simpletrace: improve parsing of sys.argv; fix files never closed.

The arguments extracted from `sys.argv` named and unpacked to make it
clear what the arguments are and what they're used for.

The two input files were opened, but never explicitly closed. File usage
changed to use `with` statement to take care of this. At the same time,
ownership of the file-object is moved up to `run` function. Added option
to process to support file-like objects.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Mads Ynddal <m.ynddal@samsung.com>
Message-id: 20230926103436.25700-4-mads@ynddal.dk
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

scripts/simpletrace.py

@@ -9,6 +9,7 @@
 #
 # For help see docs/devel/tracing.rst
 
+import sys
 import struct
 import inspect
 from tracetool import read_events, Event
@@ -51,7 +52,6 @@ def get_record(edict, idtoname, rechdr, fobj):
         try:
             event = edict[name]
         except KeyError as e:
-            import sys
             sys.stderr.write('%s event is logged but is not declared ' \
                              'in the trace events file, try using ' \
                              'trace-events-all instead.\n' % str(e))
@@ -172,11 +172,28 @@ def end(self):
         pass
 
 def process(events, log, analyzer, read_header=True):
-    """Invoke an analyzer on each event in a log."""
+    """Invoke an analyzer on each event in a log.
+    Args:
+        events (file-object or list or str): events list or file-like object or file path as str to read event data from
+        log (file-object or str): file-like object or file path as str to read log data from
+        analyzer (Analyzer): Instance of Analyzer to interpret the event data
+        read_header (bool, optional): Whether to read header data from the log data. Defaults to True.
+    """
+
     if isinstance(events, str):
-        events = read_events(open(events, 'r'), events)
+        with open(events, 'r') as f:
+            events_list = read_events(f, events)
+    elif isinstance(events, list):
+        # Treat as a list of events already produced by tracetool.read_events
+        events_list = events
+    else:
+        # Treat as an already opened file-object
+        events_list = read_events(events, events.name)
+
+    close_log = False
     if isinstance(log, str):
         log = open(log, 'rb')
+        close_log = True
 
     if read_header:
         read_trace_header(log)
@@ -187,12 +204,12 @@ def process(events, log, analyzer, read_header=True):
     edict = {"dropped": dropped_event}
     idtoname = {dropped_event_id: "dropped"}
 
-    for event in events:
+    for event in events_list:
         edict[event.name] = event
 
     # If there is no header assume event ID mapping matches events list
     if not read_header:
-        for event_id, event in enumerate(events):
+        for event_id, event in enumerate(events_list):
             idtoname[event_id] = event.name
 
     def build_fn(analyzer, event):
@@ -225,24 +242,25 @@ def build_fn(analyzer, event):
         fn_cache[event_num](event, rec)
     analyzer.end()
 
+    if close_log:
+        log.close()
+
 def run(analyzer):
     """Execute an analyzer on a trace file given on the command-line.
 
     This function is useful as a driver for simple analysis scripts.  More
     advanced scripts will want to call process() instead."""
-    import sys
-
-    read_header = True
-    if len(sys.argv) == 4 and sys.argv[1] == '--no-header':
-        read_header = False
-        del sys.argv[1]
-    elif len(sys.argv) != 3:
-        sys.stderr.write('usage: %s [--no-header] <trace-events> ' \
-                         '<trace-file>\n' % sys.argv[0])
+
+    try:
+        # NOTE: See built-in `argparse` module for a more robust cli interface
+        *no_header, trace_event_path, trace_file_path = sys.argv[1:]
+        assert no_header == [] or no_header == ['--no-header'], 'Invalid no-header argument'
+    except (AssertionError, ValueError):
+        sys.stderr.write(f'usage: {sys.argv[0]} [--no-header] <trace-events> <trace-file>\n')
         sys.exit(1)
 
-    events = read_events(open(sys.argv[1], 'r'), sys.argv[1])
-    process(events, sys.argv[2], analyzer, read_header=read_header)
+    with open(trace_event_path, 'r') as events_fobj, open(trace_file_path, 'rb') as log_fobj:
+        process(events_fobj, log_fobj, analyzer, read_header=not no_header)
 
 if __name__ == '__main__':
     class Formatter(Analyzer):