tools: Update DevTools parser flags (#40488)

Rename the `--scan` argument to `-w/--write-file` and the `--use`
argument to `-r/--read-file`. This is more aligned with `tshark`'s
syntax, and I think it is a more intuitive naming scheme.

Remove the `--filter` and `--range` arguments. They are very easily
replaced by more powerful tools like `grep` and `jq`. It seems
unnecessary to have them in this script (specially when the most useful
thing it does is exporting the capture as NDJSON for other tools to
process). This fixes an issue with the last message not being exported.

Change the default port to `6080`. This matches the current information
[in the
book](https://book.servo.org/hacking/using-devtools.html#connecting-to-servo)
on how to run Servo with DevTools enabled.

Testing: Checked with `math test-scripts`

---------

Signed-off-by: eri <eri@igalia.com>

etc/devtools_parser.py

@@ -6,7 +6,7 @@
 
 # This is a script designed to easily debug devtools messages
 # It takes the content of a pcap wireshark capture (or creates a new
-# one when using --scan) and pretty prints the JSON payloads.
+# one when using `-w`) and prints the JSON payloads.
 #
 # Wireshark (more specifically its cli tool tshark) needs to be installed
 # for this script to work. Go to https://tshark.dev/setup/install for a
@@ -17,25 +17,24 @@
 # MacOS (With homebrew):      brew install --cask wireshark
 # Windows (With chocolatey):  choco install wireshark
 #
-# To use it, launch either Servo or a Firefox debugging instance in
+# To use it, launch Servo or Firefox in devtools mode:
-# devtools mode:
 #
-# Servo: ./mach run --devtools=1234
+# Servo: ./mach run --devtools 6080
-# Firefox: firefox --new-instance --start-debugger-server 1234 --profile PROFILE
+# Firefox: firefox --new-instance --start-debugger-server 6080 --profile PROFILE
 #
-# Then run this tool in capture mode and specify the same port as before:
+# Then run this tool in capture mode, specifying the same port as before:
 #
-# ./devtools_parser.py --scan cap.pcap --port 1234
+# ./devtools_parser.py -w capture.pcap -p 6080
 #
-# Finally, open another instance of Firefox and go to about:debugging
+# Finally, open another instance of Firefox, go to about:debugging and connect
-# and connect to localhost:1234. Messages should start popping up. The
+# to localhost:6080. Messages should start popping up. The scan can be finished
-# scan can be finished by pressing Ctrl+C. Then, all of the messages will
+# by pressing Ctrl+C. After that the messages will be printed.
-# show up.
 #
-# You can also review the results of a saved scan, and filter by words
+# To review the results of the scan use the `-r` flag. It is possible to output
-# or by message range:
+# newline-delimited JSON for further processing with other tools using the
+# `--json` flag.
 #
-# ./devtools_parser.py --use cap.pcap --port 1234 --filter watcher --range 10:30
+# ./devtools_parser.py -r capture.pcap --json > capture.json
 
 import json
 import signal
@@ -171,33 +170,26 @@ def parse_message(msg, json_output=False):
 if __name__ == "__main__":
     # Program arguments
     parser = ArgumentParser()
-    parser.add_argument("-p", "--port", default="1234", help="the port where the devtools client is running")
+    parser.add_argument("-p", "--port", default="6080", help="the port where the devtools client is running")
-    parser.add_argument("-f", "--filter", help="search for the string on the messages")
-    parser.add_argument("-r", "--range", help="only parse messages from n to m, with the form of n:m")
     parser.add_argument("--json", action="store_true", help="output in newline-delimited JSON (NDJSON)")
 
     actions = parser.add_mutually_exclusive_group(required=True)
-    actions.add_argument("-s", "--scan", help="scan and save the output to a file")
+    actions.add_argument(
-    actions.add_argument("-u", "--use", help="use the scan from a file")
+        "-w", "--write-file", help="capture messages on the specified port and write the output to a .pcap file"
+    )
+    actions.add_argument("-r", "--read-file", help="parse the captured messages from a .pcap file")
 
     args = parser.parse_args()
 
     # Run tshark, either to start a capture or to read an already existing pcap file
-    if args.scan:
+    if args.write_file:
-        capture_args = ["-i", "lo", "-f", f"tcp port {args.port}", "-w", args.scan]
+        capture_args = ["-i", "lo", "-f", f"tcp port {args.port}", "-w", args.write_file]
         data = tshark(capture_args, wait=True)
     else:
-        read_args = ["-r", args.use]
+        read_args = ["-r", args.read_file]
         data = tshark(read_args)
 
     data = process_data(data)
 
-    # Set the range of messages to show
+    for msg in data:
-    min, max = 0, -2
+        parse_message(msg, json_output=args.json)
-    if args.range and len(args.range.split(":")) == 2:
-        min, max = args.range.split(":")
-
-    for msg in data[int(min) : int(max) + 1]:
-        # Filter the messages if specified
-        if not args.filter or args.filter.lower() in msg[3].lower():
-            parse_message(msg, json_output=args.json)

etc/devtools_parser_test.json

@@ -57,3 +57,4 @@
 {"to": "server1.conn0.thread-configuration15", "configuration": {"shouldPauseOnDebuggerStatement": true}, "type": "updateConfiguration"}
 {"from": "server1.conn0.thread-configuration15"}
 {"to": "server1.conn0.thread-configuration15", "configuration": {"pauseOnExceptions": false, "ignoreCaughtExceptions": false}, "type": "updateConfiguration"}
+{"from": "server1.conn0.thread-configuration15"}

python/servo/testing_commands.py

@@ -369,7 +369,7 @@ class MachCommands(CommandBase):
         if platform.system() == "Linux":
             try:
                 result = subprocess.run(
-                    ["etc/devtools_parser.py", "--json", "--use", "etc/devtools_parser_test.pcap"],
+                    ["etc/devtools_parser.py", "--json", "--read-file", "etc/devtools_parser_test.pcap"],
                     check=True,
                     capture_output=True,
                 )