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125 lines
4.7 KiB
Groff
125 lines
4.7 KiB
Groff
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.TH "SYNCTHING-GLOBALDISCO" "7" "Oct 23, 2024" "v1.28.0" "Syncthing"
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.SH NAME
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syncthing-globaldisco \- Global Discovery Protocol v3
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.SH ANNOUNCEMENTS
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.sp
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A device should announce itself at startup. It does this by an HTTPS POST to
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the announce server URL. Standard discovery currently requires the path to be
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“/v2/”, yet this can be up to the discovery server. The POST has a JSON payload
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listing connection addresses (if any):
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.INDENT 0.0
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.INDENT 3.5
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.sp
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.EX
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{
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addresses: [\(dqtcp://192.0.2.45:22000\(dq, \(dqtcp://:22202\(dq, \(dqrelay://192.0.2.99:22028\(dq],
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}
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.EE
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.UNINDENT
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.UNINDENT
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.sp
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It’s OK for the “addresses” field to be either the empty list (\fB[]\fP),
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\fBnull\fP, or missing entirely. An announcement with the field missing
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or empty is however not useful…
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.sp
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Any empty or unspecified IP addresses (i.e. addresses like \fBtcp://:22000\fP,
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\fBtcp://0.0.0.0:22000\fP, \fBtcp://[::]:22000\fP) are interpreted as referring to
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the source IP address of the announcement.
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.sp
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The device ID of the announcing device is not part of the announcement.
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Instead, the server requires that the client perform certificate
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authentication. The device ID is deduced from the presented certificate.
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.sp
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The server response is empty, with code \fB204\fP (No Content) on success. If no
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certificate was presented, status \fB403\fP (Forbidden) is returned. If the
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posted data doesn’t conform to the expected format, \fB400\fP (Bad Request) is
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returned.
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.sp
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In successful responses, the server may return a \fBReannounce\-After\fP header
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containing the number of seconds after which the client should perform a new
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announcement.
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.sp
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In error responses, the server may return a \fBRetry\-After\fP header containing
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the number of seconds after which the client should retry.
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.sp
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Performing announcements significantly more often than indicated by the
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\fBReannounce\-After\fP or \fBRetry\-After\fP headers may result in the client being
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throttled. In such cases the server may respond with status code \fB429\fP (Too
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Many Requests).
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.SH QUERIES
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.sp
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Queries are performed as HTTPS GET requests to the announce server URL. The
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requested device ID is passed as the query parameter “device”, in canonical
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string form, i.e. \fBhttps://discovery.syncthing.net/?device=ABC12345\-....\fP
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.sp
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Successful responses will have status code \fB200\fP (OK) and carry a JSON payload
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of the same format as the announcement above. The response will not contain
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empty or unspecified addresses.
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.sp
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If the “device” query parameter is missing or malformed, the status code 400
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(Bad Request) is returned.
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.sp
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If the device ID is of a valid format but not found in the registry, 404 (Not
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Found) is returned.
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.sp
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If the client has exceeded a rate limit, the server may respond with 429 (Too
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Many Requests).
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.SH AUTHENTICATION
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.sp
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Global discovery is spoken over HTTPS and is protected against attackers in
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the same manner as other HTTPS traffic. However, there are a few Syncthing
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specific considerations on top of this. As mentioned above, for
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announcements the client must provide a certificate to prove ownership of
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the announced device ID.
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.sp
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In addition, Syncthing has a mechanism to verify the identity of the
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discovery server. While this would normally be accomplished by using a CA
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signed certificate, Syncthing often runs in environments with outdated or
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simply nonexistent root CA bundles. Instead, Syncthing can verify the
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discovery server certificate fingerprint using the device ID mechanism. This
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is certificate pinning and conveyed in the Syncthing configuration as a
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synthetic “id” parameter on the discovery server URL:
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\fBhttps://discovery.syncthing.net/?id=...\fP\&. The “id” parameter is not, in
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fact, sent to the discovery server \- it’s used by Syncthing itself to know
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which certificate to expect on the server side.
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.sp
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The public discovery network uses this authentication mechanism instead of
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CA signed certificates.
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.sp
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The discovery server prints its certificate ID in this manner on startup.
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.SH AUTHOR
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The Syncthing Authors
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.SH COPYRIGHT
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2014-2019, The Syncthing Authors
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.\" Generated by docutils manpage writer.
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