ashb commented on a change in pull request #3992: [AIRFLOW-620] Feature to tail
custom number of logs instead of rendering whole log
URL: https://github.com/apache/airflow/pull/3992#discussion_r250557787
##########
File path: airflow/utils/helpers.py
##########
@@ -317,3 +317,45 @@ def render_log_filename(ti, try_number,
filename_template):
task_id=ti.task_id,
execution_date=ti.execution_date.isoformat(),
try_number=try_number)
+
+
+def tail_file(filepath, lines):
+ """
+ Tail last n lines from give file.
+ :param filepath: Path to the file we have to tail
+ :param lines: Number of lines to tail
+ :return last n lines in the file
+ """
+ def get_byte_range_file(fl, num_bytes):
+ # Get current position of file pointer
+ current_position = fl.tell()
+ if current_position < num_bytes:
+ num_bytes = current_position
+ if current_position == 0:
+ return None
+ fl.seek(-num_bytes, 1)
+ data = str(fl.read(num_bytes), 'utf-8', 'ignore')
+ fl.seek(-num_bytes, 1)
+ return data
+
+ LINE_SIZE = 200 # Assuming each line will have 200 bytes
+ lines_to_fetch = lines
+ data = ""
+
+ with open(filepath, 'rb') as fl: # Seek to a position from cur pointer is
not supported in read text mode
+ fl.seek(0, 2)
+ while True:
+ num_bytes = lines_to_fetch * LINE_SIZE # Calculate number of
bytes to fetch based on lines
+ tail_chunk = get_byte_range_file(fl, num_bytes)
+ if tail_chunk is not None:
+ data = tail_chunk + data
+ else:
+ print('Reached starting of the file.Exiting')
Review comment:
This print will show up.. somewhere unhelpful (like in the stdout of the
webserver?) so should be removed.
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