feat(tvix/store): add blobservice

This adds a BlobService trait, and an implementation for it using sled,
and one using a HashMap.

Change-Id: Id6bc1b629195d0b26fc503bd7d2dc9e43c41c317
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8087
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/store/src/blobservice/memory.rs

@@ -0,0 +1,59 @@
+use data_encoding::BASE64;
+use std::{
+    collections::HashMap,
+    sync::{Arc, RwLock},
+};
+use tracing::instrument;
+
+use crate::{proto, Error};
+
+use super::BlobService;
+
+#[derive(Clone)]
+pub struct MemoryBlobService {
+    db: Arc<RwLock<HashMap<Vec<u8>, proto::BlobMeta>>>,
+}
+
+impl MemoryBlobService {
+    pub fn new() -> Self {
+        let db = Arc::new(RwLock::new(HashMap::default()));
+
+        Self { db }
+    }
+}
+
+impl BlobService for MemoryBlobService {
+    #[instrument(skip(self, req), fields(blob.digest=BASE64.encode(&req.digest)))]
+    fn stat(&self, req: &proto::StatBlobRequest) -> Result<Option<proto::BlobMeta>, Error> {
+        if req.include_bao {
+            todo!("not implemented yet")
+        }
+
+        let db = self.db.read().unwrap();
+        // if include_chunks is also false, the user only wants to know if the
+        // blob is present at all.
+        if !req.include_chunks {
+            Ok(if db.contains_key(&req.digest) {
+                Some(proto::BlobMeta::default())
+            } else {
+                None
+            })
+        } else {
+            match db.get(&req.digest) {
+                None => Ok(None),
+                Some(blob_meta) => Ok(Some(blob_meta.clone())),
+            }
+        }
+    }
+
+    #[instrument(skip(self, blob_meta, blob_digest), fields(blob.digest = BASE64.encode(blob_digest)))]
+    fn put(&self, blob_digest: &[u8], blob_meta: proto::BlobMeta) -> Result<(), Error> {
+        let mut db = self.db.write().unwrap();
+
+        db.insert(blob_digest.to_vec(), blob_meta);
+
+        Ok(())
+        // TODO: make sure all callers make sure the chunks exist.
+        // TODO: where should we calculate the bao?
+    }
+}