82d66ede5e
Websockets would work, but the problem with using them for this is that each lockcontent call is a separate websocket connection. And that's an actual TCP connection. One TCP connection per file dropped would be too expensive. With http long polling, regular http pipelining can be used, so it will reuse a TCP connection. Unfortunately, at least with servant, bi-directional streams with long polling don't result in true bidirectional full duplex communication. Servant processes the whole client body stream before generating the server body stream. I think it's entirely possible to do full bi-directional communication over http, but it would need changes to servant. And, there's no way for the client to tell if the server successfully locked the content, since the server will keep processing the client stream no matter what.: So, added a new api endpoint, keeplocked. lockcontent will lock the key for 10 minutes with retention lock, and then a call to keeplocked will keep it locked for as long as needed. This does mean that there will need to be a Map of locks by key, and I will probably want to add some kind of lock identifier that lockcontent returns.
440 lines
14 KiB
Markdown
440 lines
14 KiB
Markdown
[[!toc ]]
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Draft 1 of a complete [[P2P_protocol]] over HTTP.
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## base64 encoding of keys, uuids, and filenames
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A git-annex key can contain text in any encoding. So can a filename,
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and it's even possible, though unlikely, that the UUID of a git-annex
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repository might.
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But this protocol requires that UTF-8 be used throughout, except
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where bodies use `Content-Type: application/octet-stream`.
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So, all git-annex keys, uuids, and filenames in this protocol are
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base64 encoded.
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## authentication
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A git-annex protocol endpoint can optionally operate in readonly mode without
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authentication.
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Authentication is required to make any changes.
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Authentication is done using HTTP basic auth.
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The user is recommended to only authenticate over HTTPS, since otherwise
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HTTP basic auth (as well as git-annex data) can be snooped. But some users
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may want git-annex to use HTTP in eg a LAN.
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## protocol version
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Each request in the protocol is versioned. The versions correspond
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to P2P protocol versions.
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The protocol version comes before the request. Eg: `/git-annex/v3/put`
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If the server does not support a particular protocol version, the
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request will fail with a 404, and the client should fall back to an earlier
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protocol version.
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## common request parameters
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Every request supports these common parameters, and unless documented
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otherwise, a request requires both of them to be included.
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* `clientuuid`
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The value is the UUID of the git-annex repository of the client.
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* `serveruuid`
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The value is the UUID of the git-annex repository that the server
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should serve.
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Any request may also optionally include these parameters:
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* `bypass`
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The value is the UUID of a cluster gateway, which the server should avoid
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connecting to when serving a cluster. This is the equivilant of the
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`BYPASS` message in the [[P2P_Protocol]].
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This parameter can be given multiple times to list several cluster
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gateway UUIDs.
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This parameter is only available for v2 and above.
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[Internally, git-annex can use these common parameters, plus the protocol
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version, to create a P2P session. The P2P session is driven through
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the AUTH, VERSION, and BYPASS messages, leaving the session ready to
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service requests.]
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## requests
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### GET /git-annex/key/$key
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This is a simple, unversioned interface to get a key from the server.
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It is not part of the P2P protocol per se, but is provided to let
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other clients than git-annex easily download the content of keys from the
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http server.
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This behaves almost the same as `GET /git-annex/v0/key/$key`, although its
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behavior may change in later versions.
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When the key is not present on the server, this returns a 404 Not Found.
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### GET /git-annex/v3/key/$key
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Get the content of a key from the server.
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This is designed so it can be used both by a peer in the P2P protocol,
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and by a regular HTTP client that just wants to download a file.
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Example:
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> GET /git-annex/v3/key/SHA1--foo&associatedfile=bar&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.1
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< X-git-annex-data-length: 3
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< Content-Type: application/octet-stream
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<
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< foo
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The key to get is the part of the url after "/git-annex/vN/key/"
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and before any url parameters.
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All parameters are optional, including the common parameters, and these:
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* `associatedfile`
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The name of a file in the git repository, for informational purposes
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only.
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* `offset`
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Number of bytes to skip sending from the beginning of the file.
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Request headers are currently ignored, so eg Range requests are
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not supported. (This would be possible to implement, up to a point.)
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The body of the request is empty.
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The server's response will have a `Content-Type` header of
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`application/octet-stream`.
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The server's response will have a `X-git-annex-data-length`
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header that indicates the number of bytes of content that are expected to
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be sent. Note that there is no Content-Length header.
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The body of the response is the content of the key.
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If the length of the body is different than what the the
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X-git-annex-data-length header indicated, then the data is invalid and
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should not be used. This can happen when eg, the data was being sent from
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an unlocked annexed file, which got modified while it was being sent.
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When the content is not present, the server will respond with
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422 Unprocessable Content.
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### GET /git-annex/v2/key/$key
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Identical to v3.
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### GET /git-annex/v1/key/$key
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Identical to v3.
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### GET /git-annex/v0/key/$key
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Same as v3, except there is no X-git-annex-data-length header.
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Additional checking client-side will be required to validate the data.
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### POST /git-annex/v3/checkpresent
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Checks if a key is currently present on the server.
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Example:
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> POST /git-annex/v3/checkpresent?key=SHA1--foo&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.1
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< {"present": true}
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There is one required additional parameter, `key`.
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The body of the request is empty.
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The server responds with a JSON object with a "present" field that is true
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if the key is present, or false if it is not present.
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### POST /git-annex/v2/checkpresent
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Identical to v3.
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### POST /git-annex/v1/checkpresent
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Identical to v3.
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### POST /git-annex/v0/checkpresent
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Identical to v3.
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### POST /git-annex/v3/lockcontent
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Locks the content of a key on the server, preventing it from being removed.
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Example:
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> POST /git-annex/v3/lockcontent?key=SHA1--foo&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.1
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< {"locked": true}
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There is one required additional parameter, `key`.
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The server will return `{"locked": true}` if it was able to lock the key,
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or `{"locked": false}` if it was not.
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The key will remain locked for 10 minutes. But, usually `keeplocked`
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is used to control the lifetime of the lock. (See below.)
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### POST /git-annex/v2/lockcontent
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Identical to v3.
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### POST /git-annex/v1/lockcontent
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Identical to v3.
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### POST /git-annex/v0/lockcontent
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Identical to v3.
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### POST /git-annex/v3/keeplocked
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Controls the lifetime of a lock on a key that was earlier obtained
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with `lockcontent`.
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Example:
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> POST /git-annex/v3/keeplocked?key=SHA1--foo&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.1
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> Connection: Keep-Alive
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> Keep-Alive: timeout=1200
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[some time later]
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> {"unlock": true}
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< {"locked": false}
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There is one required additional parameter, `key`.
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This uses long polling. So it's important to use
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Connection and Keep-Alive headers.
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This keeps an active lock from expiring until the client sends
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`{"unlock": true}`, and then it immediately unlocks it.
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The client can send `{"unlock": false}` any number of times first.
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This has no effect, but may be useful to keep the connection alive.
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This must be called within ten minutes of `lockcontent`, otherwise
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the lock will have already expired when this runs. Note that this
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does not indicate if the lock expired, it always returns
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`{"locked": false}`.
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If the connection is closed before the client sends `{"unlock": true},
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or even if the web server gets shut down, the content will remain
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locked for 10 minutes from the time it was first locked.
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### POST /git-annex/v2/keeplocked
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Identical to v3.
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### POST /git-annex/v1/keeplocked
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Identical to v3.
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### POST /git-annex/v0/keeplocked
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Identical to v3.
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### POST /git-annex/v3/remove
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Remove a key's content from the server.
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Example:
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> POST /git-annex/v3/remove?key=SHA1--foo&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.1
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< {"removed": true}
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There is one required additional parameter, `key`.
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The body of the request is empty.
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The server responds with a JSON object with a "removed" field that is true
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if the key was removed (or was not present on the server),
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or false if the key was not able to be removed.
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The JSON object can have an additional field "plusuuids" that is a list of
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UUIDs of other repositories that the content was removed from.
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If the server does not allow removing the key due to a policy
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(eg due to being read-only or append-only), it will respond with a JSON
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object with an "error" field that has an error message as its value.
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### POST /git-annex/v2/remove
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Identical to v3.
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### POST /git-annex/v1/remove
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Same as v3, except the JSON will not include "plusuuids".
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### POST /git-annex/v0/remove
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Identival to v1.
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## POST /git-annex/v3/remove-before
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Remove a key's content from the server, but only before a specified time.
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Example:
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> POST /git-annex/v3/remove-before?timestamp=4949292929&key=SHA1--foo&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.1
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< {"removed": true}
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This is the same as the `remove` request, but with an additional parameter,
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`timestamp`.
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If the server's monotonic clock is past the specified timestamp, the
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removal will fail and the server will respond with: `{"removed": false}`
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This is used to avoid removing content after a point in
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time where it is no longer locked in other repostitories.
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## POST /git-annex/v3/gettimestamp
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Gets the current timestamp from the server.
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Example:
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> POST /git-annex/v3/gettimestamp?clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.1
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< {"timestamp": 59459392}
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The body of the request is empty.
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The server responds with JSON object with a timestmap field that has the
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current value of its monotonic clock, as a number of seconds.
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Important: If multiple servers are serving this protocol for the same
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repository, they MUST all use the same monotonic clock.
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### POST /git-annex/v3/put
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Store content on the server.
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Example:
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> POST /git-annex/v3/put?key=SHA1--foo&associatedfile=bar&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.1
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> Content-Type: application/octet-stream
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> X-git-annex-data-length: 3
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>
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> foo
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< {"stored": true}
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There is one required additional parameter, `key`.
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There are are also these optional parameters:
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* `associatedfile`
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The name of a file in the git repository, for informational purposes
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only.
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* `offset`
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Number of bytes that have been omitted from the beginning of the file.
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Usually this will be determined by making a `putoffset` request.
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The `Content-Type` header should be `application/octet-stream`.
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The `X-git-annex-data-length` must be included. It indicates the number
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of bytes of content that are expected to be sent.
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Note that there is no need to send a Content-Length header.
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If the length of the body is different than what the the
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X-git-annex-data-length header indicated, then the data is invalid and
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should not be used. This can happen when eg, the data was being sent from
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an unlocked annexed file, which got modified while it was being sent.
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The server responds with a JSON object with a field "stored"
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that is true if it received the data and stored the
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content.
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The JSON object can have an additional field "plusuuids" that is a list of
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UUIDs of other repositories that the content was stored to.
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If the server does not allow storing the key due eg to a policy
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(eg due to being read-only or append-only), or due to the data being
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invalid, or because it ran out of disk space, it will respond with a
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JSON object with an "error" field that has an error message as its value.
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### POST /git-annex/v2/put
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Identical to v3.
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### POST /git-annex/v1/put
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Same as v3, except the JSON will not include "plusuuids".
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### POST /git-annex/v0/put
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Same as v1, except there is no X-git-annex-data-length header.
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Additional checking client-side will be required to validate the data.
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### POST /git-annex/v3/putoffset
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Asks the server what `offset` can be used in a `put` of a key.
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This should usually be used right before sending a `put` request.
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The offset may not be valid after some point in time, which could result in
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the `put` request failing.
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Example:
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> POST /git-annex/v3/putoffset?key=SHA1--foo&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.1
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< {"offset": 10}
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There is one required additional parameter, `key`.
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The body of the request is empty.
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The server responds with a JSON object with an "offset" field that
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is the largest allowable offset.
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If the server already has the content of the key, it will respond with a
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JSON object with an "alreadyhave" field that is set to true. This JSON
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object may also have a field "plusuuids" that lists
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the UUIDs of other repositories where the content is stored, in addition to
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the serveruuid.
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If the server does not allow storing the key due to a policy
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(eg due to being read-only or append-only), it will respond with a JSON
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object with an "error" field that has an error message as its value.
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[Implementation note: This will be implemented by sending `PUT` and
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returning the `PUT-FROM` offset. To avoid leaving the P2P protocol stuck
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part way through a `PUT`, a synthetic empty `DATA` followed by `INVALID`
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will be used to get the P2P protocol back into a state where it will accept
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any request.]
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### POST /git-annex/v2/putoffset
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Identical to v3.
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### POST /git-annex/v1/putoffset
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Same as v3, except the JSON will not include "plusuuids".
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## parts of P2P protocol that are not supported over HTTP
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`NOTIFYCHANGE` is not supported, but it would be possible to extend
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this HTTP protocol to support it.
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`CONNECT` is not supported, and due to the bi-directional message passing
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nature of it, it cannot easily be done over HTTP (would need websockets).
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It should not be necessary anyway, because the git repository itself can be
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accessed over HTTP.
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