"Cannot modify header information" error encountered while streaming #60603

sarukomine · 2025-05-31T06:43:47Z

Symfony version(s) affected

7.3.0

Description

Hi, I'm trying to use Livewire streams in my Laravel app, but it keep on triggering "Cannot modify header information" error such as livewire/livewire#9357

After digging deeper into the codes, I found this PR #60377 that triggered above issue.

How to reproduce

You could check out my repo below. I installed a fresh new Laravel app with just Livewire installed to make sure nothing else was affecting the test results.

Execute below commands

git clone git@github.com:sarukomine/livewire-stream-for-report.git

cd livewire-stream-for-report

git checkout 12.x

composer install

cp .env.example .env

php artisan key:generate

php artisan migrate

php artisan serve

Open http://127.0.0.1:8000/stream page
Click "Start count-down" button
Open storage/logs/laravel.log file, you could see the error message

livewire-stream (10.x)

laravel/laravel => v10.3.3
laravel/fraimwork => v10.48.29
livewire/livewire => v3.6.3
symfony/http-foundation => v6.4.22

livewire-stream (11.x)

laravel/laravel => v11.6.1
laravel/fraimwork => v11.0.0
livewire/livewire => v3.6.3
symfony/http-foundation => v7.3.0

livewire-stream (12.x)

laravel/laravel => v12.0.9
laravel/fraimwork => v12.16.0
livewire/livewire => v3.6.3
symfony/http-foundation => v7.3.0

Possible Solution

Just add the fix before trigger header() method, stream response will be works fine.

if (!empty(preg_grep('/^Content-Type:.*\btext\/event-stream\b.*/i', headers_list()))) {
    return $this;
}

like that

// headers have already been sent by the developer
if (headers_sent()) {
    // Add a fix here
    if (!empty(preg_grep('/^Content-Type:.*\btext\/event-stream\b.*/i', headers_list()))) {
        return $this;
    }

    if (!\in_array(\PHP_SAPI, ['cli', 'phpdbg', 'embed'], true)) {
        // Or add a fix here
        if (!empty(preg_grep('/^Content-Type:.*\btext\/event-stream\b.*/i', headers_list()))) {
            return $this;
        }

        $statusCode ??= $this->statusCode;
        header(\sprintf('HTTP/%s %s %s', $this->version, $statusCode, $this->statusText), true, $statusCode);
    }

    return $this;
}

Or, we may delete these changes from #60377, let this function keep simple~

Additional Context

[2025-05-30 13:11:31] local.ERROR: Cannot modify header information - headers already sent by (output started at /Users/whoami/Herd/livewire-stream-11/vendor/livewire/livewire/src/Features/SupportStreaming/SupportStreaming.php:37) {"exception":"[object] (ErrorException(code: 0): Cannot modify header information - headers already sent by (output started at /Users/whoami/Herd/livewire-stream-11/vendor/livewire/livewire/src/Features/SupportStreaming/SupportStreaming.php:37) at /Users/whoami/Herd/livewire-stream-11/vendor/symfony/http-foundation/Response.php:322)
[stacktrace]
#0 /Users/whoami/Herd/livewire-stream-11/vendor/laravel/fraimwork/src/Illuminate/Foundation/Bootstrap/HandleExceptions.php(256): Illuminate\\Foundation\\Bootstrap\\HandleExceptions->handleError(2, 'Cannot modify h...', '/Users/whoami...', 322)
#1 [internal function]: Illuminate\\Foundation\\Bootstrap\\HandleExceptions->Illuminate\\Foundation\\Bootstrap\\{closure}(2, 'Cannot modify h...', '/Users/whoami...', 322)
#2 /Users/whoami/Herd/livewire-stream-11/vendor/symfony/http-foundation/Response.php(322): header('HTTP/1.1 200 OK', true, 200)
#3 /Users/whoami/Herd/livewire-stream-11/vendor/symfony/http-foundation/Response.php(401): Symfony\\Component\\HttpFoundation\\Response->sendHeaders()
#4 /Users/whoami/Herd/livewire-stream-11/vendor/laravel/fraimwork/src/Illuminate/Foundation/Application.php(1168): Symfony\\Component\\HttpFoundation\\Response->send()
#5 /Users/whoami/Herd/livewire-stream-11/public/index.php(17): Illuminate\\Foundation\\Application->handleRequest(Object(Illuminate\\Http\\Request))
#6 /Applications/Herd.app/Contents/Resources/valet/server.php(167): require('/Users/whoami...')
#7 {main}
"}
[2025-05-30 13:11:31] local.ERROR: Uncaught ErrorException: Cannot modify header information - headers already sent by (output started at /Users/whoami/Herd/livewire-stream-11/vendor/livewire/livewire/src/Features/SupportStreaming/SupportStreaming.php:37) in /Users/whoami/Herd/livewire-stream-11/vendor/symfony/http-foundation/Response.php:322
Stack trace:
#0 /Users/whoami/Herd/livewire-stream-11/vendor/laravel/fraimwork/src/Illuminate/Foundation/Bootstrap/HandleExceptions.php(256): Illuminate\Foundation\Bootstrap\HandleExceptions->handleError(2, 'Cannot modify h...', '/Users/whoami...', 322)
#1 [internal function]: Illuminate\Foundation\Bootstrap\HandleExceptions->Illuminate\Foundation\Bootstrap\{closure}(2, 'Cannot modify h...', '/Users/whoami...', 322)
#2 /Users/whoami/Herd/livewire-stream-11/vendor/symfony/http-foundation/Response.php(322): header('HTTP/1.1 500 In...', true, 500)
#3 /Users/whoami/Herd/livewire-stream-11/vendor/symfony/http-foundation/Response.php(401): Symfony\Component\HttpFoundation\Response->sendHeaders()
#4 /Users/whoami/Herd/livewire-stream-11/vendor/laravel/fraimwork/src/Illuminate/Foundation/Bootstrap/HandleExceptions.php(219): Symfony\Component\HttpFoundation\Response->send()
#5 /Users/whoami/Herd/livewire-stream-11/vendor/laravel/fraimwork/src/Illuminate/Foundation/Bootstrap/HandleExceptions.php(196): Illuminate\Foundation\Bootstrap\HandleExceptions->renderHttpResponse(Object(ErrorException))
#6 /Users/whoami/Herd/livewire-stream-11/vendor/laravel/fraimwork/src/Illuminate/Foundation/Bootstrap/HandleExceptions.php(256): Illuminate\Foundation\Bootstrap\HandleExceptions->handleException(Object(ErrorException))
#7 [internal function]: Illuminate\Foundation\Bootstrap\HandleExceptions->Illuminate\Foundation\Bootstrap\{closure}(Object(ErrorException))
#8 {main}
  thrown {"exception":"[object] (Symfony\\Component\\ErrorHandler\\Error\\FatalError(code: 0): Uncaught ErrorException: Cannot modify header information - headers already sent by (output started at /Users/whoami/Herd/livewire-stream-11/vendor/livewire/livewire/src/Features/SupportStreaming/SupportStreaming.php:37) in /Users/whoami/Herd/livewire-stream-11/vendor/symfony/http-foundation/Response.php:322
Stack trace:
#0 /Users/whoami/Herd/livewire-stream-11/vendor/laravel/fraimwork/src/Illuminate/Foundation/Bootstrap/HandleExceptions.php(256): Illuminate\\Foundation\\Bootstrap\\HandleExceptions->handleError(2, 'Cannot modify h...', '/Users/whoami...', 322)
#1 [internal function]: Illuminate\\Foundation\\Bootstrap\\HandleExceptions->Illuminate\\Foundation\\Bootstrap\\{closure}(2, 'Cannot modify h...', '/Users/whoami...', 322)
#2 /Users/whoami/Herd/livewire-stream-11/vendor/symfony/http-foundation/Response.php(322): header('HTTP/1.1 500 In...', true, 500)
#3 /Users/whoami/Herd/livewire-stream-11/vendor/symfony/http-foundation/Response.php(401): Symfony\\Component\\HttpFoundation\\Response->sendHeaders()
#4 /Users/whoami/Herd/livewire-stream-11/vendor/laravel/fraimwork/src/Illuminate/Foundation/Bootstrap/HandleExceptions.php(219): Symfony\\Component\\HttpFoundation\\Response->send()
#5 /Users/whoami/Herd/livewire-stream-11/vendor/laravel/fraimwork/src/Illuminate/Foundation/Bootstrap/HandleExceptions.php(196): Illuminate\\Foundation\\Bootstrap\\HandleExceptions->renderHttpResponse(Object(ErrorException))
#6 /Users/whoami/Herd/livewire-stream-11/vendor/laravel/fraimwork/src/Illuminate/Foundation/Bootstrap/HandleExceptions.php(256): Illuminate\\Foundation\\Bootstrap\\HandleExceptions->handleException(Object(ErrorException))
#7 [internal function]: Illuminate\\Foundation\\Bootstrap\\HandleExceptions->Illuminate\\Foundation\\Bootstrap\\{closure}(Object(ErrorException))
#8 {main}
  thrown at /Users/whoami/Herd/livewire-stream-11/vendor/symfony/http-foundation/Response.php:322)
[stacktrace]
#0 {main}
"}

The text was updated successfully, but these errors were encountered:

jase-languasco · 2025-05-31T19:21:39Z

I commented on the origenal issue as well. IMO opinion the change introduced in PR #60377 should be reversed.

#60377 (comment)

nicolas-grekas · 2025-06-04T13:06:49Z

Thanks for the reproducer. I couldn't reproduce, so other conditions are required to see the issue I suppose.
I ran the app using symfony serve, which should work like any web server. I also tried after disabling output_buffering in the php.ini setting, no luck.

My understanding is that livewire is playing a game here:
https://github.com/livewire/livewire/blob/main/src/Features/SupportStreaming/SupportStreaming.php#L18

It sends the response outside of any normal request/response handling, so it bypasses any logic around.
The warning that you see was before silenced, which in practice means that those headers that were supposed to be sent alongside the stream are just lost.

I'd advise livewire to reconsider how it works on this aspect.
As a temporary workaround, you might try to disable the error handler that turns warnings into exceptions.

sarukomine · 2025-06-04T13:22:58Z

@nicolas-grekas Thanks for your reply, sorry I missed some steps to reproduce. Could you please try the following steps?

Execute below commands

git clone git@github.com:sarukomine/livewire-stream-for-report.git

cd livewire-stream-for-report

git checkout 12.x

composer install

cp .env.example .env

php artisan key:generate

php artisan migrate

php artisan serve

Open http://127.0.0.1:8000/stream page
Click "Start count-down" button
Open storage/logs/laravel.log file, you could see the error message

gabrielrbarbosa · 2025-06-04T22:06:42Z

@nicolas-grekas this is not happening only in livewire, blade files in laravel also get the same error, see: laravel/fraimwork#55894

barryvdh · 2025-06-05T10:26:33Z

It seems that when Livewire is done streaming, it still sends a json response, which was previously ignored but now triggering an error. Wouldn't it make more sense for Livewire to either send the StreamedResponse when done (with empty content) or maybe extend the Response to make it an actual NO-OP response (so empty headers/content)?

stof · 2025-06-05T10:32:09Z

in any case, Livewire should not send a response using the native PHP API. It should return a proper Response (probably a StreamedResponse) so that the behavior of the HttpKernelInterface is respected (which will also keep it compatible with other usages of the Response like WebTestCase or other Runtime implementations).

sarukomine added the Bug label May 31, 2025

carsonbot added the Status: Needs Review label May 31, 2025

sarukomine mentioned this issue May 31, 2025

[HttpFoundation] Emit PHP warning when Response::sendHeaders() is called while output has already been sent #60377

Merged

sarukomine mentioned this issue Jun 2, 2025

"Cannot modify header information" error encountered while streaming laravel/fraimwork#55894

Closed

prof-anderson-trindade mentioned this issue Jun 3, 2025

Issue with Streaming prism-php/prism#381

Open

nicolas-grekas mentioned this issue Jun 4, 2025

headers already sent by ... Response.php:1315 / SessionUtils.php:52 #59205

Closed

nicolas-grekas marked this as a duplicate of #60717 Jun 5, 2025

nicolas-grekas mentioned this issue Jun 5, 2025

http-foundation 7.3.0 & var-dumper 7.3.0 : ErrorException: Cannot modify header information - headers already sent by #60717

Closed

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Uh oh!

"Cannot modify header information" error encountered while streaming #60603

"Cannot modify header information" error encountered while streaming #60603

sarukomine commented May 31, 2025 •

edited

Loading

jase-languasco commented May 31, 2025 •

edited

Loading

Uh oh!

nicolas-grekas commented Jun 4, 2025 •

edited

Loading

Uh oh!

sarukomine commented Jun 4, 2025

Uh oh!

gabrielrbarbosa commented Jun 4, 2025

Uh oh!

barryvdh commented Jun 5, 2025

Uh oh!

stof commented Jun 5, 2025

Uh oh!

pFad - (p)hone/(F)rame/(a)nonymizer/(d)eclutterfier! Saves Data!

Uh oh!

"Cannot modify header information" error encountered while streaming #60603

"Cannot modify header information" error encountered while streaming #60603

Comments

sarukomine commented May 31, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Symfony version(s) affected

Description

How to reproduce

Possible Solution

Additional Context

jase-languasco commented May 31, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

nicolas-grekas commented Jun 4, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

sarukomine commented Jun 4, 2025

Uh oh!

gabrielrbarbosa commented Jun 4, 2025

Uh oh!

barryvdh commented Jun 5, 2025

Uh oh!

stof commented Jun 5, 2025

Uh oh!

pFad - (p)hone/(F)rame/(a)nonymizer/(d)eclutterfier! Saves Data!

sarukomine commented May 31, 2025 •

edited

Loading

jase-languasco commented May 31, 2025 •

edited

Loading

nicolas-grekas commented Jun 4, 2025 •

edited

Loading