SharedObject.md

SharedObject messages documentation

The RTMP documentation doesn't explain how Shared Object works. There is very little information online and even well know libraries like librtmp don't implement it.

This document was created by reverse engineering AMF0 messages.

 +------+------+-------+-----+-----+------+-----+ +-----+------+-----+
 |Header|Shared|Current|Flags|Event|Event |Event|.|Event|Event |Event|
 |      |Object|Version|     |Type |data  |data |.|Type |data  |data |
 |      |Name  |       |     |     |length|     |.|     |length|     |
 +------+------+-------+-----+-----+------+-----+ +-----+------+-----+
        |                                                            |
        |<- - - - - - - - - - - - - - - - - - - - - - - - - - - - - >|
        |              AMF Shared Object Message body                |

Shared Object Name

UTF8 string without marker (4 bytes UInt32BE length + UTF8 characters).

This type of string value is used in most event types and will be referred to as UTF8 string.

Current Version

Size: 4 bytes

Value: UInt32BE

Flags

Size: 8 bytes?

Value: UInt32BE + UInt32BE

Content unknown, second value seems to always be 0.

Not sure if the two values are both flags or the second one is something undocumented.

Event Type

Size: 1 byte

Value: UInt8

Event data length

Size: 4 bytes

Value: UInt32BE

Event data

Use (=1)

Flags: 16 and 0

Data: none (length 0)

Example:

1, 0, 0, 0, 0

Release (=2)

Flags: 16 and 0

Data: none (length 0)

Example:

2, 0, 0, 0, 0

Request Change (=3)

Version: client version

Flags: 16 and 0

Data: UTF8 string (property key) followed by an AMF-encoded value (property value).

Example:

3, 0, 0, 0, 11,
0, 3, 'f', 'o', 'o',
2, 0, 3, 'b', 'a', 'r'

Change (=4)

Version: server version

Flags: 16 and 0

Data: UTF8 string (property key) followed by an AMF-encoded value (property value).

Example:

4, 0, 0, 0, 11,
0, 3, 'f', 'o', 'o',
2, 0, 3, 'b', 'a', 'r'

Success (=5)

Unknown. Possibly deprecated and replaced by type 13?

SendMessage (=6)

Unknown. Could be related to .send() and handlerName()?

Status (=7)

Flags: 16 or 48 and 0

• 48 when read access has been denied as a response to use message
• 16 when write access has ben denied

Data: two UTF8 strings

First value is the code, second one is the level.

Example:

7, 0, 0, 0, 34,
0, 25, 'S', 'h', 'a', 'r', 'e', 'd', 'O', 'b', 'j', 'e', 'c', 't', '.', 'N', 'o', 'R', 'e', 'a', 'd', 'A', 'c', 'c', 'e', 's', 's',
0, 5, 'e', 'r', 'r', 'o', 'r'

Extra information:

• For NoWriteAccess error the current value of the property should also be sent back to the client.

Clear (=8)

Version: server version

Flags: 16 and 0

Data: none (length 0)

Example:

8, 0, 0, 0, 0

Remove (=9)

Version: server version

Flags: 16 and 0 (when triggered by type 10?) or 32 and 0 (when initiated by server?)

Data: UTF8 string (property key)

Example:

9, 0, 0, 0, 5,
0, 3, 'f', 'o', 'o'

Request Remove (=10)

Version: client version

Flags: 16 and 0

Data: UTF8 string (property key)

Example:

10, 0, 0, 0, 5,
0, 3, 'f', 'o', 'o'

Use Success (=11)

Version: server version

Flags: 48 and 0

Data: none (length 0)

Example:

11, 0, 0, 0, 0

Unknown type (=12)

Absolutely undocumented. Can possibly be ignored.

Could have something to do with type 4 events as the string inside is repeated from type 4 keys.

Example (including type 4 event):

4, 0, 0, 0, 11, 0, 3, 'f', 'o', 'o', 2, 0, 3, 'b', 'a', 'r',
12, 0, 0, 0, 9, 0, 3, 'f', 'o', 'o', 0, 0, 0, 1

Unknown type (=13)

Seems to be triggered by type 3, basically as an echo with the server version.

Could be change acknowledgement since type 4 is not triggered for the client from which the change originated.

Example (including type 3 event):

3, 0, 0, 0, 11, 0, 3, 'f', 'o', 'o', 2, 0, 3, 'b', 'a', 'r'
13, 0, 0, 0, 11, 0, 3, 'f', 'o', 'o', 2, 0, 3, 'b', 'a', 'r'

Unknown type (=14)

Requests to clear the Shared Object.

Version: client version

Flags: 16 and 0

Data: none (length 0)

Example:

14, 0, 0, 0, 0