From a5ad49451e80cae7ec7f5d2a216084aa30e2e704 Mon Sep 17 00:00:00 2001
From: metamuffin <metamuffin@disroot.org>
Date: Fri, 5 Jan 2024 02:38:34 +0100
Subject: atomic cache insertion

---
 base/src/cache.rs | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

(limited to 'base/src')

diff --git a/base/src/cache.rs b/base/src/cache.rs
index d2d7990..e580130 100644
--- a/base/src/cache.rs
+++ b/base/src/cache.rs
@@ -9,11 +9,15 @@ use base64::Engine;
 use bincode::{Decode, Encode};
 use jellycommon::AssetLocation;
 use log::{info, warn};
+use rand::random;
 use std::{
     any::Any,
     collections::{BTreeMap, HashMap},
+    fs::rename,
     future::Future,
     io::Seek,
+    path::PathBuf,
+    str::FromStr,
     sync::{
         atomic::{AtomicUsize, Ordering},
         Arc, LazyLock, RwLock,
@@ -58,17 +62,23 @@ where
         .await
         .context("unable to test for cache file existance")?;
     if !exists {
-        let f = tokio::fs::File::create(location.path())
+        let temp_path =
+            AssetLocation::Cache(PathBuf::from_str(&format!("temp-{:x}", random::<u128>()))?)
+                .path();
+        let f = tokio::fs::File::create(&temp_path)
             .await
             .context("creating new cache file")?;
         match generate(f).await {
             Ok(()) => (),
             Err(e) => {
                 warn!("cache generation failed, unlinking entry");
-                tokio::fs::remove_file(location.path()).await?;
+                tokio::fs::remove_file(temp_path).await?;
                 return Err(e);
             }
         }
+        tokio::fs::rename(temp_path, location.path())
+            .await
+            .context("rename cache")?;
     }
     drop(_guard);
     Ok(location)
@@ -83,15 +93,19 @@ where
     let _guard = CACHE_GENERATION_LOCKS[bucket % CACHE_GENERATION_BUCKET_COUNT].blocking_lock();
     let exists = location.path().exists();
     if !exists {
-        let f = std::fs::File::create(location.path()).context("creating new cache file")?;
+        let temp_path =
+            AssetLocation::Cache(PathBuf::from_str(&format!("temp-{:x}", random::<u128>()))?)
+                .path();
+        let f = std::fs::File::create(&temp_path).context("creating new cache file")?;
         match generate(f) {
             Ok(()) => (),
             Err(e) => {
                 warn!("cache generation failed, unlinking entry");
-                std::fs::remove_file(location.path())?;
+                std::fs::remove_file(temp_path)?;
                 return Err(e);
             }
         }
+        rename(temp_path, location.path()).context("rename cache")?;
     }
     drop(_guard);
     Ok(location)
-- 
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