Bug 1771500 Show all available printers; r=stransky

Allow to continue enumeration of the printers for all protocols
(ie. ipp and ipps).

Following advice given by cups guys to use cupsGetDests2 to avoid duplicates of printers in the list: https://bugzilla.redhat.com/show_bug.cgi?id=1983403#c18

Differential Revision: https://phabricator.services.mozilla.com/D147508

widget/nsCUPSShim.h

@@ -56,6 +56,7 @@ class nsCUPSShim {
   X(Optional::Yes, cupsLocalizeDestMedia)   \
   X(Optional::No, cupsGetDest)              \
   X(Optional::No, cupsGetDests)             \
+  X(Optional::No, cupsGetDests2)            \
   X(Optional::No, cupsGetNamedDest)         \
   X(Optional::No, cupsGetOption)            \
   X(Optional::No, cupsServer)               \

widget/nsPrinterListCUPS.cpp

@@ -98,18 +98,27 @@ nsTArray<PrinterInfo> nsPrinterListCUPS::Printers() const {
   };
 
   nsTArray<PrinterInfo> printerInfoList;
-  if (CupsShim().cupsEnumDests(
-          CUPS_DEST_FLAGS_NONE,
-          int(StaticPrefs::print_cups_enum_dests_timeout_ms()),
-          nullptr /* cancel* */, CUPS_PRINTER_LOCAL,
-          CUPS_PRINTER_FAX | CUPS_PRINTER_SCANNER, &CupsDestCallback,
-          &printerInfoList)) {
+  // cupsGetDests2 returns list of found printers without duplicates, unlike
+  // cupsEnumDests
+  cups_dest_t* printers = nullptr;
+  const auto numPrinters = CupsShim().cupsGetDests2(nullptr, &printers);
+  if (numPrinters > 0) {
+    for (auto i : mozilla::IntegerRange(0, numPrinters)) {
+      cups_dest_t* ownedDest = nullptr;
+      mozilla::DebugOnly<const int> numCopied =
+          CupsShim().cupsCopyDest(printers + i, 0, &ownedDest);
+      MOZ_ASSERT(numCopied == 1);
+
+      nsString name;
+      GetDisplayNameForPrinter(*(printers + i), name);
+      printerInfoList.AppendElement(PrinterInfo{std::move(name), ownedDest});
+    }
+    CupsShim().cupsFreeDests(numPrinters, printers);
     return printerInfoList;
   }
 
   // An error occurred - retry with CUPS_PRINTER_DISCOVERED masked out (since
   // it looks like there are a lot of error cases for that in cupsEnumDests):
-  FreeDestsAndClear(printerInfoList);
   if (CupsShim().cupsEnumDests(
           CUPS_DEST_FLAGS_NONE,
           0 /* 0 timeout should be okay when masking CUPS_PRINTER_DISCOVERED */,