Add script to update Transmission peer port

Dockerfile

@@ -224,6 +224,7 @@ ENV VPN_SERVICE_PROVIDER=pia \
 ENTRYPOINT ["/gluetun-entrypoint"]
 EXPOSE 8000/tcp 8888/tcp 8388/tcp 8388/udp
 HEALTHCHECK --interval=5s --timeout=5s --start-period=10s --retries=3 CMD /gluetun-entrypoint healthcheck
+COPY extras/scripts/transmission-port-update.sh /scripts/transmission-port-update.sh
 ARG TARGETPLATFORM
 RUN apk add --no-cache --update -l wget && \
     apk add --no-cache --update -X "https://dl-cdn.alpinelinux.org/alpine/v3.17/main" openvpn\~2.5 && \

extras/scripts/transmission-port-update.sh

@@ -0,0 +1,132 @@
+#!/bin/sh
+
+# Description: This script updates the peer port for the Transmission torrent
+# client using its RPC API.
+# Author: Juan Luis Font
+
+# default values
+DEFAULT_URL="http://localhost:9091/transmission/rpc"
+WGET_OPTS="--quiet"
+
+usage() {
+    echo "Usage: $0 [OPTIONS]"
+    echo ""
+    echo "Update Transmission peer-port via RPC API"
+    echo ""
+    echo "Options:"
+    echo "  -h, --help       Show this help message and exit."
+    echo "  -u, --user USER  Specify the Transmission RPC user name."
+    echo "                   (Omit if not required)"
+    echo "  -p, --pass PASS  Specify the Transmission RPC password."
+    echo "                   (Omit if not required)"
+    echo "  -P, --port PORT  Specify the Transmission Peer Port."
+    echo "                   If PORT is a comma-separated list of ports,"
+    echo "                   only use the first one."
+    echo "                   REQUIRED"
+    echo "  -U, --url  URL   Specify the Transmission RPC URL."
+    echo "                   DEFAULT: ${DEFAULT_URL}"
+    echo "Example:"
+    echo "  $0 -u admin -p **** 40409"
+}
+
+while [ $# -gt 0 ]; do
+    case "$1" in
+    -h | --help)
+        usage
+        exit 0
+        ;;
+    -u | --user)
+        USERNAME="$2"
+        _USECRED=true
+        shift 2
+        ;;
+    -p | --pass)
+        PASSWORD="$2"
+        _USECRED=true
+        shift 2
+        ;;
+    -P | --port)
+        PORTS="$2"
+        PORT=$(echo "$PORTS" | cut -d',' -f1)
+        shift 2
+        ;;
+    -U | --url)
+        RPC_URL="$2"
+        shift 2
+        ;;
+    *)
+        echo "Unknown option: $1"
+        usage
+        exit 1
+        ;;
+    esac
+done
+
+if [ -z "${PORT}" ]; then
+    echo "ERROR: No Transmission peer-port provided!"
+    exit 1
+fi
+
+if [ "${_USECRED}" ]; then
+    # make sure username AND password were provided
+    if [ -z "${USERNAME}" ]; then
+        echo "ERROR: Transmission RPC Username not provided."
+        exit 1
+    fi
+    if [ -z "${PASSWORD}" ]; then
+        echo "ERROR: Transmission RPC Password not provided."
+        exit 1
+    fi
+    # basic auth options, --auth-no-challenge avoids 409 Conflict
+    WGET_OPTS="
+            ${WGET_OPTS}
+            --auth-no-challenge
+            --user=${USERNAME}
+            --password=${PASSWORD}
+        "
+fi
+
+if [ -z "${RPC_URL+x}" ]; then
+    RPC_URL="${DEFAULT_URL}"
+fi
+
+# get the X-Transmission-Session-Id
+# shellcheck disable=SC2086
+SESSION_ID=$(
+    wget \
+        ${WGET_OPTS} \
+        --server-response \
+        "$RPC_URL" 2>&1 |
+        grep 'X-Transmission-Session-Id:' |
+        awk '{print $2}'
+)
+
+# generate payload string
+PAYLOAD=$(printf '{
+  "method": "session-set",
+  "arguments": {
+    "peer-port": %s
+  }
+}' "$PORT")
+
+# update peer host via API
+# shellcheck disable=SC2086
+RES=$(
+    wget \
+        ${WGET_OPTS} \
+        --header="Content-Type: application/json" \
+        --header="X-Transmission-Session-Id: $SESSION_ID" \
+        --post-data="${PAYLOAD}" \
+        "$RPC_URL" \
+        -O -
+)
+
+# check string returned by wget
+SUCCESS='{"arguments":{},"result":"success"}'
+if [ "$RES" != "$SUCCESS" ]; then
+    echo "ERROR: Could not update Transmission peer-port"
+    exit 1
+fi
+
+echo "Success! Transmission peer-port updated to ${PORT}"
+exit 0