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"""
Command line program for filtering line-based Eliot logs.
"""
if __name__ == "__main__":
import eliot.filter
eliot.filter.main()
import sys
from datetime import datetime, timedelta
from json import JSONEncoder, dumps, loads
class _DatetimeJSONEncoder(JSONEncoder):
"""
JSON encoder that supports L{datetime}.
"""
def default(self, o):
if isinstance(o, datetime):
return o.isoformat()
return JSONEncoder.default(self, o)
class EliotFilter(object):
"""
Filter Eliot log lines using a Python expression.
@ivar code: A Python code object, the compiled filter expression.
"""
_SKIP = object()
def __init__(self, expr, incoming, output):
"""
@param expr: A Python expression that will be called for each log message.
@type expr: L{str}
@param incoming: An iterable of L{bytes}, each of which is a serialized
Eliot message.
@param output: A file to which output should be written.
@type output: L{file} or a file-like object.
"""
self.code = compile(expr, "<string>", "eval")
self.incoming = incoming
self.output = output
def run(self):
"""
For each incoming message, decode the JSON, evaluate expression, encode
as JSON and write that to the output file.
"""
for line in self.incoming:
message = loads(line)
result = self._evaluate(message)
if result is self._SKIP:
continue
self.output.write(dumps(result, cls=_DatetimeJSONEncoder) + "\n")
def _evaluate(self, message):
"""
Evaluate the expression with the given Python object in its locals.
@param message: A decoded JSON input.
@return: The resulting object.
"""
return eval(
self.code,
globals(),
{
"J": message,
"timedelta": timedelta,
"datetime": datetime,
"SKIP": self._SKIP,
},
)
USAGE = """\
Usage: cat eliot.log | python -m eliot.filter <expr>
Read JSON-expression per line from stdin, and filter it using a Python
expression <expr>.
The expression will have a local `J` containing decoded JSON. `datetime` and
`timedelta` from Python's `datetime` module are also available as locals,
containing the corresponding classes. `SKIP` is also available, if it's the
expression result that indicates nothing should be output.
The output will be written to stdout using JSON serialization. `datetime`
objects will be serialized to ISO format.
Examples:
- Pass through the messages unchanged:
$ cat eliot.log | python -m eliot.filter J
- Retrieve a specific field from a specific message type, dropping messages
of other types:
$ cat eliot.log | python -m eliot.filter \\
"J['field'] if J.get('message_type') == 'my:message' else SKIP"
"""
def main(sys=sys):
"""
Run the program.
Accept arguments from L{sys.argv}, read from L{sys.stdin}, write to
L{sys.stdout}.
@param sys: An object with same interface and defaulting to the L{sys}
module.
"""
if len(sys.argv) != 2:
sys.stderr.write(USAGE)
return 1
EliotFilter(sys.argv[1], sys.stdin, sys.stdout).run()
return 0
|
