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connections/simopen: Prefix fake protocol ID with a '/' #321

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Apr 27, 2021
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connections/simopen: Prefix fake protocol ID with a '/' #321

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54 changes: 27 additions & 27 deletions connections/simopen.md
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Original file line number Diff line number Diff line change
Expand Up @@ -32,21 +32,21 @@ acting as such.

## The Protocol

When a peer acting as the initiator enters protocol negotiation, it
sends the string `iamclient` as first protocol selector. If the other
peers is a responder or doesn't support the extension, then it
responds with `na` and protocol negotiation continues as normal.
When a peer acting as the initiator enters protocol negotiation, it sends the
string `/libp2p/simultaneous-connect` as first protocol selector. If the other
peers is a responder or doesn't support the extension, then it responds with
`na` and protocol negotiation continues as normal.

If both peers believe they are the initiator, then they both send
`iamclient`. If this is the case, they enter an initiator selection
phase, where one of the peers is selected to act as the initiator. In
order to do so, they both generate a random 256-bit integer and send
it as response to the `iamclient` directive, prefixed with the
`select:` string. The integer is in big-endian format, encoded in base64.
The peer with the highest integer is selected to act
as the initator and sends an `initiator` message. The peer with the
lowest integer responds with `responder` message and both peers
transition to protocol negotiation with a distinct initiator.
`/libp2p/simultaneous-connect`. If this is the case, they enter an initiator
selection phase, where one of the peers is selected to act as the initiator. In
order to do so, they both generate a random 256-bit integer and send it as
response to the `/libp2p/simultaneous-connect` directive, prefixed with the
`select:` string. The integer is in big-endian format, encoded in base64. The
peer with the highest integer is selected to act as the initator and sends an
`initiator` message. The peer with the lowest integer responds with `responder`
message and both peers transition to protocol negotiation with a distinct
initiator.

Note the importance of the prefix in the random integer, as it allows
peers to match the selection token and ignore potentially pipelined
Expand All @@ -56,8 +56,8 @@ The following schematic illustrates, for the case where A's integer is
higher than B's integer:

```
A ---> B: iamclient
B ---> A: iamclient
A ---> B: /libp2p/simultaneous-connect
B ---> A: /libp2p/simultaneous-connect
A: generate random integer IA
B: generate random integer IB
A ---> B: select:{IA}
Expand All @@ -73,17 +73,17 @@ indicative of a bug and both peers should abort the connection.

## Implementation Considerations

The protocol is simple to implement and is backwards compatible with
vanilla multistream-select. An important consideration is avoiding RTT
overhead in the common case of a single initiator. In this case, the
initiator pipelines the security protocol negotiation together with the
selection, sending `multistream,iamclient,secproto`. If the receiving
peer is a responder, then it replies with `multistream,na,secproto`,
negotiating the security protocol without any overhead.
The protocol is simple to implement and is backwards compatible with vanilla
multistream-select. An important consideration is avoiding RTT overhead in the
common case of a single initiator. In this case, the initiator pipelines the
security protocol negotiation together with the selection, sending
`multistream,/libp2p/simultaneous-connect,secproto`. If the receiving peer is a
responder, then it replies with `multistream,na,secproto`, negotiating the
security protocol without any overhead.

If the peer is also a client, then it also sends
`multistream,iamclient,secproto`. On seeing the `iamclient` message,
both peers enter the initiator selection protocol and ignore the
`secproto` in the original packet. They can do so because the random
integer is prefixed with the `select:` string, allowing peers to match
the selection and ignore pipelined protocols.
`multistream,/libp2p/simultaneous-connect,secproto`. On seeing the
`/libp2p/simultaneous-connect` message, both peers enter the initiator selection
protocol and ignore the `secproto` in the original packet. They can do so
because the random integer is prefixed with the `select:` string, allowing peers
to match the selection and ignore pipelined protocols.