feat(previews): Support in memory preview request

This allows callers to use the API without increasing the disk usage.

Example: blurhash generation, where we request a preview for all uploaded pictures, but don't want to necessarily store that preview.
Signed-off-by: Louis Chemineau <louis@chmn.me>

lib/private/Preview/Generator.php

@@ -12,6 +12,7 @@ use OCP\Files\IAppData;
 use OCP\Files\InvalidPathException;
 use OCP\Files\NotFoundException;
 use OCP\Files\NotPermittedException;
+use OCP\Files\SimpleFS\InMemoryFile;
 use OCP\Files\SimpleFS\ISimpleFile;
 use OCP\Files\SimpleFS\ISimpleFolder;
 use OCP\IConfig;
@@ -43,17 +44,19 @@ class Generator {
 	 * The cache is searched first and if nothing usable was found then a preview is
 	 * generated by one of the providers
 	 *
-	 * @param File $file
-	 * @param int $width
-	 * @param int $height
-	 * @param bool $crop
-	 * @param string $mode
-	 * @param string|null $mimeType
 	 * @return ISimpleFile
 	 * @throws NotFoundException
 	 * @throws \InvalidArgumentException if the preview would be invalid (in case the original image is invalid)
 	 */
-	public function getPreview(File $file, $width = -1, $height = -1, $crop = false, $mode = IPreview::MODE_FILL, $mimeType = null) {
+	public function getPreview(
+		File $file,
+		int $width = -1,
+		int $height = -1,
+		bool $crop = false,
+		string $mode = IPreview::MODE_FILL,
+		?string $mimeType = null,
+		bool $cacheResult = true,
+	): ISimpleFile {
 		$specification = [
 			'width' => $width,
 			'height' => $height,
@@ -78,23 +81,19 @@ class Generator {
 			'mode' => $mode,
 			'mimeType' => $mimeType,
 		]);
-		
+
 
 		// since we only ask for one preview, and the generate method return the last one it created, it returns the one we want
-		return $this->generatePreviews($file, [$specification], $mimeType);
+		return $this->generatePreviews($file, [$specification], $mimeType, $cacheResult);
 	}
 
 	/**
 	 * Generates previews of a file
 	 *
-	 * @param File $file
-	 * @param non-empty-array $specifications
-	 * @param string $mimeType
-	 * @return ISimpleFile the last preview that was generated
 	 * @throws NotFoundException
 	 * @throws \InvalidArgumentException if the preview would be invalid (in case the original image is invalid)
 	 */
-	public function generatePreviews(File $file, array $specifications, $mimeType = null) {
+	public function generatePreviews(File $file, array $specifications, ?string $mimeType = null, bool $cacheResult = true): ISimpleFile {
 		//Make sure that we can read the file
 		if (!$file->isReadable()) {
 			$this->logger->warning('Cannot read file: {path}, skipping preview generation.', ['path' => $file->getPath()]);
@@ -167,7 +166,7 @@ class Generator {
 					}
 
 					$this->logger->warning('Cached preview not found for file {path}, generating a new preview.', ['path' => $file->getPath()]);
-					$preview = $this->generatePreview($previewFolder, $maxPreviewImage, $width, $height, $crop, $maxWidth, $maxHeight, $previewVersion);
+					$preview = $this->generatePreview($previewFolder, $maxPreviewImage, $width, $height, $crop, $maxWidth, $maxHeight, $previewVersion, $cacheResult);
 					// New file, augment our array
 					$previewFiles[] = $preview;
 				}
@@ -490,19 +489,20 @@ class Generator {
 	}
 
 	/**
-	 * @param ISimpleFolder $previewFolder
-	 * @param ISimpleFile $maxPreview
-	 * @param int $width
-	 * @param int $height
-	 * @param bool $crop
-	 * @param int $maxWidth
-	 * @param int $maxHeight
-	 * @param string $prefix
-	 * @return ISimpleFile
 	 * @throws NotFoundException
 	 * @throws \InvalidArgumentException if the preview would be invalid (in case the original image is invalid)
 	 */
-	private function generatePreview(ISimpleFolder $previewFolder, IImage $maxPreview, $width, $height, $crop, $maxWidth, $maxHeight, $prefix) {
+	private function generatePreview(
+		ISimpleFolder $previewFolder,
+		IImage $maxPreview,
+		int $width,
+		int $height,
+		bool $crop,
+		int $maxWidth,
+		int $maxHeight,
+		string $prefix,
+		bool $cacheResult,
+	): ISimpleFile {
 		$preview = $maxPreview;
 		if (!$preview->valid()) {
 			throw new \InvalidArgumentException('Failed to generate preview, failed to load image');
@@ -539,8 +539,11 @@ class Generator {
 
 		$path = $this->generatePath($width, $height, $crop, false, $preview->dataMimeType(), $prefix);
 		try {
-			$file = $previewFolder->newFile($path);
-			$file->putContent($preview->data());
+			if ($cacheResult) {
+				$file = $previewFolder->newFile($path, $preview->data());
+			} else {
+				return new InMemoryFile($path, $preview->data());
+			}
 		} catch (NotPermittedException $e) {
 			throw new NotFoundException();
 		}

lib/private/PreviewManager.php

@@ -145,29 +145,20 @@ class PreviewManager implements IPreview {
 		return $this->generator;
 	}
 
-	/**
-	 * Returns a preview of a file
-	 *
-	 * The cache is searched first and if nothing usable was found then a preview is
-	 * generated by one of the providers
-	 *
-	 * @param File $file
-	 * @param int $width
-	 * @param int $height
-	 * @param bool $crop
-	 * @param string $mode
-	 * @param string $mimeType
-	 * @return ISimpleFile
-	 * @throws NotFoundException
-	 * @throws \InvalidArgumentException if the preview would be invalid (in case the original image is invalid)
-	 * @since 11.0.0 - \InvalidArgumentException was added in 12.0.0
-	 */
-	public function getPreview(File $file, $width = -1, $height = -1, $crop = false, $mode = IPreview::MODE_FILL, $mimeType = null) {
+	public function getPreview(
+		File $file,
+		$width = -1,
+		$height = -1,
+		$crop = false,
+		$mode = IPreview::MODE_FILL,
+		$mimeType = null,
+		bool $cacheResult = true,
+	): ISimpleFile {
 		$this->throwIfPreviewsDisabled();
 		$previewConcurrency = $this->getGenerator()->getNumConcurrentPreviews('preview_concurrency_all');
 		$sem = Generator::guardWithSemaphore(Generator::SEMAPHORE_ID_ALL, $previewConcurrency);
 		try {
-			$preview = $this->getGenerator()->getPreview($file, $width, $height, $crop, $mode, $mimeType);
+			$preview = $this->getGenerator()->getPreview($file, $width, $height, $crop, $mode, $mimeType, $cacheResult);
 		} finally {
 			Generator::unguardWithSemaphore($sem);
 		}

lib/public/IPreview.php

@@ -71,12 +71,14 @@ interface IPreview {
 	 * @param bool $crop
 	 * @param string $mode
 	 * @param string $mimeType To force a given mimetype for the file (files_versions needs this)
+	 * @param bool $cacheResult Whether or not to cache the preview on the filesystem. Default to true. Can be useful to set to false to limit the amount of stored previews.
 	 * @return ISimpleFile
 	 * @throws NotFoundException
 	 * @throws \InvalidArgumentException if the preview would be invalid (in case the original image is invalid)
 	 * @since 11.0.0 - \InvalidArgumentException was added in 12.0.0
+	 * @since 32.0.0 - getPreview($cacheResult) added the $cacheResult argument to the signature
 	 */
-	public function getPreview(File $file, $width = -1, $height = -1, $crop = false, $mode = IPreview::MODE_FILL, $mimeType = null);
+	public function getPreview(File $file, $width = -1, $height = -1, $crop = false, $mode = IPreview::MODE_FILL, $mimeType = null, bool $cacheResult = true);
 
 	/**
 	 * Returns true if the passed mime type is supported