<?php
  /**
   * ownCloud
   *
   * @author Robin Appelman
   * @copyright 2012 Sam Tuke <samtuke@owncloud.com>, 2011 Robin Appelman
   * <icewind1991@gmail.com>
   *
   * This library is free software; you can redistribute it and/or
   * modify it under the terms of the GNU AFFERO GENERAL PUBLIC LICENSE
   * License as published by the Free Software Foundation; either
   * version 3 of the License, or any later version.
   *
   * This library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU AFFERO GENERAL PUBLIC LICENSE for more details.
   *
   * You should have received a copy of the GNU Affero General Public
   * License along with this library.  If not, see <http://www.gnu.org/licenses/>.
   *
   */
  
  /**
   * transparently encrypted filestream
   *
   * you can use it as wrapper around an existing stream by setting CryptStream::$sourceStreams['foo']=array('path'=>$path,'stream'=>$stream)
   * and then fopen('crypt://streams/foo');
   */
  
  namespace OCA\Encryption;
  
  /**
   * @brief Provides 'crypt://' stream wrapper protocol.
   * @note We use a stream wrapper because it is the most secure way to handle
   * decrypted content transfers. There is no safe way to decrypt the entire file
   * somewhere on the server, so we have to encrypt and decrypt blocks on the fly.
   * @note Paths used with this protocol MUST BE RELATIVE. Use URLs like:
   * crypt://filename, or crypt://subdirectory/filename, NOT
   * crypt:///home/user/owncloud/data. Otherwise keyfiles will be put in
   * [owncloud]/data/user/files_encryption/keyfiles/home/user/owncloud/data and
   * will not be accessible to other methods.
   * @note Data read and written must always be 8192 bytes long, as this is the
   * buffer size used internally by PHP. The encryption process makes the input
   * data longer, and input is chunked into smaller pieces in order to result in
   * a 8192 encrypted block size.
   * @note When files are deleted via webdav, or when they are updated and the
   * previous version deleted, this is handled by OC\Files\View, and thus the
   * encryption proxies are used and keyfiles deleted.
   */
  class Stream {
  	private $plainKey;
  	private $encKeyfiles;
  
  	private $rawPath; // The raw path relative to the data dir
  	private $relPath; // rel path to users file dir
  	private $userId;

  	private $keyId;

  	private $handle; // Resource returned by fopen
  	private $meta = array(); // Header / meta for source stream
  	private $writeCache;
  	private $size;
  	private $unencryptedSize;
  	private $publicKey;
  	private $encKeyfile;

  	private $newFile; // helper var, we only need to write the keyfile for new files

  	/**
  	 * @var \OC\Files\View
  	 */
  	private $rootView; // a fsview object set to '/'

  	/**
  	 * @var \OCA\Encryption\Session
  	 */
  	private $session;
  	private $privateKey;
  
  	/**

  	 * @param $path raw path relative to data/

  	 * @param $mode
  	 * @param $options
  	 * @param $opened_path
  	 * @return bool
  	 */
  	public function stream_open($path, $mode, $options, &$opened_path) {

  		// assume that the file already exist before we decide it finally in getKey()
  		$this->newFile = false;

  		if (!isset($this->rootView)) {
  			$this->rootView = new \OC_FilesystemView('/');
  		}

  		$this->session = new \OCA\Encryption\Session($this->rootView);

  		$this->privateKey = $this->session->getPrivateKey();

  		// rawPath is relative to the data directory
  		$this->rawPath = \OC\Files\Filesystem::normalizePath(str_replace('crypt://', '', $path));

  		$this->userId = Helper::getUser($this->rawPath);
  
  		$util = new Util($this->rootView, $this->userId);
  
  		// get the key ID which we want to use, can be the users key or the
  		// public share key
  		$this->keyId = $util->getKeyId();

  
  		// Strip identifier text from path, this gives us the path relative to data/<user>/files

  		$this->relPath = Helper::stripUserFilesPath($this->rawPath);
  		// if raw path doesn't point to a real file, check if it is a version or a file in the trash bin
  		if ($this->relPath === false) {
  			$this->relPath = Helper::getPathToRealFile($this->rawPath);
  		}

  		if($this->relPath === false) {
  			\OCP\Util::writeLog('Encryption library', 'failed to open file "' . $this->rawPath . '" expecting a path to "files", "files_versions" or "cache"', \OCP\Util::ERROR);
  			return false;
  		}

  
  		// Disable fileproxies so we can get the file size and open the source file without recursive encryption
  		$proxyStatus = \OC_FileProxy::$enabled;
  		\OC_FileProxy::$enabled = false;
  
  		if (
  			$mode === 'w'
  			or $mode === 'w+'
  			or $mode === 'wb'
  			or $mode === 'wb+'
  		) {
  
  			// We're writing a new file so start write counter with 0 bytes
  			$this->size = 0;
  			$this->unencryptedSize = 0;
  
  		} else {
  
  			if($this->privateKey === false) {
  				// if private key is not valid redirect user to a error page

  				\OCA\Encryption\Helper::redirectToErrorPage($this->session);

  			}
  
  			$this->size = $this->rootView->filesize($this->rawPath, $mode);
  		}
  
  		$this->handle = $this->rootView->fopen($this->rawPath, $mode);
  
  		\OC_FileProxy::$enabled = $proxyStatus;
  
  		if (!is_resource($this->handle)) {
  
  			\OCP\Util::writeLog('Encryption library', 'failed to open file "' . $this->rawPath . '"', \OCP\Util::ERROR);
  
  		} else {
  
  			$this->meta = stream_get_meta_data($this->handle);
  
  		}
  
  
  		return is_resource($this->handle);
  
  	}
  
  	/**
  	 * @param $offset
  	 * @param int $whence
  	 */
  	public function stream_seek($offset, $whence = SEEK_SET) {
  
  		$this->flush();
  
  		fseek($this->handle, $offset, $whence);
  
  	}
  
  	/**
  	 * @param $count
  	 * @return bool|string
  	 * @throws \Exception
  	 */
  	public function stream_read($count) {
  
  		$this->writeCache = '';
  
  		if ($count !== 8192) {
  
  			// $count will always be 8192 https://bugs.php.net/bug.php?id=21641
  			// This makes this function a lot simpler, but will break this class if the above 'bug' gets 'fixed'
  			\OCP\Util::writeLog('Encryption library', 'PHP "bug" 21641 no longer holds, decryption system requires refactoring', \OCP\Util::FATAL);
  
  			die();
  
  		}
  
  		// Get the data from the file handle
  		$data = fread($this->handle, $count);
  
  		$result = null;
  
  		if (strlen($data)) {
  
  			if (!$this->getKey()) {
  
  				// Error! We don't have a key to decrypt the file with
  				throw new \Exception(
  					'Encryption key not found for "' . $this->rawPath . '" during attempted read via stream');
  
  			} else {
  
  				// Decrypt data
  				$result = Crypt::symmetricDecryptFileContent($data, $this->plainKey);
  			}
  
  		}
  
  		return $result;
  
  	}
  
  	/**
  	 * @brief Encrypt and pad data ready for writing to disk
  	 * @param string $plainData data to be encrypted
  	 * @param string $key key to use for encryption
  	 * @return string encrypted data on success, false on failure
  	 */
  	public function preWriteEncrypt($plainData, $key) {
  
  		// Encrypt data to 'catfile', which includes IV
  		if ($encrypted = Crypt::symmetricEncryptFileContent($plainData, $key)) {
  
  			return $encrypted;
  
  		} else {
  
  			return false;
  
  		}
  
  	}
  
  	/**
  	 * @brief Fetch the plain encryption key for the file and set it as plainKey property
  	 * @internal param bool $generate if true, a new key will be generated if none can be found
  	 * @return bool true on key found and set, false on key not found and new key generated and set
  	 */
  	public function getKey() {
  
  		// Check if key is already set
  		if (isset($this->plainKey) && isset($this->encKeyfile)) {
  
  			return true;
  
  		}
  
  		// Fetch and decrypt keyfile
  		// Fetch existing keyfile

  		$util = new \OCA\Encryption\Util($this->rootView, $this->userId);
  		$this->encKeyfile = Keymanager::getFileKey($this->rootView, $util, $this->relPath);

  
  		// If a keyfile already exists
  		if ($this->encKeyfile) {

  			$shareKey = Keymanager::getShareKey($this->rootView, $this->keyId, $util, $this->relPath);

  			// if there is no valid private key return false
  			if ($this->privateKey === false) {

  				// if private key is not valid redirect user to a error page

  				\OCA\Encryption\Helper::redirectToErrorPage($this->session);

  				return false;
  			}

  			if ($shareKey === false) {
  				// if no share key is available redirect user to a error page
  				\OCA\Encryption\Helper::redirectToErrorPage($this->session, \OCA\Encryption\Crypt::ENCRYPTION_NO_SHARE_KEY_FOUND);
  				return false;
  			}

  
  			$this->plainKey = Crypt::multiKeyDecrypt($this->encKeyfile, $shareKey, $this->privateKey);
  
  			return true;
  
  		} else {

  			$this->newFile = true;

  			return false;
  
  		}
  
  	}
  
  	/**
  	 * @brief Handle plain data from the stream, and write it in 8192 byte blocks
  	 * @param string $data data to be written to disk
  	 * @note the data will be written to the path stored in the stream handle, set in stream_open()
  	 * @note $data is only ever be a maximum of 8192 bytes long. This is set by PHP internally. stream_write() is called multiple times in a loop on data larger than 8192 bytes
  	 * @note Because the encryption process used increases the length of $data, a writeCache is used to carry over data which would not fit in the required block size
  	 * @note Padding is added to each encrypted block to ensure that the resulting block is exactly 8192 bytes. This is removed during stream_read
  	 * @note PHP automatically updates the file pointer after writing data to reflect it's length. There is generally no need to update the poitner manually using fseek
  	 */
  	public function stream_write($data) {
  
  		// if there is no valid private key return false
  		if ($this->privateKey === false) {
  			$this->size = 0;
  			return strlen($data);
  		}
  
  		// Disable the file proxies so that encryption is not
  		// automatically attempted when the file is written to disk -
  		// we are handling that separately here and we don't want to
  		// get into an infinite loop
  		$proxyStatus = \OC_FileProxy::$enabled;
  		\OC_FileProxy::$enabled = false;
  
  		// Get the length of the unencrypted data that we are handling
  		$length = strlen($data);
  
  		// Find out where we are up to in the writing of data to the
  		// file
  		$pointer = ftell($this->handle);
  
  		// Get / generate the keyfile for the file we're handling
  		// If we're writing a new file (not overwriting an existing
  		// one), save the newly generated keyfile
  		if (!$this->getKey()) {
  
  			$this->plainKey = Crypt::generateKey();
  
  		}
  
  		// If extra data is left over from the last round, make sure it
  		// is integrated into the next 6126 / 8192 block
  		if ($this->writeCache) {
  
  			// Concat writeCache to start of $data
  			$data = $this->writeCache . $data;
  
  			// Clear the write cache, ready for reuse - it has been
  			// flushed and its old contents processed
  			$this->writeCache = '';
  
  		}
  
  		// While there still remains some data to be processed & written
  		while (strlen($data) > 0) {
  
  			// Remaining length for this iteration, not of the
  			// entire file (may be greater than 8192 bytes)
  			$remainingLength = strlen($data);
  
  			// If data remaining to be written is less than the
  			// size of 1 6126 byte block
  			if ($remainingLength < 6126) {
  
  				// Set writeCache to contents of $data
  				// The writeCache will be carried over to the
  				// next write round, and added to the start of
  				// $data to ensure that written blocks are
  				// always the correct length. If there is still
  				// data in writeCache after the writing round
  				// has finished, then the data will be written
  				// to disk by $this->flush().
  				$this->writeCache = $data;
  
  				// Clear $data ready for next round
  				$data = '';
  
  			} else {
  
  				// Read the chunk from the start of $data
  				$chunk = substr($data, 0, 6126);
  
  				$encrypted = $this->preWriteEncrypt($chunk, $this->plainKey);
  
  				// Write the data chunk to disk. This will be
  				// attended to the last data chunk if the file
  				// being handled totals more than 6126 bytes
  				fwrite($this->handle, $encrypted);
  
  				// Remove the chunk we just processed from
  				// $data, leaving only unprocessed data in $data
  				// var, for handling on the next round
  				$data = substr($data, 6126);
  
  			}
  
  		}
  
  		$this->size = max($this->size, $pointer + $length);
  		$this->unencryptedSize += $length;
  
  		\OC_FileProxy::$enabled = $proxyStatus;
  
  		return $length;
  
  	}
  
  
  	/**
  	 * @param $option
  	 * @param $arg1
  	 * @param $arg2
  	 */
  	public function stream_set_option($option, $arg1, $arg2) {
  		$return = false;
  		switch ($option) {
  			case STREAM_OPTION_BLOCKING:
  				$return = stream_set_blocking($this->handle, $arg1);
  				break;
  			case STREAM_OPTION_READ_TIMEOUT:
  				$return = stream_set_timeout($this->handle, $arg1, $arg2);
  				break;
  			case STREAM_OPTION_WRITE_BUFFER:
  				$return = stream_set_write_buffer($this->handle, $arg1);
  		}
  
  		return $return;
  	}
  
  	/**
  	 * @return array
  	 */
  	public function stream_stat() {
  		return fstat($this->handle);
  	}
  
  	/**
  	 * @param $mode
  	 */
  	public function stream_lock($mode) {
  		return flock($this->handle, $mode);
  	}
  
  	/**
  	 * @return bool
  	 */
  	public function stream_flush() {
  
  		return fflush($this->handle);
  		// Not a typo: http://php.net/manual/en/function.fflush.php
  
  	}
  
  	/**
  	 * @return bool
  	 */
  	public function stream_eof() {
  		return feof($this->handle);
  	}
  
  	private function flush() {
  
  		if ($this->writeCache) {
  
  			// Set keyfile property for file in question
  			$this->getKey();
  
  			$encrypted = $this->preWriteEncrypt($this->writeCache, $this->plainKey);
  
  			fwrite($this->handle, $encrypted);
  
  			$this->writeCache = '';

  		}

  	}
  
  	/**
  	 * @return bool
  	 */
  	public function stream_close() {
  
  		$this->flush();
  
  		// if there is no valid private key return false
  		if ($this->privateKey === false) {

  			// cleanup
  			if ($this->meta['mode'] !== 'r' && $this->meta['mode'] !== 'rb') {

  				// Disable encryption proxy to prevent recursive calls
  				$proxyStatus = \OC_FileProxy::$enabled;
  				\OC_FileProxy::$enabled = false;

  				if ($this->rootView->file_exists($this->rawPath) && $this->size === 0) {
  					$this->rootView->unlink($this->rawPath);

  				}

  				// Re-enable proxy - our work is done
  				\OC_FileProxy::$enabled = $proxyStatus;
  			}

  			// if private key is not valid redirect user to a error page

  			\OCA\Encryption\Helper::redirectToErrorPage($this->session);

  		}
  
  		if (

  				$this->meta['mode'] !== 'r' &&
  				$this->meta['mode'] !== 'rb' &&
  				$this->size > 0 &&
  				$this->unencryptedSize > 0

  		) {

  			// only write keyfiles if it was a new file
  			if ($this->newFile === true) {

  				// Disable encryption proxy to prevent recursive calls
  				$proxyStatus = \OC_FileProxy::$enabled;
  				\OC_FileProxy::$enabled = false;

  				// Fetch user's public key
  				$this->publicKey = Keymanager::getPublicKey($this->rootView, $this->keyId);

  				// Check if OC sharing api is enabled
  				$sharingEnabled = \OCP\Share::isEnabled();

  				$util = new Util($this->rootView, $this->userId);

  				// Get all users sharing the file includes current user
  				$uniqueUserIds = $util->getSharingUsersArray($sharingEnabled, $this->relPath, $this->userId);
  				$checkedUserIds = $util->filterShareReadyUsers($uniqueUserIds);

  				// Fetch public keys for all sharing users
  				$publicKeys = Keymanager::getPublicKeys($this->rootView, $checkedUserIds['ready']);

  				// Encrypt enc key for all sharing users
  				$this->encKeyfiles = Crypt::multiKeyEncrypt($this->plainKey, $publicKeys);

  				// Save the new encrypted file key
  				Keymanager::setFileKey($this->rootView, $util, $this->relPath, $this->encKeyfiles['data']);

  				// Save the sharekeys
  				Keymanager::setShareKeys($this->rootView, $util, $this->relPath, $this->encKeyfiles['keys']);

  				// Re-enable proxy - our work is done
  				\OC_FileProxy::$enabled = $proxyStatus;
  			}

  			// we need to update the file info for the real file, not for the
  			// part file.
  			$path = Helper::stripPartialFileExtension($this->rawPath);

  			// get file info
  			$fileInfo = $this->rootView->getFileInfo($path);
  			if (is_array($fileInfo)) {
  				// set encryption data
  				$fileInfo['encrypted'] = true;
  				$fileInfo['size'] = $this->size;
  				$fileInfo['unencrypted_size'] = $this->unencryptedSize;
  
  				// set fileinfo
  				$this->rootView->putFileInfo($path, $fileInfo);
  			}

  
  		}
  
  		return fclose($this->handle);

  	}
  
  }