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PhabricatorFileStorageEngine.php
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Sat, Jan 18, 17:08

PhabricatorFileStorageEngine.php
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<?php
/**
* Defines a storage engine which can write file data somewhere (like a
* database, local disk, Amazon S3, the A:\ drive, or a custom filer) and
* retrieve it later.
*
* You can extend this class to provide new file storage backends.
*
* For more information, see @{article:File Storage Technical Documentation}.
*
* @task construct Constructing an Engine
* @task meta Engine Metadata
* @task file Managing File Data
* @task load Loading Storage Engines
*/
abstract class PhabricatorFileStorageEngine extends Phobject {
/**
* Construct a new storage engine.
*
* @task construct
*/
final public function __construct() {
// <empty>
}
/* -( Engine Metadata )---------------------------------------------------- */
/**
* Return a unique, nonempty string which identifies this storage engine.
* This is used to look up the storage engine when files needs to be read or
* deleted. For instance, if you store files by giving them to a duck for
* safe keeping in his nest down by the pond, you might return 'duck' from
* this method.
*
* @return string Unique string for this engine, max length 32.
* @task meta
*/
abstract public function getEngineIdentifier();
/**
* Prioritize this engine relative to other engines.
*
* Engines with a smaller priority number get an opportunity to write files
* first. Generally, lower-latency filestores should have lower priority
* numbers, and higher-latency filestores should have higher priority
* numbers. Setting priority to approximately the number of milliseconds of
* read latency will generally produce reasonable results.
*
* In conjunction with filesize limits, the goal is to store small files like
* profile images, thumbnails, and text snippets in lower-latency engines,
* and store large files in higher-capacity engines.
*
* @return float Engine priority.
* @task meta
*/
abstract public function getEnginePriority();
/**
* Return `true` if the engine is currently writable.
*
* Engines that are disabled or missing configuration should return `false`
* to prevent new writes. If writes were made with this engine in the past,
* the application may still try to perform reads.
*
* @return bool True if this engine can support new writes.
* @task meta
*/
abstract public function canWriteFiles();
/**
* Return `true` if the engine has a filesize limit on storable files.
*
* The @{method:getFilesizeLimit} method can retrieve the actual limit. This
* method just removes the ambiguity around the meaning of a `0` limit.
*
* @return bool `true` if the engine has a filesize limit.
* @task meta
*/
public function hasFilesizeLimit() {
return true;
}
/**
* Return maximum storable file size, in bytes.
*
* Not all engines have a limit; use @{method:getFilesizeLimit} to check if
* an engine has a limit. Engines without a limit can store files of any
* size.
*
* By default, engines define a limit which supports chunked storage of
* large files. In most cases, you should not change this limit, even if an
* engine has vast storage capacity: chunked storage makes large files more
* manageable and enables features like resumable uploads.
*
* @return int Maximum storable file size, in bytes.
* @task meta
*/
public function getFilesizeLimit() {
// NOTE: This 8MB limit is selected to be larger than the 4MB chunk size,
// but not much larger. Files between 0MB and 8MB will be stored normally;
// files larger than 8MB will be chunked.
return (1024 * 1024 * 8);
}
/**
* Identifies storage engines that support unit tests.
*
* These engines are not used for production writes.
*
* @return bool True if this is a test engine.
* @task meta
*/
public function isTestEngine() {
return false;
}
/**
* Identifies chunking storage engines.
*
* If this is a storage engine which splits files into chunks and stores the
* chunks in other engines, it can return `true` to signal that other
* chunking engines should not try to store data here.
*
* @return bool True if this is a chunk engine.
* @task meta
*/
public function isChunkEngine() {
return false;
}
/* -( Managing File Data )------------------------------------------------- */
/**
* Write file data to the backing storage and return a handle which can later
* be used to read or delete it. For example, if the backing storage is local
* disk, the handle could be the path to the file.
*
* The caller will provide a $params array, which may be empty or may have
* some metadata keys (like "name" and "author") in it. You should be prepared
* to handle writes which specify no metadata, but might want to optionally
* use some keys in this array for debugging or logging purposes. This is
* the same dictionary passed to @{method:PhabricatorFile::newFromFileData},
* so you could conceivably do custom things with it.
*
* If you are unable to write for whatever reason (e.g., the disk is full),
* throw an exception. If there are other satisfactory but less-preferred
* storage engines available, they will be tried.
*
* @param string The file data to write.
* @param array File metadata (name, author), if available.
* @return string Unique string which identifies the stored file, max length
* 255.
* @task file
*/
abstract public function writeFile($data, array $params);
/**
* Read the contents of a file previously written by @{method:writeFile}.
*
* @param string The handle returned from @{method:writeFile} when the
* file was written.
* @return string File contents.
* @task file
*/
abstract public function readFile($handle);
/**
* Delete the data for a file previously written by @{method:writeFile}.
*
* @param string The handle returned from @{method:writeFile} when the
* file was written.
* @return void
* @task file
*/
abstract public function deleteFile($handle);
/* -( Loading Storage Engines )-------------------------------------------- */
/**
* Select viable default storage engines according to configuration. We'll
* select the MySQL and Local Disk storage engines if they are configured
* to allow a given file.
*
* @param int File size in bytes.
* @task load
*/
public static function loadStorageEngines($length) {
$engines = self::loadWritableEngines();
$writable = array();
foreach ($engines as $key => $engine) {
if ($engine->hasFilesizeLimit()) {
$limit = $engine->getFilesizeLimit();
if ($limit < $length) {
continue;
}
}
$writable[$key] = $engine;
}
return $writable;
}
/**
* @task load
*/
public static function loadAllEngines() {
return id(new PhutilClassMapQuery())
->setAncestorClass(__CLASS__)
->setUniqueMethod('getEngineIdentifier')
->setSortMethod('getEnginePriority')
->execute();
}
/**
* @task load
*/
private static function loadProductionEngines() {
$engines = self::loadAllEngines();
$active = array();
foreach ($engines as $key => $engine) {
if ($engine->isTestEngine()) {
continue;
}
$active[$key] = $engine;
}
return $active;
}
/**
* @task load
*/
public static function loadWritableEngines() {
$engines = self::loadProductionEngines();
$writable = array();
foreach ($engines as $key => $engine) {
if (!$engine->canWriteFiles()) {
continue;
}
if ($engine->isChunkEngine()) {
// Don't select chunk engines as writable.
continue;
}
$writable[$key] = $engine;
}
return $writable;
}
/**
* @task load
*/
public static function loadWritableChunkEngines() {
$engines = self::loadProductionEngines();
$chunk = array();
foreach ($engines as $key => $engine) {
if (!$engine->canWriteFiles()) {
continue;
}
if (!$engine->isChunkEngine()) {
continue;
}
$chunk[$key] = $engine;
}
return $chunk;
}
/**
* Return the largest file size which can not be uploaded in chunks.
*
* Files smaller than this will always upload in one request, so clients
* can safely skip the allocation step.
*
* @return int|null Byte size, or `null` if there is no chunk support.
*/
public static function getChunkThreshold() {
$engines = self::loadWritableChunkEngines();
$min = null;
foreach ($engines as $engine) {
if (!$min) {
$min = $engine;
continue;
}
if ($min->getChunkSize() > $engine->getChunkSize()) {
$min = $engine->getChunkSize();
}
}
if (!$min) {
return null;
}
return $engine->getChunkSize();
}
public function getFileDataIterator(PhabricatorFile $file, $begin, $end) {
// The default implementation is trivial and just loads the entire file
// upfront.
$data = $file->loadFileData();
if ($begin !== null && $end !== null) {
$data = substr($data, $begin, ($end - $begin));
} else if ($begin !== null) {
$data = substr($data, $begin);
} else if ($end !== null) {
$data = substr($data, 0, $end);
}
return array($data);
}
}

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