Global Discovery v3

Announcements

A device should announce itself at startup. It does this by an HTTPS POST to the announce server URL. Standard discovery currently requires the path to be “/v2/”, yet this can be up to the discovery server. The POST has a JSON payload listing connection addresses (if any):

{
        addresses: ["tcp://192.0.2.45:22000", "tcp://:22202", "relay://192.0.2.99:22028"],
}

It’s OK for the “addresses” field to be either the empty list ([]), null, or missing entirely. An announcement with the field missing or empty is however not useful...

Any empty or unspecified IP addresses (i.e. addresses like tcp://:22000, tcp://0.0.0.0:22000, tcp://[::]:22000) are interpreted as referring to the source IP address of the announcement.

The device ID of the announcing device is not part of the announcement. Instead, the server requires that the client perform certificate authentication. The device ID is deduced from the presented certificate.

The server response is empty, with code 204 (No Content) on success. If no certificate was presented, status 403 (Forbidden) is returned. If the posted data doesn’t conform to the expected format, 400 (Bad Request) is returned.

In successful responses, the server may return a Reannounce-After header containing the number of seconds after which the client should perform a new announcement.

In error responses, the server may return a Retry-After header containing the number of seconds after which the client should retry.

Performing announcements significantly more often than indicated by the Reannounce-After or Retry-After headers may result in the client being throttled. In such cases the server may respond with status code 429 (Too Many Requests).

Queries

Queries are performed as HTTPS GET requests to the announce server URL. The requested device ID is passed as the query parameter “device”, in canonical string form, i.e. https://announce.syncthing.net/v2/?device=ABC12345-....

Successful responses will have status code 200 (OK) and carry a JSON payload of the same format as the announcement above. The response will not contain empty or unspecified addresses.

If the “device” query parameter is missing or malformed, the status code 400 (Bad Request) is returned.

If the device ID is of a valid format but not found in the registry, 404 (Not Found) is returned.

If the client has exceeded a rate limit, the server may respond with 429 (Too Many Requests).