413 lines
14 KiB
PHP
413 lines
14 KiB
PHP
<?php
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declare(strict_types=1);
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// SPDX-FileCopyrightText: 2026 Dillard Blom
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// SPDX-License-Identifier: AGPL-3.0-or-later
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namespace OCA\NgBackup\Backend;
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/**
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* Read stream for files_external's SFTP storage that keeps several READ requests in flight.
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*
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* files_external's own read stream asks for the next 256 KiB only after the previous one has
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* arrived, so every request costs a full round trip: about 5 MB/s at 47 ms to a Hetzner Storage
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* Box, whatever the line speed. With 8 requests in flight the same connection reached 15 MB/s.
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* phpseclib's get() pipelines too, but only into memory or a local file, and only from offset 0.
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*
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* Talks to the storage's phpseclib connection through the same internal methods files_external's
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* read stream uses (_send_sftp_packet, _get_sftp_packet, _realpath); open() returns null when the
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* connection does not offer them (phpseclib 3 does not), and StorageBackend then falls back to the
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* storage's own stream. A restore must rather be slow than fail: when a read fails halfway, the
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* stream goes on from the same position with the storage's own stream. After MAX_FAILURES streams
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* in a row failed, open() returns null for the rest of the process; one that works resets the count.
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* Like that stream, it owns the connection while open: no other request may go over the same
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* connection until it is closed (PackReaderGuard takes care of that for the repository).
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*/
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final class SftpReadStream {
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private const PROTOCOL = 'ngbsftpread';
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/** Requests in flight once a stream reads sequentially; it starts at one and doubles. */
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public const DEPTH = 8;
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/** OpenSSH and the Hetzner Storage Box both answer at most 255 KiB per READ. */
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private const CHUNK = 261120;
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/** Every SFTP server must handle packets of this size (draft-ietf-secsh-filexfer-02, section 3). */
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private const MIN_CHUNK = 32768;
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private const FXP_OPEN = 3;
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private const FXP_CLOSE = 4;
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private const FXP_READ = 5;
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private const FXP_STATUS = 101;
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private const FXP_HANDLE = 102;
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private const FXP_DATA = 103;
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private const FXF_READ = 1;
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private const FX_EOF = 1;
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/**
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* READ size per connection, lowered when a server answers less than asked and then goes on, so
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* later streams over that connection ask for no more than it gives.
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*
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* @var \WeakMap<object, int>|null
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*/
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private static ?\WeakMap $chunks = null;
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private static int $requestId = 0x4e470000;
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/** Streams in a row that failed; at MAX_FAILURES only the storage's own stream is used. */
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private static int $failures = 0;
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public const MAX_FAILURES = 3;
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/** Set by stream_open() when the connection failed rather than the file. */
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private static bool $openBroke = false;
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/** @var resource|null set by PHP for stream wrappers */
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public $context;
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/**
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* The phpseclib connection. PHP creates stream wrappers without constructor arguments; it is
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* set in stream_open(), and no other method is called when that fails.
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*
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* @psalm-suppress PropertyNotSetInConstructor
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*/
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private object $sftp;
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/** The storage and the path on it, to fall back to the storage's own stream. */
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private ?object $storage = null;
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private string $file = '';
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/** @var resource|null the storage's own stream, once this one has failed */
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private $fallback = null;
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private string $handle = '';
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/** Position of the reader: the first byte of $buffer. */
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private int $pos = 0;
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/** Offset of the next READ to send. */
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private int $next = 0;
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private string $buffer = '';
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/** @var list<array{int, int, int}> request id, offset, length, in the order sent */
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private array $inFlight = [];
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private int $depth = 1;
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private bool $eof = false;
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/** This stream gave up on its own requests. */
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private bool $failed = false;
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/** The connection is in an unknown state: nothing more is sent over it or read from it. */
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private bool $broken = false;
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/** Length of the last short answer, until the next answer tells whether it was the end of the file. */
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private ?int $shortAnswer = null;
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/**
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* @param object $storage files_external's SFTP storage (getConnection(), getRoot())
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* @return resource|false|null the stream, false when the file cannot be opened, null when the
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* connection does not offer what this stream needs
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* @throws BackendException when the connection failed after the OPEN request went out: the
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* storage's own stream must not be tried on it, as it would take a
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* late answer to that request for its own
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*/
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public static function open(object $storage, string $path) {
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if (self::$failures >= self::MAX_FAILURES) {
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return null;
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}
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try {
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if (!is_callable([$storage, 'getConnection']) || !is_callable([$storage, 'getRoot'])) {
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return null;
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}
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$sftp = $storage->getConnection();
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// is_callable and get_object_vars from here only see what is public: phpseclib 3 has
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// methods of these names neither public nor at all.
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if (!is_object($sftp) || !is_callable([$sftp, '_send_sftp_packet']) || !is_callable([$sftp, '_get_sftp_packet'])
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|| !is_callable([$sftp, '_realpath']) || !array_key_exists('packet_type', get_object_vars($sftp))) {
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return null;
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}
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if (!in_array(self::PROTOCOL, stream_get_wrappers(), true)) {
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stream_wrapper_register(self::PROTOCOL, self::class);
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}
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$root = rtrim((string)$storage->getRoot(), '/');
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$context = stream_context_create([self::PROTOCOL => [
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'session' => $sftp,
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'path' => $root . '/' . ltrim($path, '/'),
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'storage' => $storage,
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'file' => $path,
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]]);
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self::$openBroke = false;
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$fh = @fopen(self::PROTOCOL . '://file', 'r', false, $context);
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} catch (\Throwable) {
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// nothing was sent yet
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self::$failures++;
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return null;
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}
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if ($fh === false && self::openBroke()) {
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throw new BackendException('SFTP connection failed while opening ' . $path);
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}
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return $fh;
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}
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/** Test hook: forget the learned READ sizes and earlier failures. */
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public static function reset(): void {
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self::$chunks = null;
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self::$failures = 0;
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}
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public function stream_open(string $url, string $mode, int $options, ?string &$openedPath): bool {
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$options = stream_context_get_options($this->context ?? stream_context_get_default())[self::PROTOCOL] ?? [];
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if (!isset($options['session'], $options['path']) || !is_object($options['session'])) {
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return false;
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}
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$this->sftp = $options['session'];
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$storage = $options['storage'] ?? null;
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$this->storage = is_object($storage) ? $storage : null;
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$this->file = (string)($options['file'] ?? '');
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try {
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$remote = $this->sftp->_realpath((string)$options['path']);
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if (!is_string($remote)) {
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return false;
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}
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$id = self::nextId();
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if (!$this->sftp->_send_sftp_packet(self::FXP_OPEN, pack('Na*N2', strlen($remote), $remote, self::FXF_READ, 0), $id)) {
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return $this->connectionFailed();
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}
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$response = $this->sftp->_get_sftp_packet($id);
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} catch (\Throwable) {
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return $this->connectionFailed();
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}
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if (!is_string($response)) {
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return $this->connectionFailed();
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}
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if ($this->sftp->packet_type !== self::FXP_HANDLE) {
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return false; // an answer, but no handle: the file cannot be opened
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}
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$this->handle = substr($response, 4);
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return true;
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}
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/** Not a missing file but a connection that does not behave as expected. */
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private function connectionFailed(): bool {
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self::$failures++;
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self::$openBroke = true;
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return false;
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}
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/** Whether the last stream_open() failed on the connection; a call, as fopen() sets it. */
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private static function openBroke(): bool {
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return self::$openBroke;
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}
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public function stream_read(int $count): string|false {
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if ($this->fallback !== null) {
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return fread($this->fallback, $count);
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}
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while (strlen($this->buffer) < $count && !$this->eof) {
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if (!$this->receive()) {
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return $this->useFallback() ? $this->stream_read($count) : false;
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}
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}
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$data = substr($this->buffer, 0, $count);
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$this->buffer = substr($this->buffer, strlen($data));
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$this->pos += strlen($data);
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return $data;
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}
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public function stream_eof(): bool {
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if ($this->fallback !== null) {
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return feof($this->fallback);
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}
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return $this->eof && $this->buffer === '';
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}
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public function stream_tell(): int {
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if ($this->fallback !== null) {
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$pos = ftell($this->fallback);
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return $pos === false ? $this->pos : $pos;
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}
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return $this->pos;
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}
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public function stream_seek(int $offset, int $whence = SEEK_SET): bool {
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if ($this->fallback !== null) {
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return fseek($this->fallback, $offset, $whence) === 0;
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}
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if ($whence === SEEK_CUR) {
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$offset += $this->pos;
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} elseif ($whence !== SEEK_SET) {
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return false; // the size is never asked for, to save a round trip
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}
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if ($offset < 0) {
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return false;
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}
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if ($this->failed) {
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$this->pos = $offset;
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return $this->useFallback();
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}
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if ($offset >= $this->pos && $offset - $this->pos <= strlen($this->buffer)) {
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$this->buffer = substr($this->buffer, $offset - $this->pos);
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} else {
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$this->drain();
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$this->buffer = '';
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$this->next = $offset;
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$this->eof = false;
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$this->depth = 1;
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$this->shortAnswer = null;
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}
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$this->pos = $offset;
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return true;
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}
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/** @return array<int|string, int> */
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public function stream_stat(): array {
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return [];
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}
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public function stream_close(): void {
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if (!$this->failed) {
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self::$failures = 0;
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}
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$fallback = $this->fallback;
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$this->fallback = null;
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if ($fallback !== null) {
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fclose($fallback);
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}
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$this->closeHandle();
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}
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/**
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* Go on with the storage's own stream from the current position, after a server error on this
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* one. The data still buffered is dropped and read again. False after a connection error, or
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* when that stream cannot be opened or positioned: then the read fails as it would have
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* without this class. Reopening by path is safe for a repository: packs and index files are
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* never rewritten, and every object is authenticated when it is decrypted.
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*/
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private function useFallback(): bool {
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$this->closeHandle();
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$this->buffer = '';
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// files_external's stream takes whatever answer comes next on the connection: after a
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// connection error, answers to this stream's requests may still be on their way.
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if ($this->broken || $this->storage === null || !is_callable([$this->storage, 'fopen'])) {
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return false;
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}
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try {
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$fh = $this->storage->fopen($this->file, 'r');
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if (!is_resource($fh)) {
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return false;
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}
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if ($this->pos > 0 && fseek($fh, $this->pos) !== 0) {
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fclose($fh);
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return false;
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}
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} catch (\Throwable) {
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return false;
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}
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$this->fallback = $fh;
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return true;
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}
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private function closeHandle(): void {
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$this->drain();
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if ($this->handle !== '' && !$this->broken) {
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try {
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$id = self::nextId();
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if (!$this->sftp->_send_sftp_packet(self::FXP_CLOSE, pack('Na*', strlen($this->handle), $this->handle), $id)
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|| !is_string($this->sftp->_get_sftp_packet($id))) {
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$this->broken = true;
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}
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} catch (\Throwable) {
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$this->broken = true;
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}
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}
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$this->handle = '';
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}
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/** Keep the pipeline full, then take the oldest answer. False on a connection or server error. */
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private function receive(): bool {
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if ($this->failed) {
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return false;
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}
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try {
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return $this->receiveOne();
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} catch (\Throwable) {
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$this->broken = true;
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return $this->fail();
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}
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}
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private function receiveOne(): bool {
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while (count($this->inFlight) < $this->depth) {
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$id = self::nextId();
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$length = self::chunk($this->sftp);
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$packet = pack('Na*N3', strlen($this->handle), $this->handle, intdiv($this->next, 4294967296), $this->next % 4294967296, $length);
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if (!$this->sftp->_send_sftp_packet(self::FXP_READ, $packet, $id)) {
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$this->broken = true;
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return $this->fail();
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}
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$this->inFlight[] = [$id, $this->next, $length];
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$this->next += $length;
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}
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[$id, $offset, $length] = array_shift($this->inFlight);
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$response = $this->sftp->_get_sftp_packet($id);
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if (!is_string($response)) {
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$this->broken = true;
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return $this->fail();
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}
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if ($this->sftp->packet_type === self::FXP_DATA) {
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$data = substr($response, 4);
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if ($data === '') {
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return $this->fail();
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}
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$this->buffer .= $data;
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$this->depth = min(self::DEPTH, $this->depth * 2);
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if ($this->shortAnswer !== null) {
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// More data after a short answer: that one was the server's cap, not the end.
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// Never below what every server must support: a one-off small answer is no cap.
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self::$chunks ??= new \WeakMap();
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self::$chunks[$this->sftp] = max(self::MIN_CHUNK, min(self::chunk($this->sftp), $this->shortAnswer));
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$this->shortAnswer = null;
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}
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if (strlen($data) < $length) {
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// Fewer bytes than asked: the end of the file, or a server that caps a READ. The
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// requests behind this one assumed a full answer, so drop them and ask again from here.
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$this->drain();
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$this->next = $offset + strlen($data);
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$this->shortAnswer = strlen($data);
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}
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return true;
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}
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$status = $this->sftp->packet_type === self::FXP_STATUS ? unpack('N', $response) : false;
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if (is_array($status) && ($status[1] ?? null) === self::FX_EOF) {
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$this->eof = true;
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$this->shortAnswer = null;
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$this->drain();
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return true;
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}
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return $this->fail();
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}
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private function fail(): bool {
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$this->drain();
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if (!$this->failed) {
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self::$failures++;
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}
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$this->failed = true;
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return false;
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}
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/** Read and drop the answers still on their way, so the connection is free again. */
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private function drain(): void {
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$inFlight = $this->inFlight;
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$this->inFlight = [];
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if ($this->broken) {
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return;
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}
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try {
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foreach ($inFlight as [$id]) {
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if (!is_string($this->sftp->_get_sftp_packet($id))) {
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$this->broken = true;
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return;
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}
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}
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} catch (\Throwable) {
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$this->broken = true;
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}
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}
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private static function chunk(object $sftp): int {
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$learned = self::$chunks?->offsetExists($sftp) === true ? self::$chunks->offsetGet($sftp) : null;
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return is_int($learned) ? $learned : self::CHUNK;
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}
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private static function nextId(): int {
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self::$requestId = self::$requestId >= 0x7fffffff ? 0x4e470000 : self::$requestId + 1;
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return self::$requestId;
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}
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}
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