Base Fields

class pcapkit.corekit.fields.field.Field(length, default=<pcapkit.corekit.fields.field.NoValueType object>, callback=<function Field.<lambda>>)

Bases: FieldBase[_T], Generic[_T]

Base class for protocol fields.

Parameters:

• length (Union[int, Callable[[dict[str, Any]], int]]) – Field size (in bytes); if a callable is given, it should return an integer value and accept the current packet as its only argument.

• default (Union[TypeVar(_T), NoValueType]) – Field default value, if any.

• callback (Callable[[Self, dict[str, Any]], None]) – Callback function to be called upon self.__call__.

property template: str

Field template.

__call__(packet)

Update field attributes.

Parameters:

packet (dict[str, Any]) – Packet data.

Return type:

Self

Returns:

New instance of Field.

This method will return a new instance of Field instead of updating the current instance.

class pcapkit.corekit.fields.field.FieldBase(*args, **kwargs)

Bases: Generic[_T]

Internal base class for protocol fields.

Important

A negative value of length indicates that the field is variable-length (i.e., length unspecified) and thus pack() should be considerate of the template format and the actual value provided for packing.

Parameters:

• *args (Any) – Arbitrary positional arguments.

• **kwargs (Any) – Arbitrary keyword arguments.

property name: str

Field name.

property default: _T | NoValueType

Field default value.

property template: str

Field template.

property length: int

Field size.

property optional: bool

Field is optional.

__call__(packet)

Update field attributes.

Parameters:

packet (dict[str, Any]) – Packet data.

Return type:

Self

Returns:

Updated field instance.

This method will return a new instance of FieldBase instead of updating the current instance.

__set_name__(owner, name)

Set field name and update field list (if applicable).

This method is to be called by the metaclass during class creation. It is used to set the field name and update the field list, i.e., Schema.__fields__ mapping dictionary.

Return type:

None

pre_process(value, packet)

Process field value before construction (packing).

Parameters:

• value (TypeVar(_T)) – Field value.

• packet (dict[str, Any]) – Packet data.

Return type:

Any

Returns:

Processed field value.

pack(value, packet)

Pack field value into bytes.

Parameters:

• value (Optional[TypeVar(_T)]) – Field value.

• packet (dict[str, Any]) – Packet data.

Return type:

bytes

Returns:

Packed field value.

post_process(value, packet)

Process field value after parsing (unpacking).

Parameters:

• value (Any) – Field value.

• packet (dict[str, Any]) – Packet data.

Return type:

TypeVar(_T)

Returns:

Processed field value.

unpack(buffer, packet)

Unpack field value from bytes.

Parameters:

• buffer (Union[bytes, IO[bytes]]) – Field buffer.

• packet (dict[str, Any]) – Packet data.

Return type:

TypeVar(_T)

Returns:

Unpacked field value.

Auxiliaries

class pcapkit.corekit.fields.field.NoValueType

Bases: object

Default value for fields.

pcapkit.corekit.fields.field.NoValue

Default value for FieldBase.default.

Type:

NoValueType

Internal Definitions

class pcapkit.corekit.fields.field.FieldMeta(name, bases, namespace, /, **kwargs)

Bases: ABCMeta, Generic[_T]

Meta class to add dynamic support to FieldBase.

This meta class is used to generate necessary attributes for the FieldBase class. It can be useful to reduce unnecessary registry calls and simplify the customisation process.

Type Variables

pcapkit.corekit.fields.field._T: Any