Add user-readable error for missing DB mount dir

src/modules/fs_utils.fnl

@@ -0,0 +1,22 @@
+;; modules/fs_utils.fnl
+;; Provides a collection of utilities for performing some filesystem operations
+
+;; -------------------------------------------------------------------------- ;;
+;; Module definition
+
+(local fs_utils {})
+
+(fn fs_utils.path_exists? [path]
+  "Return true if `path` exists and is accessible.
+Note that this misuses os.rename in order to check `path`-- mightn't want to touch anything important with this..."
+  (let [(ok? _) (os.rename path path)]
+    ok?))
+
+(fn fs_utils.dir_exists? [path]
+  "Return true if `path` is a directory and is accessible."
+  (fs_utils.path_exists? (.. path "/")))
+
+;; -------------------------------------------------------------------------- ;;
+;; Return module
+
+fs_utils

src/modules/links_db.fnl

@@ -8,6 +8,11 @@
 (local lume (require :lume))
 (local sqlite (require :sqlite))
 
+;; -------------------------------------------------------------------------- ;;
+;; Local modules
+
+(local fs_utils (require :modules.fs_utils))
+
 ;; -------------------------------------------------------------------------- ;;
 ;; Constants
 
@@ -39,6 +44,16 @@ ORDER BY created DESC")
 ;; -------------------------------------------------------------------------- ;;
 ;; Initialize database
 
+;; ---------------------------------- ;;
+;; Ensure 'db/' folder exists
+
+(when (not (fs_utils.dir_exists? "db"))
+  (print "🚨 ERROR: No 'db/' folder to place SQLite database files in.\n❓ Did you forget to mount a volume at '/usr/simple-shortener/db?'")
+  (os.exit -1))
+
+;; ---------------------------------- ;;
+;; Connect to SQLite database
+
 ;; Tables:
 ;; links | Stores information about shortened links
 ;;   link_id - The unique base62 identifying string for the shortened link

src/modules/sessions_db.fnl

@@ -11,6 +11,7 @@
 ;; Local modules
 
 (local config (require :modules.config))
+(local fs_utils (require :modules.fs_utils))
 
 ;; -------------------------------------------------------------------------- ;;
 ;; Constants
@@ -38,6 +39,16 @@ OR last_active <= strftime('%s', 'now', '-" config.session_max_idle_length_hours
 ;; -------------------------------------------------------------------------- ;;
 ;; Initialize database
 
+;; ---------------------------------- ;;
+;; Ensure 'db/' folder exists
+
+(when (not (fs_utils.dir_exists? "db"))
+  (print "🚨 ERROR: No 'db/' folder to place SQLite database files in.\n❓ Did you forget to mount a volume at '/usr/simple-shortener/db?'")
+  (os.exit -1))
+
+;; ---------------------------------- ;;
+;; Connect to SQLite database
+
 ;; Tables:
 ;; sessions | Stores information about current (authorized) client sessions
 ;;   session_id - The unique base62 identifying string for the client session