Module cell 

Cell types for the Tor relay protocol.

This module provides cell types used in ORPort communication as defined in the Tor protocol specification (tor-spec.txt). Cells are the fundamental unit of communication in the Tor relay protocol.

Overview

Cells are fixed-size or variable-size messages exchanged between Tor relays and clients. Each cell has a circuit ID, command type, and payload. The format depends on the link protocol version negotiated during connection.

Cell Types

Cells are categorized by their function:

Connection Setup

• VersionsCell - Link protocol version negotiation (section 4)
• NetinfoCell - Time and address information exchange (section 4.5)
• CertsCell - Relay certificates (section 4.2)
• AuthChallengeCell - Authentication challenge (section 4.3)

Circuit Management

• CreateFastCell - Create circuit without public key (section 5.1)
• CreatedFastCell - Circuit creation acknowledgment (section 5.1)
• DestroyCell - Tear down a circuit (section 5.4)

Data Transfer

• RelayCell - End-to-end encrypted data (section 6.1)

Padding

• PaddingCell - Fixed-size padding for traffic analysis resistance
• VPaddingCell - Variable-size padding

Cell Format

Fixed-size cells (link protocol 4+):

[ CircID (4 bytes) ][ Command (1 byte) ][ Payload (509 bytes) ]

Variable-size cells:

[ CircID (4 bytes) ][ Command (1 byte) ][ Length (2 bytes) ][ Payload ]

Example

use stem_rs::client::cell::{VersionsCell, Cell, CellType};
use stem_rs::client::datatype::LinkProtocol;

// Create a VERSIONS cell for protocol negotiation
let versions = VersionsCell::new(vec![3, 4, 5]);
let packed = versions.pack(&LinkProtocol::new(2));

// Parse a cell from bytes
let (cell, remainder) = Cell::pop(&packed, 2).unwrap();

See Also

• datatype for data types used in cell construction
• Tor Protocol Specification

Structs

AuthChallengeCell

Authentication challenge cell.

CertsCell

Relay certificates cell.

CreateFastCell

Circuit creation cell using fast handshake (no public key).

CreatedFastCell

Response to CREATE_FAST circuit creation.

DestroyCell

Circuit teardown cell.

NetinfoCell

Network information exchange cell.

PaddingCell

Fixed-size padding cell for traffic analysis resistance.

RelayCell

End-to-end encrypted relay cell.

VPaddingCell

Variable-length padding cell.

VersionsCell

Link protocol version negotiation cell.

Enums

Cell

Parsed cell from the Tor relay protocol.

CellType

Cell command types in the Tor relay protocol.

Constants

AUTH_CHALLENGE_SIZE

Size of the authentication challenge in AUTH_CHALLENGE cells (32 bytes).

CELL_TYPE_SIZE

Size type for cell command field (1 byte).

FIXED_PAYLOAD_LEN

Fixed payload length for fixed-size cells (509 bytes).

HASH_LEN

Length of SHA-1 hash used for key material (20 bytes).

PAYLOAD_LEN_SIZE

Size type for variable cell payload length field (2 bytes).

RELAY_DIGEST_SIZE

Size type for relay cell digest field (4 bytes).

STREAM_ID_DISALLOWED

Relay commands that must have a zero stream ID.

STREAM_ID_REQUIRED

Relay commands that require a non-zero stream ID.

Functions

cell_by_name

Looks up a cell type by its protocol name.

cell_by_value

Looks up a cell type by its numeric command value.