SNIFF message pipe in mojo IPC

[Rafael]

Hi all,

I have a compiled chromium at ubuntu server which can only run headless. Is there a recommended way to learn the data encapsulated in the message pipe (e.g., to figure out what would be sent between browser process and renderer process in the real world)? It can work like chromium ipc sniffer, but this only works on window. Thanks.

[Andrew Williams]

Hi Rafael,

One thing you can do is compile Chromium using the `extended_tracing_enabled = true` gn arg and then collect trace files that will include detailed information about mojo messages (including the message contents).  I wrote a work-in-progress Python script [1] to print this information given a trace file, and more detailed instructions on how to collect trace files for this purpose can be found at the top of the script.

Hope that helps!

-Andrew

[1] https://chromium-review.googlesource.com/c/chromium/src/+/3370782/3/tools/mojo_messages_log.py

On Tue, Apr 26, 2022 at 1:14 AM Rafael <shinma...@gmail.com> wrote:

Hi all,

I have a compiled chromium at ubuntu server which can only run headless. Is there a recommended way to learn the data encapsulated in the message pipe (e.g., to figure out what would be sent between browser process and renderer process in the real world)? It can work like chromium ipc sniffer, but this only works on window. Thanks.

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[David M]

Hi Rafael,

I enabled `extended_tracing_enabled = true`  and built the code in windows machine. may i know, where the mojom trace files will be placed.

Thanks in advance.

David

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[Andrew Williams]

For trace files collected via chrome://tracing, the 'Save' button will save the file in the downloads folder.  For trace files collected using the `--enable-tracing` command line argument, IIRC they will be put in the current working directory by default but you can change the path using the `--enable-tracing-output=<output file path>` command line argument.

-Andrew