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CloudLink 2 ("CL2") Protocol

CloudLink 2 was a major milestone protocol of the CloudLink project. It is characterized by its asymmetric communication format: clients send commands as multi-line strings, while the server responds with structured JSON. CL2 was the first mature version of CloudLink to use a standardized packet format that the original CloudLink failed at.

Client-to-Server Schema

All communication from a CL2 client to the server is a multi-line string, with the command header on the first line and parameters on subsequent lines separated by a newline character (\n).

Format: <%{COMMAND}}>\n{PARAM_1}\n{PARAM_2}\n...

opcode Description Dialect Notes
<%sn> Set Name. Sets the client's username. PARAM_1 is the username. Foundational command, consistent across all CL2 versions.
<%ds> Disconnect. Informs the server of disconnection. PARAM_1 is the username. Foundational command.
<%rf> Refresh. Requests a fresh user list from the server. Foundational command.
<%gs> Global Stream. Broadcasts data to all connected clients. PARAM_1 is the sender, PARAM_2 is the data. Foundational command.
<%ps> Private Stream. Sends data to a specific client. PARAM_1 is the sender, PARAM_2 is the recipient, and PARAM_3 is the data. Also used to communicate with server APIs by using a special recipient ID (e.g., %CA%) and a JSON string as the data payload. Foundational command, but its use for APIs was expanded in later versions.
<%sh> Special Handshake. Sent upon connection to request advanced features from a compatible server. Exclusive to Late CL2 (v0.1.5 / S2.2+).
<%rl> / <%rt> Register Link / Return. Establishes or breaks a direct data link with another client. Exclusive to Late CL2 (v0.1.5 / S2.2+).
<%l_g> / <%l_p> Linked Global/Private. Sends data or variables within an established client link. PARAM_1 is a numeric mode (0 for data, 1 for variable). Exclusive to Late CL2 (v0.1.5 / S2.2+).

Server-to-Client Schema

All communication from the server to a CL2 client is a JSON object.

Format: {"type": "...", "data": "...", "id": "..."}

type Description Dialect Notes
gs Global Stream. A broadcast message containing global data in the data key. Foundational response.
ps Private Stream. A private message containing data in the data key and the recipient in the id key. Foundational response.
ul User List. The data key contains a single string of all usernames, separated by semicolons (e.g., "UserA;UserB;"). The semicolon-string format is a key feature of CL2.
ru Refresh Usernames. A command from the server instructing clients to re-send their usernames for a hard sync. Foundational response.
direct A special packet containing metadata, like the server version ("data": {"type": "vers", "data": "..."}). Sent in response to a Late CL2 (v0.1.5 / S2.2+) handshake.
sf Special Feature. A wrapper packet for responses (like gs or variable updates) sent to a client that has completed a handshake. Exclusive to Late CL2 (v0.1.5 / S2.2+).
ca, cd, dd API-specific responses for CloudAccount, CloudCoin, and CloudDisk, respectively. Support for these APIs was added throughout the CL2 lifecycle.