doesn't seem to be a robust solution to this problem; if printers
+  // don't supply a serial number, we don't have any reliable way to do that
+  // differentiation.
+  std::string serial = base::UTF16ToUTF8(device.serial_number());
+  printer->set_uri(CupsURIEscape(
+      base::StringPrintf("usb://%04x/%04x?serial=%s", device.vendor_id(),
+                         device.product_id(), serial.c_str())));
+  return true;
+}
+
+}  // namespace chromeos