This largely copies over Spicy's `.clang-format` configuration file. The
one place where we deviate is header include order since Zeek depends on
headers being included in a certain order.
Conceptually, a TCP-based application analyzer should not need any
knowledge about the underlying TCP analysis; it's supposed to just
process its reassembled input stream as it's handed over. But our
analyzers break that assumption at a few places because sometimes
knowledge about the TCP state of the connection can be helpful for
heuristics. This is fine as long as there actually *is* a TCP parent
analyzer available. Sometimes, however, there isn't: if the payload
stream is encapsulated inside another application-layer protocol, the
semantic link to TCP is broken. And if the outer connection is even
UDP, then we don't have a TCP analyzer at all.
We didn't handle this situation well so far. Most analyzers needing
TCP state would just crash if there's no TCP analyzer (in debug mode
with an `assert`, in release mode with a null pointer deref ...). Only
HTTP did the right thing already: check if TCP is available and adapt
accordingly.
We know extend that check to all other analyzers as well: all accesses
to `TCP()` are guarded, with reasonable defaults if not available.
It's actually a pretty small change overall, which is evidence for how
little this layering violation actually matters.
The existing behavior is what's causing
https://github.com/corelight/zeek-spicy-openvpn/issues/3.
This enables locating the headers within the install-tree using the
dirs provided by `zeek-config --include_dir`.
To enable locating these headers within the build-tree, this change also
creates a 'build/src/include/zeek -> ..' symlink.
