Update healthcheck script to handle alternate base dir

docker/healthcheck.sh

@@ -1,8 +1,52 @@
-#!/usr/bin/env sh
+#!/bin/sh
 
-if [ -z "$ROCKET_TLS"]
-then
-  curl --fail http://localhost:${ROCKET_PORT:-"80"}/alive || exit 1
-else
-  curl --insecure --fail https://localhost:${ROCKET_PORT:-"80"}/alive || exit 1
+# Use the value of the corresponding env var (if present),
+# or a default value otherwise.
+: ${DATA_FOLDER:="data"}
+: ${ROCKET_PORT:="80"}
+
+CONFIG_FILE="${DATA_FOLDER}"/config.json
+
+# Given a config key, return the corresponding config value from the
+# config file. If the key doesn't exist, return an empty string.
+get_config_val() {
+    local key="$1"
+    # Extract a line of the form:
+    #   "domain": "https://bw.example.com/path",
+    grep "\"${key}\":" "${CONFIG_FILE}" |
+    # To extract just the value (https://bw.example.com/path), delete:
+    # (1) everything up to and including the first ':',
+    # (2) whitespace and '"' from the front,
+    # (3) ',' and '"' from the back.
+    sed -e 's/[^:]\+://' -e 's/^[ "]\+//' -e 's/[,"]\+$//'
+}
+
+# Extract the base path from a domain URL. For example:
+# - `` -> ``
+# - `https://bw.example.com` -> ``
+# - `https://bw.example.com/` -> ``
+# - `https://bw.example.com/path` -> `/path`
+# - `https://bw.example.com/multi/path` -> `/multi/path`
+get_base_path() {
+    echo "$1" |
+    # Delete:
+    # (1) everything up to and including '://',
+    # (2) everything up to '/',
+    # (3) trailing '/' from the back.
+    sed -e 's|.*://||' -e 's|[^/]\+||' -e 's|/*$||'
+}
+
+# Read domain URL from config.json, if present.
+if [ -r "${CONFIG_FILE}" ]; then
+    domain="$(get_config_val 'domain')"
+    if [ -n "${domain}" ]; then
+        # config.json 'domain' overrides the DOMAIN env var.
+        DOMAIN="${domain}"
+    fi
 fi
+
+base_path="$(get_base_path "${DOMAIN}")"
+if [ -n "${ROCKET_TLS}" ]; then
+    s='s'
+fi
+curl --insecure --fail "http${s}://localhost:${ROCKET_PORT}${base_path}/alive" || exit 1