feat(tvix/store): eliminate generics in BlobStore r/6269

To construct various stores at runtime, we need to eliminate associated
types from the BlobService trait, and return Box<dyn …> instead of
specific types.

This also means we can't consume self in the close() method, so
everything we write to is put in an Option<>, and during the first close
we take from there.

Change-Id: Ia523b6ab2f2a5276f51cb5d17e81a5925bce69b6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8647
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

4 files changed, 192 insertions, 89 deletions

diff --git a/tvix/store/src/blobservice/grpc.rs b/tvix/store/src/blobservice/grpc.rs
index 0b08fbf46ad9..46ec64bce785 100644
--- a/tvix/store/src/blobservice/grpc.rs
+++ b/tvix/store/src/blobservice/grpc.rs
@@ -47,9 +47,6 @@ impl GRPCBlobService {
 }
 
 impl BlobService for GRPCBlobService {
-    type BlobReader = Box<dyn io::Read + Send>;
-    type BlobWriter = GRPCBlobWriter;
-
     #[instrument(skip(self, digest), fields(blob.digest=%digest))]
     fn has(&self, digest: &B3Digest) -> Result<bool, crate::Error> {
         // Get a new handle to the gRPC client, and copy the digest.
@@ -76,7 +73,10 @@ impl BlobService for GRPCBlobService {
 
     // On success, this returns a Ok(Some(io::Read)), which can be used to read
     // the contents of the Blob, identified by the digest.
-    fn open_read(&self, digest: &B3Digest) -> Result<Option<Self::BlobReader>, crate::Error> {
+    fn open_read(
+        &self,
+        digest: &B3Digest,
+    ) -> Result<Option<Box<dyn io::Read + Send>>, crate::Error> {
         // Get a new handle to the gRPC client, and copy the digest.
         let mut grpc_client = self.grpc_client.clone();
         let digest = digest.clone();
@@ -123,7 +123,7 @@ impl BlobService for GRPCBlobService {
 
     /// Returns a [Self::BlobWriter], that'll internally wrap each write in a
     // [proto::BlobChunk] and which is passed to the
-    fn open_write(&self) -> Result<Self::BlobWriter, crate::Error> {
+    fn open_write(&self) -> Result<Box<dyn BlobWriter>, crate::Error> {
         let mut grpc_client = self.grpc_client.clone();
 
         // set up an mpsc channel passing around Bytes.
@@ -155,11 +155,11 @@ impl BlobService for GRPCBlobService {
         // … which is then turned into a [io::Write].
         let writer = SyncIoBridge::new(async_writer);
 
-        Ok(GRPCBlobWriter {
+        Ok(Box::new(GRPCBlobWriter {
             tokio_handle: self.tokio_handle.clone(), // TODO: is the clone() ok here?
-            task,
-            inner_writer: writer,
-        })
+            task_and_writer: Some((task, writer)),
+            digest: None,
+        }))
     }
 }
 
@@ -176,42 +176,74 @@ pub struct GRPCBlobWriter {
     /// containing the put request.
     tokio_handle: tokio::runtime::Handle,
 
-    /// The task containing the put request.
-    task: JoinHandle<Result<proto::PutBlobResponse, Status>>,
+    /// The task containing the put request, and the inner writer, if we're still writing.
+    task_and_writer: Option<(
+        JoinHandle<Result<proto::PutBlobResponse, Status>>,
+        BridgedWriter,
+    )>,
 
-    /// The inner Writer.
-    inner_writer: BridgedWriter,
+    /// The digest that has been returned, if we successfully closed.
+    digest: Option<B3Digest>,
 }
 
 impl BlobWriter for GRPCBlobWriter {
-    fn close(mut self) -> Result<B3Digest, crate::Error> {
-        // invoke shutdown, so the inner writer closes its internal tx side of
-        // the channel.
-        self.inner_writer
-            .shutdown()
-            .map_err(|e| crate::Error::StorageError(e.to_string()))?;
-
-        // block on the RPC call to return.
-        // This ensures all chunks are sent out, and have been received by the
-        // backend.
-        match self.tokio_handle.block_on(self.task)? {
-            Ok(resp) => {
-                // return the digest from the response.
-                B3Digest::from_vec(resp.digest).map_err(|_| {
-                    crate::Error::StorageError("invalid root digest length in response".to_string())
-                })
+    fn close(&mut self) -> Result<B3Digest, crate::Error> {
+        if self.task_and_writer.is_none() {
+            // if we're already closed, return the b3 digest, which must exist.
+            // If it doesn't, we already closed and failed once, and didn't handle the error.
+            match &self.digest {
+                Some(digest) => Ok(digest.clone()),
+                None => Err(crate::Error::StorageError(
+                    "previously closed with error".to_string(),
+                )),
+            }
+        } else {
+            let (task, mut writer) = self.task_and_writer.take().unwrap();
+
+            // invoke shutdown, so the inner writer closes its internal tx side of
+            // the channel.
+            writer
+                .shutdown()
+                .map_err(|e| crate::Error::StorageError(e.to_string()))?;
+
+            // block on the RPC call to return.
+            // This ensures all chunks are sent out, and have been received by the
+            // backend.
+            match self.tokio_handle.block_on(task)? {
+                Ok(resp) => {
+                    // return the digest from the response, and store it in self.digest for subsequent closes.
+                    let digest = B3Digest::from_vec(resp.digest).map_err(|_| {
+                        crate::Error::StorageError(
+                            "invalid root digest length in response".to_string(),
+                        )
+                    })?;
+                    self.digest = Some(digest.clone());
+                    Ok(digest)
+                }
+                Err(e) => Err(crate::Error::StorageError(e.to_string())),
             }
-            Err(e) => Err(crate::Error::StorageError(e.to_string())),
         }
     }
 }
 
 impl io::Write for GRPCBlobWriter {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
-        self.inner_writer.write(buf)
+        match &mut self.task_and_writer {
+            None => Err(io::Error::new(
+                io::ErrorKind::NotConnected,
+                "already closed",
+            )),
+            Some((_, ref mut writer)) => writer.write(buf),
+        }
     }
 
     fn flush(&mut self) -> io::Result<()> {
-        self.inner_writer.flush()
+        match &mut self.task_and_writer {
+            None => Err(io::Error::new(
+                io::ErrorKind::NotConnected,
+                "already closed",
+            )),
+            Some((_, ref mut writer)) => writer.flush(),
+        }
     }
 }
diff --git a/tvix/store/src/blobservice/memory.rs b/tvix/store/src/blobservice/memory.rs
index 1ee59d108743..166eeabdb6a2 100644
--- a/tvix/store/src/blobservice/memory.rs
+++ b/tvix/store/src/blobservice/memory.rs
@@ -1,4 +1,4 @@
-use std::io::Cursor;
+use std::io::{self, Cursor};
 use std::{
     collections::HashMap,
     sync::{Arc, RwLock},
@@ -14,63 +14,102 @@ pub struct MemoryBlobService {
 }
 
 impl BlobService for MemoryBlobService {
-    type BlobReader = Cursor<Vec<u8>>;
-    type BlobWriter = MemoryBlobWriter;
-
     #[instrument(skip(self, digest), fields(blob.digest=%digest))]
     fn has(&self, digest: &B3Digest) -> Result<bool, Error> {
         let db = self.db.read().unwrap();
         Ok(db.contains_key(digest))
     }
 
-    fn open_read(&self, digest: &B3Digest) -> Result<Option<Self::BlobReader>, Error> {
+    fn open_read(&self, digest: &B3Digest) -> Result<Option<Box<dyn io::Read + Send>>, Error> {
         let db = self.db.read().unwrap();
 
-        Ok(db.get(digest).map(|x| Cursor::new(x.clone())))
+        match db.get(digest).map(|x| Cursor::new(x.clone())) {
+            Some(result) => Ok(Some(Box::new(result))),
+            None => Ok(None),
+        }
     }
 
     #[instrument(skip(self))]
-    fn open_write(&self) -> Result<Self::BlobWriter, Error> {
-        Ok(MemoryBlobWriter::new(self.db.clone()))
+    fn open_write(&self) -> Result<Box<dyn BlobWriter>, Error> {
+        Ok(Box::new(MemoryBlobWriter::new(self.db.clone())))
     }
 }
 
 pub struct MemoryBlobWriter {
     db: Arc<RwLock<HashMap<B3Digest, Vec<u8>>>>,
 
-    buf: Vec<u8>,
+    /// Contains the 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 {
-            buf: Vec::new(),
             db,
+            writers: Some((Vec::new(), blake3::Hasher::new())),
+            digest: None,
         }
     }
 }
 impl std::io::Write for MemoryBlobWriter {
-    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
-        self.buf.write(buf)
+    fn write(&mut self, b: &[u8]) -> std::io::Result<usize> {
+        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(&buf[..bytes_written])
+            }
+        }
     }
 
     fn flush(&mut self) -> std::io::Result<()> {
-        self.buf.flush()
+        match &mut self.writers {
+            None => Err(io::Error::new(
+                io::ErrorKind::NotConnected,
+                "already closed",
+            )),
+            Some(_) => Ok(()),
+        }
     }
 }
 
 impl BlobWriter for MemoryBlobWriter {
-    fn close(self) -> Result<B3Digest, Error> {
-        // in this memory implementation, we don't actually bother hashing
-        // incrementally while writing, but do it at the end.
-        let mut hasher = blake3::Hasher::new();
-        hasher.update(&self.buf);
-        let digest = B3Digest::from_vec(hasher.finalize().as_bytes().to_vec()).unwrap();
-
-        // open the database for writing.
-        let mut db = self.db.write()?;
-        db.insert(digest.clone(), self.buf);
-
-        Ok(digest)
+    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::from_vec(hasher.finalize().as_bytes().to_vec()).unwrap();
+
+            // 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)
+        }
     }
 }
diff --git a/tvix/store/src/blobservice/mod.rs b/tvix/store/src/blobservice/mod.rs
index c5a2de124656..08565285c0d1 100644
--- a/tvix/store/src/blobservice/mod.rs
+++ b/tvix/store/src/blobservice/mod.rs
@@ -14,28 +14,25 @@ pub use self::sled::SledBlobService;
 /// It provides functions to check whether a given blob exists,
 /// a way to get a [io::Read] to a blob, and a method to initiate writing a new
 /// Blob, which returns a [BlobWriter], that can be used
-pub trait BlobService {
-    type BlobReader: io::Read + Send + std::marker::Unpin;
-    type BlobWriter: BlobWriter + Send;
-
+pub trait BlobService: Send + Sync {
     /// Check if the service has the blob, by its content hash.
     fn has(&self, digest: &B3Digest) -> Result<bool, Error>;
 
     /// Request a blob from the store, by its content hash. Returns a Option<BlobReader>.
-    fn open_read(&self, digest: &B3Digest) -> Result<Option<Self::BlobReader>, Error>;
+    fn open_read(&self, digest: &B3Digest) -> Result<Option<Box<dyn io::Read + Send>>, Error>;
 
     /// Insert a new blob into the store. Returns a [BlobWriter], which
     /// implements [io::Write] and a [BlobWriter::close].
     /// TODO: is there any reason we want this to be a Result<>, and not just T?
-    fn open_write(&self) -> Result<Self::BlobWriter, Error>;
+    fn open_write(&self) -> Result<Box<dyn BlobWriter>, Error>;
 }
 
 /// A [io::Write] that you need to close() afterwards, and get back the digest
 /// of the written blob.
-pub trait BlobWriter: io::Write {
+pub trait BlobWriter: io::Write + Send + Sync + 'static {
     /// Signal there's no more data to be written, and return the digest of the
     /// contents written.
     ///
-    /// This consumes self, so it's not possible to close twice.
-    fn close(self) -> Result<B3Digest, Error>;
+    /// Closing a already-closed BlobWriter is a no-op.
+    fn close(&mut self) -> Result<B3Digest, Error>;
 }
diff --git a/tvix/store/src/blobservice/sled.rs b/tvix/store/src/blobservice/sled.rs
index 2b090335344d..3b130fcd9a05 100644
--- a/tvix/store/src/blobservice/sled.rs
+++ b/tvix/store/src/blobservice/sled.rs
@@ -28,9 +28,6 @@ impl SledBlobService {
 }
 
 impl BlobService for SledBlobService {
-    type BlobReader = Cursor<Vec<u8>>;
-    type BlobWriter = SledBlobWriter;
-
     #[instrument(skip(self), fields(blob.digest=%digest))]
     fn has(&self, digest: &B3Digest) -> Result<bool, Error> {
         match self.db.contains_key(digest.to_vec()) {
@@ -40,55 +37,93 @@ impl BlobService for SledBlobService {
     }
 
     #[instrument(skip(self), fields(blob.digest=%digest))]
-    fn open_read(&self, digest: &B3Digest) -> Result<Option<Self::BlobReader>, Error> {
+    fn open_read(&self, digest: &B3Digest) -> Result<Option<Box<dyn io::Read + Send>>, Error> {
         match self.db.get(digest.to_vec()) {
             Ok(None) => Ok(None),
-            Ok(Some(data)) => Ok(Some(Cursor::new(data[..].to_vec()))),
+            Ok(Some(data)) => Ok(Some(Box::new(Cursor::new(data[..].to_vec())))),
             Err(e) => Err(Error::StorageError(e.to_string())),
         }
     }
 
     #[instrument(skip(self))]
-    fn open_write(&self) -> Result<Self::BlobWriter, Error> {
-        Ok(SledBlobWriter::new(self.db.clone()))
+    fn open_write(&self) -> Result<Box<dyn BlobWriter>, Error> {
+        Ok(Box::new(SledBlobWriter::new(self.db.clone())))
     }
 }
 
 pub struct SledBlobWriter {
     db: sled::Db,
-    buf: Vec<u8>,
-    hasher: blake3::Hasher,
+
+    /// Contains the 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 SledBlobWriter {
     pub fn new(db: sled::Db) -> Self {
         Self {
-            buf: Vec::default(),
             db,
-            hasher: blake3::Hasher::new(),
+            writers: Some((Vec::new(), blake3::Hasher::new())),
+            digest: None,
         }
     }
 }
 
 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 write(&mut self, b: &[u8]) -> io::Result<usize> {
+        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(&buf[..bytes_written])
+            }
+        }
     }
 
     fn flush(&mut self) -> io::Result<()> {
-        self.buf.flush()
+        match &mut self.writers {
+            None => Err(io::Error::new(
+                io::ErrorKind::NotConnected,
+                "already closed",
+            )),
+            Some(_) => Ok(()),
+        }
     }
 }
 
 impl BlobWriter for SledBlobWriter {
-    fn close(self) -> Result<B3Digest, 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)))?;
-
-        // We know self.hasher is doing blake3 hashing, so this won't fail.
-        Ok(B3Digest::from_vec(digest.as_bytes().to_vec()).unwrap())
+    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::from_vec(hasher.finalize().as_bytes().to_vec()).unwrap();
+
+            // Only insert if the blob doesn't already exist.
+            if !self.db.contains_key(&digest.to_vec()).map_err(|e| {
+                Error::StorageError(format!("Unable to check if we have blob {}: {}", digest, e))
+            })? {
+                // put buf in there. This will move buf out.
+                self.db
+                    .insert(digest.to_vec(), buf)
+                    .map_err(|e| Error::StorageError(format!("unable to insert blob: {}", e)))?;
+            }
+
+            self.digest = Some(digest.clone());
+
+            Ok(digest)
+        }
     }
 }