pw_bluetooth_proxy: Write Identifier in signaling command headers

Bug: 380076024
Change-Id: Ib95f17ae01cb628ad0e999076677fd1790126af0
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/252952
Commit-Queue: Ali Saeed <saeedali@google.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Reviewed-by: David Rees <drees@google.com>
Docs-Not-Needed: Ali Saeed <saeedali@google.com>
Reviewed-by: Ben Lawson <benlawson@google.com>

pw_bluetooth_proxy/l2cap_signaling_channel.cc

@@ -278,6 +278,7 @@ Status L2capSignalingChannel::SendFlowControlCreditInd(uint16_t cid,
           cframe.payload().SizeInBytes());
   ind.command_header().code().Write(
       emboss::L2capSignalingPacketCode::FLOW_CONTROL_CREDIT_IND);
+  ind.command_header().identifier().Write(GetNextIdentifierAndIncrement());
   ind.command_header().data_length().Write(
       emboss::L2capFlowControlCreditInd::IntrinsicSizeInBytes() -
       emboss::L2capSignalingCommandHeader::IntrinsicSizeInBytes());
@@ -287,4 +288,12 @@ Status L2capSignalingChannel::SendFlowControlCreditInd(uint16_t cid,
   return QueuePacket(std::move(h4_packet));
 }
 
+uint8_t L2capSignalingChannel::GetNextIdentifierAndIncrement() {
+  if (next_identifier_ == UINT8_MAX) {
+    next_identifier_ = 1;
+    return UINT8_MAX;
+  }
+  return next_identifier_++;
+}
+
 }  // namespace pw::bluetooth::proxy

pw_bluetooth_proxy/proxy_host_test.cc

@@ -3996,6 +3996,15 @@ TEST(L2capSignalingTest, RxAdditionalCreditsSentOnL2capCocAcquisition) {
             emboss::MakeL2capFlowControlCreditIndView(
                 cframe.payload().BackingStorage().data(),
                 cframe.payload().SizeInBytes());
+        EXPECT_EQ(ind.command_header().code().Read(),
+                  emboss::L2capSignalingPacketCode::FLOW_CONTROL_CREDIT_IND);
+        // TODO: https://pwbug.dev/382553099 - Test to ensure we are properly
+        // incrementing Identifier when sending multiple signaling packets.
+        EXPECT_EQ(ind.command_header().identifier().Read(), 1);
+        EXPECT_EQ(
+            ind.command_header().data_length().Read(),
+            emboss::L2capFlowControlCreditInd::IntrinsicSizeInBytes() -
+                emboss::L2capSignalingCommandHeader::IntrinsicSizeInBytes());
         EXPECT_EQ(ind.cid().Read(), capture.local_cid);
         EXPECT_EQ(ind.credits().Read(), capture.credits);
       });

pw_bluetooth_proxy/public/pw_bluetooth_proxy/internal/l2cap_signaling_channel.h

@@ -14,7 +14,6 @@
 
 #pragma once
 
-#include "pw_bluetooth/hci_data.emb.h"
 #include "pw_bluetooth/l2cap_frames.emb.h"
 #include "pw_bluetooth_proxy/basic_l2cap_channel.h"
 #include "pw_bluetooth_proxy/l2cap_status_delegate.h"
@@ -89,6 +88,10 @@ class L2capSignalingChannel : public BasicL2capChannel {
 
   bool HandlePduFromHost(pw::span<uint8_t> cframe) override;
 
+  // Get the next Identifier value that should be written to a signaling
+  // command and increment the Identifier.
+  uint8_t GetNextIdentifierAndIncrement();
+
   L2capChannelManager& l2cap_channel_manager_;
 
  private:
@@ -107,6 +110,16 @@ class L2capSignalingChannel : public BasicL2capChannel {
       PW_GUARDED_BY(mutex_){};
 
   sync::Mutex mutex_;
+
+  // Core Spec v6.0 Vol 3, Part A, Section 4: "The Identifier field is one octet
+  // long and matches responses with requests. The requesting device sets this
+  // field and the responding device uses the same value in its response. Within
+  // each signaling channel a different Identifier shall be used for each
+  // successive command. Following the original transmission of an Identifier in
+  // a command, the Identifier may be recycled if all other Identifiers have
+  // subsequently been used."
+  // TODO: https://pwbug.dev/382553099 - Synchronize this value with AP host.
+  uint8_t next_identifier_ = 1;
 };
 
 }  // namespace pw::bluetooth::proxy