Add a launcher script to use a config file from a user writeable

area in the home directory. It will also copy the example config
in to the same location so that people can use it as a reference.

snap/default_config.conf

@@ -0,0 +1,2 @@
+port 1883
+persistence false

snap/launcher.sh

@@ -0,0 +1,31 @@
+#!/bin/sh
+# Wrapper to check for custom config in $SNAP_USER_COMMON and use it
+# otherwise fall back to the included basic config which will at least
+# allow mosquitto to run and do something.
+# This script will also copy the full example config in to SNAP_USER_COMMON
+# so that people can refer to it.
+
+CONFIG_FILE="$SNAP/default_config.conf"
+CUSTOM_CONFIG="$SNAP_USER_COMMON/mosquitto.conf"
+
+
+# Copy the example config if it doesn't exist
+if [ ! -e "$SNAP_USER_COMMON/mosquitto_example.conf" ]
+then
+  echo "Copying example config to $SNAP_USER_COMMON/mosquitto_example.conf"
+  echo "You can create a custom config by creating a file called $CUSTOM_CONFIG"
+  cp $SNAP/mosquitto.conf $SNAP_USER_COMMON/mosquitto_example.conf
+fi
+
+
+# Does the custom config exist?  If so use it.
+if [ -e "$CUSTOM_CONFIG" ]
+then
+  echo "Found config in $CUSTOM_CONFIG"
+  CONFIG_FILE=$CUSTOM_CONFIG
+else
+  echo "Using default config from $CONFIG_FILE"
+fi
+
+# Launch the snap
+$SNAP/usr/local/sbin/mosquitto -c $CONFIG_FILE $@

snap/mosquitto.conf

@@ -1,3 +0,0 @@
-port 1883
-persistence true
-user root

snap/snapcraft.yaml

@@ -9,10 +9,11 @@ description: This is a message broker that supports version 3.1 and 3.1.1 of the
     where a sensor or other simple device may be implemented using an arduino for
     example.
 confinement: strict
+grade: stable
 
 apps:
   mosquitto:
-    command: usr/local/sbin/mosquitto -c $SNAP/mosquitto.conf
+    command: launcher.sh
     daemon: simple
     restart-condition: always
     plugs: [network, network-bind]
@@ -23,7 +24,14 @@ parts:
     plugin: dump
     source: snap/
     prime:
-    - mosquitto.conf
+      - default_config.conf
+      - launcher.sh
+  config:
+    plugin: dump
+    source: .
+    prime:
+      - mosquitto.conf
+
 
 
   mosquitto:
@@ -42,8 +50,7 @@ parts:
       - libuuid1
       - libc-ares2
     prime:
-    - usr/local/sbin/mosquitto
-    - lib/*-linux-gnu/libcrypto.so*
-    - lib/*-linux-gnu/libssl.so*
-    - lib/*-linux-gnu/libuuid.so*
-
+      - usr/local/sbin/mosquitto
+      - lib/*-linux-gnu/libcrypto.so*
+      - lib/*-linux-gnu/libssl.so*
+      - lib/*-linux-gnu/libuuid.so*