PHP `exit;` fails to produce a CGI response

[fd]

When exit; is called and the headers have not yet been flushed the CGI response is completely empty. The issue seems to be that the shutdown procedures are not called on exit;.

Reproduction

<?php
// test-exit-flush-fail.php
header('X-Test: 123');
exit;

<?php
// test-exit-flush-ok.php
header('X-Test: 123');
// Note: at least one byte needs to be sent.
echo "X";
exit;

When I run the scripts with a native php-cgi binary it produces the expected CGI responses.

> docker run --rm -ti -v $PWD:/app php:7.4.32-cli /usr/local/bin/php-cgi /app/test-exit-flush-ok.php
X-Powered-By: PHP/7.4.32
X-Test: 123
Content-type: text/html; charset=UTF-8

X

> docker run --rm -ti -v $PWD:/app php:7.4.32-cli /usr/local/bin/php-cgi /app/test-exit-flush-fail.php
X-Powered-By: PHP/7.4.32
X-Test: 123
Content-type: text/html; charset=UTF-8

But when I run the test-exit-flush-fail.php with wasmtime it fails to produce a CGI response.

> wasmtime --mapdir=./::./ php-cgi -- test-exit-flush-ok.php 
X-Powered-By: PHP/7.4.32
X-Test: 123
Content-type: text/html; charset=UTF-8

X

> wasmtime --mapdir=./::./ php-cgi -- test-exit-flush-fail.php 

[fd]

I did some investigating today. This bug is related to the lack of setjmp/longjmp support, obviously.

Ruby has a working version of the setjmp api. It relies on asyncify. I believe this approach was already mentioned in a blog post but not yet implemented.

I integrated the ruby code with php v7.4.32 and it seems to work well. I'd like to open a PR with the patch but I'm unsure how to produce the actual patch file from the build-staging directory.

[ereslibre]

Hello @fd! Thank you for taking the time to investigate this issue. You are absolutely right, this issue is due to the fact of a missing setjmp/longjmp emulation.

We are super interested in looking at your patch and integrating it!

When you clone the repo locally, you can add your patch to https://github.com/vmware-labs/webassembly-language-runtimes/tree/main/php/php-7.4.32/patches, and then from the root of the repo you should be able to build PHP by running make php/php-7.4.32.

You need docker or podman for this build to succeed. After it has been built, you can find the PHP artifact at php/build-output/php/php-7.4.32/bin.

[assambar]

I integrated the ruby code with php v7.4.32 and it seems to work well. I'd like to open a PR with the patch but I'm unsure how to produce the actual patch file from the build-staging directory.

In case you did your changes in build-staging/php/php-7.4.32/checkout, here is what you can do to ensure the patch format is the same as the other patches.

1. Commit your changes via pushd build-staging/php/php-7.4.32/checkout && git commit -m "..." && popd
2. From the webassembly-language-runtimes repository root set up the build environment like source scripts/wl-env.sh php/php-7.4.32
3. Update the patches via ./scripts/wl-update-patches.sh
4. Cleanup the build environment via wl-env-unset
5. Commit the updated patches and create a PR.

I'm looking forward to seeing what you did as we're working on enabling PHP 8 fibers via asyncify so this can be combined with your work to a better end.

[fd]

I prepared the patch here https://github.com/vmware-labs/webassembly-language-runtimes/pull/28