Detect when exe launched via Google Chrome Native Message Passing

Question

I'm trying to retrofit an existing NPAPI plugin to use Google's native message passing technology. Since it's an existing exe, we already have some console behavior programmed in so that users can call our program from the terminal. Is there any way for us to detect, in a C# application, that the exe has been launched by Google Chrome for message passing? If we could do that, we could launch the message passing loop if we're called from Chrome but resume normal behavior if called from Powershell/cmd.

I've tried inspecting the command line arguments passed to the program when launched by Chrome, but there are none. Having a configurable option there would solve this for us, but as far as I can tell it's not possible. I haven't yet had a chance to inspect the current working directory in case it could also be used as an identifier.

Answer 1

The API doesn't support passing command line arguments, but your host process should be able to inspect its own parent process to determine if it was launched by Chrome or something else.

Answer 2

Actually, yes, I believe it is possible.

When, for example, a C# console application is started as a native message client host, it is passed two arguments:

--parent-window=<number>

and

chrome-extension://<extension identifier>/

I think the second argument is probably the ideal one for determining that not only was it Chrome that launched the process, but that the specific extension you authored and intended to call it launched it!

Please make note in the above, the "<" and ">" are not literally part of the argument, and just used to denote the beginning and end of that part of the message, much like double quotes.

Alternatively, just have your extension invoke a script (.bat, .sh, etc.) that passes special arguments to your native host. This way you could pass specific arguments of your own.

Answer 3

An alternative to checking the arguments as suggested by @aikeru would be to check for the existence of certain environment variables that were passed from Chrome to the native messaging host. My host has the following variables that seem to be specific to Chrome (found with Sysinternals Process Monitor):

CHROME_ALLOCATOR=TCMALLOC
CHROME_BREAKPAD_PIPE_NAME=\\.\pipe\GoogleCrashServices\S-1-5-18
CHROME_MAIN_TIME=13037817851797830
CHROME_METRO_DLL=0
CHROME_PRE_READ_EXPERIMENT=100-pct-default
CHROME_RESTART=Google Chrome|Whoa! Google Chrome has crashed. Relaunch now?|LEFT_TO_RIGHT
CHROME_VERSION=33.0.1750.117