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import io
import sys
from threading import RLock
from time import sleep, time
# The maximum length of a log message in bytes, including the level marker and
# tag, is defined as LOGGER_ENTRY_MAX_PAYLOAD at
# https://cs.android.com/android/platform/superproject/+/android-14.0.0_r1:system/logging/liblog/include/log/log.h;l=71.
# Messages longer than this will be be truncated by logcat. This limit has already
# been reduced at least once in the history of Android (from 4076 to 4068 between
# API level 23 and 26), so leave some headroom.
MAX_BYTES_PER_WRITE = 4000
# UTF-8 uses a maximum of 4 bytes per character, so limiting text writes to this
# size ensures that we can always avoid exceeding MAX_BYTES_PER_WRITE.
# However, if the actual number of bytes per character is smaller than that,
# then we may still join multiple consecutive text writes into binary
# writes containing a larger number of characters.
MAX_CHARS_PER_WRITE = MAX_BYTES_PER_WRITE // 4
# When embedded in an app on current versions of Android, there's no easy way to
# monitor the C-level stdout and stderr. The testbed comes with a .c file to
# redirect them to the system log using a pipe, but that wouldn't be convenient
# or appropriate for all apps. So we redirect at the Python level instead.
def init_streams(android_log_write, stdout_prio, stderr_prio):
if sys.executable:
return # Not embedded in an app.
global logcat
logcat = Logcat(android_log_write)
sys.stdout = TextLogStream(
stdout_prio, "python.stdout", sys.stdout.fileno())
sys.stderr = TextLogStream(
stderr_prio, "python.stderr", sys.stderr.fileno())
class TextLogStream(io.TextIOWrapper):
def __init__(self, prio, tag, fileno=None, **kwargs):
# The default is surrogateescape for stdout and backslashreplace for
# stderr, but in the context of an Android log, readability is more
# important than reversibility.
kwargs.setdefault("encoding", "UTF-8")
kwargs.setdefault("errors", "backslashreplace")
super().__init__(BinaryLogStream(prio, tag, fileno), **kwargs)
self._lock = RLock()
self._pending_bytes = []
self._pending_bytes_count = 0
def __repr__(self):
return f"<TextLogStream {self.buffer.tag!r}>"
def write(self, s):
if not isinstance(s, str):
raise TypeError(
f"write() argument must be str, not {type(s).__name__}")
# In case `s` is a str subclass that writes itself to stdout or stderr
# when we call its methods, convert it to an actual str.
s = str.__str__(s)
# We want to emit one log message per line wherever possible, so split
# the string into lines first. Note that "".splitlines() == [], so
# nothing will be logged for an empty string.
with self._lock:
for line in s.splitlines(keepends=True):
while line:
chunk = line[:MAX_CHARS_PER_WRITE]
line = line[MAX_CHARS_PER_WRITE:]
self._write_chunk(chunk)
return len(s)
# The size and behavior of TextIOWrapper's buffer is not part of its public
# API, so we handle buffering ourselves to avoid truncation.
def _write_chunk(self, s):
b = s.encode(self.encoding, self.errors)
if self._pending_bytes_count + len(b) > MAX_BYTES_PER_WRITE:
self.flush()
self._pending_bytes.append(b)
self._pending_bytes_count += len(b)
if (
self.write_through
or b.endswith(b"\n")
or self._pending_bytes_count > MAX_BYTES_PER_WRITE
):
self.flush()
def flush(self):
with self._lock:
self.buffer.write(b"".join(self._pending_bytes))
self._pending_bytes.clear()
self._pending_bytes_count = 0
# Since this is a line-based logging system, line buffering cannot be turned
# off, i.e. a newline always causes a flush.
@property
def line_buffering(self):
return True
class BinaryLogStream(io.RawIOBase):
def __init__(self, prio, tag, fileno=None):
self.prio = prio
self.tag = tag
self._fileno = fileno
def __repr__(self):
return f"<BinaryLogStream {self.tag!r}>"
def writable(self):
return True
def write(self, b):
if type(b) is not bytes:
try:
b = bytes(memoryview(b))
except TypeError:
raise TypeError(
f"write() argument must be bytes-like, not {type(b).__name__}"
) from None
# Writing an empty string to the stream should have no effect.
if b:
logcat.write(self.prio, self.tag, b)
return len(b)
# This is needed by the test suite --timeout option, which uses faulthandler.
def fileno(self):
if self._fileno is None:
raise io.UnsupportedOperation("fileno")
return self._fileno
# When a large volume of data is written to logcat at once, e.g. when a test
# module fails in --verbose3 mode, there's a risk of overflowing logcat's own
# buffer and losing messages. We avoid this by imposing a rate limit using the
# token bucket algorithm, based on a conservative estimate of how fast `adb
# logcat` can consume data.
MAX_BYTES_PER_SECOND = 1024 * 1024
# The logcat buffer size of a device can be determined by running `logcat -g`.
# We set the token bucket size to half of the buffer size of our current minimum
# API level, because other things on the system will be producing messages as
# well.
BUCKET_SIZE = 128 * 1024
# https://cs.android.com/android/platform/superproject/+/android-14.0.0_r1:system/logging/liblog/include/log/log_read.h;l=39
PER_MESSAGE_OVERHEAD = 28
class Logcat:
def __init__(self, android_log_write):
self.android_log_write = android_log_write
self._lock = RLock()
self._bucket_level = 0
self._prev_write_time = time()
def write(self, prio, tag, message):
# Encode null bytes using "modified UTF-8" to avoid them truncating the
# message.
message = message.replace(b"\x00", b"\xc0\x80")
with self._lock:
now = time()
self._bucket_level += (
(now - self._prev_write_time) * MAX_BYTES_PER_SECOND)
# If the bucket level is still below zero, the clock must have gone
# backwards, so reset it to zero and continue.
self._bucket_level = max(0, min(self._bucket_level, BUCKET_SIZE))
self._prev_write_time = now
self._bucket_level -= PER_MESSAGE_OVERHEAD + len(tag) + len(message)
if self._bucket_level < 0:
sleep(-self._bucket_level / MAX_BYTES_PER_SECOND)
self.android_log_write(prio, tag, message)
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