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TLV (Type-Length-Value) Codec

The TLV codec provides a structured way to encode and decode hierarchical binary data. It uses an Envelope containing multiple Frames, where each frame consists of several Parameters.

Structure

  • Envelope: The top-level container.
  • Frame: A logical grouping of data within the envelope.
  • Param: An individual piece of data with a specific type, length, and value.

Defining a Protocol

To use the TLV codec, you must define a protocol by implementing the ProtocolDefinitionInterface. This defines how IDs are mapped to protocols, frames, and parameter types.

use Charcoal\Buffers\Contracts\Codecs\TLV\ProtocolDefinitionInterface;

class MyProtocolDefinition implements ProtocolDefinitionInterface {
    // Implement mapping methods...
}

Encoding Data

Encoding involves building an Envelope structure and passing it to the TlvBinaryCodec:

use Charcoal\Buffers\Codecs\TLV\TlvBinaryCodec;
use Charcoal\Buffers\Codecs\TLV\Envelope;
use Charcoal\Buffers\Codecs\TLV\Frame;
use Charcoal\Buffers\Codecs\TLV\Param;

$envelope = new Envelope(
    MyProtocol::Ping,
    new Frame(
        MyFrame::Request,
        new Param(MyParam::Timestamp, time()),
        new Param(MyParam::Payload, "Hello")
    )
);

$binary = TlvBinaryCodec::encode($envelope);

Decoding Data

Decoding converts raw bytes back into an Envelope object using your protocol definition:

$bytes = "... binary data ...";
$protocol = new MyProtocolDefinition();

$envelope = TlvBinaryCodec::decode($protocol, $bytes);

echo $envelope->protocol->name; // "Ping"
$firstFrame = $envelope->frames[0];
$firstParam = $firstFrame->params[0];
echo $firstParam->value;

Features

  • Endianness Support: The protocol determines the byte order for length fields.
  • Validation: The codec automatically checks for frame caps, parameter caps, and maximum allowed lengths.
  • Trailing Bytes: You can configure whether the codec should allow or reject unexpected trailing bytes after the last frame.
  • Custom Types: Parameter values are encoded/decoded by their respective types, allowing for custom data structures (e.g., nested objects, encrypted strings) within the TLV stream.