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fix(core): avoid blocking THP when send buffer is full #5618

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fix(core): avoid blocking THP when send buffer is full #5618

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17 changes: 14 additions & 3 deletions core/src/trezor/wire/thp/channel.py
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Original file line number Diff line number Diff line change
Expand Up @@ -21,7 +21,7 @@
is_there_a_channel_to_replace,
)
from trezor import protobuf, utils, workflow
from trezor.loop import Timeout
from trezor.loop import Timeout, race, sleep

from ..protocol_common import Message
from . import (
Expand Down Expand Up @@ -58,6 +58,11 @@
_MAX_RETRANSMISSION_COUNT = const(50)
_MIN_RETRANSMISSION_COUNT = const(2)

# Stop retransmission if writes are blocked - e.g. due to USB flow control.
# It allows restarting the event loop to handle other THP channels.
_WRITE_TIMEOUT_MS = const(5_000)
_WRITE_TIMEOUT = sleep(_WRITE_TIMEOUT_MS)


class Reassembler:
def __init__(self, cid: int, read_buf: ThpBuffer) -> None:
Expand Down Expand Up @@ -391,7 +396,12 @@ async def write_encrypted_payload(self, ctrl_byte: int, payload: bytes) -> None:
ABP.set_sending_allowed(self.channel_cache, False)

for i in range(_MAX_RETRANSMISSION_COUNT):
await self.ctx.write_payload(header, payload)
result = await race(self.ctx.write_payload(header, payload), _WRITE_TIMEOUT)
if isinstance(result, int):
if __debug__:
log.error(__name__, "Sending is stuck for %d ms", _WRITE_TIMEOUT_MS)
break

# starting from 100ms till ~3.42s
timeout_ms = round(10200 - 1010000 / (100 + i))
try:
Expand All @@ -406,7 +416,8 @@ async def write_encrypted_payload(self, ctrl_byte: int, payload: bytes) -> None:
ABP.set_send_seq_bit_to_opposite(self.channel_cache)
return

raise ThpError("Retransmission timeout")
# restart event loop due to unresponsive channel
raise Timeout("THP retransmission timeout")

def _encrypt(self, buffer: utils.BufferType, noise_payload_len: int) -> None:
if __debug__:
Expand Down