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[Filesystem] Add readFileInChunks method to read files in fixed-size chunks #60916

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[Filesystem] Add readFileInChunks method to read files in fixed-size chunks #60916

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5 changes: 5 additions & 0 deletions src/Symfony/Component/Filesystem/CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -1,6 +1,11 @@
CHANGELOG
=========

7.4
---

* Add the `Filesystem::readFileInChunks()` method

7.1
---

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51 changes: 51 additions & 0 deletions src/Symfony/Component/Filesystem/Filesystem.php
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Expand Up @@ -728,6 +728,57 @@ public function readFile(string $filename): string
return $content;
}

/**
* Reads a file in fixed-size chunks and yields them one at a time.
*
* @param string $filename The full path to the file
*
* @return \Traversable<string> Yields file content as strings in chunks
*
* @throws IOException If the file cannot be opened or read, or if it's a directory
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this is wrong in the current implementation. This exception is not thrown when calling this method, but when starting the iteration (your test is hiding that by using iterator_to_array).
To properly perform the validation synchronously (which is easier for error handling and documentation), you would need to move the iteration to a private method (defining the generator) while the validation runs in the public method before calling that private method. We use that approach in symfony/cache for instance (where we are required to validate keys synchronously to respect PSR-6)

*/
public function readFileInChunks(string $filename, int $size = 8192): \Traversable
{
if (is_dir($filename)) {
throw new IOException(\sprintf('Failed to read file "%s": It is a directory.', $filename));
}

$stream = self::box('fopen', $filename, 'rb');
if (false === $stream) {
throw new IOException(\sprintf('Failed to open file "%s": "%s"', $filename, self::$lastError ?? 'Unknown error'), 0, null, $filename);
}

return $this->yieldStreamChunks($stream, $size);
}

/**
* @param resource $stream A readable stream resource
*/
private function yieldStreamChunks($stream, int $size): \Traversable
{
if (!\is_resource($stream)) {
throw new InvalidArgumentException('The stream is not a resource.');
}

try {
while (!feof($stream)) {
$chunk = self::box('fread', $stream, $size);

if (false === $chunk) {
throw new IOException(\sprintf('Error reading from stream: "%s"', self::$lastError ?? 'Unknown error'));
}

if ('' === $chunk) {
break;
}

yield $chunk;
}
} finally {
self::box('fclose', $stream);
}
}

private function toIterable(string|iterable $files): iterable
{
return is_iterable($files) ? $files : [$files];
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56 changes: 56 additions & 0 deletions src/Symfony/Component/Filesystem/Tests/FilesystemTest.php
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Expand Up @@ -1852,6 +1852,62 @@ public function testReadDirectory()
$this->filesystem->readFile(__DIR__);
}

public function testReadFileInChunks()
{
$licenseFile = \dirname(__DIR__).'/LICENSE';
$expectedContent = file_get_contents($licenseFile);

$chunks = '';
foreach ($this->filesystem->readFileInChunks($licenseFile) as $chunk) {
$chunks .= $chunk;
}

$this->assertSame($expectedContent, $chunks);
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Should there also be assertions/test cases about the chunk size?

}

/**
* @dataProvider provideValidChunkSizes
*/
public function testEachChunkIsLessThanOrEqualToSpecifiedSize(int $chunkSize)
{
$licenseFile = \dirname(__DIR__).'/LICENSE';

foreach ($this->filesystem->readFileInChunks($licenseFile, $chunkSize) as $chunk) {
$this->assertLessThanOrEqual($chunkSize, \strlen($chunk));
}
}

public static function provideValidChunkSizes(): array
{
return [
'1 KB chunk' => [1024],
'2 KB chunk' => [2048],
'8 KB chunk' => [8192],
];
}

public function testReadFileInChunksNonExistent()
{
$this->expectException(IOException::class);
$this->expectExceptionMessageMatches(\sprintf(
'#^Failed to open file ".+%1$sTests/invalid"\\: #',
preg_quote(\DIRECTORY_SEPARATOR)
));

$this->filesystem->readFileInChunks(__DIR__.'/invalid');
}

public function testReadFileInChunksFromDirectory()
{
$this->expectException(IOException::class);
$this->expectExceptionMessageMatches(\sprintf(
'#^Failed to read file ".+%sTests"\\: It is a directory\\.$#',
preg_quote(\DIRECTORY_SEPARATOR)
));

$this->filesystem->readFileInChunks(__DIR__);
}

public function testReadUnreadableFile()
{
$this->markAsSkippedIfChmodIsMissing();
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