falk-werner_webfuse/doc/protocol.md

Webfuse2 Protocol

Scope

This document describes the webfuse 2 communication protocol. The protocol is used to transfer messages between a webfuse service and a webfuse provider. In contrast to legacy webfuse, which is based on JSON RPC the webfuse2 protocol is a binary protocol.

Definitions

Webfuse Service

A webfuse service is both,

• a websocket service providing the webfuse protocol
• a fuse filesystem attached to a local mountpoint

The webfuse service awaits incoming connections from a webfuse provider. Once connected, it communicates all the filesystem requests originated by the libfuse to the connected webfuse provider using the websocket-based webfuse protocol.

By doing so, webfuse allows to inject a filesystem to a remote device.

Webfuse Provider

A webfuse provider provides a filesystem to a remote device using the websocket-based webfuse protocol. Therefore, a webfuse provider implements a websocket client.

Websocket protocol name

The webfuse2 protocol uses the following websocket protocol name: webfuse2.

Message exchange

Once connected, the webfuse2 protocol implements a strict request-response scheme, where

• all requests are send by the webfuse service,
• all requests require a response and
• all responses are send by the webfuse provider

Note that this communication is reversed the typical client-server-communication scheme. In webfuse the webfuse service (server) sends all the requests and the webfuse provider (client) sends the responses.

For message transfer, the websocket protocol is used. All messages are in binary form, plain text messages are never used by the webfuse protocol.

Endianness

All numeric data types are transferred in Big Endian.
For instance, the uint32 value 1 will be transferred as

00 00 00 01

Data Types

Basic data types

Data Type	Width	Description
bool	8 bit	boolean value
u8	8 bit	8 bit unsigned integer
u32	32 bit	32 bit unsigned integer
u64	64 bit	64 bit unsigned integer
i32	32 bit	32 bit signed integer

Derrived integral types

Data Type	Base Type	Description
uid	u32	user ID
gid	u32	group ID
dev	u64	device ID
handle	u64	file handle

Flags and Enums

Data Type	Base Type	Description
result	i32	result type of methods
access_mode	u32	mode of access method
mode	u32	file type and permissions
open_flags	i32	flags of open method
rename_flags	u8	flags of rename method

result

Value Range	Description
0	method call succeed
negative value	error code (see below)
positive value	amount of bytes read or written (read and write only)

Error Code	Value	Description
E2BIG	-7	argument list too long
EACCES	-13	permission denied
EAGAIN	-11	resource temporarily unavailable
EBADF	-9	bad file descriptor
EBUSY	-16	device or resource busy
EDESTADDRREQ	-89	destination address required
EDQUOT	-122	disk quota exceeded
EEXIST	-17	file exists
EFAULT	-14	bad address
EFBIG	-27	file too large
EINTR	-4	interrupt function call
EINVAL	-22	invalid argument
EIO	-5	input / output error
EISDIR	-21	is a directory
ELOOP	-40	too many levels of symbolic links
EMFILE	-24	too many open files
EMLINK	-31	too many links
ENAMETOOLONG	-36	filename too long
ENFILE	-23	too many open files in system
ENODATA	-61	the named attribute does not exist, or the process has not access to this attribute
ENODEV	-19	no such device
ENOENT	-2	no such file or directory
ENOMEM	-12	not enough space / cannot allocate memory
ENOSPC	-28	no space left on device
ENOSYS	-38	function not implemented
ENOTDIR	-20	not a directory
ENOTEMPTY	-39	directory not empty
ENOTSUP	-95	operation not supported
ENXIO	-6	no such device or address
EOVERFLOW	-75	value too large to be stored in data type
EPERM	-1	operation not permitted
EPIPE	-32	broken pipe
ERANGE	-34	result too large
EROFS	-30	read-only filesystem
ETXTBSY	-26	text file busy
EXDEV	-18	improper link
EWOULDBLOCK	-11	resource temporarily unavailable

access mode

Mode	Value	Description
F_OK	0	Tests, whether the file exists
X_OK	1	Tests, whether the file is executable
W_OK	2	Tests, whether the file is writable
R_OK	4	Tests, whether the file is readable

mode

Note that the following numbers are in octal notation.

Fields and Flags	Mask	Description
Protection mask	0o000777	Cointains the file protection flags (rwx for owner, group and others)
Sticky mask	0o007000	Sticky bits
S_ISVTX	0o001000	Sticky bit
S_ISGID	0o002000	Set-Group-ID bit
S_ISUID	0o004000	Set-User-ID bit
Filetype mask	0o170000	Filetype mask
S_IFREG	0o100000	regular file
S_IFDIR	0o040000	directory
S_IFCHR	0o020000	character device
S_IFBLK	0o060000	block device
S_IFIFO	0o010000	named pipe
S_IFLNK	0o120000	link
S_IFSOCK	0o140000	socket

open_flags

Note that the following numbers are in octal notation.

Flags	Value	Description
O_ACCMODE	0o03	Access mode mask
O_RDONLY	0o00	open file read-only
O_WRONLY	0o01	open file write-only
O_RDWR	0o02	open file for reading and writing
O_APPEND	0o000002000	open file in append mode
O_ASYNC	0o000020000	enable signal-driven I/O
O_CLOEXEC	0o002000000	enable close-on-exec
O_CREAT	0o000000100	create file if path does not exists
O_DIRECT	0o000040000	try to minimize cache effects on I/O
O_DIRECTORY	0o000200000	open a directory
O_DSYNC	0o000010000	write with synchronized I/O data integrity
O_EXCL	0o000000200	ensure that file exists when specified in conjunction with O_CREATE
O_LARGEFILE	0o000100000	allow large files to be opened
O_NOATIME	0o001000000	do not update file last access time
O_NOCTTY	0o000000400	make device the process's controlling terminal
O_NOFOLLOW	0o000400000	fail to open, if basename is a symbolic link
O_NONBLOCK	0o000004000	open in nonblocking mode
O_NDELAY	0o000004000	open in nonblocking mode
O_PATH	0o010000000	see manual entry of open(2) for details
O_SYNC	0o004010000	write using synchronized I/O
O_TMPFILE	0o020200000	create an unnamed temporary file
O_TRUNC	0o000001000	truncate fole to length 0

rename_flags

Flag	Value	Description
RENAME_NOREPLACE	1	do not overwrite the new file
RENAME_EXCHANGE	2	atomically exchange the files

Complex Types

Data Type	Description
string	UTF-8 string
strings	list of strings
bytes	array of bytes
timestamp	date and time
attributes	file attributes
statistics	filesystem statistics

string

Field	Data Type	Description
size	u32	length of the string in bytes
data	u8[]	string data (UTF-8)

strings

Field	Data Type	Description
size	u32	count of the elements in the list
data	string[]	strings

bytes

Field	Data Type	Description
size	u32	length of the byte array
data	u8[]	array data

timestamp

Field	Data Type	Description
seconds	u64	seconds sind epoch (1.1.1970)
nsec	u32	nano seconds

attributes

Field	Data Type	Description
inode	u64	Inode value
nlink	u64	Number of hard links
mode	mode (u32)	file mode flags
uid	uid (u32)	user ID
gid	gid (u32)	group ID
rdev	dev (u64)	device ID
size	u64	file size
blocks	u64	number 512-byte blocks
atime	timestamp	time of last access
mtime	timestamp	time of last modification
ctime	timestamp	time of last status change

statistics

Field	Data Type	Description
bsize	u64	Filesystem block size
frsize	u64	Fragment size
blocks	u64	Size of the filesystem if frsize units
bfree	u64	Number of free blocks
bavail	u64	Number of free blocks for unprivileged users
files	u64	Number of inodes
ffree	u64	Number of free inodes
namemax	u64	Maximum filename length

Messages

Field	Type	Descripton
id	u32	Unique ID of the message
type	u8	Type of the message
payload	u8[]	Payload according to the message type

The id is just a number without any meaning for the webfuse provider. It is set by the webfuse service of a request and is copied by the webfuse provider to the response. A webfuse service implementation might choose to keep track on pending requests using the id.

Erroneous Responses

Most responses contain a result encoding the status of the operation. While successful responses may contain additional data, erroneous responses must not be decoded by a webfuse service implementation beyond the result value.

Unknown requests

There are two reserved message types:

• 0x00: Unknown request
• 0x80: Unknown response

A webfuse service may send a request of type unknown request for conformance testing reasons.

Since each request requires a response, a webfuse provider must respond to any unknown requests with a message of unknown response type. This allows to add new request types in future.

Accept additional data in requests

Both, a webfuse provider and a webfuse service must accept messages that contain more data than specified. This allows to add optional fields to existing requests and / or responses in future.

Note there are no optional fields in the current revision of the webfuse2 protocol yet.

Message Types

Note that the following numbers are in hexadecimal notation.

Method	Request	Response
access	0x01	0x81
getattr	0x02	0x82
readlink	0x03	0x83
symlink	0x04	0x84
link	0x05	0x85
rename	0x06	0x86
chmod	0x07	0x87
chown	0x08	0x88
truncate	0x09	0x89
fsync	0x0a	0x8a
open	0x0b	0x8b
mknod	0x0c	0x8c
create	0x0d	0x8d
release	0x0e	0x8e
unlink	0x0f	0x8f
read	0x10	0x90
write	0x11	0x91
mkdir	0x12	0x92
readdir	0x13	0x93
rmdir	0x14	0x94
statfs	0x15	0x95
utimens	0x16	0x96

Methods

Since webfuse aims to communicate the libfuse API over a websocket connection, webfuse methods are tightly connected to fuse operations which itself have a tight connection to posix filesystem operations. Therefore, additional information about most webfuse operations can be found in the fuse operations documentation and / or the man pages.

access

Checks the user's permissions for a file (see man access(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x01)
path	string	path of file to check
mode	access_mode (i8)	access mode to check

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x81)
result	result	operation status

getattr

Retrieve file attributes (see man getattr(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x02)
path	string	path

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x82)
result	result	operation status
attibutes	attributes	attributes of file

readlink

Read value of a symbolik link (see man readlink(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x03)
path	string	path of link

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x83)
result	result	operation status
resolved	string	resolved path

symlink

Make a new name of a file (see man symlink(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x04)
target	string	target of link
linkpath	string	name of the link

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x84)
result	result	operation status

link

Make a new name for a file (see man link(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x05)
old_path	string	path of the existing file
new_path	string	new name of the file

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x85)
result	result	operation status

rename

Change the name of a file (see man rename(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x06)
old_path	string	old name of the file
new_path	string	new name of the file
flags	rename_flags (u8)	flags to control the rename operation

The following flags are defined:

• 0x00: move the file from old_path to new_path
• 0x01 (RENAME_NOREPLACE): do not override new_path
  This results in an error, when new_path already exists.
• 0x02 (RENAME_EXCHANGE): atomically exchange the files

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x86)
result	result	operation status

chmod

Change permissions of a file (see man chmod(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x07)
path	string	path of the file
mode	mode (u32)	new file permissions

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x87)
result	result	operation status

chown

Change ownership of a file (see man chown(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x08)
path	string	path of the file
uid	uid (u32)	user id of the new owner
gid	gid (u32)	group id of the new owning group

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x88)
result	result	operation status

truncate

Truncate a file to a specified length (see man truncate(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x09)
path	string	path of the file
size	u64	new file size
handle	handle (u64)	handle of the file

Note that handle might be invalid (-1), even if the file is open.

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x89)
result	result	operation status

fsync

Sychronize a file's in-core state with storage device (see man fsync(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x0a)
path	string	path of the file
is_datasync	bool	if true, sync only user data
handle	handle (u64)	handle of the file

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x8a)
result	result	operation status

open

Open and possibly create a file (man open(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x0b)
path	string	path of the file
flags	open_flags (i32)	flags

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x8b)
result	result	operation status
handle	handle (u64)	handle of the file

mknod

Create a special or ordinary file (see man mknod(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x0c)
path	string	path of the file
mode	mode (u32)	mode of the file
dev	dev (64)	device type

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x8c)
result	result	operation status

create

Create a new file or rewrite an existing one (see man creat(3p)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x0d)
path	string	path of the file
mode	mode (u32)	mode of the file

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x8d)
result	result	operation status
handle	handle (u64)	handle of the file

release

Releases a file handle (see man close(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x0e)
path	string	path of the file
handle	handle (u64)	handle of the file

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x8e)
result	result	operation status

unlink

Delete a name and possibly the file it refers to (man unlink(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x0f)
path	string	path of the file

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x8f)
result	result	operation status

read

Read from a file description (see man read(2), man pread(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x10)
path	string	path of the file
buffer_size	u32	max. amount of bytes requested
offset	u64	offset of the file
handle	handle (u64)	handle of the file

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x90)
result	result	amount of byte read or error code
data	bytes	requested data

Note that results returns the amount of bytes read on success.

write

Write to a file (see man write(2), man pread(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x17)
data	bytes	data to write
offset	u64	offset to write to
handle	handle (u64)	handle of the file

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x91)
result	result	amount of bytes written or error code

Note that results returns the amount of bytes written on success.

mkdir

Create a directory (see man mkdir(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x12)
path	string	path of the directory
mode	mode (u32)	directory permissions

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x92)
result	result	operation status

readdir

Reads the contents of a directory.

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x13)
path	string	path of the directory

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x93)
result	result	operation status
items	strings	names of the directory entries

rmdir

Delete a directory (see man rmdir(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x14)
path	string	path of the directory

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x94)
result	result	operation status

statfs

Get filesystem statistics (see man statvfs(3)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x15)
path	string	path of the file

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x95)
result	result	operation status
statistics	statistics	filesystem statistics

utimens

Change the file timestamps with nanosecond precision (man utimesat(2)).

Request

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x16)
path	string	path of the file
atime	timestamp	new last access time
mtime	timestamp	new last modified time
handle	handle (u64)	handle of the file

Note that handle might be invalid (-1), even if the file is open.

Response

Field	Data Type	Description
id	u32	message id
type	u8	message type (0x96)
result	result	operation status

Examples

Get file attributes

service  -> provider:
    00 00 00 01 # message id   = 1
    02          # message type = getattr request
    00 00 00 01 # path.size    = 1
    '/'         # path         = "/"

provider -> service:
    00 00 00 01              # message id        = 1
    82                       # message type      = getattr response
    00 00 00 00              # result            = 0 (OK)
    00 00 00 00 00 00 00 01  # attributes.inode  = 1
    00 00 00 00 00 00 00 02  # attributes.nlink  = 2
    00 00 41 a4              # attributes.mode   = 0o40644 (S_IDDIR | 0o0644)
    00 00 03 e8              # attributes.uid    = 1000
    00 00 03 e8              # attributes.gid    = 1000
    00 00 00 00 00 00 00 00  # attributes.size   = 0
    00 00 00 00 00 00 00 00  # attributes.blocks = 0
    00 00 00 00 00 00 00 00  # attrbites.atime.sec  = 0
    00 00 00 00 00           # attributs.atime.nsec = 0
    00 00 00 00 00 00 00 00  # attrbites.mtime.sec  = 0
    00 00 00 00 00           # attributs.mtime.nsec = 0
    00 00 00 00 00 00 00 00  # attrbites.ctime.sec  = 0
    00 00 00 00 00           # attributs.ctime.nsec = 0

Get file attributes (Failure)

Note that attributs are skipped in case of an error.

service  -> provider:
    00 00 00 01 # message id   = 1
    02          # message type = getattr request
    00 00 00 04 # path.size    = 4
    "/foo"      # path         = "/foo"

provider -> service:
    00 00 00 01              # message id        = 1
    82                       # message type      = getattr response
    ff ff ff fe              # result            = -2 (ENOENT)

List directory contents

Note that '.' and '..' should not be included in the response.

service -> provider:
    00 00 00 02 # message id   = 2
    13          # message type = readdir request
    00 00 00 04 # path.size    = 4
    '/dir'      # path         = "/dir"

provider -> service:
    00 00 00 02 # message id    = 2
    93          # message type  = readdir response
    00 00 00 00 # result        = 0 (OK)
    00 00 00 03 # items.size    = 3
    00 00 00 03 # items[0].size = 3
    "foo"       # items[0]      = "foo"
    00 00 00 03 # items[0].size = 3
    "bar"       # items[0]      = "bar"
    00 00 00 03 # items[0].size = 3
    "baz"       # items[0]      = "baz"

Unknown request

service -> provider:
    00 00 00 23 # message id   = 0x23
    42          # message type = ??? (not specified yet)
    ...         # some more data

provider -> service:
    00 00 00 23 # message id   = 0x23
    80          # message type = unknown response