download_url

download_url: 这个函数从一个给定的URL检索一个文件，并将其保存到服务器上的指定位置。它可以用来从远程服务器上以编程方式下载和保存文件。

使用WordPress HTTP API下载一个URL到一个本地临时文件。

请注意，调用函数必须unlink()这个文件。

function download_url( $url, $timeout = 300, $signature_verification = false ) {
	// WARNING: The file is not automatically deleted, the script must unlink() the file.
	if ( ! $url ) {
		return new WP_Error( 'http_no_url', __( 'Invalid URL Provided.' ) );
	}

	$url_path     = parse_url( $url, PHP_URL_PATH );
	$url_filename = '';
	if ( is_string( $url_path ) && '' !== $url_path ) {
		$url_filename = basename( $url_path );
	}

	$tmpfname = wp_tempnam( $url_filename );
	if ( ! $tmpfname ) {
		return new WP_Error( 'http_no_file', __( 'Could not create temporary file.' ) );
	}

	$response = wp_safe_remote_get(
		$url,
		array(
			'timeout'  => $timeout,
			'stream'   => true,
			'filename' => $tmpfname,
		)
	);

	if ( is_wp_error( $response ) ) {
		unlink( $tmpfname );
		return $response;
	}

	$response_code = wp_remote_retrieve_response_code( $response );

	if ( 200 !== $response_code ) {
		$data = array(
			'code' => $response_code,
		);

		// Retrieve a sample of the response body for debugging purposes.
		$tmpf = fopen( $tmpfname, 'rb' );

		if ( $tmpf ) {
			/**
			 * Filters the maximum error response body size in `download_url()`.
			 *
			 * @since 5.1.0
			 *
			 * @see download_url()
			 *
			 * @param int $size The maximum error response body size. Default 1 KB.
			 */
			$response_size = apply_filters( 'download_url_error_max_body_size', KB_IN_BYTES );

			$data['body'] = fread( $tmpf, $response_size );
			fclose( $tmpf );
		}

		unlink( $tmpfname );

		return new WP_Error( 'http_404', trim( wp_remote_retrieve_response_message( $response ) ), $data );
	}

	$content_disposition = wp_remote_retrieve_header( $response, 'content-disposition' );

	if ( $content_disposition ) {
		$content_disposition = strtolower( $content_disposition );

		if ( 0 === strpos( $content_disposition, 'attachment; filename=' ) ) {
			$tmpfname_disposition = sanitize_file_name( substr( $content_disposition, 21 ) );
		} else {
			$tmpfname_disposition = '';
		}

		// Potential file name must be valid string.
		if ( $tmpfname_disposition && is_string( $tmpfname_disposition )
			&& ( 0 === validate_file( $tmpfname_disposition ) )
		) {
			$tmpfname_disposition = dirname( $tmpfname ) . '/' . $tmpfname_disposition;

			if ( rename( $tmpfname, $tmpfname_disposition ) ) {
				$tmpfname = $tmpfname_disposition;
			}

			if ( ( $tmpfname !== $tmpfname_disposition ) && file_exists( $tmpfname_disposition ) ) {
				unlink( $tmpfname_disposition );
			}
		}
	}

	$content_md5 = wp_remote_retrieve_header( $response, 'content-md5' );

	if ( $content_md5 ) {
		$md5_check = verify_file_md5( $tmpfname, $content_md5 );

		if ( is_wp_error( $md5_check ) ) {
			unlink( $tmpfname );
			return $md5_check;
		}
	}

	// If the caller expects signature verification to occur, check to see if this URL supports it.
	if ( $signature_verification ) {
		/**
		 * Filters the list of hosts which should have Signature Verification attempted on.
		 *
		 * @since 5.2.0
		 *
		 * @param string[] $hostnames List of hostnames.
		 */
		$signed_hostnames = apply_filters( 'wp_signature_hosts', array( 'wordpress.org', 'downloads.wordpress.org', 's.w.org' ) );

		$signature_verification = in_array( parse_url( $url, PHP_URL_HOST ), $signed_hostnames, true );
	}

	// Perform signature valiation if supported.
	if ( $signature_verification ) {
		$signature = wp_remote_retrieve_header( $response, 'x-content-signature' );

		if ( ! $signature ) {
			// Retrieve signatures from a file if the header wasn't included.
			// WordPress.org stores signatures at $package_url.sig.

			$signature_url = false;

			if ( is_string( $url_path ) && ( '.zip' === substr( $url_path, -4 ) || '.tar.gz' === substr( $url_path, -7 ) ) ) {
				$signature_url = str_replace( $url_path, $url_path . '.sig', $url );
			}

			/**
			 * Filters the URL where the signature for a file is located.
			 *
			 * @since 5.2.0
			 *
			 * @param false|string $signature_url The URL where signatures can be found for a file, or false if none are known.
			 * @param string $url                 The URL being verified.
			 */
			$signature_url = apply_filters( 'wp_signature_url', $signature_url, $url );

			if ( $signature_url ) {
				$signature_request = wp_safe_remote_get(
					$signature_url,
					array(
						'limit_response_size' => 10 * KB_IN_BYTES, // 10KB should be large enough for quite a few signatures.
					)
				);

				if ( ! is_wp_error( $signature_request ) && 200 === wp_remote_retrieve_response_code( $signature_request ) ) {
					$signature = explode( "n", wp_remote_retrieve_body( $signature_request ) );
				}
			}
		}

		// Perform the checks.
		$signature_verification = verify_file_signature( $tmpfname, $signature, $url_filename );
	}

	if ( is_wp_error( $signature_verification ) ) {
		if (
			/**
			 * Filters whether Signature Verification failures should be allowed to soft fail.
			 *
			 * WARNING: This may be removed from a future release.
			 *
			 * @since 5.2.0
			 *
			 * @param bool   $signature_softfail If a softfail is allowed.
			 * @param string $url                The url being accessed.
			 */
			apply_filters( 'wp_signature_softfail', true, $url )
		) {
			$signature_verification->add_data( $tmpfname, 'softfail-filename' );
		} else {
			// Hard-fail.
			unlink( $tmpfname );
		}

		return $signature_verification;
	}

	return $tmpfname;
}