1 // Copyright 2024 The Pigweed Authors
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License"); you may not
4 // use this file except in compliance with the License. You may obtain a copy of
5 // the License at
6 //
7 //     https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
11 // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12 // License for the specific language governing permissions and limitations under
13 // the License.
14 
15 #include "pw_bluetooth_sapphire/internal/host/l2cap/credit_based_flow_control_rx_engine.h"
16 
17 #include <pw_bluetooth/l2cap_frames.emb.h>
18 
19 #include "pw_bluetooth_sapphire/internal/host/common/assert.h"
20 
21 namespace bt::l2cap::internal {
22 
23 namespace emboss = pw::bluetooth::emboss;
24 constexpr auto kSduHeaderSize =
25     pw::bluetooth::emboss::KFrameSduHeader::IntrinsicSizeInBytes();
26 
CreditBasedFlowControlRxEngine(FailureCallback failure_callback)27 CreditBasedFlowControlRxEngine::CreditBasedFlowControlRxEngine(
28     FailureCallback failure_callback)
29     : failure_callback_(std::move(failure_callback)) {}
30 
ProcessPdu(PDU pdu)31 ByteBufferPtr CreditBasedFlowControlRxEngine::ProcessPdu(PDU pdu) {
32   if (!pdu.is_valid()) {
33     OnFailure();
34     return nullptr;
35   }
36 
37   size_t sdu_offset = 0;
38   if (!next_sdu_) {
39     if (pdu.length() < kSduHeaderSize) {
40       // This is a PDU containing the start of a new K-Frame SDU, but the
41       // payload isn't large enough to contain the SDU size field as required
42       // by the spec.
43       OnFailure();
44       return nullptr;
45     }
46 
47     StaticByteBuffer<kSduHeaderSize> sdu_size_buffer;
48     pdu.Copy(&sdu_size_buffer, 0, kSduHeaderSize);
49     auto sdu_size =
50         emboss::MakeKFrameSduHeaderView(&sdu_size_buffer).sdu_length().Read();
51 
52     next_sdu_ = std::make_unique<DynamicByteBuffer>(sdu_size);
53 
54     // Skip the SDU header when copying the payload.
55     sdu_offset = kSduHeaderSize;
56   }
57 
58   if (valid_bytes_ + pdu.length() - sdu_offset > next_sdu_->size()) {
59     // Invalid PDU is larger than the number of remaining bytes in the SDU.
60     OnFailure();
61     return nullptr;
62   }
63   auto view = next_sdu_->mutable_view(valid_bytes_);
64   valid_bytes_ += pdu.Copy(&view, sdu_offset);
65 
66   if (valid_bytes_ < next_sdu_->size()) {
67     // Segmented SDU, wait for additional PDU(s) to complete.
68     return nullptr;
69   }
70 
71   valid_bytes_ = 0;
72   return std::move(next_sdu_);
73 }
74 
OnFailure()75 void CreditBasedFlowControlRxEngine::OnFailure() {
76   failure_callback_();
77   valid_bytes_ = 0;
78   next_sdu_ = nullptr;
79 }
80 
81 }  // namespace bt::l2cap::internal
82