Create a new print backend for the updated CUPS APIs

printing/backend/cups_connection.cc

+// Copyright 2016 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 "printing/backend/cups_connection.h"
+
+#include <string>
+#include <utility>
+
+#include "base/logging.h"
+#include "base/memory/ptr_util.h"
+#include "base/strings/stringprintf.h"
+
+namespace {
+
+static const int kTimeoutMs = 3000;
+
+class DestinationEnumerator {
+ public:
+  static int cups_callback(void* user_data, unsigned flags, cups_dest_t* dest) {
+    cups_dest_t* copied_dest;
+    cupsCopyDest(dest, 0, &copied_dest);
+    reinterpret_cast<DestinationEnumerator*>(user_data)->store_dest(
+        copied_dest);
+
+    //  keep going
+    return 1;
+  }
+
+  void store_dest(cups_dest_t* dest) { dests_.emplace_back(dest); }
+
+  // Returns the collected destinations.  Remove desired destinations from the
+  // vector or they will be cleaned up when this object is destroyed.
+  std::vector<std::unique_ptr<cups_dest_t, printing::DestinationDeleter>>&

[Lei Zhang, 2016/07/19 22:26:39]

Getting a bit unwieldy to write. Might be good to add a using Foo =
std::vector<...> line and reuse Foo here and on line 40.

[skau, 2016/07/20 23:58:22]

Moving the class into the printing namespace worked out.

+  get_dests() {
+    return dests_;
+  }
+
+ private:
+  std::vector<std::unique_ptr<cups_dest_t, printing::DestinationDeleter>>
+      dests_;
+};
+
+}  // namespace
+
+namespace printing {
+
+CupsConnection::Impl::Impl(http_t* http)
+    : cups_http_(http), http_factory_(http) {}
+
+CupsConnection::Impl::~Impl() {
+  http_factory_.InvalidateWeakPtrs();
+}
+
+base::WeakPtr<http_t> CupsConnection::Impl::GetHttp() {
+  return http_factory_.GetWeakPtr();
+}
+
+CupsConnection::CupsConnection(const GURL& print_server_url,
+                               http_encryption_t encryption,
+                               bool blocking)
+    : print_server_url_(print_server_url),
+      cups_encryption_(encryption),
+      blocking_(blocking),
+      impl_(nullptr),
+      cups_http_(nullptr) {}
+
+CupsConnection::CupsConnection(CupsConnection&& connection)
+    : print_server_url_(connection.print_server_url_),
+      cups_encryption_(connection.cups_encryption_),
+      blocking_(connection.blocking_),
+      impl_(std::move(connection.impl_)),
+      cups_http_(std::move(connection.cups_http_)) {}
+
+CupsConnection::~CupsConnection() {}
+
+bool CupsConnection::Connect() {
+  if (cups_http_)
+    return true;  // we're already connected
+
+  std::string host;
+  int port;
+
+  if (!print_server_url_.is_empty()) {
+    host = print_server_url_.host();
+    port = print_server_url_.IntPort();
+  } else {
+    host = cupsServer();
+    port = ippPort();
+  }
+
+  http_t* connection =
+      httpConnect2(host.c_str(), port, nullptr, AF_UNSPEC, cups_encryption_,
+                   blocking_ ? 1 : 0, kTimeoutMs, nullptr);
+
+  if (!connection)
+    return false;
+
+  impl_ = base::MakeUnique<Impl>(connection);
+  cups_http_ = impl_->GetHttp();
+  return true;
+}
+
+std::vector<CupsPrinter> CupsConnection::GetDests() {
+  if (!Connect()) {
+    LOG(WARNING) << "CUPS connection failed";
+    return std::vector<CupsPrinter>();
+  }
+
+  DestinationEnumerator enumerator;
+  int success =
+      cupsEnumDests(CUPS_DEST_FLAGS_NONE, kTimeoutMs,
+                    nullptr,               // no cancel signal
+                    0,                     // all the printers
+                    CUPS_PRINTER_SCANNER,  // except the scanners
+                    &DestinationEnumerator::cups_callback, &enumerator);
+
+  if (!success) {
+    LOG(WARNING) << "Enumerating printers failed";
+    return std::vector<CupsPrinter>();
+  }
+
+  auto& dests = enumerator.get_dests();
+  std::vector<CupsPrinter> printers;
+  for (auto& dest : dests) {
+    printers.emplace_back(impl_->GetHttp(), std::move(dest), nullptr);
+  }
+
+  dests.clear();  // CupsPrinter takes ownership of all the cups_dest_t objects

[Lei Zhang, 2016/07/19 22:26:39]

Do you feel it would be clearer if we did:

auto dests = std::move(enumerator.get_dests());
std::vector<CupsPrinter> printers;
for (...) { ... }
// no need to clear here
return printers;

[skau, 2016/07/20 23:58:22]

That seems reasonable.  I'll defer to you as to if it's clearer.  The affect of
the move isn't immediately clear to me.  It's because get_dests() returns a 
reference correct? 

+
+  return printers;
+}
+
+std::unique_ptr<CupsPrinter> CupsConnection::GetPrinter(
+    const std::string& name) {
+  if (!Connect())
+    return nullptr;
+
+  cups_dest_t* dest = cupsGetNamedDest(cups_http_.get(), name.c_str(), nullptr);
+  if (!dest)
+    return nullptr;
+
+  cups_dinfo_t* info = cupsCopyDestInfo(cups_http_.get(), dest);
+  return base::MakeUnique<CupsPrinter>(
+      impl_->GetHttp(), std::unique_ptr<cups_dest_t, DestinationDeleter>(dest),
+      std::unique_ptr<cups_dinfo_t, DestInfoDeleter>(info));
+}
+
+std::string CupsConnection::server_name() const {
+  return print_server_url_.host();
+}
+
+int CupsConnection::last_error() const {
+  return cupsLastError();
+}
+
+}  // namespace printing