Bisecting dashed curved lines ala Threat Model - graphviz

Question

Is there a way to add a curved dash line similar to the one present here for Privilege Boundaries? I'd like to have a threat model checked into GIT that is procedurally generated as part of my CI/CD builds as apposed to drawing it online or in some tool like OmniGraffle and exporting image only to loose the original docs.

Answer 1

You can get fairly close by adding some extra edges and invisible nodes and using attribute for extra edge arrowhead=icurve, but it will not be a dashed line. Graphviz allows you to draw dashed cluster boundaries, or dashed edges from node to node, but the perpendicular line to the one or two edges will be impossible to draw without manual positioning, as you drawing it online, and as I assume you need to draw without human involvement.
Also with some extra effort with PostScript you can create half-drawn nodes with dashed border like A -> Internet Boundary [shape=yourshape color=red] -> B, but this is also not actually a line crossing.
Image:
and script for arrowhead=icurve variant:
digraph threat_model {
graph [
splines=false
ranksep=0
nodesep=2]
User [shape=box xlabel=<<FONT COLOR="ORANGE"><B>Actor</B></FONT>>]
a [shape=circle label=<<FONT><B>a. Static<BR/>front-end<BR/>files</B></FONT>> xlabel=<<FONT COLOR="ORANGE"><B>Process</B></FONT>>]
b [shape=circle label=<<FONT><B>b. App<BR/>back-end</B></FONT>> xlabel=<<FONT COLOR="ORANGE"><B>Data<BR/>Flow</B></FONT>>]
// Two extra nodes:
boundary_User_b_1 [shape=point height=.01]
boundary_User_b_2 [shape=point height=.01]
User -> a [minlen=3 dir=both xlabel="1. Retrieve static\nfront-end files"]
// Three extra edges:
User -> boundary_User_b_1 [minlen=3 dir=back xlabel="2. Modify report"]
boundary_User_b_1 -> boundary_User_b_2 [arrowhead=icurve arrowsize=6 color=red headlabel=<<FONT COLOR="RED">Internet<BR/>Boundary</FONT>>]
boundary_User_b_2 -> b [minlen=3]
}
Another fairly close variant using cluster, note that the arrow can rest against boundary, with the compound=true attribute for graph and lhead attribute for arrow:
digraph {
graph[
ranksep=1
compound=true
]
A
B
subgraph cluster_IB {
graph [
label="Internet Boundary"
fontcolor=red
margin=20
style="dashed, rounded"
color=red
]
C
}
A -> C
B -> C [lhead="cluster_IB"]
}