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Circuit padding header.

Browse Source 
This is a good code review start point, to get an overview of the interfaces
and types used in circuit padding.

Co-authored-by: George Kadianakis <desnacked@riseup.net>
This commit is contained in:
Mike Perry
2018-10-23 19:48:16 +00:00
committed by George Kadianakis
parent 3ba7581129
commit 2a24e21fb0
1 changed files with 685 additions and 0 deletions
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src/core/or/circuitpadding.h
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/*
* Copyright (c) 2017, The Tor Project, Inc. */
/* See LICENSE for licensing information */
/**
* \file circuitpadding.h
* \brief Header file for circuitpadding.c.
**/
#ifndef TOR_CIRCUITPADDING_H
#define TOR_CIRCUITPADDING_H
#include "circpad_negotiation.h"
#include "lib/evloop/timers.h"
typedef struct circuit_t circuit_t;
typedef struct origin_circuit_t origin_circuit_t;
typedef struct cell_t cell_t;
/**
* Signed error return with the specific property that negative
* values mean error codes of various semantics, 0 means success,
* and positive values are unused.
*
* XXX: Tor uses this concept a lot but just calls it int. Should we move
* this somewhere centralized? Where?
*/
typedef int signed_error_t;
/**
* These constants specify the types of events that can cause
* transitions between state machine states.
*
* Note that SENT and RECV are relative to this endpoint. For
* relays, SENT means packets destined towards the client and
* RECV means packets destined towards the relay. On the client,
* SENT means packets destined towards the relay, where as RECV
* means packets destined towards the client.
*/
typedef enum {
/* A non-padding cell was received. */
CIRCPAD_EVENT_NONPADDING_RECV = 0,
/* A non-padding cell was sent. */
CIRCPAD_EVENT_NONPADDING_SENT = 1,
/* A padding cell (RELAY_COMMAND_DROP) was sent. */
CIRCPAD_EVENT_PADDING_SENT = 2,
/* A padding cell was received. */
CIRCPAD_EVENT_PADDING_RECV = 3,
/* We tried to schedule padding but we ended up picking the infinity bin
* which means that padding was delayed infinitely */
CIRCPAD_EVENT_INFINITY = 4,
/* All histogram bins are empty (we are out of tokens) */
CIRCPAD_EVENT_BINS_EMPTY = 5,
/* just a counter of the events above */
CIRCPAD_EVENT_LENGTH_COUNT = 6
} circpad_event_t;
#define CIRCPAD_NUM_EVENTS ((int)CIRCPAD_EVENT_LENGTH_COUNT+1)
/** Boolean type that says if we decided to transition states or not */
typedef enum {
CIRCPAD_STATE_UNCHANGED = 0,
CIRCPAD_STATE_CHANGED = 1
} circpad_decision_t;
/** The type for the things in histogram bins (aka tokens) */
typedef uint32_t circpad_hist_token_t;
/** The type for histogram indexes (needs to be negative for errors) */
typedef int8_t circpad_hist_index_t;
/** The type for absolute time, from monotime_absolute_usec() */
typedef uint64_t circpad_time_t;
/** The type for timer delays, in microseconds */
typedef uint32_t circpad_delay_t;
/**
* An infinite padding cell delay means don't schedule any padding --
* simply wait until a different event triggers a transition.
*
* This means that the maximum delay we can scedule is UINT32_MAX-1
* microseconds, or about 4300 seconds (1.25 hours).
* XXX: Is this enough if we want to simulate light, intermittent
* activity on an onion service?
*/
#define CIRCPAD_DELAY_INFINITE (UINT32_MAX)
/**
* Macro to clarify when we're checking the infinity bin.
*
* Works with either circpad_state_t or circpad_machineinfo_t
*/
#define CIRCPAD_INFINITY_BIN(mi) ((mi)->histogram_len-1)
/**
* These constants form a bitfield that specifies when a state machine
* should be applied to a circuit.
*
* If any of these elements is set, then the circuit will be tested against
* that specific condition. If an element is unset, then we don't test it.
* (E.g. If neither NO_STREAMS or STREAMS are set, then we will not care
* whether a circuit has streams attached when we apply a state machine)
*
* The helper function circpad_circuit_state() converts circuit state
* flags into this more compact representation.
*/
typedef enum {
/* Only apply machine if the circuit is still building */
CIRCPAD_CIRC_BUILDING = 1<<0,
/* Only apply machine if the circuit is open */
CIRCPAD_CIRC_OPENED = 1<<1,
/* Only apply machine if the circuit has no attached streams */
CIRCPAD_CIRC_NO_STREAMS = 1<<2,
/* Only apply machine if the circuit has attached streams */
CIRCPAD_CIRC_STREAMS = 1<<3,
/* Only apply machine if the circuit still allows RELAY_EARLY cells */
CIRCPAD_CIRC_HAS_RELAY_EARLY = 1<<4,
/* Only apply machine if the circuit has depleted its RELAY_EARLY cells
* allowance. */
CIRCPAD_CIRC_HAS_NO_RELAY_EARLY = 1<<5
} circpad_circuit_state_t;
/** Bitmask that says "apply this machine to all states" */
#define CIRCPAD_STATE_ALL \
(CIRCPAD_CIRC_BUILDING|CIRCPAD_CIRC_OPENED| \
CIRCPAD_CIRC_STREAMS|CIRCPAD_CIRC_NO_STREAMS| \
CIRCPAD_CIRC_HAS_RELAY_EARLY|CIRCPAD_CIRC_HAS_NO_RELAY_EARLY)
/**
* A compact circuit purpose bitfield mask that allows us to compactly
* specify which circuit purposes a machine should apply to.
*
* The helper function circpad_circ_purpose_to_mask() converts circuit
* purposes into bit positions in this bitmask.
*/
typedef uint32_t circpad_purpose_mask_t;
/** Bitmask that says "apply this machine to all purposes". */
#define CIRCPAD_PURPOSE_ALL (0xFFFFFFFF)
/**
* This type specifies all of the conditions that must be met before
* a client decides to initiate padding on a circuit.
*
* A circuit must satisfy every sub-field in this type in order
* to be considered to match the conditions.
*/
typedef struct circpad_machine_conditions_t {
/** Only apply the machine *if* the circuit has at least this many hops */
unsigned min_hops : 3;
/** Only apply the machine *if* vanguards are enabled */
unsigned requires_vanguards : 1;
/** Only apply the machine *if* the circuit's state matches any of
* the bits set in this bitmask. */
circpad_circuit_state_t state_mask;
/** Only apply a machine *if* the circuit's purpose matches one
* of the bits set in this bitmask */
circpad_purpose_mask_t purpose_mask;
} circpad_machine_conditions_t;
/**
* Token removal strategy options.
*
* The WTF-PAD histograms are meant to specify a target distribution to shape
* traffic towards. This is accomplished by removing tokens from the histogram
* when either padding or non-padding cells are sent.
*
* When we see a non-padding cell at a particular time since the last cell, you
* remove a token from the corresponding delay bin. These flags specify
* which bin to choose if that bin is already empty.
*/
typedef enum {
/** Don't remove any tokens */
CIRCPAD_TOKEN_REMOVAL_NONE = 0,
/**
* Remove from the first non-zero higher bin index when current is zero.
* This is the recommended strategy from the Adaptive Padding paper. */
CIRCPAD_TOKEN_REMOVAL_HIGHER = 1,
/** Remove from the first non-zero lower bin index when current is empty. */
CIRCPAD_TOKEN_REMOVAL_LOWER = 2,
/** Remove from the closest non-zero bin index when current is empty. */
CIRCPAD_TOKEN_REMOVAL_CLOSEST = 3,
/** Remove from the closest bin by time value (since bins are
* exponentially spaced). */
CIRCPAD_TOKEN_REMOVAL_CLOSEST_USEC = 4,
/** Only remove from the exact bin corresponding to this delay. If
* the bin is 0, simply do nothing. Don't pick another bin. */
CIRCPAD_TOKEN_REMOVAL_EXACT = 5
} circpad_removal_t;
/**
* Distribution types supported by circpad_distribution_sample().
*
* These can be used instead of histograms for the inter-packet
* timing distribution, or to specify a distribution on the number
* of cells that can be sent while in a specific state of the state
* machine. */
typedef enum {
CIRCPAD_DIST_NONE = 0,
CIRCPAD_DIST_UNIFORM = 1,
CIRCPAD_DIST_LOGISTIC = 2,
CIRCPAD_DIST_LOG_LOGISTIC = 3,
CIRCPAD_DIST_GEOMETRIC = 4,
CIRCPAD_DIST_WEIBULL = 5,
CIRCPAD_DIST_PARETO = 6
} circpad_distribution_type_t;
/**
* Distribution information.
*
* This type specifies a specific distribution above, as well as
* up to two parameters for that distribution. The specific
* per-distribution meaning of these parameters is specified
* in circpad_distribution_sample().
*/
typedef struct circpad_distribution_t {
circpad_distribution_type_t type;
double param1;
double param2;
} circpad_distribution_t;
/** State number type. Represents current state of state machine. */
typedef uint16_t circpad_statenum_t;
#define CIRCPAD_STATENUM_MAX (UINT16_MAX)
/** A histogram is used to sample padding delays given a machine state. This
* constant defines the maximum histogram width (i.e. the max number of bins)
*
* Each histogram bin is twice as large as the previous. Two exceptions: The
* first bin has zero width (which means that minimum delay is applied to the
* next padding cell), and the last bin (infinity bin) has infinite width
* (which means that the next padding cell will be delayed infinitely). */
#define CIRCPAD_MAX_HISTOGRAM_LEN (sizeof(circpad_delay_t)*8 + 1)
/**
* A state of a padding machine. The information here are immutable and
* represent the initial form of the state; it does not get updated as things
* happen. The mutable information that gets updated in runtime are carried in
* a circpad_machineinfo_t.
*
* This struct describes the histograms and parameters of a single
* state in the adaptive padding machine. Instances of this struct
* exist in global circpad machine definitions that come from torrc
* or the consensus.
*/
typedef struct circpad_state_t {
/** If a histogram is used for this state, this specifies the number of bins
* of this histogram. Histograms must have at least 2 bins.
*
* If a delay probability distribution is used for this state, this is set
* to 0. */
circpad_hist_index_t histogram_len;
/** The histogram itself: an array of uint16s of tokens, whose
* widths are exponentially spaced, in microseconds */
circpad_hist_token_t histogram[CIRCPAD_MAX_HISTOGRAM_LEN];
/** Total number of tokens in this histogram. This is a constant and is *not*
* decremented every time we spend a token. It's used for initializing and
* refilling the histogram. */
uint32_t histogram_total_tokens;
/** Minimum padding delay of this state in microseconds.
*
* If histograms are used, this is the left (and right) bound of the first
* bin (since it has zero width).
*
* If a delay probability distribution is used, this represents the minimum
* delay we can sample from the distribution.
*/
circpad_delay_t start_usec;
/** If histograms are used, this is the width of the whole histogram in
* microseconds, and it's used to calculate individual bin width.
*
* If a delay probability distribution is used, this is used as the max
* delay we can sample from the distribution.
*/
circpad_delay_t range_usec;
/**
* Represents a delay probability distribution (aka IAT distribution). It's a
* parametrized way of encoding inter-packet delay information in
* microseconds. It can be used instead of histograms.
*
* If it is used, token_removal below must be set to
* CIRCPAD_TOKEN_REMOVAL_NONE.
*
* Start_usec, range_sec, and rtt_estimates are still applied to the
* results of sampling from this distribution (range_sec is used as a max).
*/
circpad_distribution_t iat_dist;
/**
* The length dist is a parameterized way of encoding how long this
* state machine runs in terms of sent padding cells or all
* sent cells. Values are sampled from this distribution, clamped
* to max_len, and then start_len is added to that value.
*
* It may be specified instead of or in addition to
* the infinity bins and bins empty conditions. */
circpad_distribution_t length_dist;
/** A minimum length value, added to the output of length_dist */
uint16_t start_length;
/** A cap on the length value that can be sampled from the length_dist */
uint64_t max_length;
/** Should we decrement length when we see a nonpadding packet?
* XXX: Are there any machines that actually want to set this to 0? There may
* not be. OTOH, it's only a bit.. */
unsigned length_includes_nonpadding : 1;
/**
* This is an array that specifies the next state to transition to upon
* receipt an event matching the indicated array index.
*
* This aborts our scheduled packet and switches to the state
* corresponding to the index of the array. Tokens are filled upon
* this transition.
*
* States are allowed to transition to themselves, which means re-schedule
* a new padding timer. They are also allowed to temporarily "transition"
* to the "IGNORE" and "CANCEL" pseudo-states. See #defines below
* for details on state behavior and meaning.
*/
circpad_statenum_t next_state[CIRCPAD_NUM_EVENTS];
/**
* If true, estimate the RTT from this relay to the exit/website and add that
* to start_usec for use as the histogram bin 0 start delay.
*
* Right now this is only supported for relay-side state machines.
*/
unsigned use_rtt_estimate : 1;
/** This specifies the token removal strategy to use upon padding and
* non-padding activity. */
circpad_removal_t token_removal;
} circpad_state_t;
/**
* The start state for this machine.
*
* In the original WTF-PAD, this is only used for transition to/from
* the burst state. All other fields are not used. But to simplify the
* code we've made it a first-class state. This has no performance
* consequences, but may make naive serialization of the state machine
* large, if we're not careful about how we represent empty fields.
*/
#define CIRCPAD_STATE_START 0
/**
* The burst state for this machine.
*
* In the original Adaptive Padding algorithm and in WTF-PAD
* (https://www.freehaven.net/anonbib/cache/ShWa-Timing06.pdf and
* https://www.cs.kau.se/pulls/hot/thebasketcase-wtfpad/), the burst
* state serves to detect bursts in traffic. This is done by using longer
* delays in its histogram, which represent the expected delays between
* bursts of packets in the target stream. If this delay expires without a
* real packet being sent, the burst state sends a padding packet and then
* immediately transitions to the gap state, which is used to generate
* a synthetic padding packet train. In this implementation, this transition
* needs to be explicitly specified in the burst state's transition events.
*
* Because of this flexibility, other padding mechanisms can transition
* between these two states arbitrarily, to encode other dynamics of
* target traffic.
*/
#define CIRCPAD_STATE_BURST 1
/**
* The gap state for this machine.
*
* In the original Adaptive Padding algorithm and in WTF-PAD, the gap
* state serves to simulate an artificial packet train composed of padding
* packets. It does this by specifying much lower inter-packet delays than
* the burst state, and transitioning back to itself after padding is sent
* if these timers expire before real traffic is sent. If real traffic is
* sent, it transitions back to the burst state.
*
* Again, in this implementation, these transitions must be specified
* explicitly, and other transitions are also permitted.
*/
#define CIRCPAD_STATE_GAP 2
/**
* End is a pseudo-state that causes the machine to go completely
* idle, and optionally get torn down (depending on the
* value of circpad_machine_t.should_negotiate_end)
*
* End MUST NOT occupy a slot in the machine state array.
*/
#define CIRCPAD_STATE_END CIRCPAD_STATENUM_MAX
/**
* "Ignore" is a pseudo-state that means "do not react to this
* event".
*
* "Ignore" MUST NOT occupy a slot in the machine state array.
*/
#define CIRCPAD_STATE_IGNORE (CIRCPAD_STATENUM_MAX-1)
/**
* "Cancel" is a pseudo-state that means "cancel pending timers,
* but remain in your current state".
*
* Cancel MUST NOT occupy a slot in the machine state array.
*/
#define CIRCPAD_STATE_CANCEL (CIRCPAD_STATENUM_MAX-2)
/**
* Since we have 3 pseudo-states, the max state array length is
* up to one less than cancel's statenum.
*/
#define CIRCPAD_MAX_MACHINE_STATES (CIRCPAD_STATE_CANCEL-1)
/**
* Mutable padding machine info.
*
* This structure contains mutable information about a padding
* machine. The mutable information must be kept separate because
* it exists per-circuit, where as the machines themselves are global.
* This separation is done to conserve space in the circuit structure.
*
* This is the per-circuit state that changes regarding the global state
* machine. Some parts of it are optional (ie NULL).
*
* XXX: Play with layout to minimize space on x64 Linux (most common relay).
*/
typedef struct circpad_machineinfo_t {
/** The callback pointer for the padding callbacks.
*
* These timers stick around the machineinfo until the machineinfo's circuit
* is closed, at which point the timer is cancelled. For this reason it's
* safe to assume that the machineinfo exists if this timer gets
* triggered. */
tor_timer_t *padding_timer;
/** The circuit for this machine */
circuit_t *on_circ;
/** A mutable copy of the histogram for the current state.
* NULL if remove_tokens is false for that state */
circpad_hist_token_t *histogram;
/** Length of the above histogram.
* XXX: This field *could* be removed at the expense of added
* complexity+overhead for reaching back into the immutable machine
* state every time we need to inspect the histogram. It's only a byte,
* though, so it seemed worth it.
*/
circpad_hist_index_t histogram_len;
/** Remove token from this index upon sending padding */
circpad_hist_index_t chosen_bin;
/** Stop padding/transition if this many cells sent */
uint64_t state_length;
#define CIRCPAD_STATE_LENGTH_INFINITE UINT64_MAX
/** A scaled count of padding packets sent, used to limit padding overhead.
* When this reaches UINT16_MAX, we cut it and nonpadding_sent in half. */
uint16_t padding_sent;
/** A scaled count of non-padding packets sent, used to limit padding
* overhead. When this reaches UINT16_MAX, we cut it and padding_sent in
* half. */
uint16_t nonpadding_sent;
/**
* EWMA estimate of the RTT of the circuit from this hop
* to the exit end, in microseconds. */
circpad_delay_t rtt_estimate_usec;
/**
* The last time we got an event relevant to estimating
* the RTT. Monotonic time in microseconds since system
* start.
*/
circpad_time_t last_received_time_usec;
/**
* The time at which we scheduled a non-padding packet,
* or selected an infinite delay.
*
* Monotonic time in microseconds since system start.
* This is 0 if we haven't chosen a padding delay.
*/
circpad_time_t padding_scheduled_at_usec;
/** What state is this machine in? */
circpad_statenum_t current_state;
/**
* True if we have scheduled a timer for padding.
*
* This is 1 if a timer is pending. It is 0 if
* no timer is scheduled. (It can be 0 even when
* padding_was_scheduled_at_usec is non-zero).
*/
unsigned is_padding_timer_scheduled : 1;
/**
* If this is true, we have seen full duplex behavior.
* Stop updating the RTT.
*/
unsigned stop_rtt_update : 1;
/** Max number of padding machines on each circuit. If changed,
* also ensure the machine_index bitwith supports the new size. */
#define CIRCPAD_MAX_MACHINES (2)
/** Which padding machine index was this for.
* (make sure changes to the bitwidth can support the
* CIRCPAD_MAX_MACHINES define). */
unsigned machine_index : 1;
} circpad_machineinfo_t;
/** Helper macro to get an actual state machine from a machineinfo */
#define CIRCPAD_GET_MACHINE(machineinfo) \
((machineinfo)->on_circ->padding_machine[(machineinfo)->machine_index])
/**
* This specifies a particular padding machine to use after negotiation.
*
* The constants for machine_num_t are in trunnel.
* We want to be able to define extra numbers in the consensus/torrc, though.
*/
typedef uint8_t circpad_machine_num_t;
/** Global state machine structure from the consensus */
typedef struct circpad_machine_t {
/** Global machine number */
circpad_machine_num_t machine_num;
/** Which machine index slot should this machine go into in
* the array on the circuit_t */
unsigned machine_index : 1;
/** Send a padding negotiate to shut down machine at end state? */
unsigned should_negotiate_end : 1;
// These next three fields are origin machine-only...
/** Origin side or relay side */
unsigned is_origin_side : 1;
/** Which hop in the circuit should we send padding to/from?
* 1-indexed (ie: hop #1 is guard, #2 middle, #3 exit). */
unsigned target_hopnum : 3;
/** This machine only kills fascists if the following conditions are met. */
circpad_machine_conditions_t conditions;
/** How many padding cells can be sent before we apply overhead limits?
* XXX: Note that we can only allow up to 64k of padding cells on an
* otherwise quiet circuit. Is this enough? It's 33MB. */
uint16_t allowed_padding_count;
/** Padding percent cap: Stop padding if we exceed this percent overhead.
* 0 means no limit. Overhead is defined as percent of total traffic, so
* that we can use 0..100 here. This is the same definition as used in
* Prop#265. */
uint8_t max_padding_percent;
/** State array: indexed by circpad_statenum_t */
circpad_state_t *states;
/**
* Number of states this machine has (ie: length of the states array).
* XXX: This field is not needed other than for safety. */
circpad_statenum_t num_states;
} circpad_machine_t;
void circpad_new_consensus_params(const networkstatus_t *ns);
/**
* The following are event call-in points that are of interest to
* the state machines. They are called during cell processing. */
void circpad_deliver_unrecognized_cell_events(circuit_t *circ,
cell_direction_t dir);
void circpad_deliver_sent_relay_cell_events(circuit_t *circ,
uint8_t relay_command);
void circpad_deliver_recognized_relay_cell_events(circuit_t *circ,
uint8_t relay_command,
crypt_path_t *layer_hint);
/** Cell events are delivered by the above delivery functions */
void circpad_cell_event_nonpadding_sent(circuit_t *on_circ);
void circpad_cell_event_nonpadding_received(circuit_t *on_circ);
void circpad_cell_event_padding_sent(circuit_t *on_circ);
void circpad_cell_event_padding_received(circuit_t *on_circ);
/** Internal events are events the machines send to themselves */
circpad_decision_t circpad_internal_event_infinity(circpad_machineinfo_t *mi);
circpad_decision_t circpad_internal_event_bins_empty(circpad_machineinfo_t *);
circpad_decision_t circpad_internal_event_state_length_up(
circpad_machineinfo_t *);
/** Machine creation events are events that cause us to set up or
* tear down padding state machines. */
void circpad_machine_event_circ_added_hop(origin_circuit_t *on_circ);
void circpad_machine_event_circ_built(origin_circuit_t *circ);
void circpad_machine_event_circ_purpose_changed(origin_circuit_t *circ);
void circpad_machine_event_circ_has_streams(origin_circuit_t *circ);
void circpad_machine_event_circ_has_no_streams(origin_circuit_t *circ);
void circpad_machine_event_circ_has_no_relay_early(origin_circuit_t *circ);
void circpad_machines_init(void);
void circpad_machines_free(void);
void circpad_machine_states_init(circpad_machine_t *machine,
circpad_statenum_t num_states);
void circpad_circuit_free_all_machineinfos(circuit_t *circ);
bool circpad_padding_is_from_expected_hop(circuit_t *circ,
crypt_path_t *from_hop);
/** Serializaton functions for writing to/from torrc and consensus */
char *circpad_machine_to_string(const circpad_machine_t *machine);
const circpad_machine_t *circpad_string_to_machine(const char *str);
/* Padding negotiation between client and middle */
signed_error_t circpad_handle_padding_negotiate(circuit_t *circ, cell_t *cell);
signed_error_t circpad_handle_padding_negotiated(circuit_t *circ, cell_t *cell,
crypt_path_t *layer_hint);
signed_error_t circpad_negotiate_padding(origin_circuit_t *circ,
circpad_machine_num_t machine,
uint8_t target_hopnum,
uint8_t command);
bool circpad_padding_negotiated(circuit_t *circ,
circpad_machine_num_t machine,
uint8_t command,
uint8_t response);
MOCK_DECL(circpad_decision_t,
circpad_machine_schedule_padding,(circpad_machineinfo_t *));
MOCK_DECL(circpad_decision_t,
circpad_machine_transition, (circpad_machineinfo_t *mi,
circpad_event_t event));
circpad_decision_t circpad_send_padding_cell_for_callback(
circpad_machineinfo_t *mi);
#ifdef CIRCUITPADDING_PRIVATE
STATIC circpad_delay_t
circpad_machine_sample_delay(circpad_machineinfo_t *mi);
STATIC bool
circpad_machine_reached_padding_limit(circpad_machineinfo_t *mi);
STATIC
circpad_decision_t circpad_machine_remove_token(circpad_machineinfo_t *mi);
STATIC circpad_delay_t
circpad_histogram_bin_to_usec(const circpad_machineinfo_t *mi,
circpad_hist_index_t bin);
STATIC const circpad_state_t *
circpad_machine_current_state(const circpad_machineinfo_t *mi);
STATIC circpad_hist_index_t circpad_histogram_usec_to_bin(
const circpad_machineinfo_t *mi,
circpad_delay_t us);
STATIC circpad_machineinfo_t *circpad_circuit_machineinfo_new(
circuit_t *on_circ,
int machine_index);
STATIC void circpad_machine_remove_higher_token(circpad_machineinfo_t *mi,
circpad_delay_t target_bin_us);
STATIC void circpad_machine_remove_lower_token(circpad_machineinfo_t *mi,
circpad_delay_t target_bin_us);
STATIC void circpad_machine_remove_closest_token(circpad_machineinfo_t *mi,
circpad_delay_t target_bin_us,
bool use_usec);
STATIC void circpad_machine_setup_tokens(circpad_machineinfo_t *mi);
#ifdef TOR_UNIT_TESTS
extern smartlist_t *origin_padding_machines;
extern smartlist_t *relay_padding_machines;
#endif
#endif
#endif