Placeholders name or syntax

[mhy239]

Hello Mathieu,

I try to play with processor and placeholders but I face to some problems.

In fact, after (... a lot of tests ...), processor work fine on simple case, but when I have some % symbols in the code (not for delimitation of placeholder but for something else like modulo or real percentage is requested for printing) the function process try to catch and finally found nothing to replace and return an empty String, this situation scratch what is waiting in the browser.

I purpose to be more restrictive for placeholders name
centred in % like actually
name start and finish with underscore
name in only in uppercase, no space symbol
name including _ symbols need to be between 4 and 16 chars

so if i adapt to your example:
Placeholders are delimited with % symbols. Like this: %TEMPLATE_PLACEHOLDER%.
become
Placeholders names start with %_ and finish by _%, using only uppercase letters, nor space symbol and length between % char is 4 to 16 char . Like this: %_PLACEHOLDER_%
start with %_ : Ok
finish with _%: Ok
uppercase: Ok
no space: Ok
Length of PLACEHOLDER is 13 so more than 4 and less than 16: Ok

and for sure, I delegate the correspondant treatment inside library (I'm not able to do this)

[mathieucarbou]

Hello,

I think more context is required to fully understand... You are using templates, right ?

If yes, just know that there won't be any enhancements for that part in 3.x.

3.x line is only for bug fixes, and a new 4.x line will be started in a few months.

And this is psosible that 4.x will drop templating support, except if someone is really motivated to implement it correctly., and with a standard templating engine (we need to discuss that with @me-no-dev).

The current templating support is ok-ish, but now, there are several template engines available on ESP32 that are far more better than what ESP32AsyncWS has. It is also not the goal of a webserver to act as a template engine.

So I strongly advise to look at integrating another engine (example: https://techtutorialsx.com/2021/09/13/esp32-inja-html-template-engine/), which will work for both 3.x and 4.x later. Do not rely on 3.x template engine if it cannot cover your needs.

[DeeEmm]

I've been through this issue with my project and posted up previously on the old repo. me-no-dev#1249 It was also commonly reported elsewhere - https://github.com/me-no-dev/ESPAsyncWebServer/issues?q=is%3Aissue%20delimiter

The % delimiter is a BAD choice as it is a valid / common character in CSS.

So when the template engine comes across the % character in CSS, it breaks the template engine.

The previous solution given to use %% instead to escape the character produces non-compliant CSS, which will fails CSS tests. This is obviously bad for the semantic web. (see my comments here)

So ideally the character should be changed to one that does not clash with any of the common web based languages (css / html / xml / javascript / etc).

Of course the change should also be backwards compatible with the current % character.

There is a workaround...

You can set a build flag in platformio.ini to change the placeholder...

[common]
build_flags = 
	"-D TEMPLATE_PLACEHOLDER='~'"

However it is far more elegant and semantically correct to not use the % in the first place.

/DM

[mhy239]

I agree to change '%' by '~'.

With Arduino IDE, I don't know where I can impact TEMPLATE_PLACEHOLDER='~'

I try to add : #define TEMPLATE_PLACEHOLDER '~'
just before #include <ESPAsynWebServer.h>

unfortunatly, Arduino IDE using precompiled library doesn't take in consideration this

with a modification in file WebResponseImpl.h, (I don't like, my code can't be share without a lot of explainations ... and survey at each new release)
Arduino IDE considere a change in file and restart compilation so this solution work

maybe someone can help me to avoid modification in file "WebResponseImpl.h" ?

M

[DeeEmm]

I don't know where I can impact TEMPLATE_PLACEHOLDER='~'

This goes into your platformio.ini - assuming that you are using VSCode + platformio

There should be a section called 'build_flags' if not you can add it. The instruction goes underneath this.

It is an instruction to the compiler to 'define' the variable at compile time. Hence the -D prefix.

You can read more about platformio build flags here

[DeeEmm]

Ahh sorry. I now see that you are using the Arduino IDE. I am not sure how or even if it is possible with Arduino to change the compiler in this way. From my recollection the only compile time directives available are those predefined ones in the drop down menu.

Whilst there is a bit of a learning curve, I definitely recommend VSCode and PlatformIO for ESP development. Issues like this one are really where its advantages are seen.

[me-no-dev]

PlatformIO is no longer supported, because PlatformIO no longer supports our new releases. There is pioarduino which is community fork of PlatformIO that does support it, but anyway, you can add the build flag even to Arduino IDE builds. All you need to do is create a file called build_opt.h in your sketch directory and add the flags in there (it's not actually treated as header file)

[DeeEmm]

Interesting. Had not come across pioarduino before.

Current release appears to be listed on PIO.

[mathieucarbou]

Current release appears to be listed on PIO.

Do not confuse:

1. PlatformIO registry (which hosts libraries)
2. PlatformIO tooling (pio bash command and platfromio.ini file)
3. PlatformIO espressif platform (which is the glue between PlatformIO and Arduino Core - which is what was dropped by PlatformIO)
4. PlatformIO vscode extension

1 and 2 and still very relevant and used for development.

3 and 4 are replaced by pioarduino and pioarduino vscode extension since Arduino Core 3.

• https://github.com/pioarduino/platform-espressif32
• https://marketplace.visualstudio.com/items?itemName=pioarduino.pioarduino-ide

[mhy239]

Thanks to DeeEmm and me-no-dev for the way,
after some unsucces : '~' or "~" not working / Arduino follow to use precompiled files ...

I summarize a solution working like a charm
add file named build_opt.h
in this file, I place just one line, without space
-DTEMPLATE_PLACEHOLDER=0x7E

deletion of pre compiled libraries (only one time) // not necessary if you start with a new sketch :
go in folder containing compiled code, delete the folder libraries
then, export sketchbook to the card
thanks also to mathieucarbou as maintainer ,