refactor(tvix/store): remove ChunkService

Whether chunking is involved or not, is an implementation detail of each
Blobstore. Consumers of a whole blob shouldn't need to worry about that.
It currently is not visible in the gRPC interface either. It
shouldn't bleed into everything.

Let the BlobService trait provide `open_read` and `open_write` methods,
which return handles providing io::Read or io::Write, and leave the
details up to the implementation.

This means, our custom BlobReader module can go away, and all the
chunking bits in there, too.

In the future, we might still want to add more chunking-aware syncing,
but as a syncing strategy some stores can expose, not as a fundamental
protocol component.

This currently needs "SyncReadIntoAsyncRead", taken and vendored in from
https://github.com/tokio-rs/tokio/pull/5669.
It provides a AsyncRead for a sync Read, which is necessary to connect
our (sync) BlobReader interface to a GRPC server implementation.

As an alternative, we could also make the BlobReader itself async, and
let consumers of the trait (EvalIO) deal with the async-ness, but this
is less of a change for now.

In terms of vendoring, I initially tried to move our tokio crate to
these commits, but ended up in version incompatibilities, so let's
vendor it in for now.

Change-Id: I5969ebbc4c0e1ceece47981be3b9e7cfb3f59ad0
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8551
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/store/src/blobservice/sled.rs

@@ -1,13 +1,13 @@
-use std::path::PathBuf;
+use std::{
+    io::{self, Cursor},
+    path::PathBuf,
+};
 
+use super::{BlobService, BlobWriter};
+use crate::Error;
 use data_encoding::BASE64;
-use prost::Message;
 use tracing::instrument;
 
-use crate::{proto, Error};
-
-use super::BlobService;
-
 #[derive(Clone)]
 pub struct SledBlobService {
     db: sled::Db,
@@ -30,44 +30,69 @@ impl SledBlobService {
 }
 
 impl BlobService for SledBlobService {
-    #[instrument(name = "SledBlobService::stat", 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")
-        }
+    type BlobReader = Cursor<Vec<u8>>;
+    type BlobWriter = SledBlobWriter;
 
-        // if include_chunks is also false, the user only wants to know if the
-        // blob is present at all.
-        if !req.include_chunks {
-            match self.db.contains_key(&req.digest) {
-                Ok(false) => Ok(None),
-                Ok(true) => Ok(Some(proto::BlobMeta::default())),
-                Err(e) => Err(Error::StorageError(e.to_string())),
-            }
-        } else {
-            match self.db.get(&req.digest) {
-                Ok(None) => Ok(None),
-                Ok(Some(data)) => match proto::BlobMeta::decode(&*data) {
-                    Ok(blob_meta) => Ok(Some(blob_meta)),
-                    Err(e) => Err(Error::StorageError(format!(
-                        "unable to parse blobmeta message for blob {}: {}",
-                        BASE64.encode(&req.digest),
-                        e
-                    ))),
-                },
-                Err(e) => Err(Error::StorageError(e.to_string())),
-            }
+    #[instrument(name = "SledBlobService::has", skip(self), fields(blob.digest=BASE64.encode(digest)))]
+    fn has(&self, digest: &[u8; 32]) -> Result<bool, Error> {
+        match self.db.contains_key(digest) {
+            Ok(has) => Ok(has),
+            Err(e) => Err(Error::StorageError(e.to_string())),
         }
     }
 
-    #[instrument(name = "SledBlobService::put", 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 result = self.db.insert(blob_digest, blob_meta.encode_to_vec());
-        if let Err(e) = result {
-            return Err(Error::StorageError(e.to_string()));
+    #[instrument(name = "SledBlobService::open_read", skip(self), fields(blob.digest=BASE64.encode(digest)))]
+    fn open_read(&self, digest: &[u8; 32]) -> Result<Option<Self::BlobReader>, Error> {
+        match self.db.get(digest) {
+            Ok(None) => Ok(None),
+            Ok(Some(data)) => Ok(Some(Cursor::new(data[..].to_vec()))),
+            Err(e) => Err(Error::StorageError(e.to_string())),
         }
-        Ok(())
-        // TODO: make sure all callers make sure the chunks exist.
-        // TODO: where should we calculate the bao?
+    }
+
+    #[instrument(name = "SledBlobService::open_write", skip(self))]
+    fn open_write(&self) -> Result<Self::BlobWriter, Error> {
+        Ok(SledBlobWriter::new(self.db.clone()))
+    }
+}
+
+pub struct SledBlobWriter {
+    db: sled::Db,
+    buf: Vec<u8>,
+    hasher: blake3::Hasher,
+}
+
+impl SledBlobWriter {
+    pub fn new(db: sled::Db) -> Self {
+        Self {
+            buf: Vec::default(),
+            db,
+            hasher: blake3::Hasher::new(),
+        }
+    }
+}
+
+impl io::Write for SledBlobWriter {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        let bytes_written = self.buf.write(buf)?;
+        self.hasher.write(&buf[..bytes_written])
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        self.buf.flush()
+    }
+}
+
+impl BlobWriter for SledBlobWriter {
+    fn close(self) -> Result<[u8; 32], Error> {
+        let digest = self.hasher.finalize();
+        self.db.insert(digest.as_bytes(), self.buf).map_err(|e| {
+            Error::StorageError(format!("unable to insert blob: {}", e.to_string()))
+        })?;
+
+        Ok(digest
+            .to_owned()
+            .try_into()
+            .map_err(|_| Error::StorageError("invalid digest length in response".to_string()))?)
     }
 }