Public Types | Public Member Functions | Data Fields
channel_t Struct Reference

#include <channel.h>

Public Types


Public Member Functions

 HT_ENTRY (channel_t) gidmap_node
 HANDLE_ENTRY (channel, channel_t)
 TOR_LIST_ENTRY (channel_t) next_with_same_id

Data Fields

uint32_t magic
channel_state_t state
uint64_t global_identifier
unsigned char registered:1
unsigned int has_been_open:1
unsigned int padding_enabled:1
unsigned int currently_padding:1
unsigned int pending_padding_callback:1
unsigned int is_canonical_to_peer:1
channel_usage_info_t channel_usage
monotime_coarse_t next_padding_time
struct tor_timer_t * padding_timer
struct channel_handle_t * timer_handle
tor_addr_t addr_according_to_peer
uint16_t padding_timeout_low_ms
uint16_t padding_timeout_high_ms
enum channel_t:: { ... }  reason_for_closing
enum channel_t:: { ... }  scheduler_state
int sched_heap_idx
time_t timestamp_created
time_t timestamp_active
monotime_coarse_t timestamp_xfer
void(* free_fn )(channel_t *)
void(* close )(channel_t *)
const char *(* describe_transport )(channel_t *)
void(* dumpstats )(channel_t *, int)
channel_cell_handler_fn_ptr cell_handler
double(* get_overhead_estimate )(channel_t *)
int(* get_remote_addr )(const channel_t *, tor_addr_t *)
int(* get_transport_name )(channel_t *chan, char **transport_out)
const char *(* describe_peer )(const channel_t *)
int(* has_queued_writes )(channel_t *)
int(* is_canonical )(channel_t *)
int(* matches_extend_info )(channel_t *, extend_info_t *)
int(* matches_target )(channel_t *, const tor_addr_t *)
size_t(* num_bytes_queued )(channel_t *)
int(* num_cells_writeable )(channel_t *)
int(* write_cell )(channel_t *, cell_t *)
int(* write_packed_cell )(channel_t *, packed_cell_t *)
int(* write_var_cell )(channel_t *, var_cell_t *)
char identity_digest [DIGEST_LEN]
struct ed25519_public_key_t ed25519_identity
circuitmux_t * cmux
circ_id_type_bitfield_t circ_id_type:2
unsigned wide_circ_ids:1
unsigned int num_n_circuits
unsigned int num_p_circuits
unsigned int is_bad_for_new_circs:1
unsigned int is_client:1
unsigned int is_incoming:1
unsigned int is_local:1
ratelim_t last_warned_circ_ids_exhausted
time_t timestamp_client
time_t timestamp_recv
time_t timestamp_xmit
time_t timestamp_last_had_circuits
uint64_t dirreq_id
uint64_t n_cells_recved
uint64_t n_bytes_recved
uint64_t n_cells_xmitted
uint64_t n_bytes_xmitted

Detailed Description

Channel struct; see the channel_t typedef in or.h. A channel is an abstract interface for the OR-to-OR connection, similar to connection_or_t, but without the strong coupling to the underlying TLS implementation. They are constructed by calling a protocol-specific function to open a channel to a particular node, and once constructed support the abstract operations defined below.

Definition at line 181 of file channel.h.

Member Enumeration Documentation

◆ anonymous enum

anonymous enum

Why did we close?

Definition at line 264 of file channel.h.

◆ anonymous enum

anonymous enum

State variable for use by the scheduler


The channel is not open, or it has a full output buffer but no queued cells.


The channel has space on its output buffer to write, but no queued cells.


The scheduler has queued cells but no output buffer space to write.


The scheduler has both queued cells and output buffer space, and is eligible for the scheduler loop.

Definition at line 272 of file channel.h.

Member Function Documentation


HANDLE_ENTRY ( channel  ,

Handle entry for handle-based lookup


HT_ENTRY ( channel_t  )

List entry for hashtable for global-identifier lookup.


TOR_LIST_ENTRY ( channel_t  )

Linked list of channels with the same RSA identity digest, for use with the digest->channel map

Field Documentation

◆ addr_according_to_peer

tor_addr_t addr_according_to_peer

If not UNSPEC, the address that the peer says we have.

Definition at line 240 of file channel.h.

◆ cell_handler

channel_cell_handler_fn_ptr cell_handler

Registered handlers for incoming cells

Definition at line 325 of file channel.h.

◆ channel_usage

channel_usage_info_t channel_usage

Has this channel ever been used for non-directory traffic? Used to decide what channels to pad, and when.

Definition at line 228 of file channel.h.

Referenced by channelpadding_decide_to_pad_channel().

◆ circ_id_type

circ_id_type_bitfield_t circ_id_type

Circuit ID generation stuff for use by circuitbuild.c When we send CREATE cells along this connection, which half of the space should we use?

Definition at line 405 of file channel.h.

Referenced by channel_set_circid_type(), and get_unique_circ_id_by_chan().

◆ close

void(* close) (channel_t *)

Close an open channel

Definition at line 318 of file channel.h.

Referenced by channel_mark_for_close().

◆ cmux

circuitmux_t* cmux

◆ currently_padding

unsigned int currently_padding

Cached value of our decision to pad (to avoid expensive checks during critical path statistics counting).

Definition at line 218 of file channel.h.

◆ describe_peer

const char*(* describe_peer) (const channel_t *)

Get a human-readable text description of the remote endpoint, for logging.

Definition at line 346 of file channel.h.

Referenced by channel_describe_peer().

◆ describe_transport

const char*(* describe_transport) (channel_t *)

Describe the transport subclass for this channel

Definition at line 320 of file channel.h.

Referenced by channel_describe_transport().

◆ dirreq_id

uint64_t dirreq_id

Unique ID for measuring direct network status requests;vtunneled ones come over a circuit_t, which has a dirreq_id field as well, but is a distinct namespace.

Definition at line 453 of file channel.h.

Referenced by channel_notify_flushed().

◆ dumpstats

void(* dumpstats) (channel_t *, int)

Optional method to dump transport-specific statistics on the channel

Definition at line 322 of file channel.h.

Referenced by channel_dump_transport_statistics().

◆ ed25519_identity

struct ed25519_public_key_t ed25519_identity

Ed25519 key for the other side of this channel – or zeroes if we don't have an Ed25519 identity in mind for the other side, and it hasn't shown us one.

Note that this is the identity that we hope the other side has – not necessarily its true identity. Don't believe this identity unless authentication has happened.

Definition at line 378 of file channel.h.

Referenced by connection_or_client_learned_peer_id().

◆ free_fn

void(* free_fn) (channel_t *)

Free a channel

Definition at line 316 of file channel.h.

◆ get_overhead_estimate

double(* get_overhead_estimate) (channel_t *)

Ask the lower layer for an estimate of the average overhead for transmissions on this channel.

Definition at line 333 of file channel.h.

◆ global_identifier

uint64_t global_identifier

◆ has_been_open

unsigned int has_been_open

has this channel ever been open?

Definition at line 203 of file channel.h.

Referenced by channel_change_state_open().

◆ has_queued_writes

int(* has_queued_writes) (channel_t *)

Check if the lower layer has queued writes

Definition at line 348 of file channel.h.

Referenced by channel_has_queued_writes().

◆ identity_digest

char identity_digest[DIGEST_LEN]

Hash of the public RSA key for the other side's RSA identity key – or zeroes if we don't have an RSA identity in mind for the other side, and it hasn't shown us one.

Note that this is the RSA identity that we hope the other side has – not necessarily its true identity. Don't believe this identity unless authentication has happened.

Definition at line 378 of file channel.h.

Referenced by channel_do_open_actions(), channel_dump_statistics(), channel_get_for_extend(), and circuit_get_all_pending_on_channel().

◆ is_bad_for_new_circs

unsigned int is_bad_for_new_circs

True iff this channel shouldn't get any new circs attached to it, because the connection is too old, or because there's a better one. More generally, this flag is used to note an unhealthy connection; for example, if a bad connection fails we shouldn't assume that the router itself has a problem.

Definition at line 419 of file channel.h.

Referenced by channel_is_bad_for_new_circs(), and channel_mark_bad_for_new_circs().

◆ is_canonical

int(* is_canonical) (channel_t *)

Ask the lower layer if this is 'canonical', for a transport-specific definition of canonical.

Definition at line 353 of file channel.h.

Referenced by channel_is_canonical().

◆ is_canonical_to_peer

unsigned int is_canonical_to_peer

Is our peer likely to consider this channel canonical?

Definition at line 224 of file channel.h.

Referenced by channel_is_better().

◆ is_client

unsigned int is_client

True iff we have decided that the other end of this connection is a client or bridge relay. Connections with this flag set should never be used to satisfy an EXTEND request.

Definition at line 424 of file channel.h.

Referenced by channel_clear_client(), channel_is_client(), and channel_mark_client().

◆ is_incoming

unsigned int is_incoming

Set if the channel was initiated remotely (came from a listener)

Definition at line 427 of file channel.h.

Referenced by channel_is_incoming(), channel_is_outgoing(), channel_mark_incoming(), and channel_mark_outgoing().

◆ is_local

unsigned int is_local

Set by lower layer if this is local; i.e., everything it communicates with for this channel returns true for is_local_addr(). This is used to decide whether to declare reachability when we receive something on this channel in circuitbuild.c

Definition at line 434 of file channel.h.

Referenced by channel_is_local(), channel_mark_local(), and channel_mark_remote().

◆ last_warned_circ_ids_exhausted

ratelim_t last_warned_circ_ids_exhausted

Have we logged a warning about circID exhaustion on this channel? If so, when?

Definition at line 438 of file channel.h.

◆ magic

uint32_t magic

Magic number for type-checking cast macros

Definition at line 183 of file channel.h.

Referenced by channel_tls_common_init(), and channel_tls_from_base().

◆ matches_extend_info

int(* matches_extend_info) (channel_t *, extend_info_t *)

Check if this channel matches a specified extend_info_t

Definition at line 355 of file channel.h.

Referenced by channel_matches_extend_info().

◆ matches_target

int(* matches_target) (channel_t *, const tor_addr_t *)

Check if this channel matches a target address when extending

Definition at line 357 of file channel.h.

Referenced by channel_matches_target_addr_for_extend().

◆ n_cells_recved

uint64_t n_cells_recved

Channel counters for cells and bytes we have received.

Definition at line 456 of file channel.h.

◆ n_cells_xmitted

uint64_t n_cells_xmitted

Channel counters for cells and bytes we have sent.

Definition at line 458 of file channel.h.

◆ next_padding_time

monotime_coarse_t next_padding_time

When should we send a cell for netflow padding? 0 means no padding is scheduled.

Definition at line 232 of file channel.h.

◆ num_n_circuits

unsigned int num_n_circuits

For how many circuits are we n_chan? What about p_chan?

Definition at line 410 of file channel.h.

Referenced by channel_num_circuits(), and channel_unlink_all_circuits().

◆ padding_enabled

unsigned int padding_enabled

This field indicates if the other side has enabled or disabled padding via either the link protocol version or channelpadding_negotiate cells.

Clients can override this with ConnectionPadding in torrc to disable or force padding to relays, but relays cannot override the client's request.

Definition at line 214 of file channel.h.

Referenced by channelpadding_disable_padding_on_channel(), and channelpadding_reduce_padding_on_channel().

◆ padding_timeout_low_ms

uint16_t padding_timeout_low_ms

These two fields specify the minimum and maximum negotiated timeout values for inactivity (send or receive) before we decide to pad a channel. These fields can be set either via a PADDING_NEGOTIATE cell, or the torrc option ReducedConnectionPadding. The consensus parameters nf_ito_low and nf_ito_high are used to ensure that padding can only be negotiated to be less frequent than what is specified in the consensus. (This is done to prevent wingnut clients from requesting excessive padding).

The actual timeout value is randomly chosen between these two values as per the table in channelpadding_get_netflow_inactive_timeout_ms(), after ensuring that these values do not specify lower timeouts than the consensus parameters.

If these are 0, we have not negotiated or specified custom padding times, and instead use consensus defaults.

Definition at line 259 of file channel.h.

Referenced by channelpadding_get_netflow_inactive_timeout_ms(), and channelpadding_reduce_padding_on_channel().

◆ padding_timer

struct tor_timer_t* padding_timer

The callback pointer for the padding callbacks

Definition at line 235 of file channel.h.

◆ pending_padding_callback

unsigned int pending_padding_callback

Is there a pending netflow padding callback?

Definition at line 221 of file channel.h.

Referenced by channelpadding_schedule_padding(), and channelpadding_send_padding_cell_for_callback().

◆ reason_for_closing

enum { ... } reason_for_closing

Why did we close?

◆ registered

unsigned char registered

Should we expect to see this channel in the channel lists?

Definition at line 200 of file channel.h.

Referenced by channel_register(), and channel_unregister().

◆ sched_heap_idx

int sched_heap_idx

Heap index for use by the scheduler

Definition at line 295 of file channel.h.

Referenced by scheduler_channel_has_waiting_cells(), and scheduler_channel_wants_writes().

◆ scheduler_state

enum { ... } scheduler_state

◆ state

◆ timer_handle

struct channel_handle_t* timer_handle

The handle to this channel (to free on canceled timers)

Definition at line 237 of file channel.h.

◆ timestamp_client

time_t timestamp_client

Channel timestamps for cell channels

Definition at line 441 of file channel.h.

Referenced by channel_timestamp_client(), and channel_when_last_client().

◆ timestamp_created

time_t timestamp_created

Timestamps for both cell channels and listeners

Definition at line 298 of file channel.h.

Referenced by channel_dump_statistics(), channel_timestamp_created(), and channel_when_created().

◆ timestamp_last_had_circuits

time_t timestamp_last_had_circuits

Timestamp for run_connection_housekeeping(). We update this once a second when we run housekeeping and find a circuit on this channel, and whenever we add a circuit to the channel.

Definition at line 448 of file channel.h.

Referenced by circuit_set_n_circid_chan(), and circuit_set_p_circid_chan().

◆ timestamp_recv

time_t timestamp_recv

Cell received from lower layer

Definition at line 442 of file channel.h.

◆ timestamp_xfer

monotime_coarse_t timestamp_xfer

This is a monotonic timestamp that marks when we believe the channel has actually sent or received data to/from the wire. Right now, it is used to determine when we should send a padding cell for channelpadding.

XXX: Are we setting timestamp_xfer_ms in the right places to accurately reflect actual network data transfer? Or might this be very wrong wrt when bytes actually go on the wire?

Definition at line 311 of file channel.h.

◆ timestamp_xmit

time_t timestamp_xmit

Cell sent to lower layer

Definition at line 443 of file channel.h.

Referenced by channel_when_last_xmit().

◆ write_packed_cell

int(* write_packed_cell) (channel_t *, packed_cell_t *)

Write a packed cell to an open channel

Definition at line 365 of file channel.h.

◆ write_var_cell

int(* write_var_cell) (channel_t *, var_cell_t *)

Write a variable-length cell to an open channel

Definition at line 367 of file channel.h.

The documentation for this struct was generated from the following file: