Add a generic job scheduler

Also rewrite deletion of old sends using the job scheduler.

src/main.rs

@@ -16,6 +16,7 @@ extern crate diesel;
 #[macro_use]
 extern crate diesel_migrations;
 
+use job_scheduler::{JobScheduler, Job};
 use std::{
     fs::create_dir_all,
     panic,
@@ -23,6 +24,7 @@ use std::{
     process::{exit, Command},
     str::FromStr,
     thread,
+    time::Duration,
 };
 
 #[macro_use]
@@ -56,7 +58,9 @@ fn main() {
 
     create_icon_cache_folder();
 
-    launch_rocket(extra_debug);
+    let pool = create_db_pool();
+    schedule_jobs(pool.clone());
+    launch_rocket(pool, extra_debug); // Blocks until program termination.
 }
 
 const HELP: &str = "\
@@ -301,17 +305,17 @@ fn check_web_vault() {
     }
 }
 
-fn launch_rocket(extra_debug: bool) {
-    let pool = match util::retry_db(db::DbPool::from_config, CONFIG.db_connection_retries()) {
+fn create_db_pool() -> db::DbPool {
+    match util::retry_db(db::DbPool::from_config, CONFIG.db_connection_retries()) {
         Ok(p) => p,
         Err(e) => {
             error!("Error creating database pool: {:?}", e);
             exit(1);
         }
-    };
-
-    api::start_send_deletion_scheduler(pool.clone());
+    }
+}
 
+fn launch_rocket(pool: db::DbPool, extra_debug: bool) {
     let basepath = &CONFIG.domain_path();
 
     // If adding more paths here, consider also adding them to
@@ -334,3 +338,30 @@ fn launch_rocket(extra_debug: bool) {
     // The launch will restore the original logging level
     error!("Launch error {:#?}", result);
 }
+
+fn schedule_jobs(pool: db::DbPool) {
+    if CONFIG.job_poll_interval_ms() == 0 {
+        info!("Job scheduler disabled.");
+        return;
+    }
+    thread::Builder::new().name("job-scheduler".to_string()).spawn(move || {
+        let mut sched = JobScheduler::new();
+
+        // Purge sends that are past their deletion date.
+        if !CONFIG.send_purge_schedule().is_empty() {
+            sched.add(Job::new(CONFIG.send_purge_schedule().parse().unwrap(), || {
+                api::purge_sends(pool.clone());
+            }));
+        }
+
+        // Periodically check for jobs to run. We probably won't need any
+        // jobs that run more often than once a minute, so a default poll
+        // interval of 30 seconds should be sufficient. Users who want to
+        // schedule jobs to run more frequently for some reason can reduce
+        // the poll interval accordingly.
+        loop {
+            sched.tick();
+            thread::sleep(Duration::from_millis(CONFIG.job_poll_interval_ms()));
+        }
+    }).expect("Error spawning job scheduler thread");
+}