host/sdp/client.cc

// Copyright 2023 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.

#include "pw_bluetooth_sapphire/internal/host/sdp/client.h"

#include <functional>
#include <optional>

namespace bt::sdp {

namespace {

// Increased after some particularly slow devices taking a long time for
// transactions with continuations.
constexpr pw::chrono::SystemClock::duration kTransactionTimeout =
    std::chrono::seconds(10);

class Impl final : public Client {
 public:
  explicit Impl(l2cap::Channel::WeakPtr channel,
                pw::async::Dispatcher& dispatcher);

  ~Impl() override;

 private:
  void ServiceSearchAttributes(
      std::unordered_set<UUID> search_pattern,
      const std::unordered_set<AttributeId>& req_attributes,
      SearchResultFunction result_cb) override;

  // Information about a transaction that hasn't finished yet.
  struct Transaction {
    Transaction(TransactionId id,
                ServiceSearchAttributeRequest req,
                SearchResultFunction cb);
    // The TransactionId used for this request.  This will be reused until the
    // transaction is complete.
    TransactionId id;
    // Request PDU for this transaction.
    ServiceSearchAttributeRequest request;
    // Callback for results.
    SearchResultFunction callback;
    // The response, built from responses from the remote server.
    ServiceSearchAttributeResponse response;
  };

  // Callbacks for l2cap::Channel
  void OnRxFrame(ByteBufferPtr data);
  void OnChannelClosed();

  // Finishes a pending transaction on this client, completing their callbacks.
  void Finish(TransactionId id);

  // Cancels a pending transaction this client has started, completing the
  // callback with the given reason as an error.
  void Cancel(TransactionId id, HostError reason);

  // Cancels all remaining transactions without sending them, with the given
  // reason as an error.
  void CancelAll(HostError reason);

  // Get the next available transaction id
  TransactionId GetNextId();

  // Try to send the next pending request, if possible.
  void TrySendNextTransaction();

  pw::async::Dispatcher& pw_dispatcher_;
  // The channel that this client is running on.
  l2cap::ScopedChannel channel_;
  // THe next transaction id that we should use
  TransactionId next_tid_ = 0;
  // Any transactions that are not completed.
  std::unordered_map<TransactionId, Transaction> pending_;
  // Timeout for the current transaction. false if none are waiting for a
  // response.
  std::optional<SmartTask> pending_timeout_;

  WeakSelf<Impl> weak_self_{this};

  BT_DISALLOW_COPY_AND_ASSIGN_ALLOW_MOVE(Impl);
};

Impl::Impl(l2cap::Channel::WeakPtr channel, pw::async::Dispatcher& dispatcher)
    : pw_dispatcher_(dispatcher), channel_(std::move(channel)) {
  auto self = weak_self_.GetWeakPtr();
  bool activated = channel_->Activate(
      [self](auto packet) {
        if (self.is_alive()) {
          self->OnRxFrame(std::move(packet));
        }
      },
      [self] {
        if (self.is_alive()) {
          self->OnChannelClosed();
        }
      });
  if (!activated) {
    bt_log(INFO, "sdp", "failed to activate channel");
    channel_ = nullptr;
  }
}

Impl::~Impl() { CancelAll(HostError::kCanceled); }

void Impl::CancelAll(HostError reason) {
  // Avoid using |this| in case callbacks destroy this object.
  auto pending = std::move(pending_);
  pending_.clear();
  for (auto& it : pending) {
    it.second.callback(ToResult(reason).take_error());
  }
}

void Impl::TrySendNextTransaction() {
  if (pending_timeout_) {
    // Waiting on a transaction to finish.
    return;
  }

  if (!channel_) {
    bt_log(INFO,
           "sdp",
           "Failed to send %zu requests: link closed",
           pending_.size());
    CancelAll(HostError::kLinkDisconnected);
    return;
  }

  if (pending_.empty()) {
    return;
  }

  auto& next = pending_.begin()->second;

  if (!channel_->Send(next.request.GetPDU(next.id))) {
    bt_log(INFO, "sdp", "Failed to send request: channel send failed");
    Cancel(next.id, HostError::kFailed);
    return;
  }

  auto& timeout = pending_timeout_.emplace(pw_dispatcher_);

  // Timeouts are held in this so it is safe to use.
  timeout.set_function(
      [this, id = next.id](pw::async::Context /*ctx*/, pw::Status status) {
        if (!status.ok()) {
          return;
        }
        bt_log(WARN, "sdp", "Transaction %d timed out, removing!", id);
        Cancel(id, HostError::kTimedOut);
      });
  timeout.PostAfter(kTransactionTimeout);
}

void Impl::ServiceSearchAttributes(
    std::unordered_set<UUID> search_pattern,
    const std::unordered_set<AttributeId>& req_attributes,
    SearchResultFunction result_cb) {
  ServiceSearchAttributeRequest req;
  req.set_search_pattern(std::move(search_pattern));
  if (req_attributes.empty()) {
    req.AddAttributeRange(0, 0xFFFF);
  } else {
    for (const auto& id : req_attributes) {
      req.AddAttribute(id);
    }
  }
  TransactionId next = GetNextId();

  auto [iter, placed] =
      pending_.try_emplace(next, next, std::move(req), std::move(result_cb));
  BT_DEBUG_ASSERT_MSG(placed, "Should not have repeat transaction ID %u", next);

  TrySendNextTransaction();
}

void Impl::Finish(TransactionId id) {
  auto node = pending_.extract(id);
  BT_DEBUG_ASSERT(node);
  auto& state = node.mapped();
  pending_timeout_.reset();
  if (!state.callback) {
    return;
  }
  BT_DEBUG_ASSERT_MSG(state.response.complete(),
                      "Finished without complete response");

  auto self = weak_self_.GetWeakPtr();

  size_t count = state.response.num_attribute_lists();
  for (size_t idx = 0; idx <= count; idx++) {
    if (idx == count) {
      state.callback(fit::error(Error(HostError::kNotFound)));
      break;
    }
    // |count| and |idx| are at most std::numeric_limits<uint32_t>::max() + 1,
    // which is caught by the above if statement.
    BT_DEBUG_ASSERT(idx <= std::numeric_limits<uint32_t>::max());
    if (!state.callback(fit::ok(std::cref(
            state.response.attributes(static_cast<uint32_t>(idx)))))) {
      break;
    }
  }

  // Callbacks may have destroyed this object.
  if (!self.is_alive()) {
    return;
  }

  TrySendNextTransaction();
}

Impl::Transaction::Transaction(TransactionId id,
                               ServiceSearchAttributeRequest req,
                               SearchResultFunction cb)
    : id(id), request(std::move(req)), callback(std::move(cb)) {}

void Impl::Cancel(TransactionId id, HostError reason) {
  auto node = pending_.extract(id);
  if (!node) {
    return;
  }

  auto self = weak_self_.GetWeakPtr();
  node.mapped().callback(ToResult(reason).take_error());
  if (!self.is_alive()) {
    return;
  }

  TrySendNextTransaction();
}

void Impl::OnRxFrame(ByteBufferPtr data) {
  TRACE_DURATION("bluetooth", "sdp::Client::Impl::OnRxFrame");
  // Each SDU in SDP is one request or one response. Core 5.0 Vol 3 Part B, 4.2
  PacketView<sdp::Header> packet(data.get());
  size_t pkt_params_len = data->size() - sizeof(Header);
  uint16_t params_len = be16toh(packet.header().param_length);
  if (params_len != pkt_params_len) {
    bt_log(INFO,
           "sdp",
           "bad params length (len %zu != %u), dropping",
           pkt_params_len,
           params_len);
    return;
  }
  packet.Resize(params_len);
  TransactionId tid = be16toh(packet.header().tid);
  auto it = pending_.find(tid);
  if (it == pending_.end()) {
    bt_log(INFO, "sdp", "Received unknown transaction id (%u)", tid);
    return;
  }
  auto& transaction = it->second;
  fit::result<Error<>> parse_status =
      transaction.response.Parse(packet.payload_data());
  if (parse_status.is_error()) {
    if (parse_status.error_value().is(HostError::kInProgress)) {
      bt_log(INFO, "sdp", "Requesting continuation of id (%u)", tid);
      transaction.request.SetContinuationState(
          transaction.response.ContinuationState());
      if (!channel_->Send(transaction.request.GetPDU(tid))) {
        bt_log(INFO, "sdp", "Failed to send continuation of transaction!");
      }
      return;
    }
    bt_log(INFO,
           "sdp",
           "Failed to parse packet for tid %u: %s",
           tid,
           bt_str(parse_status));
    // Drop the transaction with the error.
    Cancel(tid, parse_status.error_value().host_error());
    return;
  }
  if (transaction.response.complete()) {
    bt_log(DEBUG, "sdp", "Rx complete, finishing tid %u", tid);
    Finish(tid);
  }
}

void Impl::OnChannelClosed() {
  bt_log(INFO, "sdp", "client channel closed");
  channel_ = nullptr;
  CancelAll(HostError::kLinkDisconnected);
}

TransactionId Impl::GetNextId() {
  TransactionId next = next_tid_++;
  BT_DEBUG_ASSERT(pending_.size() < std::numeric_limits<TransactionId>::max());
  while (pending_.count(next)) {
    next = next_tid_++;  // Note: overflow is fine
  }
  return next;
}

}  // namespace

std::unique_ptr<Client> Client::Create(l2cap::Channel::WeakPtr channel,
                                       pw::async::Dispatcher& dispatcher) {
  BT_DEBUG_ASSERT(channel.is_alive());
  return std::make_unique<Impl>(std::move(channel), dispatcher);
}

}  // namespace bt::sdp