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import io
import sys
# The maximum length of a log message in bytes, including the level marker and
# tag, is defined as LOGGER_ENTRY_MAX_PAYLOAD in
# platform/system/logging/liblog/include/log/log.h. As of API level 30, 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 TextIOWrapper can always avoid exceeding MAX_BYTES_PER_WRITE.
# However, if the actual number of bytes per character is smaller than that,
# then TextIOWrapper 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.
sys.stdout = TextLogStream(
android_log_write, stdout_prio, "python.stdout", errors=sys.stdout.errors)
sys.stderr = TextLogStream(
android_log_write, stderr_prio, "python.stderr", errors=sys.stderr.errors)
class TextLogStream(io.TextIOWrapper):
def __init__(self, android_log_write, prio, tag, **kwargs):
kwargs.setdefault("encoding", "UTF-8")
kwargs.setdefault("line_buffering", True)
super().__init__(BinaryLogStream(android_log_write, prio, tag), **kwargs)
self._CHUNK_SIZE = MAX_BYTES_PER_WRITE
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 before sending it to the superclass. Note that
# "".splitlines() == [], so nothing will be logged for an empty string.
for line in s.splitlines(keepends=True):
while line:
super().write(line[:MAX_CHARS_PER_WRITE])
line = line[MAX_CHARS_PER_WRITE:]
return len(s)
class BinaryLogStream(io.RawIOBase):
def __init__(self, android_log_write, prio, tag):
self.android_log_write = android_log_write
self.prio = prio
self.tag = tag
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:
# Encode null bytes using "modified UTF-8" to avoid truncating the
# message. This should not affect the return value, as the caller
# may be expecting it to match the length of the input.
self.android_log_write(self.prio, self.tag,
b.replace(b"\x00", b"\xc0\x80"))
return len(b)
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