Handle SIGTERM (#782)

* Handle SIGTERM

Resolve #781

* Add `Caught signal ...` messages

Container log when sending a `SIGHUP` signal and then a `SIGTERM` signal using
`docker kill --signal ...` :

```
Starting tileserver-gl v4.4.8
[INFO] Automatically creating config file for zurich_switzerland.mbtiles
[INFO] Only a basic preview style will be used.
[INFO] See documentation to learn how to create config.json file.
Run with --verbose to see the config file here.
Starting server
Listening at http://[::]:8080/
Startup complete
Caught signal SIGHUP, refreshing
Stopping server and reloading config
Starting server
Listening at http://[::]:8080/
Startup complete
Caught signal SIGTERM, stopping gracefully
```

Note that the numeric signal values, as used in the shell version, were
replaced by signal names, as used in nodeJS.

* run 'npm run lint:js:fix'

---------

Co-authored-by: acalcutt <acalcutt@techidiots.net>

src/server.js

@@ -590,6 +590,16 @@ function start(opts) {
   };
 }
 
+/**
+ * Stop the server gracefully
+ *
+ * @param {string} signal Name of the received signal
+ */
+function stopGracefully(signal) {
+  console.log(`Caught signal ${signal}, stopping gracefully`);
+  process.exit();
+}
+
 /**
  *
  * @param opts
@@ -602,11 +612,11 @@ export function server(opts) {
     process.exit(1);
   });
 
-  process.on('SIGINT', () => {
-    process.exit();
-  });
+  process.on('SIGINT', stopGracefully);
+  process.on('SIGTERM', stopGracefully);
 
-  process.on('SIGHUP', () => {
+  process.on('SIGHUP', (signal) => {
+    console.log(`Caught signal ${signal}, refreshing`);
     console.log('Stopping server and reloading config');
 
     running.server.shutdown(() => {

src/utils.js

@@ -8,9 +8,11 @@ import glyphCompose from '@mapbox/glyph-pbf-composite';
 
 /**
  * Generate new URL object
+ *
+ * @param req
  * @params {object} req - Express request
  * @returns {URL} object
- **/
+ */
 const getUrlObject = (req) => {
   const urlObject = new URL(`${req.protocol}://${req.headers.host}/`);
   // support overriding hostname by sending X-Forwarded-Host http header