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Thanks for your question.

The response bytes in the sample output are the raw packets sent over BLE. It looks like this:

Creating response: Command_GET_DEVICE_INFORMATION
New Tx Transaction [1] :: Stream [0]
Tx Progress [36/36] :: Stream [0] :: Transaction [1]
>>>>> Response from Gadget -> Echo:
Packet [1/1] contains: 01 00 00 00 24 24 08 14  4a 20 1a 1e 0a 07 61 61 
                       62 62 63 63 64 12 0a 47  61 64 67 65 74 4e 61 6d 
                       65 1a 01 00 22 04 77 78  79 7a 

where the first 6 bytes 01 00 00 00 24 24 are the header containing

• 01: StreamId: 0: control stream and transactionId: 1.
• 00: sequence number: 0, type: initial transaction (type 0), Ack: false and Extended length: false
• 00: reserved
• 00 24: total transaction length 36 bytes (big endian).
• 24: payload length: 36 bytes.

When total transaction length = payload length, it indicates that this is the transaction consists on only one packet (this packet).

The following 36 bytes are a protobuf3 encoded message. Ideally, the byte sequence that follows the header should be passed to a protobuf decoder library, like nanopb. For the purpose of demonstration only, here is the breakdown of the payload according to the protobuf encoding rules:

• 08: Wire type 0 (varint), field number 1 (command)
• 14: Value: GET_DEVICE_INFORMATION
• 4a: Wire type 2 (embedded message), field number 9 (response)
• 20: response length = 32 bytes.
• 1a: Wire type 2 (embedded message), field number 3 (device_information)
• 1e: device_information length = 30 bytes.
• 0a: Wire type 2 (string), field number 1 (serial_number)
• 07: serial_number length = 7 bytes
• 61 61 62 62 63 63 64 = example serial number value “aabbccd”
• 12: Wire type 2 (string), field number 2 (name)
• 0a: name length = 10 bytes
• 47 61 64 67 65 74 4e 61 6d 65 = example name value “GadgetName”
• 1a: Wire type 2 (repeated field), field number 3 (supported_transports)
• 01: supported_transports length = 1 byte.
• 00: Supported transport value: BLUETOOTH_LOW_ENERGY.
• 22: Wire type 2 (string), field number 4 (device_type)
• 04: device_type length: 4 bytes.
• 77 78 79 7a: = example device_type value “wxyz”

Regarding the GetDeviceFeature response:

Creating response: Command_GET_DEVICE_FEATURES
New Tx Transaction [3] :: Stream [0]
Tx Progress [9/9] :: Stream [0] :: Transaction [3]
>>>>> Response from Gadget -> Echo:
Packet [1/1] contains: 03 00 00 00 09 09 08 1c  4a 05 e2 01 02 08 13 

the first 6 bytes 03 00 00 00 09 09 decode similarly as a packet header as follows:

• 03: StreamId: 0: control stream and transactionId: 3.
• 00: sequence number: 0, type: initial transaction (type 0), Ack: false and Extended length: false
• 00: reserved
• 00 09: total transaction length 9 bytes (big endian).
• 09: payload length: 9 bytes.

The following 9 bytes are a protobuf message:

• 08: Wire type 0 (varint), field number 1 (command)
• 1c: Value: GET_DEVICE_FEATURES
• 4a: Wire type 2 (embedded message), field number 9 (response)
• 05: response length = 5 bytes.
• e2 01: Wire type 2 (embedded message), field number 28 (device_features)
• 02: device_features length = 2 bytes.
• 08: Wire type 0 (varint), field number 1 (features)
• 13: features values. Supports Alexa Gadgets Toolkit and OTA.