Avoid panics (#392)

- Use `Result` as much as possible
- Display errors instead of panicking

TODO (maybe in another PR? this one is already quite big):
- Find a way to merge Ructe/ErrorPage types, so that we can have routes returning `Result<X, ErrorPage>` instead of panicking when we have an `Error`
- Display more details about the error, to make it easier to debug

(sorry, this isn't going to be fun to review, the diff is huge, but it is always the same changes)

src/main.rs

@@ -38,8 +38,11 @@ extern crate webfinger;
 use diesel::r2d2::ConnectionManager;
 use rocket::State;
 use rocket_csrf::CsrfFairingBuilder;
-use plume_models::{DATABASE_URL, Connection,
-    db_conn::{DbPool, PragmaForeignKey}, search::Searcher as UnmanagedSearcher};
+use plume_models::{
+    DATABASE_URL, Connection, Error,
+    db_conn::{DbPool, PragmaForeignKey},
+    search::{Searcher as UnmanagedSearcher, SearcherError},
+};
 use scheduled_thread_pool::ScheduledThreadPool;
 use std::process::exit;
 use std::sync::Arc;
@@ -65,10 +68,23 @@ fn init_pool() -> Option<DbPool> {
 }
 
 fn main() {
-
     let dbpool = init_pool().expect("main: database pool initialization error");
     let workpool = ScheduledThreadPool::with_name("worker {}", num_cpus::get());
-    let searcher = Arc::new(UnmanagedSearcher::open(&"search_index").unwrap());
+    let searcher = match UnmanagedSearcher::open(&"search_index") {
+        Err(Error::Search(e)) => match e {
+            SearcherError::WriteLockAcquisitionError => panic!(
+r#"Your search index is locked. Plume can't start. To fix this issue
+make sure no other Plume instance is started, and run:
+
+    plm search unlock
+
+Then try to restart Plume.
+"#),
+            e => Err(e).unwrap()
+        },
+        Err(_) => panic!("Unexpected error while opening search index"),
+        Ok(s) => Arc::new(s)
+    };
 
     let commiter = searcher.clone();
     workpool.execute_with_fixed_delay(Duration::from_secs(5), Duration::from_secs(60*30), move || commiter.commit());