printing: don't construct StringPiece from nullptr

This change modifies several call sites in printing code to avoid
constructing base::StringPiece instances from nullptr.

Bug: 1102941
Fixes: 1102941
Test: autoninja ... chrome printing_unittests
Test: ./printing_unittests
Change-Id: If5797f6d41a03c9cfdf9eb5d40f063159a9193e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2313978
Commit-Queue: Kalvin Lee <kdlee@chromium.org>
Reviewed-by: Bailey Berro <baileyberro@chromium.org>
Reviewed-by: Sean Kau <skau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791622}

printing/backend/cups_ipp_helper.cc

@@ -87,7 +87,8 @@ ColorModel DefaultColorModel(const CupsOptionProvider& printer) {
   if (!attr)
     return UNKNOWN_COLOR_MODEL;
 
-  return ColorModelFromIppColor(ippGetString(attr, 0, nullptr));
+  const char* const value = ippGetString(attr, 0, nullptr);
+  return value ? ColorModelFromIppColor(value) : UNKNOWN_COLOR_MODEL;
 }
 
 std::vector<ColorModel> SupportedColorModels(
@@ -145,10 +146,16 @@ void ExtractDuplexModes(const CupsOptionProvider& printer,
     if (duplex_mode != mojom::DuplexMode::kUnknownDuplexMode)
       printer_info->duplex_modes.push_back(duplex_mode);
   }
+
   ipp_attribute_t* attr = printer.GetDefaultOptionValue(kIppDuplex);
+  if (!attr) {
+    printer_info->duplex_default = mojom::DuplexMode::kUnknownDuplexMode;
+    return;
+  }
+
+  const char* const value = ippGetString(attr, 0, nullptr);
   printer_info->duplex_default =
-      attr ? DuplexModeFromIpp(ippGetString(attr, 0, nullptr))
-           : mojom::DuplexMode::kUnknownDuplexMode;
+      value ? DuplexModeFromIpp(value) : mojom::DuplexMode::kUnknownDuplexMode;
 }
 
 void CopiesRange(const CupsOptionProvider& printer,
@@ -241,8 +248,8 @@ bool CollateDefault(const CupsOptionProvider& printer) {
   if (!attr)
     return false;
 
-  base::StringPiece name = ippGetString(attr, 0, nullptr);
-  return name.compare(kCollated) == 0;
+  const char* const name = ippGetString(attr, 0, nullptr);
+  return name ? base::StringPiece(name).compare(kCollated) == 0 : false;
 }
 
 #if defined(OS_CHROMEOS)

printing/backend/cups_ipp_helper_unittest.cc

@@ -40,7 +40,11 @@ class MockCupsOptionProvider : public CupsOptionProvider {
     std::vector<base::StringPiece> strings;
     int size = ippGetCount(attr);
     for (int i = 0; i < size; ++i) {
-      strings.emplace_back(ippGetString(attr, i, nullptr));
+      const char* const value = ippGetString(attr, i, nullptr);
+      if (!value) {
+        continue;
+      }
+      strings.emplace_back(value);
     }
 
     return strings;

printing/backend/cups_jobs.cc

@@ -244,8 +244,10 @@ void ParseCollection(ipp_attribute_t* attr,
                      std::vector<std::string>* collection) {
   int count = ippGetCount(attr);
   for (int i = 0; i < count; i++) {
-    base::StringPiece value = ippGetString(attr, i, nullptr);
-    collection->push_back(value.as_string());
+    const char* const value = ippGetString(attr, i, nullptr);
+    if (value) {
+      collection->push_back(value);
+    }
   }
 }
 
@@ -288,9 +290,9 @@ void ParseJobs(ipp_t* response,
   CupsJob* current_job = NewJob(printer_id, jobs);
   for (ipp_attribute_t* attr = starting_attr; attr != nullptr;
        attr = ippNextAttribute(response)) {
-    base::StringPiece attribute_name = ippGetName(attr);
+    const char* const attribute_name = ippGetName(attr);
     // Separators indicate a new job.  Separators have empty names.
-    if (attribute_name.empty()) {
+    if (!attribute_name) {
       current_job = NewJob(printer_id, jobs);
       continue;
     }
@@ -306,7 +308,11 @@ void ParseJobs(ipp_t* response,
 bool ParsePrinterInfo(ipp_t* response, PrinterInfo* printer_info) {
   for (ipp_attribute_t* attr = ippFirstAttribute(response); attr != nullptr;
        attr = ippNextAttribute(response)) {
-    base::StringPiece name = ippGetName(attr);
+    const char* const value = ippGetName(attr);
+    if (!value) {
+      continue;
+    }
+    base::StringPiece name(value);
     if (name == base::StringPiece(kPrinterMakeAndModel)) {
       DCHECK_EQ(IPP_TAG_TEXT, ippGetValueTag(attr));
       const char* make_and_model_string = ippGetString(attr, 0, nullptr);
@@ -421,8 +427,8 @@ void ParsePrinterStatus(ipp_t* response, PrinterStatus* printer_status) {
 
   for (ipp_attribute_t* attr = ippFirstAttribute(response); attr != nullptr;
        attr = ippNextAttribute(response)) {
-    base::StringPiece name = ippGetName(attr);
-    if (name.empty()) {
+    const char* const name = ippGetName(attr);
+    if (!name) {
       continue;
     }
 

printing/backend/cups_printer.cc

@@ -47,10 +47,12 @@ std::vector<base::StringPiece> CupsPrinter::GetSupportedOptionValueStrings(
   if (!attr)
     return values;
 
-  base::StringPiece value;
   int num_options = ippGetCount(attr);
   for (int i = 0; i < num_options; ++i) {
-    value = ippGetString(attr, i, nullptr);
+    const char* const value = ippGetString(attr, i, nullptr);
+    if (!value) {
+      continue;
+    }
     values.push_back(value);
   }