_wp_handle_upload

function _wp_handle_upload( &$file, $overrides, $time, $action ) {
	// The default error handler.
	if ( ! function_exists( 'wp_handle_upload_error' ) ) {
		function wp_handle_upload_error( &$file, $message ) {
			return array( 'error' => $message );
		}
	}

	/**
	 * Filters the data for a file before it is uploaded to WordPress.
	 *
	 * The dynamic portion of the hook name, `$action`, refers to the post action.
	 *
	 * @since 2.9.0 as 'wp_handle_upload_prefilter'.
	 * @since 4.0.0 Converted to a dynamic hook with `$action`.
	 *
	 * @param string[] $file An array of data for a single file.
	 */
	$file = apply_filters( "{$action}_prefilter", $file );

	// You may define your own function and pass the name in $overrides['upload_error_handler'].
	$upload_error_handler = 'wp_handle_upload_error';
	if ( isset( $overrides['upload_error_handler'] ) ) {
		$upload_error_handler = $overrides['upload_error_handler'];
	}

	// You may have had one or more 'wp_handle_upload_prefilter' functions error out the file. Handle that gracefully.
	if ( isset( $file['error'] ) && ! is_numeric( $file['error'] ) && $file['error'] ) {
		return call_user_func_array( $upload_error_handler, array( &$file, $file['error'] ) );
	}

	// Install user overrides. Did we mention that this voids your warranty?

	// You may define your own function and pass the name in $overrides['unique_filename_callback'].
	$unique_filename_callback = null;
	if ( isset( $overrides['unique_filename_callback'] ) ) {
		$unique_filename_callback = $overrides['unique_filename_callback'];
	}

	/*
	 * This may not have originally been intended to be overridable,
	 * but historically has been.
	 */
	if ( isset( $overrides['upload_error_strings'] ) ) {
		$upload_error_strings = $overrides['upload_error_strings'];
	} else {
		// Courtesy of php.net, the strings that describe the error indicated in $_FILES[{form field}]['error'].
		$upload_error_strings = array(
			false,
			sprintf(
				/* translators: 1: upload_max_filesize, 2: php.ini */
				__( 'The uploaded file exceeds the %1$s directive in %2$s.' ),
				'upload_max_filesize',
				'php.ini'
			),
			sprintf(
				/* translators: %s: MAX_FILE_SIZE */
				__( 'The uploaded file exceeds the %s directive that was specified in the HTML form.' ),
				'MAX_FILE_SIZE'
			),
			__( 'The uploaded file was only partially uploaded.' ),
			__( 'No file was uploaded.' ),
			'',
			__( 'Missing a temporary folder.' ),
			__( 'Failed to write file to disk.' ),
			__( 'File upload stopped by extension.' ),
		);
	}

	// All tests are on by default. Most can be turned off by $overrides[{test_name}] = false;
	$test_form = isset( $overrides['test_form'] ) ? $overrides['test_form'] : true;
	$test_size = isset( $overrides['test_size'] ) ? $overrides['test_size'] : true;

	// If you override this, you must provide $ext and $type!!
	$test_type = isset( $overrides['test_type'] ) ? $overrides['test_type'] : true;
	$mimes     = isset( $overrides['mimes'] ) ? $overrides['mimes'] : false;

	// A correct form post will pass this test.
	if ( $test_form && ( ! isset( $_POST['action'] ) || ( $_POST['action'] != $action ) ) ) {
		return call_user_func_array( $upload_error_handler, array( &$file, __( 'Invalid form submission.' ) ) );
	}
	// A successful upload will pass this test. It makes no sense to override this one.
	if ( isset( $file['error'] ) && $file['error'] > 0 ) {
		return call_user_func_array( $upload_error_handler, array( &$file, $upload_error_strings[ $file['error'] ] ) );
	}

	// A properly uploaded file will pass this test. There should be no reason to override this one.
	$test_uploaded_file = 'wp_handle_upload' === $action ? is_uploaded_file( $file['tmp_name'] ) : @is_readable( $file['tmp_name'] );
	if ( ! $test_uploaded_file ) {
		return call_user_func_array( $upload_error_handler, array( &$file, __( 'Specified file failed upload test.' ) ) );
	}

	$test_file_size = 'wp_handle_upload' === $action ? $file['size'] : filesize( $file['tmp_name'] );
	// A non-empty file will pass this test.
	if ( $test_size && ! ( $test_file_size > 0 ) ) {
		if ( is_multisite() ) {
			$error_msg = __( 'File is empty. Please upload something more substantial.' );
		} else {
			$error_msg = sprintf(
				/* translators: 1: php.ini, 2: post_max_size, 3: upload_max_filesize */
				__( 'File is empty. Please upload something more substantial. This error could also be caused by uploads being disabled in your %1$s file or by %2$s being defined as smaller than %3$s in %1$s.' ),
				'php.ini',
				'post_max_size',
				'upload_max_filesize'
			);
		}
		return call_user_func_array( $upload_error_handler, array( &$file, $error_msg ) );
	}

	// A correct MIME type will pass this test. Override $mimes or use the upload_mimes filter.
	if ( $test_type ) {
		$wp_filetype     = wp_check_filetype_and_ext( $file['tmp_name'], $file['name'], $mimes );
		$ext             = empty( $wp_filetype['ext'] ) ? '' : $wp_filetype['ext'];
		$type            = empty( $wp_filetype['type'] ) ? '' : $wp_filetype['type'];
		$proper_filename = empty( $wp_filetype['proper_filename'] ) ? '' : $wp_filetype['proper_filename'];

		// Check to see if wp_check_filetype_and_ext() determined the filename was incorrect.
		if ( $proper_filename ) {
			$file['name'] = $proper_filename;
		}
		if ( ( ! $type || ! $ext ) && ! current_user_can( 'unfiltered_upload' ) ) {
			return call_user_func_array( $upload_error_handler, array( &$file, __( 'Sorry, this file type is not permitted for security reasons.' ) ) );
		}
		if ( ! $type ) {
			$type = $file['type'];
		}
	} else {
		$type = '';
	}

	/*
	 * A writable uploads dir will pass this test. Again, there's no point
	 * overriding this one.
	 */
	$uploads = wp_upload_dir( $time );
	if ( ! ( $uploads && false === $uploads['error'] ) ) {
		return call_user_func_array( $upload_error_handler, array( &$file, $uploads['error'] ) );
	}

	$filename = wp_unique_filename( $uploads['path'], $file['name'], $unique_filename_callback );

	// Move the file to the uploads dir.
	$new_file = $uploads['path'] . "/$filename";

	/**
	 * Filters whether to short-circuit moving the uploaded file after passing all checks.
	 *
	 * If a non-null value is returned from the filter, moving the file and any related
	 * error reporting will be completely skipped.
	 *
	 * @since 4.9.0
	 *
	 * @param mixed    $move_new_file If null (default) move the file after the upload.
	 * @param string[] $file          An array of data for a single file.
	 * @param string   $new_file      Filename of the newly-uploaded file.
	 * @param string   $type          Mime type of the newly-uploaded file.
	 */
	$move_new_file = apply_filters( 'pre_move_uploaded_file', null, $file, $new_file, $type );

	if ( null === $move_new_file ) {
		if ( 'wp_handle_upload' === $action ) {
			$move_new_file = @move_uploaded_file( $file['tmp_name'], $new_file );
		} else {
			// Use copy and unlink because rename breaks streams.
			// phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
			$move_new_file = @copy( $file['tmp_name'], $new_file );
			unlink( $file['tmp_name'] );
		}

		if ( false === $move_new_file ) {
			if ( 0 === strpos( $uploads['basedir'], ABSPATH ) ) {
				$error_path = str_replace( ABSPATH, '', $uploads['basedir'] ) . $uploads['subdir'];
			} else {
				$error_path = basename( $uploads['basedir'] ) . $uploads['subdir'];
			}
			return $upload_error_handler(
				$file,
				sprintf(
					/* translators: %s: Destination file path. */
					__( 'The uploaded file could not be moved to %s.' ),
					$error_path
				)
			);
		}
	}

	// Set correct file permissions.
	$stat  = stat( dirname( $new_file ) );
	$perms = $stat['mode'] & 0000666;
	chmod( $new_file, $perms );

	// Compute the URL.
	$url = $uploads['url'] . "/$filename";

	if ( is_multisite() ) {
		delete_transient( 'dirsize_cache' );
	}

	/**
	 * Filters the data array for the uploaded file.
	 *
	 * @since 2.1.0
	 *
	 * @param array  $upload {
	 *     Array of upload data.
	 *
	 *     @type string $file Filename of the newly-uploaded file.
	 *     @type string $url  URL of the newly-uploaded file.
	 *     @type string $type Mime type of the newly-uploaded file.
	 * }
	 * @param string $context The type of upload action. Values include 'upload' or 'sideload'.
	 */
	return apply_filters(
		'wp_handle_upload',
		array(
			'file' => $new_file,
			'url'  => $url,
			'type' => $type,
		),
		'wp_handle_sideload' === $action ? 'sideload' : 'upload'
	);
}