# Known Issues

## Fibers

Calling PHP functions and language constructs that themselves call [cgo](https://go.dev/blog/cgo) in [Fibers](https://www.php.net/manual/en/language.fibers.php) is known to cause crashes.

This issue [is being worked on by the Go project](https://github.com/golang/go/issues/62130).

In the meantime, one solution is not to use constructs (like `echo`) and functions (like `header()`) that delegate to Go from inside Fibers.

This code will likely crash because it uses `echo` in the Fiber:

```php
$fiber = new Fiber(function() {
    echo 'In the Fiber'.PHP_EOL;
    echo 'Still inside'.PHP_EOL;
});
$fiber->start();
```

Instead, return the value from the Fiber and use it outside:

```php
$fiber = new Fiber(function() {
    Fiber::suspend('In the Fiber'.PHP_EOL));
    Fiber::suspend('Still inside'.PHP_EOL));
});
echo $fiber->start();
echo $fiber->resume();
$fiber->resume();
```

## Unsupported PHP Extensions

The following extensions are known not to be compatible with FrankenPHP:

| Name                                                        | Reason          | Alternatives                                                                                                         |
| ----------------------------------------------------------- | --------------- | -------------------------------------------------------------------------------------------------------------------- |
| [imap](https://www.php.net/manual/en/imap.installation.php) | Not thread-safe | [javanile/php-imap2](https://github.com/javanile/php-imap2), [webklex/php-imap](https://github.com/Webklex/php-imap) |

## get_browser

The [get_browser()](https://www.php.net/manual/en/function.get-browser.php) function seems to perform badly after a while. A workaround is to cache (e.g. with APCU) the results per User Agent, as they are static.

## Standalone Binary and Alpine-based Docker Images

The standalone binary and Alpine-based docker images (`dunglas/frankenphp:*-alpine`) use [musl libc](https://musl.libc.org/) instead of [glibc and friends](https://www.etalabs.net/compare_libcs.html), to keep a smaller binary size. This may lead to some compatibility issues. In particular, the glob flag `GLOB_BRACE` is [not available](https://www.php.net/manual/en/function.glob.php)

## Using `https://127.0.0.1` with Docker

By default, FrankenPHP generates a TLS certificate for `localhost`.
It's the easiest and recommended option for local development.

If you really want to use `127.0.0.1` as a host instead, it's possible to configure it to generate a certificate for it by setting the server name to `127.0.0.1`.

Unfortunately, this is not enough when using Docker because of [its networking system](https://docs.docker.com/network/).
You will get a TLS error similar to `curl: (35) LibreSSL/3.3.6: error:1404B438:SSL routines:ST_CONNECT:tlsv1 alert internal error`.

If you're using Linux, a solution is to use [the host networking driver](https://docs.docker.com/network/network-tutorial-host/):

```console
docker run \
    -e SERVER_NAME="127.0.0.1" \
    -v $PWD:/app/public \
    --network host \
    dunglas/frankenphp
```

The host networking driver isn't supported on Mac and Windows. On these platforms, you will have to guess the IP address of the container and include it in the server names.

Run the `docker network inspect bridge` and look at the `Containers` key to identify the last currently assigned IP address under the `IPv4Address` key, and increment it by one. If no container is running, the first assigned IP address is usually `172.17.0.2`.

Then, include this in the `SERVER_NAME` environment variable:

```console
docker run \
    -e SERVER_NAME="127.0.0.1, 172.17.0.3" \
    -v $PWD:/app/public \
    -p 80:80 -p 443:443 -p 443:443/udp \
    dunglas/frankenphp
```

> ![CAUTION]
>
> Be sure to replace `172.17.0.3` with the IP that will be assigned to your container.

You should now be able to access `https://127.0.0.1` from the host machine.

If that's not the case, start FrankenPHP in debug mode to try to figure out the problem:

```console
docker run \
    -e CADDY_GLOBAL_OPTIONS="debug"
    -e SERVER_NAME="127.0.0.1" \
    -v $PWD:/app/public \
    -p 80:80 -p 443:443 -p 443:443/udp \
    dunglas/frankenphp
```