cups_ipp_util: hide special papers

This change modifies the CUPS IPP backend to suppress papers whose
vendor IDs are not meant for users' eyes - i.e. the "custom_min" and
"custom_max" sizes that CUPS incidentally exposes.

Bug: 1026938
Change-Id: I047844030e7f7a161bda32755754494567e7734c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1935173Reviewed-by: Sean Kau <skau@chromium.org>
Commit-Queue: Kalvin Lee <kdlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720578}

printing/backend/cups_ipp_util.cc

@@ -40,6 +40,12 @@ constexpr double kMMPerInch = 25.4;
 constexpr double kMicronsPerInch = kMMPerInch * kMicronsPerMM;
 constexpr double kCmPerInch = kMMPerInch * 0.1;
 
+// Defines two prefixes of a special breed of media sizes not meant for
+// users' eyes. CUPS incidentally returns these IPP values to us, but
+// we have no use for them.
+constexpr base::StringPiece kMediaCustomMinPrefix = "custom_min";
+constexpr base::StringPiece kMediaCustomMaxPrefix = "custom_max";
+
 enum Unit {
   INCHES,
   MILLIMETERS,
@@ -138,8 +144,11 @@ PrinterSemanticCapsAndDefaults::Paper ParsePaper(base::StringPiece value) {
 
   std::vector<base::StringPiece> pieces = base::SplitStringPiece(
       value, "_", base::TRIM_WHITESPACE, base::SPLIT_WANT_NONEMPTY);
-  // we expect at least a display string and a dimension string
-  if (pieces.size() < 2)
+  // We expect at least a display string and a dimension string.
+  // Additionally, we drop the "custom_min*" and "custom_max*" special
+  // "sizes" (not for users' eyes).
+  if (pieces.size() < 2 || value.starts_with(kMediaCustomMinPrefix) ||
+      value.starts_with(kMediaCustomMaxPrefix))
     return PrinterSemanticCapsAndDefaults::Paper();
 
   base::StringPiece dimensions = pieces.back();

printing/backend/cups_ipp_util_unittest.cc

@@ -207,8 +207,8 @@ TEST_F(PrintBackendCupsIppUtilTest, LegalPaperDefault) {
   EXPECT_EQ(355600, caps.default_paper.size_um.height());
 }
 
-// Tests that CapsAndDefaultsFromPrinter does not propagate papers with
-// badly formatted vendor IDs - such papers will not transform into
+// Tests that CapsAndDefaultsFromPrinter() does not propagate papers
+// with badly formatted vendor IDs - such papers will not transform into
 // meaningful ParsedPaper instances and are sometimes inimical to
 // ARC++.
 TEST_F(PrintBackendCupsIppUtilTest, OmitPapersWithoutVendorIds) {
@@ -236,6 +236,44 @@ TEST_F(PrintBackendCupsIppUtilTest, OmitPapersWithoutVendorIds) {
                          "iso b5")));
 }
 
+// Tests that CapsAndDefaultsFromPrinter() does not propagate the
+// special IPP values that CUPS happens to expose to the Chromium print
+// backend.
+TEST_F(PrintBackendCupsIppUtilTest, OmitPapersWithSpecialVendorIds) {
+  // Maintainer's note: there's no reason why a printer would deliver
+  // two discrete sizes for custom_min* and custom_max*; in practice,
+  // we always see the fully qualified custom_m(in|ax)_<DIMENSIONS>
+  // delivered to the Chromium print backend.
+  printer_->SetSupportedOptions(
+      "media",
+      MakeStringCollection(
+          ipp_, {"na_number-11_4.5x10.375in", "custom_max", "custom_min_0x0in",
+                 "na_govt-letter_8x10in", "custom_min",
+                 "custom_max_1000x1000in", "iso_b0_1000x1414mm"}));
+
+  PrinterSemanticCapsAndDefaults caps;
+  CapsAndDefaultsFromPrinter(*printer_, &caps);
+
+  // The printer reports that it supports seven media sizes, four of
+  // which are not meant for users' eyes (``custom_min*'' and
+  // ``custom_max*''). The preceding call to
+  // CapsAndDefaultsFromPrinter() will have dropped these sizes,
+  // refusing to propagate them out of the backend.
+  ASSERT_EQ(3U, caps.papers.size());
+
+  // While not directly pertinent to this test, we expect a certain
+  // format for the other supported papers.
+  EXPECT_THAT(
+      caps.papers,
+      testing::UnorderedElementsAre(
+          testing::Field(&PrinterSemanticCapsAndDefaults::Paper::display_name,
+                         "na number-11"),
+          testing::Field(&PrinterSemanticCapsAndDefaults::Paper::display_name,
+                         "na govt-letter"),
+          testing::Field(&PrinterSemanticCapsAndDefaults::Paper::display_name,
+                         "iso b0")));
+}
+
 TEST_F(PrintBackendCupsIppUtilTest, PinSupported) {
   printer_->SetSupportedOptions("job-password", MakeInteger(ipp_, 4));
   printer_->SetSupportedOptions("job-password-encryption",