marshal library

Descriptor-driven protobuf message marshaling (encoding).

Encodes a message represented as Map<String, Object?> into protobuf binary bytes, using a field descriptor list to determine field numbers, types, and encoding rules.

Each field descriptor is a Map<String, Object?> with:

• 'name' : field name (String)
• 'number' : field number (int)
• 'type' : protobuf type string, e.g. 'TYPE_INT32', 'TYPE_STRING'
• 'label' : 'LABEL_REPEATED' for repeated fields; absent or other value for singular fields
• 'typeName' : for TYPE_MESSAGE / TYPE_ENUM, the fully-qualified message or enum type name (optional for scalar types)
• 'mapEntry' : if present and true, indicates this message type is a map entry (has key = 1 and value = 2)
• 'keyType' : for map fields, the protobuf type of the key
• 'valueType': for map fields, the protobuf type of the value
• 'messageDescriptor' : for TYPE_MESSAGE fields, the nested field descriptor list for the submessage

Proto3 rules applied:

• Singular scalar fields with default values (0, false, "", empty list/map) are not serialized.
• Repeated scalar fields use packed encoding by default.
• Map fields are serialized as repeated message fields with key=1, value=2.

References:

• https://protobuf.dev/programming-guides/encoding/
• https://protobuf.dev/programming-guides/proto3/#maps

Functions

encodeGroupField(List<int> buffer, int fieldNumber, List<int> body) → List<int>

Encodes a message field using DELIMITED (group) wire format: a START_GROUP tag (wire type 3), the submessage body, then a matching END_GROUP tag (wire type 4). This is the editions message_encoding = DELIMITED representation (and the proto2 group encoding). Unlike length-prefixed (wire type 2) the body is NOT length-prefixed — it is terminated by the END_GROUP tag.

marshal(Map<String, Object?> message, List<Map<String, Object?>> descriptor) → List<int>

Marshals a message (message) to protobuf binary bytes using descriptor.

marshalField(List<int> buffer, int fieldNumber, String type, Object? value, {bool repeated = false, bool explicitPresence = false, bool delimited = false, List<Map<String, Object?>>? messageDescriptor}) → List<int>

Marshals a single scalar field value and appends it to buffer.

marshalMapField(List<int> buffer, int fieldNumber, Map<Object?, Object?> mapValue, String keyType, String valueType, {List<Map<String, Object?>>? valueDescriptor}) → List<int>

Marshals a map field as repeated key-value pair messages.

marshalRepeated(List<int> buffer, int fieldNumber, String type, List<Object?> values) → List<int>

Marshals a repeated scalar field using packed encoding and appends it to buffer.

sizeOfMessage(Map<String, Object?> message, List<Map<String, Object?>> descriptor) → int

Calculates the encoded byte size of message without producing output.

wireTypeForFieldType(String type) → int

Returns the wire type for a protobuf field type string.