avrcp_controller: reassemble fragmented AVCTP packets

CHANGELOG.md

@@ -29,6 +29,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - AVRCP: new field `button_pressed` in `AVRCP_SUBEVENT_OPERATION`
 - AVRCP: `AVRCP_SUBEVENT_OPERATION` emitted for button release
 - AVRCP Controller: avrcp_controller_start_press_and_hold_cmd helps to support device buttons
+- AVRCP Controller: reassemble fragmented AVCTP packets
 - AVDTP: `avdtp_register_media_config_validator` allows to validate media codec configuration
 - A2DP Source: `ENABLE_A2DP_SOURCE_EXPLICIT_CONFIG` disables auto config. Requires call to `a2dp_source_set_config_{CODEC}'
 

src/classic/avrcp.h

@@ -111,6 +111,14 @@ typedef enum {
     AVRCP_END_PACKET
 } avrcp_packet_type_t;
 
+
+typedef enum {
+    AVCTP_SINGLE_PACKET= 0,
+    AVCTP_START_PACKET    ,
+    AVCTP_CONTINUE_PACKET ,
+    AVCTP_END_PACKET
+} avctp_packet_type_t;
+
 typedef enum {
     AVRCP_COMMAND_FRAME = 0,
     AVRCP_RESPONSE_FRAME    
@@ -375,7 +383,7 @@ typedef struct {
     avctp_connection_state_t state;
     bool     wait_to_send;
     uint8_t  transaction_label;
-    // used for AVCTP fragmentation
+    // used for fragmentation
     uint8_t  num_packets;
     uint16_t bytes_to_send;
 
@@ -555,6 +563,12 @@ typedef struct {
     uint8_t num_received_fragments;
 
     uint8_t accept_response;
+
+#ifdef ENABLE_AVCTP_FRAGMENTATION
+    uint16_t avctp_reassembly_size;
+    uint8_t  avctp_reassembly_buffer[200];
+#endif
+
 } avrcp_connection_t;
 
 typedef struct {

src/classic/avrcp_controller.c

@@ -690,27 +690,86 @@ avrcp_controller_handle_notification(avrcp_connection_t *connection, avrcp_comma
     avrcp_controller_emit_notification_for_event_id(connection->avrcp_cid, event_id, ctype, payload + pos, size - pos);
 }
 
+#ifdef ENABLE_AVCTP_FRAGMENTATION
+static void avctp_reassemble_message(avrcp_connection_t * connection, avctp_packet_type_t packet_type, uint8_t *packet, uint16_t size){
+    // after header (transaction label and packet type)
+    uint16_t pos;
+    uint16_t bytes_to_store;
+    
+    switch (packet_type){
+        case AVCTP_START_PACKET:
+            if (size < 2) return;
+            
+            // store header
+            pos = 0;
+            connection->avctp_reassembly_buffer[pos] = packet[pos];
+            pos++;
+            connection->avctp_reassembly_size = pos;
+
+            // NOTE: num packets not needed for reassembly, ignoring it does not pose security risk -> no need to store it
+            pos++;
+            
+            // PID in reassembled packet is at offset 1, it will be read later after the avctp_reassemble_message with AVCTP_END_PACKET is called
+            
+            bytes_to_store = btstack_min(size - pos, sizeof(connection->avctp_reassembly_buffer) - connection->avctp_reassembly_size);
+            memcpy(&connection->avctp_reassembly_buffer[connection->avctp_reassembly_size], &packet[pos], bytes_to_store);
+            connection->avctp_reassembly_size += bytes_to_store;
+            break;
+        
+        case AVCTP_CONTINUE_PACKET:
+        case AVCTP_END_PACKET:
+            if (size < 1) return;
+            
+            // store remaining data, ignore header
+            pos = 1;
+            bytes_to_store = btstack_min(size - pos, sizeof(connection->avctp_reassembly_buffer) - connection->avctp_reassembly_size);
+            memcpy(&connection->avctp_reassembly_buffer[connection->avctp_reassembly_size], &packet[pos], bytes_to_store);
+            connection->avctp_reassembly_size += bytes_to_store;
+            break;
+        
+        default:
+            return;
+    }
+}
+#endif
+
 static void avrcp_handle_l2cap_data_packet_for_signaling_connection(avrcp_connection_t * connection, uint8_t *packet, uint16_t size){
     if (size < 6u) return;
-    
     uint8_t  pdu_id;
-    uint8_t  vendor_dependent_packet_type;
+    avrcp_packet_type_t  vendor_dependent_packet_type;
 
-    connection->last_confirmed_transaction_id = packet[0] >> 4;
+    uint16_t pos = 0;
+    connection->last_confirmed_transaction_id = packet[pos] >> 4;
+    avrcp_frame_type_t  frame_type =  (avrcp_frame_type_t)((packet[pos] >> 1) & 0x01);
+    avctp_packet_type_t packet_type = (avctp_packet_type_t)((packet[pos] >> 2) & 0x03);
+    pos++;
 
-    avrcp_frame_type_t  frame_type = (avrcp_frame_type_t)((packet[0] >> 1) & 0x01);
     if (frame_type != AVRCP_RESPONSE_FRAME) return;
         
-    avrcp_packet_type_t packet_type = (avrcp_packet_type_t)((packet[0] >> 2) & 0x03);
     switch (packet_type){
-        case AVRCP_SINGLE_PACKET:
+        case AVCTP_SINGLE_PACKET:
             break;
+        
+#ifdef ENABLE_AVCTP_FRAGMENTATION
+        case AVCTP_START_PACKET:
+        case AVCTP_CONTINUE_PACKET:
+            avctp_reassemble_message(connection, packet_type, packet, size);
+            return;
+        
+        case AVCTP_END_PACKET:
+            avctp_reassemble_message(connection, packet_type, packet, size);
+
+            packet = connection->avctp_reassembly_buffer;
+            size   = connection->avctp_reassembly_size; 
+            break;
+#endif
+        
         default:
-            log_info("Fragmentation is not supported");
             return;
     }
 
-    uint16_t pos = 3;
+    pos += 2; // PID
+
     avrcp_command_type_t ctype = (avrcp_command_type_t) packet[pos++];
     
 #ifdef ENABLE_LOG_INFO
@@ -763,7 +822,6 @@ static void avrcp_handle_l2cap_data_packet_for_signaling_connection(avrcp_connec
             vendor_dependent_packet_type = (avrcp_packet_type_t)(packet[pos++] & 0x03);            
             param_length = big_endian_read_16(packet, pos);
             pos += 2;
-            log_info("operands length %d, remaining size %d", param_length, size - pos);
             
             if ((size - pos) < param_length) return;
 

test/btstack_config.h

@@ -28,6 +28,7 @@
 #define ENABLE_LE_PERIPHERAL
 #define ENABLE_LE_SIGNED_WRITE
 #define ENABLE_SDP_EXTRA_QUERIES
+#define ENABLE_AVCTP_FRAGMENTATION
 
 // BTstack configuration. buffers, sizes, ...
 #define HCI_ACL_PAYLOAD_SIZE 1024