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+#import "/common.typ": post
+
+#show: post.with(
+    title: "schachtmeister2",
+    date: datetime(year: 2020, month: 8, day: 15),
+)
+
+`schachtmeister2` is a daemon for white- and blacklisting specified ISPs, hosting providers and so on. It was created for the Der Bunker Tremulous server to combat malicious players evading bans.
+
+The source code is available #link("https://redman.xyz/git/schachtmeister2")[here].
+
+The daemon works by looking up a given IP address in WHOIS databases and reverse DNS records and analyzing the results. Its configuration file, `schachts.list`, is a list of keywords to be searched for along with a *partial rating*. The program's output, the *rating*, is the sum of partial ratings of all matched keywords.
+
+= Usage
+
+Since the daemon is meant to be used with a Tremulous server, it communicates over UDP. The protocol is extremely simple. To query `schachtmeister2` send an UDP packet (port 1337) that looks like:
+
+```
+\xff\xff\xff\xffsm2query ADDRESS
+```
+
+Note the four leading `0xFF` bytes. The daemon will send a reply to the sender's address and port that will look like:
+
+```
+\xff\xff\xff\xffsm2reply ADDRESS RATING
+```
+
+Here's an example using BSD's netcat, asking for the rating of `8.8.8.8` (Google's DNS):
+
+```
+$ printf "\xff\xff\xff\xffsm2query 8.8.8.8" | nc -u 127.0.0.1 1337
+����sm2reply 8.8.8.8 0
+```
+
+= The list
+
+The daemon needs a list of keywords to operate meaningfully. The program looks for a file named `schachts.list` in its working directory. Below is an example list:
+
+```
+// a few known VPS and VPN providers
+revdns	-50	tcpvpn.com
+revdns	-50	vultr.com
+
+whois	-50	"OVH"
+whois	-50	"DigitalOcean"
+whois	-50	"Digital Ocean"
+
+// Desala's ISP
+revdns	-10	.dynamic.chello.pl
+```
+
+The columns are:
+
+- Where to look for the substring: `revdns` or `whois`?
+- The partial rating or how much the total rating changes if this substring is found.
+- The substring to look for. Use quotation marks if you need spaces. The program does not support regular expressions yet.
+
+Whitespace doesn't matter but I recommend tabs for proper alignment. You can use C++-style one-line comments.
+
+= Reloading on the fly
+
+Restarting the daemon clears its cache, so you might want to avoid it. To make `schachtmeister2` reload the list, send `SIGUSR1` to the process.
+
+= Limitations
+
+This is one of those programs that I've written quickly, as crude prototypes, but have worked exceedingly well.  As I couldn't be bothered to rewrite the program better, it's not very flexible and works well only in a single application. I might continue working on it if there's demand outside of Tremulous.