falk-werner_webfuse-provider/doc/protocol.md

Webfuse Protocol

Requests, responses and notifications

There are three types of messages, used for communication between webfuse daemon and filesystem provider. All message types are encoded in JSON and strongly inspired by JSON-RPC.

Request

A request is used by a sender to invoke a method on the receiver. The sender awaits a response from the receiver. Since requests and responses can be sendet or answered in any order, an id is provided in each request to identify it.

{
  "method": <method_name>,
  "params": <params>,
  "id"    : <id>
}

Item	Data type	Description
method_name	string	name of the method to invoke
params	array	method specific parameters
id	integer	id, which is repeated in response

Response

A response is used to answer a prior request. There are two kinds of responses:

Successful Results

{
   "result": <result>,
   "id": <id>
}

Item	Data type	Description
result	any	request specific result
id	integer	id, same as request

Error notifications

{
   "error": {
     "code": <code>
   },
   "id": <id>
}

Item	Data type	Description
code	integer	error code
id	integer	id, same as request

Error codes

Symbolic name	Code	Description
GOOD	0	no error
BAD	1	generic error
BAD_NOTIMPLEMENTED	2	method not implemented
BAD_TIMEOUT	3	timeout occured
BAD_BUSY	4	resource busy
BAD_FORMAT	5	invalid formt
BAD_NOENTRY	101	invalid entry
BAD_ACCESS_DENIED	102	access not allowed

Notification

Notfications are used to inform a receiver about something. Unlike requests, notifications are not answered. Therefore, an id is not supplied.

{
  "method": <method_name>,
  "params": <params>
}

Item	Data type	Description
method_name	string	name of the method to invoke
params	array	method specific parameters

Requests (Adapter -> Provider)

lookup

Retrieve information about a filesystem entry by name.

webfuse daemon: {"method": "lookup", "params": [<filesystem>, <parent>, <name>], "id": <id>}
fs provider: {"result": {
    "inode": <inode>,
    "mode" : <mode>,
    "type" : <type>,
    "size" : <size>,
    "atime": <atime>,
    "mtime": <mtime>,
    "ctime": <ctime>
    }, "id": <id>}

Item	Data type	Description
filesystem	string	name of the filesystem
parent	integer	inode of parent directory (1 = root)
name	string	name of the filesystem object to look up
inode	integer	inode of the filesystem object
mode	integer	unix file mode
type	"file" or "dir"	type of filesystem object
size	integer	required for files; file size in bytes
atime	integer	optional; unix time of last access
mtime	integer	optional; unix time of last modification
ctime	intefer	optional; unix time of last metadata change

getattr

Get file attributes.

webfuse daemon: {"method": "getattr", "params": [<filesystem>, <inode>], "id": <id>}
fs provider: {"result": {
    "mode" : <mode>,
    "type" : <type>,
    "size" : <size>,
    "atime": <atime>,
    "mtime": <mtime>,
    "ctime": <ctime>
    }, "id": <id>}

Item	Data type	Description
filesystem	string	name of the filesystem
inode	integer	inode of the filesystem object
mode	integer	unix file mode
type	"file" or "dir"	type of filesystem object
size	integer	required for files; file size in bytes
atime	integer	optional; unix time of last access
mtime	integer	optional; unix time of last modification
ctime	intefer	optional; unix time of last metadata change

readdir

Read directory contents.
Result is an array of name-inode pairs for each entry. The generic entries "." and ".." should also be provided.

webfuse daemon: {"method": "readdir", "params": [<filesystem>, <dir_inode>], "id": <id>}
fs provider: {"result": [
    {"name": <name>, "inode": <inode>},
    ...
    ], "id": <id>}

Item	Data type	Description
filesystem	string	name of the filesystem
dir_inode	integer	inode of the directory to read
name	integer	name of the entry
inode	integer	inode of the entry

open

Open a file.

webfuse daemon: {"method": "readdir", "params": [<filesystem>, <inode>, <flags>], "id": <id>}
fs provider: {"result": {"handle": <handle>}, "id": <id>}

Item	Data type	Description
filesystem	string	name of the filesystem
inode	integer	inode of the file
flags	integer	access mode flags (see below)
handle	integer	handle of the file

Flags

Symbolic name	Code	Description
O_ACCMODE	0x003	access mode mask
O_RDONLY	0x000	open for reading only
O_WRONLY	0x001	open for writing only
O_RDWR	0x002	open for reading an writing
O_CREAT	0x040	create (a new) file
O_EXCL	0x080	open file exclusivly
O_TRUNC	0x200	open file to truncate
O_APPEND	0x400	open file to append

close

Informs filesystem provider, that a file is closed.
Since close is a notification, it cannot fail.

webfuse daemon: {"method": "close", "params": [<filesystem>, <inode>, <handle>, <flags>], "id": <id>}

Item	Data type	Description
filesystem	string	name of the filesystem
inode	integer	inode of the file
handle	integer	handle of the file
flags	integer	access mode flags (see open)

read

Read from an open file.

webfuse daemon: {"method": "close", "params": [<filesystem>, <inode>, <handle>, <offset>, <length>], "id": <id>}
fs provider: {"result": {
    "data": <data>,
    "format": <format>,
    "count": <count>
    }, "id": <id>}

Item	Data type	Description
filesystem	string	name of the filesystem
inode	integer	inode of the file
handle	integer	handle of the file
offset	integer	Offet to start read operation
length	integer	Max. number of bytes to read
data	integer	handle of the file
format	string	Encoding of data (see below)
count	integer	Actual number of bytes read

Format

Format	Description
"identiy"	Use data as is; note that JSON strings are UTF-8 encoded
"base64"	data is base64 encoded

Requests (Client -> Server)

Note: The following requests are initiated by the client and responded by the server. Depending on the use case, a provider can be a client (e.g. a webbrowser which want's to inject a filesystem to an IoT device) or a server (e.g. a cloud based service, an adapter connects to and requests a filesystem).

add_filesystem

Adds a filesystem.

client: {"method": "add_filesystem", "params": [<name>], "id": <id>}
server: {"result": {"id": <name>}, "id": <id>}

Item	Data type	Description
name	string	name and id of filesystem

authtenticate

Authenticate the provider.
If authentication is enabled, a client must be authenticated by the server before filesystems can be added.

client: {"method": "authenticate", "params": [<type>, <credentials>], "id": <id>}
server: {"result": {}, "id": <id>}

Item	Data type	Description
type	string	authentication type (see below)
credentials	object	credentials to authenticate

authentication types

• username: authenticate via username and password
  {"username": <username>, "password": <password>}