// Copyright 2020 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 "ui/gfx/x/connection.h"

#include <xcb/xcb.h>
#include <xcb/xcbext.h>

#include <algorithm>
#include <string>

#include "base/auto_reset.h"
#include "base/command_line.h"
#include "base/memory/ptr_util.h"
#include "base/memory/scoped_refptr.h"
#include "base/no_destructor.h"
#include "base/threading/thread_local.h"
#include "base/trace_event/trace_event.h"
#include "ui/gfx/x/bigreq.h"
#include "ui/gfx/x/event.h"
#include "ui/gfx/x/keyboard_state.h"
#include "ui/gfx/x/randr.h"
#include "ui/gfx/x/x11_switches.h"
#include "ui/gfx/x/xkb.h"
#include "ui/gfx/x/xproto.h"
#include "ui/gfx/x/xproto_internal.h"
#include "ui/gfx/x/xproto_types.h"

namespace x11 {

namespace {

// On the wire, sequence IDs are 16 bits.  In xcb, they're usually extended to
// 32 and sometimes 64 bits.  In Xlib, they're extended to unsigned long, which
// may be 32 or 64 bits depending on the platform.  This function is intended to
// prevent bugs caused by comparing two differently sized sequences.  Also
// handles rollover.  To use, compare the result of this function with 0.  For
// example, to compare seq1 <= seq2, use CompareSequenceIds(seq1, seq2) <= 0.
template <typename T, typename U>
auto CompareSequenceIds(T t, U u) {
  static_assert(std::is_unsigned<T>::value, "");
  static_assert(std::is_unsigned<U>::value, "");
  // Cast to the smaller of the two types so that comparisons will always work.
  // If we casted to the larger type, then the smaller type will be zero-padded
  // and may incorrectly compare less than the other value.
  using SmallerType =
      typename std::conditional<sizeof(T) <= sizeof(U), T, U>::type;
  SmallerType t0 = static_cast<SmallerType>(t);
  SmallerType u0 = static_cast<SmallerType>(u);
  using SignedType = typename std::make_signed<SmallerType>::type;
  return static_cast<SignedType>(t0 - u0);
}

base::ThreadLocalOwnedPointer<Connection>& GetConnectionTLS() {
  static base::NoDestructor<base::ThreadLocalOwnedPointer<Connection>> tls;
  return *tls;
}

void DefaultErrorHandler(const Error* error, const char* request_name) {
  LOG(WARNING) << "X error received.  Request: " << request_name
               << "Request, Error: " << error->ToString();
}

void DefaultIOErrorHandler() {
  LOG(ERROR) << "X connection error received.";
}

class UnknownError : public Error {
 public:
  explicit UnknownError(Connection::RawError error_bytes)
      : error_bytes_(error_bytes) {}

  ~UnknownError() override = default;

  std::string ToString() const override {
    std::stringstream ss;
    ss << "UnknownError{";
    // Errors are always a fixed 32 bytes.
    for (size_t i = 0; i < 32; i++) {
      char buf[3];
      sprintf(buf, "%02x", error_bytes_->data()[i]);
      ss << "0x" << buf;
      if (i != 31)
        ss << ", ";
    }
    ss << "}";
    return ss.str();
  }

 private:
  Connection::RawError error_bytes_;
};

}  // namespace

// static
Connection* Connection::Get() {
  auto& tls = GetConnectionTLS();
  if (Connection* connection = tls.Get())
    return connection;
  auto connection = std::make_unique<Connection>();
  auto* p_connection = connection.get();
  tls.Set(std::move(connection));
  return p_connection;
}

// static
void Connection::Set(std::unique_ptr<Connection> connection) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(connection->sequence_checker_);
  auto& tls = GetConnectionTLS();
  DCHECK(!tls.Get());
  tls.Set(std::move(connection));
}

Connection::Connection(const std::string& address)
    : XProto(this),
      display_string_(
          address.empty()
              ? base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
                    switches::kX11Display)
              : address),
      error_handler_(base::BindRepeating(DefaultErrorHandler)),
      io_error_handler_(base::BindOnce(DefaultIOErrorHandler)) {
  connection_ =
      xcb_connect(display_string_.empty() ? nullptr : display_string_.c_str(),
                  &default_screen_id_);
  DCHECK(connection_);
  if (Ready()) {
    auto buf = ReadBuffer(base::MakeRefCounted<UnretainedRefCountedMemory>(
                              xcb_get_setup(XcbConnection())),
                          true);
    setup_ = Read<Setup>(&buf);
    default_screen_ = &setup_.roots[DefaultScreenId()];
    InitRootDepthAndVisual();
  } else {
    // Default-initialize the setup data so we always have something to return.
    setup_.roots.emplace_back();
    default_screen_ = &setup_.roots[0];
    default_screen_->allowed_depths.emplace_back();
    default_root_depth_ = &default_screen_->allowed_depths[0];
    default_root_depth_->visuals.emplace_back();
    default_root_visual_ = &default_root_depth_->visuals[0];
  }

  ExtensionManager::Init(this);
  auto enable_bigreq = bigreq().Enable();
  // Xlib enables XKB on display creation, so we do that here to maintain
  // compatibility.
  xkb()
      .UseExtension({Xkb::major_version, Xkb::minor_version})
      .OnResponse(base::BindOnce([](Xkb::UseExtensionResponse response) {
        if (!response || !response->supported)
          DVLOG(1) << "Xkb extension not available.";
      }));
  Flush();
  if (auto response = enable_bigreq.Sync())
    extended_max_request_length_ = response->maximum_request_length;

  const Format* formats[256];
  memset(formats, 0, sizeof(formats));
  for (const auto& format : setup_.pixmap_formats)
    formats[format.depth] = &format;

  std::vector<std::pair<VisualId, VisualInfo>> default_screen_visuals;
  for (const auto& depth : default_screen().allowed_depths) {
    const Format* format = formats[depth.depth];
    for (const auto& visual : depth.visuals) {
      default_screen_visuals.emplace_back(visual.visual_id,
                                          VisualInfo{format, &visual});
    }
  }
  default_screen_visuals_ =
      base::flat_map<VisualId, VisualInfo>(std::move(default_screen_visuals));

  keyboard_state_ = CreateKeyboardState(this);

  InitErrorParsers();
}

Connection::~Connection() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  platform_event_source.reset();
  xcb_disconnect(connection_);
}

size_t Connection::MaxRequestSizeInBytes() const {
  return 4 * std::max<size_t>(extended_max_request_length_,
                              setup_.maximum_request_length);
}

XlibDisplayWrapper Connection::GetXlibDisplay(XlibDisplayType type) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  if (!xlib_display_)
    xlib_display_ = base::WrapUnique(new XlibDisplay(display_string_));
  return XlibDisplayWrapper(xlib_display_->display_, type);
}

Connection::FutureImpl::FutureImpl(Connection* connection,
                                   SequenceType sequence,
                                   bool generates_reply,
                                   const char* request_name_for_tracing)
    : connection(connection),
      sequence(sequence),
      generates_reply(generates_reply),
      request_name_for_tracing(request_name_for_tracing) {}

void Connection::FutureImpl::Wait() {
  connection->WaitForResponse(this);
  ProcessResponse();
}

void Connection::FutureImpl::Sync(RawReply* raw_reply,
                                  std::unique_ptr<Error>* error) {
  connection->WaitForResponse(this);
  TakeResponse(raw_reply, error);
}

void Connection::FutureImpl::OnResponse(ResponseCallback callback) {
  UpdateRequestHandler(std::move(callback));
}

void Connection::FutureImpl::UpdateRequestHandler(ResponseCallback callback) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(connection->sequence_checker_);
  DCHECK(callback);

  auto* request = connection->GetRequestForFuture(this);
  // Make sure we haven't processed this request yet.
  DCHECK(request->callback);

  request->callback = std::move(callback);
}

void Connection::FutureImpl::ProcessResponse() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(connection->sequence_checker_);

  auto* request = connection->GetRequestForFuture(this);
  DCHECK(request->callback);
  DCHECK(request->have_response);

  std::move(request->callback)
      .Run(std::move(request->reply), std::move(request->error));
}

void Connection::FutureImpl::TakeResponse(RawReply* raw_reply,
                                          std::unique_ptr<Error>* error) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(connection->sequence_checker_);

  auto* request = connection->GetRequestForFuture(this);
  DCHECK(request->callback);
  DCHECK(request->have_response);

  *raw_reply = std::move(request->reply);
  *error = std::move(request->error);
  request->callback.Reset();
}

Connection::Request::Request(ResponseCallback callback)
    : callback(std::move(callback)) {
  DCHECK(this->callback);
}

Connection::Request::Request(Request&& other) = default;

Connection::Request::~Request() = default;

void Connection::Request::SetResponse(Connection* connection,
                                      void* raw_reply,
                                      void* raw_error) {
  have_response = true;
  if (raw_reply)
    reply = base::MakeRefCounted<MallocedRefCountedMemory>(raw_reply);
  if (raw_error) {
    error = connection->ParseError(
        base::MakeRefCounted<MallocedRefCountedMemory>(raw_error));
  }
}

bool Connection::HasNextResponse() {
  if (requests_.empty())
    return false;
  auto& request = requests_.front();
  if (request.have_response)
    return true;

  void* reply = nullptr;
  xcb_generic_error_t* error = nullptr;
  if (!xcb_poll_for_reply(XcbConnection(), first_request_id_, &reply, &error))
    return false;

  request.SetResponse(this, reply, error);
  return true;
}

bool Connection::HasNextEvent() {
  while (!events_.empty()) {
    if (events_.front().Initialized())
      return true;
    events_.pop_front();
  }
  return false;
}

int Connection::GetFd() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  return Ready() ? xcb_get_file_descriptor(XcbConnection()) : -1;
}

const std::string& Connection::DisplayString() const {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  return display_string_;
}

std::string Connection::GetConnectionHostname() const {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  char* host = nullptr;
  int display_id = 0;
  int screen = 0;
  if (xcb_parse_display(display_string_.c_str(), &host, &display_id, &screen)) {
    std::string name = host;
    free(host);
    return name;
  }
  return std::string();
}

int Connection::DefaultScreenId() const {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  // This is not part of the setup data as the server has no concept of a
  // default screen. Instead, it's part of the display name. Eg in
  // "localhost:0.0", the screen ID is the second "0".
  return default_screen_id_;
}

bool Connection::Ready() const {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  return !xcb_connection_has_error(connection_);
}

void Connection::Flush() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  xcb_flush(connection_);
}

void Connection::Sync() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  if (syncing_)
    return;
  {
    base::AutoReset<bool> auto_reset(&syncing_, true);
    GetInputFocus().Sync();
  }
}

void Connection::SynchronizeForTest(bool synchronous) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  synchronous_ = synchronous;
  if (synchronous_)
    Sync();
}

void Connection::ReadResponses() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  while (ReadResponse(false)) {
  }
}

bool Connection::ReadResponse(bool queued) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  auto* event = queued ? xcb_poll_for_queued_event(XcbConnection())
                       : xcb_poll_for_event(XcbConnection());
  if (event) {
    events_.emplace_back(base::MakeRefCounted<MallocedRefCountedMemory>(event),
                         this);
  }
  return event;
}

Event Connection::WaitForNextEvent() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  if (HasNextEvent()) {
    Event event = std::move(events_.front());
    events_.pop_front();
    return event;
  }
  if (auto* xcb_event = xcb_wait_for_event(XcbConnection())) {
    return Event(base::MakeRefCounted<MallocedRefCountedMemory>(xcb_event),
                 this);
  }
  return Event();
}

bool Connection::HasPendingResponses() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  return HasNextEvent() || HasNextResponse();
}

const Connection::VisualInfo* Connection::GetVisualInfoFromId(
    VisualId id) const {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  auto it = default_screen_visuals_.find(id);
  if (it != default_screen_visuals_.end())
    return &it->second;
  return nullptr;
}

KeyCode Connection::KeysymToKeycode(uint32_t keysym) const {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  return keyboard_state_->KeysymToKeycode(keysym);
}

uint32_t Connection::KeycodeToKeysym(KeyCode keycode,
                                     uint32_t modifiers) const {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  return keyboard_state_->KeycodeToKeysym(keycode, modifiers);
}

std::unique_ptr<Connection> Connection::Clone() const {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  return std::make_unique<Connection>(display_string_);
}

void Connection::DetachFromSequence() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DETACH_FROM_SEQUENCE(sequence_checker_);
}

bool Connection::Dispatch() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  if (HasNextResponse() && HasNextEvent()) {
    auto next_response_sequence = first_request_id_;
    auto next_event_sequence = events_.front().sequence();

    // All events have the sequence number of the last processed request
    // included in them.  So if a reply and an event have the same sequence,
    // the reply must have been received first.
    if (CompareSequenceIds(next_event_sequence, next_response_sequence) <= 0)
      ProcessNextResponse();
    else
      ProcessNextEvent();
  } else if (HasNextResponse()) {
    ProcessNextResponse();
  } else if (HasNextEvent()) {
    ProcessNextEvent();
  } else {
    return false;
  }
  return true;
}

void Connection::DispatchAll() {
  do {
    Flush();
    ReadResponses();
  } while (Dispatch());
}

void Connection::DispatchEvent(const Event& event) {
  PreDispatchEvent(event);

  // NB: The event should be reset to nullptr when this function
  // returns, not to its initial value, otherwise nested message loops
  // will incorrectly think that the current event being dispatched is
  // an old event.  This means base::AutoReset should not be used.
  dispatching_event_ = &event;
  for (auto& observer : event_observers_)
    observer.OnEvent(event);
  dispatching_event_ = nullptr;
}

Connection::ErrorHandler Connection::SetErrorHandler(ErrorHandler new_handler) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  return std::exchange(error_handler_, new_handler);
}

void Connection::SetIOErrorHandler(IOErrorHandler new_handler) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  io_error_handler_ = std::move(new_handler);
}

void Connection::AddEventObserver(EventObserver* observer) {
  event_observers_.AddObserver(observer);
}

void Connection::RemoveEventObserver(EventObserver* observer) {
  event_observers_.RemoveObserver(observer);
}

xcb_connection_t* Connection::XcbConnection() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  if (io_error_handler_ && xcb_connection_has_error(connection_))
    std::move(io_error_handler_).Run();
  return connection_;
}

void Connection::InitRootDepthAndVisual() {
  for (auto& depth : default_screen_->allowed_depths) {
    for (auto& visual : depth.visuals) {
      if (visual.visual_id == default_screen_->root_visual) {
        default_root_depth_ = &depth;
        default_root_visual_ = &visual;
        return;
      }
    }
  }
  NOTREACHED();
}

void Connection::ProcessNextEvent() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DCHECK(HasNextEvent());

  Event event = std::move(events_.front());
  events_.pop_front();

  DispatchEvent(event);
}

void Connection::ProcessNextResponse() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DCHECK(!requests_.empty());
  DCHECK(requests_.front().have_response);

  Request request = std::move(requests_.front());
  requests_.pop_front();
  if (last_non_void_request_id_.has_value() &&
      last_non_void_request_id_.value() == first_request_id_) {
    last_non_void_request_id_ = absl::nullopt;
  }
  first_request_id_++;
  if (request.callback) {
    std::move(request.callback)
        .Run(std::move(request.reply), std::move(request.error));
  }
}

std::unique_ptr<Connection::FutureImpl> Connection::SendRequest(
    WriteBuffer* buf,
    const char* request_name_for_tracing,
    bool generates_reply,
    bool reply_has_fds) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  xcb_protocol_request_t xpr{
      .ext = nullptr,
      .isvoid = !generates_reply,
  };

  struct RequestHeader {
    uint8_t major_opcode;
    uint8_t minor_opcode;
    uint16_t length;
  };

  struct ExtendedRequestHeader {
    RequestHeader header;
    uint32_t long_length;
  };
  static_assert(sizeof(ExtendedRequestHeader) == 8, "");

  auto& first_buffer = buf->GetBuffers()[0];
  DCHECK_GE(first_buffer->size(), sizeof(RequestHeader));
  auto* old_header = reinterpret_cast<RequestHeader*>(
      const_cast<uint8_t*>(first_buffer->data()));
  ExtendedRequestHeader new_header{*old_header, 0};

  // Requests are always a multiple of 4 bytes on the wire.  Because of this,
  // the length field represents the size in chunks of 4 bytes.
  DCHECK_EQ(buf->offset() % 4, 0UL);
  size_t size32 = buf->offset() / 4;

  // XCB requires 2 iovecs for its own internal usage.
  std::vector<struct iovec> io{{nullptr, 0}, {nullptr, 0}};
  if (size32 < setup_.maximum_request_length) {
    // Regular request
    old_header->length = size32;
  } else if (size32 < extended_max_request_length_) {
    // BigRequests extension request
    DCHECK_EQ(new_header.header.length, 0U);
    new_header.long_length = size32 + 1;

    io.push_back({&new_header, sizeof(ExtendedRequestHeader)});
    first_buffer = base::MakeRefCounted<OffsetRefCountedMemory>(
        first_buffer, sizeof(RequestHeader),
        first_buffer->size() - sizeof(RequestHeader));
  } else {
    LOG(ERROR) << "Cannot send request of length " << buf->offset();
    return nullptr;
  }

  for (auto& buffer : buf->GetBuffers())
    io.push_back({const_cast<uint8_t*>(buffer->data()), buffer->size()});
  xpr.count = io.size() - 2;

  xcb_connection_t* conn = XcbConnection();
  auto flags = XCB_REQUEST_CHECKED | XCB_REQUEST_RAW;
  if (reply_has_fds)
    flags |= XCB_REQUEST_REPLY_FDS;

  for (int fd : buf->fds())
    xcb_send_fd(conn, fd);
  SequenceType sequence = xcb_send_request(conn, flags, &io[2], &xpr);

  if (xcb_connection_has_error(conn))
    return nullptr;

  SequenceType next_request_id = first_request_id_ + requests_.size();
  DCHECK_EQ(CompareSequenceIds(next_request_id, sequence), 0);

  // If we ever reach 2^32 outstanding requests, then bail because sequence IDs
  // would no longer be unique.
  next_request_id++;
  CHECK_NE(next_request_id, first_request_id_);

  // Install a default response-handler that throws away the reply and prints
  // the error if there is one.  This handler may be overridden by clients.
  auto callback = base::BindOnce(
      [](const char* request_name, Connection::ErrorHandler error_handler,
         RawReply raw_reply, std::unique_ptr<Error> error) {
        if (error)
          error_handler.Run(error.get(), request_name);
      },
      request_name_for_tracing, error_handler_);
  requests_.emplace_back(std::move(callback));
  if (generates_reply)
    last_non_void_request_id_ = sequence;
  if (synchronous_)
    Sync();

  return std::make_unique<FutureImpl>(this, sequence, generates_reply,
                                      request_name_for_tracing);
}

void Connection::WaitForResponse(FutureImpl* future) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  auto* request = GetRequestForFuture(future);
  DCHECK(request->callback);
  if (request->have_response)
    return;

  xcb_generic_error_t* error = nullptr;
  void* reply = nullptr;
  if (future->generates_reply) {
    if (!xcb_poll_for_reply(XcbConnection(), future->sequence, &reply,
                            &error)) {
      TRACE_EVENT1("ui", "xcb_wait_for_reply", "request",
                   future->request_name_for_tracing);
      reply = xcb_wait_for_reply(XcbConnection(), future->sequence, &error);
    }
  } else {
    // There's a special case here.  This request doesn't generate a reply, and
    // may not generate an error, so the only way to know if it finished is to
    // send another request that we know will generate a reply or error.  Once
    // the new request finishes, we know this request has finished, since the
    // server is guaranteed to process requests in order.  Normally, the
    // xcb_request_check() below would do this for us automatically, but we need
    // to keep track of the sequence count ourselves, so we explicitly make a
    // GetInputFocus request if necessary (which is the request xcb would have
    // made -- GetInputFocus is chosen since it has the minimum size request and
    // reply, and can be made at any time).
    bool needs_extra_request_for_check = false;
    if (!last_non_void_request_id_.has_value()) {
      needs_extra_request_for_check = true;
    } else {
      SequenceType last_non_void_offset =
          last_non_void_request_id_.value() - first_request_id_;
      SequenceType sequence_offset = future->sequence - first_request_id_;
      needs_extra_request_for_check = sequence_offset > last_non_void_offset;
    }
    if (needs_extra_request_for_check) {
      GetInputFocus().IgnoreError();
      // The circular_deque may have swapped buffers, so we need to get a fresh
      // pointer to the request.
      request = GetRequestForFuture(future);
    }

    // libxcb has a bug where it doesn't flush in xcb_request_check() under some
    // circumstances, leading to deadlock [1], so always perform a manual flush.
    // [1] https://gitlab.freedesktop.org/xorg/lib/libxcb/-/issues/53
    Flush();

    {
      TRACE_EVENT1("ui", "xcb_request_check", "request",
                   future->request_name_for_tracing);
      error = xcb_request_check(XcbConnection(), {future->sequence});
    }
  }
  request->SetResponse(this, reply, error);
}

Connection::Request* Connection::GetRequestForFuture(FutureImpl* future) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  SequenceType offset = future->sequence - first_request_id_;
  DCHECK_LT(offset, requests_.size());
  return &requests_[offset];
}

void Connection::PreDispatchEvent(const Event& event) {
  if (auto* mapping = event.As<MappingNotifyEvent>()) {
    if (mapping->request == Mapping::Modifier ||
        mapping->request == Mapping::Keyboard) {
      setup_.min_keycode = mapping->first_keycode;
      setup_.max_keycode = static_cast<KeyCode>(
          static_cast<int>(mapping->first_keycode) + mapping->count - 1);
      keyboard_state_->UpdateMapping();
    }
  }
  if (auto* notify = event.As<Xkb::NewKeyboardNotifyEvent>()) {
    setup_.min_keycode = notify->minKeyCode;
    setup_.max_keycode = notify->maxKeyCode;
    keyboard_state_->UpdateMapping();
  }

  // This is adapted from XRRUpdateConfiguration.
  if (auto* configure = event.As<ConfigureNotifyEvent>()) {
    int index = ScreenIndexFromRootWindow(configure->window);
    if (index != -1) {
      setup_.roots[index].width_in_pixels = configure->width;
      setup_.roots[index].height_in_pixels = configure->height;
    }
  } else if (auto* screen = event.As<RandR::ScreenChangeNotifyEvent>()) {
    int index = ScreenIndexFromRootWindow(screen->root);
    DCHECK_GE(index, 0);
    bool portrait =
        static_cast<bool>(screen->rotation & (RandR::Rotation::Rotate_90 |
                                              RandR::Rotation::Rotate_270));
    if (portrait) {
      setup_.roots[index].width_in_pixels = screen->height;
      setup_.roots[index].height_in_pixels = screen->width;
      setup_.roots[index].width_in_millimeters = screen->mheight;
      setup_.roots[index].height_in_millimeters = screen->mwidth;
    } else {
      setup_.roots[index].width_in_pixels = screen->width;
      setup_.roots[index].height_in_pixels = screen->height;
      setup_.roots[index].width_in_millimeters = screen->mwidth;
      setup_.roots[index].height_in_millimeters = screen->mheight;
    }
  }
}

int Connection::ScreenIndexFromRootWindow(Window root) const {
  for (size_t i = 0; i < setup_.roots.size(); i++) {
    if (setup_.roots[i].root == root)
      return i;
  }
  return -1;
}

std::unique_ptr<Error> Connection::ParseError(RawError error_bytes) {
  if (!error_bytes)
    return nullptr;
  struct ErrorHeader {
    uint8_t response_type;
    uint8_t error_code;
    uint16_t sequence;
  };
  auto error_code = error_bytes->front_as<ErrorHeader>()->error_code;
  if (auto parser = error_parsers_[error_code])
    return parser(error_bytes);
  return std::make_unique<UnknownError>(error_bytes);
}

uint32_t Connection::GenerateIdImpl() {
  return xcb_generate_id(connection_);
}

}  // namespace x11