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Editing: _android_support.py
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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