feat: force flush non-overflowed in-memory buffers (#310)

* feat: force flush non-overflowed in-memory buffers

* fix: increase shutdown period

NOTE: necessary for safely handling force flush to disk

* log: successful force flush

* doc: update comment

* fix: `try_recv` to trigger storage flush

NOTE: needs to be verified for any realistic possibility of data loss

* fix: ignore empty buffers

* fix: write not read buffer

* fix: ignore empty write buffers

* fix: wait max 2 secs for data flushed from bridge

storage/src/lib.rs

@@ -16,6 +16,8 @@ pub enum Error {
     NotBackup,
     #[error("Corrupted backup file")]
     CorruptedFile,
+    #[error("Empty write buffer")]
+    NoWrites,
 }
 
 pub struct Storage {
@@ -85,6 +87,14 @@ impl Storage {
             return Ok(None);
         }
 
+        self.flush()
+    }
+
+    /// Force flush the contents of write buffer onto disk
+    pub fn flush(&mut self) -> Result<Option<u64>, Error> {
+        if self.current_write_file.is_empty() {
+            return Err(Error::NoWrites);
+        }
         match &mut self.persistence {
             Some(persistence) => {
                 let hash = hash(&self.current_write_file[..]);

uplink/src/base/serializer/mod.rs

@@ -2,6 +2,7 @@ mod metrics;
 
 use std::collections::{HashMap, VecDeque};
 use std::io::{self, Write};
+use std::time::Instant;
 use std::{sync::Arc, time::Duration};
 
 use bytes::Bytes;
@@ -58,6 +59,8 @@ pub enum Error {
     EmptyStorage,
     #[error("Permission denied while accessing persistence directory \"{0}\"")]
     Persistence(String),
+    #[error("Serializer has shutdown after handling crash")]
+    Shutdown,
 }
 
 #[derive(Debug, PartialEq)]
@@ -203,6 +206,16 @@ impl StorageHandler {
 
         None
     }
+
+    fn flush_all(&mut self) {
+        for (stream_name, storage) in self.map.iter_mut() {
+            match storage.flush() {
+                Ok(_) => trace!("Force flushed stream = {stream_name} onto disk"),
+                Err(storage::Error::NoWrites) => {}
+                Err(e) => error!("Error when force flushing storage = {stream_name}; error = {e}"),
+            }
+        }
+    }
 }
 
 pub struct SerializerShutdown;
@@ -298,8 +311,13 @@ impl<C: MqttClient> Serializer<C> {
         }
 
         loop {
-            // Collect next data packet and write to disk
-            let data = self.collector_rx.recv_async().await?;
+            // Collect remaining data packets and write to disk
+            // NOTE: wait 2s to allow bridge to shutdown and flush leftover data.
+            let deadline = Instant::now() + Duration::from_secs(2);
+            let Ok(data) = self.collector_rx.recv_deadline(deadline) else {
+                self.storage_handler.flush_all();
+                return Err(Error::Shutdown);
+            };
             let publish = construct_publish(data)?;
             let storage = self.storage_handler.select(&publish.topic);
             match write_to_disk(publish, storage) {

uplink/src/main.rs

@@ -203,7 +203,7 @@ fn main() -> Result<(), Error> {
         uplink.resolve_on_shutdown().await.unwrap();
         info!("Uplink shutting down...");
         // NOTE: wait 5s to allow serializer to write to network/disk
-        sleep(Duration::from_secs(5)).await;
+        sleep(Duration::from_secs(10)).await;
     });
 
     Ok(())