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drafting P2P protocol over http

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Joey Hess 2024-07-02 16:14:45 -04:00
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@ -201,6 +201,9 @@ was being sent.
The client replies with SUCCESS or FAILURE. The client replies with SUCCESS or FAILURE.
Note that the client responding with SUCCESS does not indicate to the
server that it has stored the content. It may receive it and throw it away.
## Connection to services ## Connection to services
This is used to connect to services like git-upload-pack and This is used to connect to services like git-upload-pack and

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@ -72,20 +72,31 @@ needs to know that a series of requests are part of the same P2P protocol
session. In the example above, it would not have a good way to do that. session. In the example above, it would not have a good way to do that.
One solution would be to add a session identifier UUID to each request. One solution would be to add a session identifier UUID to each request.
## approach 2: HTTP API ## approach 2: websockets
The client connects to the server over a websocket. From there on,
the protocol is encapsulated in websockets.
This seems nice and simple, but again not very web native.
Some requests like `LOCKCONTENT` seem likely to need full duplex
communication like websockets provide. But, it might be more web native to
only use websockets for that request, and not for everything.
## approach 3: HTTP API
Another approach is to define a web-native API with endpoints that Another approach is to define a web-native API with endpoints that
correspond to each action in the P2P protocol. correspond to each action in the P2P protocol.
Something like this: Something like this:
> GET /git-annex/v1/AUTH?clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925 HTTP/1.0 > POST /git-annex/v1/AUTH?clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925 HTTP/1.0
< AUTH-SUCCESS ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 < AUTH-SUCCESS ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6
> GET /git-annex/v1/CHECKPRESENT?key=SHA1--foo&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.0 > POST /git-annex/v1/CHECKPRESENT?key=SHA1--foo&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.0
> SUCCESS > SUCCESS
> GET /git-annex/v1/PUT-FROM?key=SHA1--foo&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.0 > POST /git-annex/v1/PUT-FROM?key=SHA1--foo&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.0
< PUT-FROM 0 < PUT-FROM 0
> POST /git-annex/v1/PUT?key=SHA1--foo&associatedfile=bar&put-from=0&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.0 > POST /git-annex/v1/PUT?key=SHA1--foo&associatedfile=bar&put-from=0&clientuuid=79a5a1f4-07e8-11ef-873d-97f93ca91925&serveruuid=ecf6d4ca-07e8-11ef-8990-9b8c1f696bf6 HTTP/1.0
@ -102,6 +113,8 @@ This needs a more complex spec. But it's easier for others to implement,
especially since it does not need a session identifier, so the HTTP server can especially since it does not need a session identifier, so the HTTP server can
be stateless. be stateless.
A full draft protocol for this is being developed at [[p2p_protocol_over_http/draft1]].
## HTTP GET ## HTTP GET
It should be possible to support a regular HTTP get of a key, with It should be possible to support a regular HTTP get of a key, with
@ -122,4 +135,11 @@ The CONNECT message allows both sides of the P2P protocol to send DATA
messages in any order. This seems difficult to encapsulate in HTTP. messages in any order. This seems difficult to encapsulate in HTTP.
Probably this can be not implemented, it's probably not needed for a HTTP Probably this can be not implemented, it's probably not needed for a HTTP
remote? remote? This is used to tunnel git protocol over the P2P protocol, but for
a HTTP remote the git repository can be accessed over HTTP as well.
## security
Should support HTTPS and/or be limited to only HTTPS.
Authentication via http basic auth?

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@ -0,0 +1,273 @@
[[!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.