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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 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)

sys.stderr = TextLogStream(stderr_prio, "python.stderr", sys.stderr)

class TextLogStream(io.TextIOWrapper):

def __init__(self, prio, tag, original=None, **kwargs):

# Respect the -u option.

if original:

kwargs.setdefault("write_through", original.write_through)

fileno = original.fileno()

else:

fileno = None

# 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")

# On API level 30 and higher, Logcat will strip any number of leading

# newlines. This is visible in all `logcat` modes, even --binary. Work

# around this by adding a leading space, which shouldn't make any

# difference to the log's usability.

if message.startswith(b"\n"):

message = b" " + message

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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