mbed_config.h not interpreting wifi passwords inserted into mbed_app.json if they include " char in the password

Gerriko commented 2 years ago

Description of defect

This error relates to Wireless LAN and the WiFi example (mbed-os-snippet-TCPSocketWiFi) as found in GitHub repository: https://github.com/ARMmbed/mbed-os-snippet-TCPSocketWiFi/tree/v6.15

As per README.md it informs that we should edit mbed_app.json to include correct SSID and Password.

Now, as passwords can include any ASCII readable character, the mbed OS process to convert the password provided in mbed_app.json to what's contained in the mbed_config.h (as found in the Mbed Studio build folder) has a problem if the " character (0x22) is included in the password.

So if for example you use: my"P"assword as your password

"config": {
    "wifi-ssid": {
        "help": "WiFi SSID",
        "value": "\"SSID\""
    },
    "wifi-password": {
        "help": "WiFi Password",
        "value": "\"my\"P\"assword\""
    }
},

The mbed_config.h file creates: #define MBED_CONF_APP_WIFI_PASSWORD "my"P"assword" but then clang misinterprets this as "my" P "assword" which creates an error in the code when used.

However, if I manually change mbed_config.h to #define MBED_CONF_APP_WIFI_PASSWORD "my\"P\"assword"

clang is happy in terms of removing error lines in IDE... but of course it still won't compile (as mbed_config.h is runtime generated). If I manually create my own password define using the above password and use that defined param to connect then it works. E.g. where MY_OWN_APP_WIFI_PASSWORD is my own #define. However this is defined in the code rather in mbed_app.json

#define MY_OWN_APP_WIFI_PASSWORD "my\"P\"assword"
[.... rest of code ....]
int ret = wifi.connect(MBED_CONF_APP_WIFI_SSID, MY_OWN_APP_WIFI_PASSWORD, NSAPI_SECURITY_WPA_WPA2);

Target(s) affected by this defect ?

all targets that accept wifi API.

Toolchain(s) (name and version) displaying this defect ?

What version of Mbed-os are you using (tag or sha) ?

Mbed OS version 6.15.1

What version(s) of tools are you using. List all that apply (E.g. mbed-cli)

All development and compiling done using Mbed Studio 1.4.3

How is this defect reproduced ?

Use WiFi example (mbed-os-snippet-TCPSocketWiFi) as found in GitHub repository: https://github.com/ARMmbed/mbed-os-snippet-TCPSocketWiFi/tree/v6.15

and add in parameters as instructed in mbed_app.json and use the password as described with a " char in the password. Then try to compile.

mbedmain commented 2 years ago

@Gerriko thank you for raising this issue.Please take a look at the following comments:

It would help if you could also specify the versions of any tools you are using? How can we reproduce your issue?

NOTE: If there are fields which are not applicable then please just add 'n/a' or 'None'. This indicates to us that at least all the fields have been considered. Please update the issue header with the missing information.

pea-pod commented 2 years ago

If you want a quotation mark to appear in your final C code, you have to work backwards from what you want to where you start. You start with the final double quote mark, get it's C equivalent, and get that intermediary's json equivalent.

We'll take your example (my"P"assword) as the example.

In order to get this to compile in C/C++, you need to escape the middle quotation marks. So the C version would look like this:

#define MBED_CONF_APP_WIFI_PASSWORD "my\"P\"assword"

That gets us back to C, but you need to pop the stack one more time, since you're starting with a .json file. It will treat double quotes as starting and ending lines as well. So you need to make sure that you are also escaping those as well. You did that correctly, I believe. But the final change is to make sure that the backslashes also make it into the .h file, so you need to escape those in the .json file as well.

In the relevant portion of your mbed_app.json file, you would have this:

    "value": "\"my\\\"P\\\"assword\""

Because of the double conversions \\\" in json becomes \" in C, which then gets changed to the double quote in the compiled string that you're expecting. I know this because I ran into the same issue about the same time you did.

Gerriko commented 2 years ago

Wow, thanks for that. I'm glad you figured this one out. Well done.

On Thu, 24 Mar 2022 at 00:06, pea-pod @.***> wrote:

If you want a quotation mark to appear in your final C code, you have to work backwards from what you want to where you start. You start with the final double quote mark, get it's C equivalent, and get that intermediary's json equivalent.

We'll take your example (my"P"assword) as the example.

In order to get this to compile in C/C++, you need to escape the middle quotation marks. So the C version would look like this:

define MBED_CONF_APP_WIFI_PASSWORD "my\"P\"assword"

That gets us back to C, but you need to pop the stack one more time, since you're starting with a .json file. It will treat double quotes as starting and ending lines as well. So you need to make sure that you are also escaping those as well. You did that correctly, I believe. But the final change is to make sure that the backslashes also make it into the .h file, so you need to escape those in the .json file as well.

In the relevant portion of your mbed_app.json file, you would have this:
"value": "\"my\\\"P\\\"assword\""
Because of the double conversions \\" in json becomes \" in C, which then gets changed to the double quote in the compiled string that you're expecting. I know this because I ran into the same issue about the same time you did.

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0xc0170 commented 2 years ago

Thank you @pea-pod for the answer.

I'll close this as resolved.

If you consider this should be covered in the docs, please add it to the https://github.com/ARMmbed/mbed-os-5-docs/blob/development/docs/program-setup/advanced/configuration.md#using-configuration-data-in-code section

ARMmbed / mbed-os