move caching to its own file

1 files changed, 60 insertions, 0 deletions

diff --git a/base/src/cache.rs b/base/src/cache.rs
new file mode 100644
index 0000000..2fa2680
--- /dev/null
+++ b/base/src/cache.rs
@@ -0,0 +1,60 @@
+use crate::AssetLocationExt;
+use base64::Engine;
+use jellycommon::AssetLocation;
+use std::{future::Future, sync::LazyLock};
+use tokio::sync::Mutex;
+
+pub fn cache_location(seed: &[&str]) -> (usize, AssetLocation) {
+    use sha2::Digest;
+    let mut d = sha2::Sha512::new();
+    for s in seed {
+        d.update(s.as_bytes());
+        d.update(b"\0");
+    }
+    let d = d.finalize();
+    let n = d[0] as usize | (d[1] as usize) << 8 | (d[2] as usize) << 16 | (d[3] as usize) << 24;
+    let fname = base64::engine::general_purpose::URL_SAFE.encode(d);
+    let fname = &fname[..22]; // about 128 bits
+    (n, AssetLocation::Cache(fname.into()))
+}
+
+const CACHE_GENERATION_BUCKET_COUNT: usize = 1024;
+pub static CACHE_GENERATION_LOCKS: LazyLock<[Mutex<()>; CACHE_GENERATION_BUCKET_COUNT]> =
+    LazyLock::new(|| [(); CACHE_GENERATION_BUCKET_COUNT].map(|_| Mutex::new(())));
+
+pub async fn async_cache_file<Fun, Fut>(
+    seed: &[&str],
+    generate: Fun,
+) -> Result<AssetLocation, anyhow::Error>
+where
+    Fun: FnOnce(tokio::fs::File) -> Fut,
+    Fut: Future<Output = Result<(), anyhow::Error>>,
+{
+    let (bucket, location) = cache_location(seed);
+    // we need a lock even if it exists since somebody might be still in the process of writing.
+    let _guard = CACHE_GENERATION_LOCKS[bucket % CACHE_GENERATION_BUCKET_COUNT].lock();
+    let exists = tokio::fs::try_exists(location.path()).await?;
+    if !exists {
+        let f = tokio::fs::File::create(location.path()).await?;
+        generate(f).await?;
+    }
+    drop(_guard);
+    Ok(location)
+}
+
+pub fn cache_file<Fun>(seed: &[&str], mut generate: Fun) -> Result<AssetLocation, anyhow::Error>
+where
+    Fun: FnMut(std::fs::File) -> Result<(), anyhow::Error>,
+{
+    let (bucket, location) = cache_location(seed);
+    // we need a lock even if it exists since somebody might be still in the process of writing.
+    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())?;
+        generate(f)?;
+    }
+    drop(_guard);
+    Ok(location)
+}
+