1 files changed, 196 insertions, 0 deletions
diff --git a/tvix/castore/src/blobservice/memory.rs b/tvix/castore/src/blobservice/memory.rs
new file mode 100644
index 0000000000..383127344a
--- /dev/null
+++ b/tvix/castore/src/blobservice/memory.rs
@@ -0,0 +1,196 @@
+use std::io::{self, Cursor, Write};
+use std::task::Poll;
+use std::{
+    collections::HashMap,
+    sync::{Arc, RwLock},
+};
+use tonic::async_trait;
+use tracing::instrument;
+
+use super::{BlobReader, BlobService, BlobWriter};
+use crate::{B3Digest, Error};
+
+#[derive(Clone, Default)]
+pub struct MemoryBlobService {
+    db: Arc<RwLock<HashMap<B3Digest, Vec<u8>>>>,
+}
+
+#[async_trait]
+impl BlobService for MemoryBlobService {
+    /// Constructs a [MemoryBlobService] from the passed [url::Url]:
+    /// - scheme has to be `memory://`
+    /// - there may not be a host.
+    /// - there may not be a path.
+    fn from_url(url: &url::Url) -> Result<Self, Error> {
+        if url.scheme() != "memory" {
+            return Err(crate::Error::StorageError("invalid scheme".to_string()));
+        }
+
+        if url.has_host() || !url.path().is_empty() {
+            return Err(crate::Error::StorageError("invalid url".to_string()));
+        }
+
+        Ok(Self::default())
+    }
+
+    #[instrument(skip(self, digest), fields(blob.digest=%digest))]
+    async fn has(&self, digest: &B3Digest) -> Result<bool, Error> {
+        let db = self.db.read().unwrap();
+        Ok(db.contains_key(digest))
+    }
+
+    async fn open_read(&self, digest: &B3Digest) -> Result<Option<Box<dyn BlobReader>>, Error> {
+        let db = self.db.read().unwrap();
+
+        match db.get(digest).map(|x| Cursor::new(x.clone())) {
+            Some(result) => Ok(Some(Box::new(result))),
+            None => Ok(None),
+        }
+    }
+
+    #[instrument(skip(self))]
+    async fn open_write(&self) -> Box<dyn BlobWriter> {
+        Box::new(MemoryBlobWriter::new(self.db.clone()))
+    }
+}
+
+pub struct MemoryBlobWriter {
+    db: Arc<RwLock<HashMap<B3Digest, Vec<u8>>>>,
+
+    /// Contains the buffer Vec and hasher, or None if already closed
+    writers: Option<(Vec<u8>, blake3::Hasher)>,
+
+    /// The digest that has been returned, if we successfully closed.
+    digest: Option<B3Digest>,
+}
+
+impl MemoryBlobWriter {
+    fn new(db: Arc<RwLock<HashMap<B3Digest, Vec<u8>>>>) -> Self {
+        Self {
+            db,
+            writers: Some((Vec::new(), blake3::Hasher::new())),
+            digest: None,
+        }
+    }
+}
+impl tokio::io::AsyncWrite for MemoryBlobWriter {
+    fn poll_write(
+        mut self: std::pin::Pin<&mut Self>,
+        _cx: &mut std::task::Context<'_>,
+        b: &[u8],
+    ) -> std::task::Poll<Result<usize, io::Error>> {
+        Poll::Ready(match &mut self.writers {
+            None => Err(io::Error::new(
+                io::ErrorKind::NotConnected,
+                "already closed",
+            )),
+            Some((ref mut buf, ref mut hasher)) => {
+                let bytes_written = buf.write(b)?;
+                hasher.write(&b[..bytes_written])
+            }
+        })
+    }
+
+    fn poll_flush(
+        self: std::pin::Pin<&mut Self>,
+        _cx: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Result<(), io::Error>> {
+        Poll::Ready(match self.writers {
+            None => Err(io::Error::new(
+                io::ErrorKind::NotConnected,
+                "already closed",
+            )),
+            Some(_) => Ok(()),
+        })
+    }
+
+    fn poll_shutdown(
+        self: std::pin::Pin<&mut Self>,
+        _cx: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Result<(), io::Error>> {
+        // shutdown is "instantaneous", we only write to memory.
+        Poll::Ready(Ok(()))
+    }
+}
+
+#[async_trait]
+impl BlobWriter for MemoryBlobWriter {
+    async fn close(&mut self) -> Result<B3Digest, Error> {
+        if self.writers.is_none() {
+            match &self.digest {
+                Some(digest) => Ok(digest.clone()),
+                None => Err(crate::Error::StorageError(
+                    "previously closed with error".to_string(),
+                )),
+            }
+        } else {
+            let (buf, hasher) = self.writers.take().unwrap();
+
+            // We know self.hasher is doing blake3 hashing, so this won't fail.
+            let digest: B3Digest = hasher.finalize().as_bytes().into();
+
+            // Only insert if the blob doesn't already exist.
+            let db = self.db.read()?;
+            if !db.contains_key(&digest) {
+                // drop the read lock, so we can open for writing.
+                drop(db);
+
+                // open the database for writing.
+                let mut db = self.db.write()?;
+
+                // and put buf in there. This will move buf out.
+                db.insert(digest.clone(), buf);
+            }
+
+            self.digest = Some(digest.clone());
+
+            Ok(digest)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::BlobService;
+    use super::MemoryBlobService;
+
+    /// This uses a wrong scheme.
+    #[test]
+    fn test_invalid_scheme() {
+        let url = url::Url::parse("http://foo.example/test").expect("must parse");
+
+        assert!(MemoryBlobService::from_url(&url).is_err());
+    }
+
+    /// This correctly sets the scheme, and doesn't set a path.
+    #[test]
+    fn test_valid_scheme() {
+        let url = url::Url::parse("memory://").expect("must parse");
+
+        assert!(MemoryBlobService::from_url(&url).is_ok());
+    }
+
+    /// This sets the host to `foo`
+    #[test]
+    fn test_invalid_host() {
+        let url = url::Url::parse("memory://foo").expect("must parse");
+
+        assert!(MemoryBlobService::from_url(&url).is_err());
+    }
+
+    /// This has the path "/", which is invalid.
+    #[test]
+    fn test_invalid_has_path() {
+        let url = url::Url::parse("memory:///").expect("must parse");
+
+        assert!(MemoryBlobService::from_url(&url).is_err());
+    }
+
+    /// This has the path "/foo", which is invalid.
+    #[test]
+    fn test_invalid_path2() {
+        let url = url::Url::parse("memory:///foo").expect("must parse");
+
+        assert!(MemoryBlobService::from_url(&url).is_err());
+    }
+}