Can I pass information from my C++ program to Lua Server Pages?

[Jurie Horneman]

I was wondering if there is a way to pass arbitrary information from C++ through Mongoose so it's accessible in Lua? I want to pass some variables to Javascript and just passing them as literal Javascript in a script tag is a technique I find often works well (as opposed to asking for the data using a JSON call).

(Example: My C++ code has a variable magic_string which contains "Mongoose rocks". And I want to pass that to my Javascript code, so I want to generate this using Lua:

<script>

   var magic_string = "Mongoose rocks";

</script> )

I looked at the manual and the code but I can't figure out if there is a way. Short of using environment variables I can't think of a way of doing it from Lua either.

A way of hooking into prepare_lua_environment (e.g. passing in a list of strings) might do the trick. (No idea if that's the Mongoose way, sorry.)

Thanks in advance for any help.

Jurie

[Sergey Lyubka]

Hi Jurie,

There is no mechanism currently that makes the modification of Lua state easy. You have to patch prepare_lua_environment().

Your suggestion to make a hook is a way to go - a new MG_LUA event could be introduced, and event handler can add whatever variables to the new Lua state.

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[Jurie Horneman]

Hi Sergey,

> Your suggestion to make a hook is a way to go - a new MG_LUA event could be introduced, and event handler can add whatever variables to the new Lua state.

I looked into it a bit, and here is how I think one could do it:

- Add a MG_LUA_SETUP event type.
- Add a pointer to the Lua state to mg_connection, because otherwise the event handler can't access it.
- Add a call_user() call to prepare_lua_environment. The return value can be ignored.
- Expose the Lua support functions (reg_string etc.) in mongoose.h. (I haven't looked into how embedding in Lua works, I'm just saying this based on what I see in prepare_lua_environment.)

Does that make sense?

Jurie

> On Thu, Mar 6, 2014 at 2:11 PM, Jurie Horneman <jurie.h...@gmail.com> wrote:
> I was wondering if there is a way to pass arbitrary information from C++ through Mongoose so it's accessible in Lua? I want to pass some variables to Javascript and just passing them as literal Javascript in a script tag is a technique I find often works well (as opposed to asking for the data using a JSON call).
>
> (Example: My C++ code has a variable magic_string which contains "Mongoose rocks". And I want to pass that to my Javascript code, so I want to generate this using Lua:
>
> <script>
> var magic_string = "Mongoose rocks";
> </script> )
>
> I looked at the manual and the code but I can't figure out if there is a way. Short of using environment variables I can't think of a way of doing it from Lua either.
>
> A way of hooking into prepare_lua_environment (e.g. passing in a list of strings) might do the trick. (No idea if that's the Mongoose way, sorry.)
>
> Thanks in advance for any help.
>
> Jurie
>
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[Sergey Lyubka]

On Thu, Mar 6, 2014 at 9:50 PM, Jurie Horneman <ju...@jurie.org> wrote:

Hi Sergey,

> Your suggestion to make a hook is a way to go - a new MG_LUA event could be introduced, and event handler can add whatever variables to the new Lua state.

I looked into it a bit, and here is how I think one could do it:

- Add a MG_LUA_SETUP event type.
- Add a pointer to the Lua state to mg_connection, because otherwise the event handler can't access it.
- Add a call_user() call to prepare_lua_environment. The return value can be ignored.
- Expose the Lua support functions (reg_string etc.) in mongoose.h. (I haven't looked into how embedding in Lua works, I'm just saying this based on what I see in prepare_lua_environment.)

Does that make sense?

Yes it does make sense, it's exactly how it should be done, thank you!

[Jurie Horneman]

Cool :) Do you want me to send a pull request? Or open an issue? I forked Mongoose but I haven't tried compiling it or writing a test program for this case.

[Sergey Lyubka]

Pull request would be appreciated. If not, just open an issue please.

For more options, visit https://groups.google.com/d/optout.

[Sergey Lyubka]

Pushed https://github.com/cesanta/mongoose/commit/976b5f37c1b8592903a3a1d3e977078727bfa975

Convenience functions are not exposed though.

[Jurie Horneman]

Awesome! Sorry for not sending a pull request yet.

On 09 Mar 2014, at 20:32 , Sergey Lyubka <val...@gmail.com> wrote:

> Pushed https://github.com/cesanta/mongoose/commit/976b5f37c1b8592903a3a1d3e977078727bfa975
> Convenience functions are not exposed though.
>

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