[[!toc ]] Draft 1 of a complete [[P2P_protocol]] over HTTP. ## git-annex protocol endpoint and version The git-annex protocol endpoint is "/git-annex" appended to the HTTP url of a git remote. ## authentication A git-annex protocol endpoint can optionally operate in readonly mode without authentication. Authentication is required to make any changes. Authentication is done using HTTP basic auth. The user is recommended to only authenticate over HTTPS, since otherwise HTTP basic auth (as well as git-annex data) can be snooped. But some users may want git-annex to use HTTP in eg a LAN. ## protocol version Each request in the protocol is versioned. The versions correspond to P2P protocol versions, but for simplicity, the minimum version supported over HTTP is version 2. Every implementation of the HTTP protocol must support version 2. The protocol version comes before the request. Eg: `/git-annex/v2/put` If the server does not support a particular protocol version, the request will fail with a 404, and the client should fall back to an earlier protocol version, eg version 2. ## common request parameters Every request has some common parameters that are always included: * `clientuuid` The value is the UUID of the git-annex repository of the client. * `serveruuid` The value is the UUID of the git-annex repository that the server should serve. Any request may also optionally include these parameters: * `bypass` The value is the UUID of a cluster gateway, which the server should avoid connecting to when serving a cluster. This is the equivilant of the `BYPASS` message in the [[P2P_Protocol]]. This parameter can be given multiple times to list several cluster gateway UUIDs. [Internally, git-annex can use these common parameters, plus the protocol version, to create a P2P session. The P2P session is driven through the AUTH, VERSION, and BYPASS messages, leaving the session ready to service requests.] ## request messages All the requests below are sent with the HTTP POST method. ### checkpresent Checks if a key is currently present on the server. Example: > POST /git-annex/v2/checkpresent?key=SHA1--foo&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.1 < SUCCESS There is one required additional parameter, `key`. The body of the request is empty. The server responds with "SUCCESS" if the key is present or "FAILURE" if it is not present. ### lockcontent Locks the content of a key on the server, preventing it from being removed. There is one required additional parameter, `key`. This request opens a websocket between the client and the server. The server sends "SUCCESS" over the websocket once it has locked the content. Or it sends "FAILURE" if it is unable to lock the content. Once the server has sent "SUCCESS", the content remains locked as long as the client remains connected to the websocket. When the client disconnects, or closes the websocket, the server unlocks the content. XXX What happens if the connection times out? Will the client notice that in time? How does this work with P2P over ssh? ### remove Remove a key's content from the server. Example: > POST /git-annex/v2/remove?key=SHA1--foo&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.1 < SUCCESS There is one required additional parameter, `key`. The body of the request is empty. The server responds with "SUCCESS" if the key was removed, or "FAILURE" if the key was not able to be removed. The server can also respond with "SUCCESS-PLUS" or "FAILURE-PLUS". Each has a subsequent list of UUIDs of repositories that the content was removed from. For example: SUCCESS-PLUS 702ce472-38a1-11ef-864f-23851a2edf71 707dea20-38a1-11ef-96a4-fb7e8c8369f0 If the server was prevented from trying to remove the key due to a policy (eg due to being read-only or append-only, it will respond with "ERROR", followed by a space and an error message. ### put Store content on the server. Example: > POST /git-annex/v2/put?key=SHA1--foo&associatedfile=bar&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.1 > Content-Type: application/octet-stream > Content-Length: 4 > foo1 < SUCCESS There is one required additional parameter, `key`. There is are also these optional parameters: * `associatedfile` The name of a file in the git repository, for informational purposes only. * `offset` Number of bytes that have been omitted from the beginning of the file. Usually this will be determined by making a `putoffset` request. The body of the request is the content of the key, starting from the specified offset or from the beginning. After the content of the key, there is one more byte. The additional byte is "1" to indicate that the content was not changed while it was being sent, or "0" to indicate that modified content was sent and should be disregarded by the server. (This corresponds to the `VALID` and `INVALID` messages in the P2P protocol.) The `Content-Type` header should be `application/octet-stream`. The `Content-Length` header should be set to the length of the body. The server responds with `SUCCESS` if it received the data and stored the content. If it was unable to do so, it responds with `FAILURE`. The server can also reply with `SUCCESS-PLUS`, which has a subsequent list of UUIDs of repositories that the content was stored to. For example: SUCCESS-PLUS 702ce472-38a1-11ef-864f-23851a2edf71 707dea20-38a1-11ef-96a4-fb7e8c8369f0 If the server was prevented from storing the key due to a policy (eg due to being read-only), it will respond with "ERROR", followed by a space and an error message. ### putoffset Asks the server what `offset` can be used in a `put` of a key. This should usually be used right before sending a `put` request. The offset may not be valid after some point in time, which could result in the `put` request failing. Example: > POST /git-annex/v2/putoffset?key=SHA1--foo&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.1 < 10 There is one required additional parameter, `key`. The body of the request is empty. The server responds with the largest allowable offset. If the server was prevented from storing the key due to a policy (eg due to being read-only), it will respond with "ERROR", followed by a space and an error message. [Implementation note: This will be implemented by sending `PUT` and returning the `PUT-FROM` offset. To avoid leaving the P2P protocol stuck part way through a `PUT`, a synthetic empty `DATA` followed by `INVALID` will be used to get the P2P protocol back into a state where it will accept any request.] ### get Get content from the server. Example: > POST /git-annex/v2/get?key=SHA1--foo&associatedfile=bar&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.1 < Content-Type: application/octet-stream < Content-Length: 4 < foo1 There is one required additional parameter, `key`. There is are also these optional parameters: * `associatedfile` The name of a file in the git repository, for informational purposes only. * `offset` Number of bytes to skip sending from the beginning of the file. The body of the request is empty. The server's response will have a `Content-Type` header of `application/octet-stream`. The server's response will have a `Content-Length` header set to the length of the body. The server's response body is the content of the key, from the specified offset. After the content of the key, there is one more byte. The additional byte is "1" to indicate that the content was not changed while it was being sent, or "0" to indicate that modified content was sent and should be discarded by the client. (This corresponds to the `VALID` and `INVALID` messages in the P2P protocol.) Note that, if the server is not able to send the content of the requested key, its response body will consist of "0", eg 0 bytes of content which is not valid. On the other hand, a response body of "1" is used for an empty key which is valid. ## simple HTTP GET The git-annex protocol endpoint also supports a regular HTTP get of a key. This is not part of the P2P protocol, but is provided for convenience, to allow other clients than git-annex to easily download the content of a key. > GET /git-annex/key/SHA1--foo HTTP/1.1 < Content-Type: application/octet-stream < Content-Length: 3 < foo ## parts of P2P protocol that are not supported over HTTP `NOTIFYCHANGE` is not supported, but it would be possible to extend this HTTP protocol to support it. `CONNECT` is not supported, and due to the bi-directional message passing nature of it, it cannot easily be done over HTTP. It should not be necessary anyway, because the git repository itself can be accessed over HTTP.