Bug 1658300 - Implement NamedPrinter() for nsPrinterListWin, and remove the base implementation. r=bobowen

Differential Revision: https://phabricator.services.mozilla.com/D87450

widget/nsPrinterListBase.cpp

@@ -70,11 +70,6 @@ NS_IMETHODIMP nsPrinterListBase::GetNamedOrDefaultPrinter(
                                     nsString{aPrinterName});
 }
 
-Maybe<PrinterInfo> nsPrinterListBase::NamedPrinter(nsString aName) const {
-  // TODO: This should be removed once the Win32 backend lands.
-  return Nothing();
-}
-
 Maybe<PrinterInfo> nsPrinterListBase::NamedOrDefaultPrinter(
     nsString aName) const {
   if (Maybe<PrinterInfo> value = NamedPrinter(std::move(aName))) {

widget/nsPrinterListBase.h

@@ -52,10 +52,11 @@ class nsPrinterListBase : public nsIPrinterList {
   nsPrinterListBase();
   virtual ~nsPrinterListBase();
 
-  // Implemented in terms of Printers() and then searching the returned printer
-  // info for a printer of the given name. Backends might have more efficient
-  // methods of implementing this.
-  virtual Maybe<PrinterInfo> NamedPrinter(nsString aName) const;
+  // This could be implemented in terms of Printers() and then searching the
+  // returned printer info for a printer of the given name, but we expect
+  // backends to have more efficient methods of implementing this.
+  virtual Maybe<PrinterInfo> NamedPrinter(nsString aName) const = 0;
+
   // This is implemented separately from the IDL interface version so that it
   // can be made const, which allows it to be used while resolving promises.
   virtual nsresult SystemDefaultPrinterName(nsAString&) const = 0;

widget/windows/nsDeviceContextSpecWin.cpp

@@ -484,12 +484,10 @@ nsresult nsDeviceContextSpecWin::GetDataFromPrinter(const nsAString& aName,
 
 nsPrinterListWin::~nsPrinterListWin() = default;
 
-nsTArray<nsPrinterListBase::PrinterInfo> nsPrinterListWin::Printers() const {
-  PR_PL(("EnumerateNativePrinters\n"));
-
+// Helper to get the array of PRINTER_INFO_4 records from the OS into a
+// caller-supplied byte array; returns the number of records present.
+static unsigned GetPrinterInfo4(nsTArray<BYTE>& aBuffer) {
   const DWORD kLevel = 4;
-  using RecType = PRINTER_INFO_4;
-
   DWORD needed = 0;
   DWORD count = 0;
   const DWORD kFlags = PRINTER_ENUM_LOCAL | PRINTER_ENUM_CONNECTIONS;
@@ -500,20 +498,30 @@ nsTArray<nsPrinterListBase::PrinterInfo> nsPrinterListWin::Printers() const {
                          0,        // cbBuf (buffer size)
                          &needed,  // Bytes needed in buffer
                          &count);
-
-  AutoTArray<BYTE, 1024> buffer;
   if (needed > 0) {
-    buffer.SetLength(needed);
-    ok = EnumPrinters(kFlags, nullptr, kLevel, buffer.Elements(),
-                      buffer.Length(), &needed, &count);
+    aBuffer.SetLength(needed);
+    ok = EnumPrinters(kFlags, nullptr, kLevel, aBuffer.Elements(),
+                      aBuffer.Length(), &needed, &count);
+  }
+  if (!ok || !count) {
+    return 0;
+  }
+  return count;
 }
 
-  if (!ok || !count) {
+nsTArray<nsPrinterListBase::PrinterInfo> nsPrinterListWin::Printers() const {
+  PR_PL(("nsPrinterListWin::Printers\n"));
+
+  AutoTArray<BYTE, 1024> buffer;
+  unsigned count = GetPrinterInfo4(buffer);
+
+  if (!count) {
     PR_PL(("[No printers found]\n"));
     return {};
   }
 
-  auto* printers = reinterpret_cast<const RecType*>(buffer.Elements());
+  const auto* printers =
+      reinterpret_cast<const PRINTER_INFO_4*>(buffer.Elements());
   nsTArray<PrinterInfo> list;
   for (unsigned i = 0; i < count; i++) {
     list.AppendElement(PrinterInfo{nsString(printers[i].pPrinterName)});
@@ -524,6 +532,25 @@ nsTArray<nsPrinterListBase::PrinterInfo> nsPrinterListWin::Printers() const {
   return list;
 }
 
+Maybe<nsPrinterListBase::PrinterInfo> nsPrinterListWin::NamedPrinter(
+    nsString aName) const {
+  Maybe<PrinterInfo> rv;
+
+  AutoTArray<BYTE, 1024> buffer;
+  unsigned count = GetPrinterInfo4(buffer);
+
+  const auto* printers =
+      reinterpret_cast<const PRINTER_INFO_4*>(buffer.Elements());
+  for (unsigned i = 0; i < count; ++i) {
+    if (aName.Equals(nsString(printers[i].pPrinterName))) {
+      rv.emplace(PrinterInfo{aName});
+      break;
+    }
+  }
+
+  return rv;
+}
+
 RefPtr<nsIPrinter> nsPrinterListWin::CreatePrinter(PrinterInfo aInfo) const {
   return nsPrinterWin::Create(std::move(aInfo.mName));
 }

widget/windows/nsDeviceContextSpecWin.h

@@ -96,6 +96,8 @@ class nsPrinterListWin final : public nsPrinterListBase {
  protected:
   nsresult SystemDefaultPrinterName(nsAString&) const final;
 
+  Maybe<PrinterInfo> NamedPrinter(nsString) const final;
+
  private:
   ~nsPrinterListWin();
 };