symfony/http-foundation · error · LogicException

You cannot guess the extension as the Mime component is not…

Error message

You cannot guess the extension as the Mime component is not installed. Try running "composer require symfony/mime".

What it means

A LogicException feature guard thrown by UploadedFile::guessClientExtension() when the symfony/mime package is not installed. The method maps the client-supplied mime type to a file extension, which is impossible without MimeTypes, so the call aborts; it signals a missing dependency rather than bad input.

Solutions

1. Run composer require symfony/mime to enable extension guessing
2. Guard with class_exists(MimeTypes::class) and return a default extension or null instead of guessing
3. Parse the extension from the original client filename (pathinfo($file->getClientOriginalName(), PATHINFO_EXTENSION)) as a fallback

When it happens

Trigger: Thrown at File/UploadedFile.php:149 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of symfony/http-foundation@5aea19cd67 (2026-09-13). Data as JSON: /api/errors/67b3e2bb28f8fa4b. Report an issue: GitHub.

Appendix: source

Thrown at File/UploadedFile.php:149

    public function guessClientExtension(): ?string
    {
        if (!class_exists(MimeTypes::class)) {
            throw new \LogicException('You cannot guess the extension as the Mime component is not installed. Try running "composer require symfony/mime".');
        }

        return MimeTypes::getDefault()->getExtensions($this->getClientMimeType())[0] ?? null;
    }

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