# Sequence Diagram

The following sequence diagram covers the "Happy path" for the startup of a NoPorts session. When a step fails with an error, then the client halts the process, all existing connections automatically timeout and shutdown after a short period of time.

{% hint style="info" %}
To view this diagram in more detail, click `Export as PDF` in the top right corner of the page, then zoom in using the built-in browser zoom functionality.
{% endhint %}

{% @mermaid/diagram content="sequenceDiagram
participant c as client
participant cs as client atServer
participant rs as relay atServer
participant r as relay
participant ds as daemon atServer
participant d as daemon

```
note over c,d: Phase - Background services startup
par
    r ->> rs: connect
    r ->> rs: pkam authenticate
    r ->> rs: monitor for notifications
and
    d ->> ds: connect
    d ->> ds: pkam authenticate
    d ->> ds: monitor for notifications
end


note over c,d: Phase - Ping daemon
c ->> cs: connect & pkam authenticate
c ->> cs: monitor for notifications
alt
    c ->> d: ping the daemon
    activate d
else actual data flow
    c -->> cs: 
    cs -->> ds: 
    ds -->> d: 
end


note over c,d: Phase - Request relay session
alt
    c ->> r: request two public ports from relay: {session id, nonce from client}
else actual data flow
    c -->> cs: 
    cs -->> rs: 
    rs -->> r: 
end
r ->> r: Request ephemeral ports from OS
alt
    r ->> c: ports response from relay: {session id, host1:port1, host2:port2, nonce from relay}
else actual data flow
    r -->> rs: 
    rs -->> cs: 
    cs -->> c: 
end

note over c,d: Phase - Receive ping response from daemon: {list of available features}
alt
    d ->> c: ping response (device info / features) from daemon
    deactivate d
else actual data flow
    d -->> ds: 
    ds -->> cs: 
    cs -->> c: 
end
c ->> c: Validate request against daemon ping info

note over c,d: Phase - Request daemon session
c ->> c: generate new aes encryption key & iv nonce
alt
    c ->> d: send session request to the daemon: {host2:port2 from relay, aes stream encryption key, aes iv nonce, requested service to access (host:port), nonce from relay, nonce from client}
else actual data flow
    c -->> cs: 
    cs -->> ds: 
    ds -->> d: 
end
d ->> d: Verify perimissions for client's request (based on session request info - i.e. is client allowed to connect?)
d -x r: [TCP - A] Reverse TCP the requested service to open relay host2:port2
d -x r: [TCP - A] Send auth string (signed json payload of: session id, nonce from relay,  nonce from client)
r ->> r: [TCP - A] Verify auth string
alt 
    d ->> c: session (success) response from daemon
else actual data flow
    d -->> ds: 
    ds -->> cs: 
    cs -->> c: 
end
note over c,d: Phase - Client TCP connect
c ->> c: Bind a local socket to expose the service on
c -x r: [TCP - B] TCP connect to the other open relay port
c -x r: [TCP - B] Send auth string (signed json payload of: session id, nonce from relay,  nonce from client)
r ->> r: [TCP - B] Verify auth string
note over c,d: Phase - internal traffic relays (lasts  entire duration of the session)
par
    r -->> r: relay all traffic from [TCP - A] to [TCP - B] and vice-versa
and
    c -->> c: relay all traffic from [TCP - A] to local socket and vice-versa
end
note over c,d: Phase - using the connection
c ->> c: You connect to the local socket as if it were the remote service!" %}
```


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