configfile: allow selecting slow watch behavior via env var

Changes.md

@@ -1,6 +1,8 @@
 
 ## 1.N.NN - 20YY-MM-DD
 
+- configfile: allow selecting slow watch behavior via env var
+
 ## 1.0.19 - 2019-MM-DD
 
 - configfile: convert to es6 class

README.md

@@ -329,3 +329,8 @@ in a plugins register() function are read *before* Haraka drops privileges.
 Be sure that Haraka's user/group has permission to read these files else
 Haraka will be unable to update them after changes.
 
+### Network filesystems
+
+Auto-reload is not supported on an FS that doesn't implement proper file changes notify mechanism. 
+
+Imagine you've got several Haraka nodes that keep their config dir on a network FS. You have updated a configuration file on the network server and would like to let all Haraka nodes know your file has been updated. For that, you have to login to all your Haraka nodes and `touch` the relevant config file manually. Obviously, this really resembles plain old `scp` copy, except that you only touch files instead of copying data. It almost makes no point of using a network FS then. So, for those people who desire all this drama to be irrelevant, we've made a special option available that allows to poll files for changes periodically instead of relying on notify mechanism. It is very slow and triggers traffic on network FS during the poll, but it's the only way around. Set `HARAKA_CONFIG_SLOWWATCH` env var to desired poll interval (> 10 recommended) and you'll have your config files reloaded (in > 15 secs) after the file update.

config.js

@@ -116,7 +116,7 @@ class Config {
     }
 
     module_config (defaults_path, overrides_path) {
-        const cfg = new Config(path.join(defaults_path, 'config'), true);
+        const cfg = new Config(process.env.HARAKA_CONFIG_CUSTOM_DIR || path.join(defaults_path, 'config'), true);
         if (overrides_path) {
             cfg.overrides_path = path.join(overrides_path, 'config');
         }

configfile.js

@@ -35,9 +35,17 @@ class cfreader {
             is_truth:       /^(?:true|yes|ok|enabled|on|1)$/i,
             is_array:       /(.+)\[\]$/,
         }
+
+        let watch_interval = process.env.HARAKA_CONFIG_SLOWWATCH
+        if (watch_interval) console.error(`configfile.js: Requested to use SLOW config watchers with POLL interval ${watch_interval} secs`)
     }
 
     get_path_to_config_dir () {
+        if (process.env.HARAKA_CONFIG_CUSTOM_DIR) {
+            this.config_path = process.env.HARAKA_CONFIG_CUSTOM_DIR
+            return
+        }
+
         if (process.env.HARAKA) {
             // console.log(`process.env.HARAKA: ${process.env.HARAKA}`);
             this.config_path = path.join(process.env.HARAKA, 'config');
@@ -103,6 +111,25 @@ class cfreader {
         }
     }
 
+    on_slowwatch_event (name, type, options, cb) {
+        return (fstat_cur, fstat_prev) => {
+            // skipping initial missing file watch reload
+            if (fstat_prev.mtimeMs === 0 && fstat_cur.mtimeMs === 0) return
+
+            console.log(`WATCH EVENT: ${fstat_prev.mtime} -> ${fstat_cur.mtime}, will trigger reload in 5secs`)
+
+            if (this._sedation_timers[name]) {
+                clearTimeout(this._sedation_timers[name]);
+            }
+            this._sedation_timers[name] = setTimeout(() => {
+                console.log(`Reloading file: ${name}`);
+                this.load_config(name, type, options);
+                delete this._sedation_timers[name];
+                if (typeof cb === 'function') cb();
+            }, 5 * 1000);
+        }
+    }
+
     watch_dir () {
         // NOTE: Has OS platform limitations:
         // https://nodejs.org/api/fs.html#fs_fs_watch_filename_options_listener
@@ -155,6 +182,14 @@ class cfreader {
         }
     }
 
+    slowwatch_file (name, type, cb, options) {
+        if (this._watchers[name] || (options && options.no_watch)) return;
+
+        this._watchers[name] = fs.watchFile(name,
+            { persistent: false, interval: process.env.HARAKA_CONFIG_SLOWWATCH * 1000 },
+            this.on_slowwatch_event(name, type, options, cb))
+    }
+
     get_cache_key (name, options) {
 
         // Ignore options etc. if this is an overriden value
@@ -198,6 +233,12 @@ class cfreader {
         const result = this.load_config(name, type, options);
         if (!this.watch_files) return result;
 
+        if (process.env.HARAKA_CONFIG_SLOWWATCH) {
+            this.slowwatch_file(name, type, cb, options)
+
+            return result
+        }
+
         // We can watch the directory on these platforms which
         // allows us to notice when files are newly created.
         switch (process.platform) {
@@ -284,10 +325,12 @@ class cfreader {
         }
 
         let cfrType = this.get_filetype_reader(type);
+        const cache_key = this.get_cache_key(name, options);
 
         if (!fs.existsSync(name)) {
             if (!/\.h?json$/.test(name)) {
-                return cfrType.empty(options, type);
+                // console.error(`ENOENT ${name}`)
+                return this._config_cache[cache_key] = cfrType.empty(options, type)
             }
 
             const yaml_name = name.replace(/\.h?json$/, '.yaml');
@@ -299,7 +342,6 @@ class cfreader {
             cfrType = this.get_filetype_reader(type);
         }
 
-        const cache_key = this.get_cache_key(name, options);
         try {
             switch (type) {
                 case 'ini':