cap total connections, and document the P2P port 8444

The daemon has always listened on 8444 and nothing published it, so every
node built from this image was outbound-only. Publishing it is now a
documented choice rather than an omission -- including the two things that
are not obvious from the config: peers are told the port from `port` in
keys.dat rather than the one you mapped it to (so only 8444:8444 works),
and the node's own address is never configured at all, because every peer
replaces the hardcoded 127.0.0.1 in the version message with the IP it
sees on the socket.

An open port needs a brake, hence BITMESSAGE_MAXTOTALCONNECTIONS. It
defaults to the PyBitmessage stock 200, so nothing changes for existing
users of the image. The key is inserted when the stock config lacks it
instead of trusting the substitution: the PyBitmessage clone is unpinned,
and a silent no-op would ship a node that looks capped and is not.

The API port in the example compose moves to loopback, which is what the
README already prescribed.

docker/Dockerfile

@@ -45,7 +45,11 @@ RUN f=/usr/local/lib/python2.7/dist-packages/pybitmessage/helper_sql.py \
 
 FROM ubuntu:bionic
 
+# 8442 is the XML-RPC API (keep it on loopback), 8444 the Bitmessage P2P port.
+# The daemon listens on both regardless; publishing 8444 is what makes the node
+# reachable for inbound peers.
 EXPOSE 8442/tcp
+EXPOSE 8444/tcp
 
 ENV USER_UID=2000
 ENV USER_GID=2000

docker/run.sh

@@ -9,6 +9,18 @@ export BITMESSAGE_API_PORT="${BITMESSAGE_API_PORT:-8442}"
 export BITMESSAGE_TTL="${BITMESSAGE_TTL:-172800}"
 export BITMESSAGE_STOPRESENDINGAFTERXDAYS="${BITMESSAGE_STOPRESENDINGAFTERXDAYS:-30}"
 export BITMESSAGE_APIVARIANT="${BITMESSAGE_APIVARIANT:-legacy}"
+export BITMESSAGE_MAXTOTALCONNECTIONS="${BITMESSAGE_MAXTOTALCONNECTIONS:-200}"
+
+# Reject anything but a plain number: this value is written into keys.dat, and
+# unlike the credentials below it has no business containing characters that
+# esc() would have to neutralise. A typo here would otherwise land in the config
+# as a key the daemon silently ignores.
+case "$BITMESSAGE_MAXTOTALCONNECTIONS" in
+	'' | *[!0-9]*)
+		echo "BITMESSAGE_MAXTOTALCONNECTIONS must be a positive integer" >&2
+		exit 1
+		;;
+esac
 
 if [ -z "${BITMESSAGE_SEED_PHRASE:-}" ]
 then
@@ -32,6 +44,18 @@ then
 	chmod 600 keys.dat
 fi
 
+# maxtotalconnections is the only brake on a node whose P2P port (8444) is
+# published: it caps inbound sockets at the total minus maxoutboundconnections.
+# The substitution below is a no-op when the key is missing, which would ship a
+# node that looks capped and is not -- and the PyBitmessage clone in the
+# Dockerfile is unpinned, so the stock config is whatever upstream generates
+# today. Add the key rather than trust the substitution alone; line 1 is the
+# [bitmessagesettings] header the daemon reads it from.
+if ! grep -q "^maxtotalconnections = " keys.dat
+then
+	gosu bitmessage sed -i "1a maxtotalconnections = $BITMESSAGE_MAXTOTALCONNECTIONS" keys.dat
+fi
+
 # Set config values. Every expression is anchored to the start of the line and
 # names its key in the replacement, so no backreference is involved and nothing
 # in another section can match. With set -e a failure here now stops the
@@ -46,6 +70,7 @@ gosu bitmessage sed -i \
 	-e "s|^apienabled = .*|apienabled = True|" \
 	-e "s|^ttl = .*|ttl = $(esc "$BITMESSAGE_TTL")|" \
 	-e "s|^stopresendingafterxdays = .*|stopresendingafterxdays = $(esc "$BITMESSAGE_STOPRESENDINGAFTERXDAYS")|" \
+	-e "s|^maxtotalconnections = .*|maxtotalconnections = $BITMESSAGE_MAXTOTALCONNECTIONS|" \
 	-e "s|^udp = .*|udp = False|" keys.dat
 
 # generate address from seed