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Prop#324: Stream flow control functions

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Mike Perry 2021-09-28 22:28:26 +00:00 committed by David Goulet
parent 0b376a9e82
commit a89a71cd7b
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src/core/or/congestion_control_flow.c Normal file
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/* Copyright (c) 2019-2021, The Tor Project, Inc. */
/* See LICENSE for licensing information */
/**
* \file congestion_control_flow.c
* \brief Code that implements flow control for congestion controlled
* circuits.
*/
#define TOR_CONGESTION_CONTROL_FLOW_PRIVATE
#include "core/or/or.h"
#include "core/or/relay.h"
#include "core/mainloop/connection.h"
#include "core/or/connection_edge.h"
#include "core/mainloop/mainloop.h"
#include "core/or/congestion_control_common.h"
#include "core/or/congestion_control_flow.h"
#include "core/or/congestion_control_st.h"
#include "core/or/circuitlist.h"
#include "core/or/trace_probes_cc.h"
#include "feature/nodelist/networkstatus.h"
#include "trunnel/flow_control_cells.h"
#include "core/or/connection_st.h"
#include "core/or/cell_st.h"
#include "app/config/config.h"
/** Cache consensus parameters */
static uint32_t xoff_client;
static uint32_t xoff_exit;
static uint32_t xon_change_pct;
static uint32_t xon_rate_bytes;
static uint32_t xon_ewma_cnt;
/** In normal operation, we can get a burst of up to 32 cells before
* returning to libevent to flush the outbuf. This is a heuristic from
* hardcoded values and strange logic in connection_bucket_get_share(). */
#define MAX_EXPECTED_CELL_BURST 32
/**
* The following three are for dropmark rate limiting. They define when
* we scale down our XON, XOFF, and xmit byte counts. Early scaling
* is beneficial because it limits the ability of spurious XON/XOFF
* to be sent after large amounts of data without XON/XOFF. At these
* limits, after 10MB of data (or more), an adversary can only inject
* (log2(10MB)-log2(200*500))*100 ~= 1000 cells of fake XOFF/XON before
* the xmit byte * count will be halved enough to triggering a limit. */
#define XON_COUNT_SCALE_AT 200
#define XOFF_COUNT_SCALE_AT 200
#define ONE_MEGABYTE (UINT64_C(1) << 20)
#define TOTAL_XMIT_SCALE_AT 10*ONE_MEGABYTE
static const congestion_control_t *
edge_get_ccontrol(const edge_connection_t *edge)
{
if (edge->cpath_layer)
return edge->cpath_layer->ccontrol;
else if (edge->on_circuit)
return edge->on_circuit->ccontrol;
else
return NULL;
}
void
flow_control_new_consensus_params(const networkstatus_t *ns)
{
#define CC_XOFF_CLIENT_DFLT 500
#define CC_XOFF_CLIENT_MIN 1
#define CC_XOFF_CLIENT_MAX 10000
xoff_client = networkstatus_get_param(ns, "cc_xoff_client",
CC_XOFF_CLIENT_DFLT,
CC_XOFF_CLIENT_MIN,
CC_XOFF_CLIENT_MAX)*RELAY_PAYLOAD_SIZE;
#define CC_XOFF_EXIT_DFLT 500
#define CC_XOFF_EXIT_MIN 1
#define CC_XOFF_EXIT_MAX 10000
xoff_exit = networkstatus_get_param(ns, "cc_xoff_exit",
CC_XOFF_EXIT_DFLT,
CC_XOFF_EXIT_MIN,
CC_XOFF_EXIT_MAX)*RELAY_PAYLOAD_SIZE;
#define CC_XON_CHANGE_PCT_DFLT 25
#define CC_XON_CHANGE_PCT_MIN 1
#define CC_XON_CHANGE_PCT_MAX 99
xon_change_pct = networkstatus_get_param(ns, "cc_xon_change_pct",
CC_XON_CHANGE_PCT_DFLT,
CC_XON_CHANGE_PCT_MIN,
CC_XON_CHANGE_PCT_MAX);
#define CC_XON_RATE_BYTES_DFLT (500)
#define CC_XON_RATE_BYTES_MIN (1)
#define CC_XON_RATE_BYTES_MAX (5000)
xon_rate_bytes = networkstatus_get_param(ns, "cc_xon_rate",
CC_XON_RATE_BYTES_DFLT,
CC_XON_RATE_BYTES_MIN,
CC_XON_RATE_BYTES_MAX)*RELAY_PAYLOAD_SIZE;
#define CC_XON_EWMA_CNT_DFLT (2)
#define CC_XON_EWMA_CNT_MIN (1)
#define CC_XON_EWMA_CNT_MAX (100)
xon_ewma_cnt = networkstatus_get_param(ns, "cc_xon_ewma_cnt",
CC_XON_EWMA_CNT_DFLT,
CC_XON_EWMA_CNT_MIN,
CC_XON_EWMA_CNT_MAX);
}
/**
* Send an XOFF for this stream, and note that we sent one
*/
static void
circuit_send_stream_xoff(edge_connection_t *stream)
{
xoff_cell_t xoff;
uint8_t payload[CELL_PAYLOAD_SIZE];
ssize_t xoff_size;
memset(&xoff, 0, sizeof(xoff));
memset(payload, 0, sizeof(payload));
xoff_cell_set_version(&xoff, 0);
if ((xoff_size = xoff_cell_encode(payload, CELL_PAYLOAD_SIZE, &xoff)) < 0) {
log_warn(LD_BUG, "Failed to encode xon cell");
return;
}
if (connection_edge_send_command(stream, RELAY_COMMAND_XOFF,
(char*)payload, (size_t)xoff_size) == 0) {
stream->xoff_sent = true;
}
}
/**
* Compute the recent drain rate (write rate) for this edge
* connection and return it, in KB/sec (1000 bytes/sec).
*
* Returns 0 if the monotime clock is busted.
*/
static inline uint32_t
compute_drain_rate(const edge_connection_t *stream)
{
if (BUG(!is_monotime_clock_reliable())) {
log_warn(LD_BUG, "Computing drain rate with stalled monotime clock");
return 0;
}
uint64_t delta = monotime_absolute_usec() - stream->drain_start_usec;
if (delta == 0) {
log_warn(LD_BUG, "Computing stream drain rate with zero time delta");
return 0;
}
/* Overflow checks */
if (stream->prev_drained_bytes > INT32_MAX/1000 || /* Intermediate */
stream->prev_drained_bytes/delta > INT32_MAX/1000) { /* full value */
return INT32_MAX;
}
/* kb/sec = bytes/usec * 1000 usec/msec * 1000 msec/sec * kb/1000bytes */
return MAX(1, (uint32_t)(stream->prev_drained_bytes * 1000)/delta);
}
/**
* Send an XON for this stream, with appropriate advisory rate information.
*
* Reverts the xoff sent status, and stores the rate information we sent,
* in case it changes.
*/
static void
circuit_send_stream_xon(edge_connection_t *stream)
{
xon_cell_t xon;
uint8_t payload[CELL_PAYLOAD_SIZE];
ssize_t xon_size;
memset(&xon, 0, sizeof(xon));
memset(payload, 0, sizeof(payload));
xon_cell_set_version(&xon, 0);
xon_cell_set_kbps_ewma(&xon, stream->ewma_drain_rate);
if ((xon_size = xon_cell_encode(payload, CELL_PAYLOAD_SIZE, &xon)) < 0) {
log_warn(LD_BUG, "Failed to encode xon cell");
return;
}
/* Store the advisory rate information, to send advisory updates if
* it changes */
stream->ewma_rate_last_sent = stream->ewma_drain_rate;
if (connection_edge_send_command(stream, RELAY_COMMAND_XON, (char*)payload,
(size_t)xon_size) == 0) {
/* Revert the xoff sent status, so we can send another one if need be */
stream->xoff_sent = false;
}
}
/**
* Process a stream XOFF, parsing it, and then stopping reading on
* the edge connection.
*
* Record that we have recieved an xoff, so we know not to resume
* reading on this edge conn until we get an XON.
*
* Returns false if the XOFF did not validate; true if it does.
*/
bool
circuit_process_stream_xoff(edge_connection_t *conn,
const crypt_path_t *layer_hint,
const cell_t *cell)
{
(void)cell;
bool retval = true;
if (BUG(!conn)) {
log_fn(LOG_PROTOCOL_WARN, LD_EDGE,
"Got XOFF on invalid stream?");
return false;
}
/* Make sure this XOFF came from the right hop */
if (layer_hint && layer_hint != conn->cpath_layer) {
log_fn(LOG_PROTOCOL_WARN, LD_EDGE,
"Got XOFF from wrong hop.");
return false;
}
if (edge_get_ccontrol(conn) == NULL) {
log_fn(LOG_PROTOCOL_WARN, LD_EDGE,
"Got XOFF for non-congestion control circuit");
return false;
}
if (conn->xoff_received) {
log_fn(LOG_PROTOCOL_WARN, LD_EDGE,
"Got multiple XOFF on connection");
return false;
}
/* If we are near the max, scale everything down */
if (conn->num_xoff_recv == XOFF_COUNT_SCALE_AT) {
log_info(LD_EDGE, "Scaling down for XOFF count: %d %d %d",
conn->total_bytes_xmit,
conn->num_xoff_recv,
conn->num_xon_recv);
conn->total_bytes_xmit /= 2;
conn->num_xoff_recv /= 2;
conn->num_xon_recv /= 2;
}
conn->num_xoff_recv++;
/* Client-side check to make sure that XOFF is not sent too early,
* for dropmark attacks. The main sidechannel risk is early cells,
* but we also check to make sure that we have not received more XOFFs
* than could have been generated by the bytes we sent.
*/
if (TO_CONN(conn)->type == CONN_TYPE_AP || conn->hs_ident != NULL) {
uint32_t limit = 0;
/* TODO: This limit technically needs to come from negotiation,
* and be bounds checked for sanity, because the other endpoint
* may have a different consensus */
if (conn->hs_ident)
limit = xoff_client;
else
limit = xoff_exit;
if (conn->total_bytes_xmit < limit*conn->num_xoff_recv) {
log_fn(LOG_PROTOCOL_WARN, LD_EDGE,
"Got extra XOFF for bytes sent. Got %d, expected max %d",
conn->num_xoff_recv, conn->total_bytes_xmit/limit);
/* We still process this, because the only dropmark defenses
* in C tor are via the vanguards addon's use of the read valid
* cells. So just signal that we think this is not valid protocol
* data and proceed. */
retval = false;
}
}
// TODO: Count how many xoffs we have; log if "too many", for shadow
// analysis of chatter. Possibly add to extra-info?
log_info(LD_EDGE, "Got XOFF!");
connection_stop_reading(TO_CONN(conn));
conn->xoff_received = true;
return retval;
}
/**
* Process a stream XON, and if it validates, clear the xoff
* flag and resume reading on this edge connection.
*
* Also, use provided rate information to rate limit
* reading on this edge (or packagaing from it onto
* the circuit), to avoid XON/XOFF chatter.
*
* Returns true if the XON validates, false otherwise.
*/
bool
circuit_process_stream_xon(edge_connection_t *conn,
const crypt_path_t *layer_hint,
const cell_t *cell)
{
xon_cell_t *xon;
bool retval = true;
if (BUG(!conn)) {
log_fn(LOG_PROTOCOL_WARN, LD_EDGE,
"Got XON on invalid stream?");
return false;
}
/* Make sure this XON came from the right hop */
if (layer_hint && layer_hint != conn->cpath_layer) {
log_fn(LOG_PROTOCOL_WARN, LD_EDGE,
"Got XON from wrong hop.");
return false;
}
if (edge_get_ccontrol(conn) == NULL) {
log_fn(LOG_PROTOCOL_WARN, LD_EDGE,
"Got XON for non-congestion control circuit");
return false;
}
if (xon_cell_parse(&xon, cell->payload+RELAY_HEADER_SIZE,
CELL_PAYLOAD_SIZE-RELAY_HEADER_SIZE) < 0) {
log_fn(LOG_PROTOCOL_WARN, LD_EDGE,
"Received malformed XON cell.");
return false;
}
/* If we are near the max, scale everything down */
if (conn->num_xon_recv == XON_COUNT_SCALE_AT) {
log_info(LD_EDGE, "Scaling down for XON count: %d %d %d",
conn->total_bytes_xmit,
conn->num_xoff_recv,
conn->num_xon_recv);
conn->total_bytes_xmit /= 2;
conn->num_xoff_recv /= 2;
conn->num_xon_recv /= 2;
}
conn->num_xon_recv++;
/* Client-side check to make sure that XON is not sent too early,
* for dropmark attacks. The main sidechannel risk is early cells,
* but we also check to see that we did not get more XONs than make
* sense for the number of bytes we sent.
*/
if (TO_CONN(conn)->type == CONN_TYPE_AP || conn->hs_ident != NULL) {
uint32_t limit = 0;
/* TODO: This limit technically needs to come from negotiation,
* and be bounds checked for sanity, because the other endpoint
* may have a different consensus */
if (conn->hs_ident)
limit = MIN(xoff_client, xon_rate_bytes);
else
limit = MIN(xoff_exit, xon_rate_bytes);
if (conn->total_bytes_xmit < limit*conn->num_xon_recv) {
log_fn(LOG_PROTOCOL_WARN, LD_EDGE,
"Got extra XON for bytes sent. Got %d, expected max %d",
conn->num_xon_recv, conn->total_bytes_xmit/limit);
/* We still process this, because the only dropmark defenses
* in C tor are via the vanguards addon's use of the read valid
* cells. So just signal that we think this is not valid protocol
* data and proceed. */
retval = false;
}
}
log_info(LD_EDGE, "Got XON: %d", xon->kbps_ewma);
/* Adjust the token bucket of this edge connection with the drain rate in
* the XON. Rate is in bytes from kilobit (kpbs). */
uint64_t rate = xon_cell_get_kbps_ewma(xon) * 1000;
if (rate == 0 || INT32_MAX < rate) {
/* No rate. */
rate = INT32_MAX;
}
token_bucket_rw_adjust(&conn->bucket, (uint32_t) rate, (uint32_t) rate);
if (conn->xoff_received) {
/* Clear the fact that we got an XOFF, so that this edge can
* start and stop reading normally */
conn->xoff_received = false;
connection_start_reading(TO_CONN(conn));
}
xon_cell_free(xon);
return retval;
}
/**
* Called from sendme_stream_data_received(), when data arrives
* from a circuit to our edge's outbuf, to decide if we need to send
* an XOFF.
*
* Returns the amount of cells remaining until the buffer is full, at
* which point it sends an XOFF, and returns 0.
*
* Returns less than 0 if we have queued more than a congestion window
* worth of data and need to close the circuit.
*/
int
flow_control_decide_xoff(edge_connection_t *stream)
{
size_t total_buffered = connection_get_outbuf_len(TO_CONN(stream));
uint32_t buffer_limit_xoff = 0;
if (BUG(edge_get_ccontrol(stream) == NULL)) {
log_err(LD_BUG, "Flow control called for non-congestion control circuit");
return -1;
}
/* Onion services and clients are typically localhost edges, so they
* need different buffering limits than exits do */
if (TO_CONN(stream)->type == CONN_TYPE_AP || stream->hs_ident != NULL) {
buffer_limit_xoff = xoff_client;
} else {
buffer_limit_xoff = xoff_exit;
}
if (total_buffered > buffer_limit_xoff) {
if (!stream->xoff_sent) {
log_info(LD_EDGE, "Sending XOFF: %ld %d",
total_buffered, buffer_limit_xoff);
tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xoff_sending), stream);
circuit_send_stream_xoff(stream);
/* Clear the drain rate. It is considered wrong if we
* got all the way to XOFF */
stream->ewma_drain_rate = 0;
}
}
/* If the outbuf has accumulated more than the expected burst limit of
* cells, then assume it is not draining, and call decide_xon. We must
* do this because writes only happen when the socket unblocks, so
* may not otherwise notice accumulation of data in the outbuf for
* advisory XONs. */
if (total_buffered > MAX_EXPECTED_CELL_BURST*RELAY_PAYLOAD_SIZE) {
flow_control_decide_xon(stream, 0);
}
/* Flow control always takes more data; we rely on the oomkiller to
* handle misbehavior. */
return 0;
}
/**
* Returns true if the stream's drain rate has changed significantly.
*
* Returns false if the monotime clock is stalled, or if we have
* no previous drain rate information.
*/
static bool
stream_drain_rate_changed(const edge_connection_t *stream)
{
if (!is_monotime_clock_reliable()) {
return false;
}
if (!stream->ewma_rate_last_sent) {
return false;
}
if (stream->ewma_drain_rate >
(100+(uint64_t)xon_change_pct)*stream->ewma_rate_last_sent/100) {
return true;
}
if (stream->ewma_drain_rate <
(100-(uint64_t)xon_change_pct)*stream->ewma_rate_last_sent/100) {
return true;
}
return false;
}
/**
* Called whenever we drain an edge connection outbuf by writing on
* its socket, to decide if it is time to send an xon.
*
* The n_written parameter tells us how many bytes we have written
* this time, which is used to compute the advisory drain rate fields.
*/
void
flow_control_decide_xon(edge_connection_t *stream, size_t n_written)
{
size_t total_buffered = connection_get_outbuf_len(TO_CONN(stream));
/* Bounds check the number of drained bytes, and scale */
if (stream->drained_bytes >= UINT32_MAX - n_written) {
/* Cut the bytes in half, and move the start time up halfway to now
* (if we have one). */
stream->drained_bytes /= 2;
if (stream->drain_start_usec) {
uint64_t now = monotime_absolute_usec();
stream->drain_start_usec = now - (now-stream->drain_start_usec)/2;
}
}
/* Accumulate drained bytes since last rate computation */
stream->drained_bytes += n_written;
tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xon), stream, n_written);
/* Check for bad monotime clock and bytecount wrap */
if (!is_monotime_clock_reliable()) {
/* If the monotime clock ever goes wrong, the safest thing to do
* is just clear our short-term rate info and wait for the clock to
* become reliable again.. */
stream->drain_start_usec = 0;
stream->drained_bytes = 0;
} else {
/* If we have no drain start timestamp, and we still have
* remaining buffer, start the buffering counter */
if (!stream->drain_start_usec && total_buffered > 0) {
log_debug(LD_EDGE, "Began edge buffering: %d %d %ld",
stream->ewma_rate_last_sent,
stream->ewma_drain_rate,
total_buffered);
tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xon_drain_start),
stream);
stream->drain_start_usec = monotime_absolute_usec();
stream->drained_bytes = 0;
}
}
if (stream->drain_start_usec) {
/* If we have spent enough time in a queued state, update our drain
* rate. */
if (stream->drained_bytes > xon_rate_bytes) {
/* No previous drained bytes means it is the first time we are computing
* it so use the value we just drained onto the socket as a baseline. It
* won't be accurate but it will be a start towards the right value.
*
* We have to do this in order to have a drain rate else we could be
* sending a drain rate of 0 in an XON which would be undesirable and
* basically like sending an XOFF. */
if (stream->prev_drained_bytes == 0) {
stream->prev_drained_bytes = stream->drained_bytes;
}
uint32_t drain_rate = compute_drain_rate(stream);
/* Once the drain rate has been computed, note how many bytes we just
* drained so it can be used at the next calculation. We do this here
* because it gets reset once the rate is changed. */
stream->prev_drained_bytes = stream->drained_bytes;
if (drain_rate) {
stream->ewma_drain_rate =
(uint32_t)n_count_ewma(drain_rate,
stream->ewma_drain_rate,
xon_ewma_cnt);
log_debug(LD_EDGE, "Updating drain rate: %d %d %ld",
drain_rate,
stream->ewma_drain_rate,
total_buffered);
tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xon_drain_update),
stream, drain_rate);
/* Reset recent byte counts. This prevents us from sending advisory
* XONs more frequent than every xon_rate_bytes. */
stream->drained_bytes = 0;
stream->drain_start_usec = 0;
}
}
}
/* If we don't have an XOFF outstanding, consider updating an
* old rate */
if (!stream->xoff_sent) {
if (stream_drain_rate_changed(stream)) {
/* If we are still buffering and the rate changed, update
* advisory XON */
log_info(LD_EDGE, "Sending rate-change XON: %d %d %ld",
stream->ewma_rate_last_sent,
stream->ewma_drain_rate,
total_buffered);
tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xon_rate_change), stream);
circuit_send_stream_xon(stream);
}
} else if (total_buffered == 0) {
log_info(LD_EDGE, "Sending XON: %d %d %ld",
stream->ewma_rate_last_sent,
stream->ewma_drain_rate,
total_buffered);
tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xon_partial_drain), stream);
circuit_send_stream_xon(stream);
}
/* If the buffer has fully emptied, clear the drain timestamp,
* so we can total only bytes drained while outbuf is 0. */
if (total_buffered == 0) {
stream->drain_start_usec = 0;
/* After we've spent 'xon_rate_bytes' with the queue fully drained,
* double any rate we sent. */
if (stream->drained_bytes >= xon_rate_bytes &&
stream->ewma_rate_last_sent) {
stream->ewma_drain_rate = MIN(INT32_MAX, 2*stream->ewma_drain_rate);
log_debug(LD_EDGE,
"Queue empty for xon_rate_limit bytes: %d %d",
stream->ewma_rate_last_sent,
stream->ewma_drain_rate);
tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xon_drain_doubled), stream);
/* Resetting the drained bytes count. We need to keep its value as a
* previous so the drain rate calculation takes into account what was
* actually drain the last time. */
stream->prev_drained_bytes = stream->drained_bytes;
stream->drained_bytes = 0;
}
}
return;
}
/**
* Note that we packaged some data on this stream. Used to enforce
* client-side dropmark limits
*/
void
flow_control_note_sent_data(edge_connection_t *stream, size_t len)
{
/* If we are near the max, scale everything down */
if (stream->total_bytes_xmit >= TOTAL_XMIT_SCALE_AT-len) {
log_info(LD_EDGE, "Scaling down for flow control xmit bytes:: %d %d %d",
stream->total_bytes_xmit,
stream->num_xoff_recv,
stream->num_xon_recv);
stream->total_bytes_xmit /= 2;
stream->num_xoff_recv /= 2;
stream->num_xon_recv /= 2;
}
stream->total_bytes_xmit += len;
}
/** Returns true if an edge connection uses flow control */
bool
edge_uses_flow_control(const edge_connection_t *stream)
{
bool ret = (stream->on_circuit && stream->on_circuit->ccontrol) ||
(stream->cpath_layer && stream->cpath_layer->ccontrol);
/* All circuits with congestion control use flow control */
return ret;
}
/**
* Returns the max RTT for the circuit that carries this stream,
* as observed by congestion control.
*/
uint64_t
edge_get_max_rtt(const edge_connection_t *stream)
{
if (stream->on_circuit && stream->on_circuit->ccontrol)
return stream->on_circuit->ccontrol->max_rtt_usec;
else if (stream->cpath_layer && stream->cpath_layer->ccontrol)
return stream->cpath_layer->ccontrol->max_rtt_usec;
return 0;
}
/** Returns true if a connection is an edge conn that uses flow control */
bool
conn_uses_flow_control(connection_t *conn)
{
bool ret = false;
if (CONN_IS_EDGE(conn)) {
edge_connection_t *edge = TO_EDGE_CONN(conn);
if (edge_uses_flow_control(edge)) {
ret = true;
}
}
return ret;
}

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/* Copyright (c) 2019-2021, The Tor Project, Inc. */
/* See LICENSE for licensing information */
/**
* \file congestion_control_flow.h
* \brief APIs for stream flow control on congestion controlled circuits.
**/
#ifndef TOR_CONGESTION_CONTROL_FLOW_H
#define TOR_CONGESTION_CONTROL_FLOW_H
#include "core/or/crypt_path_st.h"
#include "core/or/circuit_st.h"
#include "core/or/edge_connection_st.h"
void flow_control_new_consensus_params(const struct networkstatus_t *);
bool circuit_process_stream_xoff(edge_connection_t *conn,
const crypt_path_t *layer_hint,
const cell_t *cell);
bool circuit_process_stream_xon(edge_connection_t *conn,
const crypt_path_t *layer_hint,
const cell_t *cell);
int flow_control_decide_xoff(edge_connection_t *stream);
void flow_control_decide_xon(edge_connection_t *stream, size_t n_written);
void flow_control_note_sent_data(edge_connection_t *stream, size_t len);
bool edge_uses_flow_control(const edge_connection_t *stream);
bool conn_uses_flow_control(connection_t *stream);
uint64_t edge_get_max_rtt(const edge_connection_t *);
/* Private section starts. */
#ifdef TOR_CONGESTION_CONTROL_FLOW_PRIVATE
/*
* Unit tests declaractions.
*/
#ifdef TOR_UNIT_TESTS
#endif /* defined(TOR_UNIT_TESTS) */
#endif /* defined(TOR_CONGESTION_CONTROL_FLOW_PRIVATE) */
#endif /* !defined(TOR_CONGESTION_CONTROL_FLOW_H) */