feat(tvix/store): add SledDirectoryService r/5722

Change-Id: I8e97a59da2c6623f4cca746efa741097a6dbe5b1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7871
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

1 files changed, 249 insertions, 0 deletions

diff --git a/tvix/store/src/sled_directory_service.rs b/tvix/store/src/sled_directory_service.rs
new file mode 100644
index 000000000000..a966601fc423
--- /dev/null
+++ b/tvix/store/src/sled_directory_service.rs
@@ -0,0 +1,249 @@
+use data_encoding::BASE64;
+use std::collections::HashSet;
+use std::collections::VecDeque;
+use std::path::PathBuf;
+use tokio::sync::mpsc::channel;
+use tokio::sync::mpsc::Sender;
+
+use prost::Message;
+use tokio::task;
+use tokio_stream::wrappers::ReceiverStream;
+
+use crate::proto::directory_service_server::DirectoryService;
+use crate::proto::get_directory_request::ByWhat;
+use crate::proto::Directory;
+use crate::proto::GetDirectoryRequest;
+use crate::proto::PutDirectoryResponse;
+use tonic::{Request, Response, Result, Status, Streaming};
+use tracing::{debug, instrument, warn};
+
+pub struct SledDirectoryService {
+    db: sled::Db,
+}
+
+impl SledDirectoryService {
+    pub fn new(p: PathBuf) -> Result<Self, anyhow::Error> {
+        let config = sled::Config::default().use_compression(true).path(p);
+        let db = config.open()?;
+
+        Ok(Self { db })
+    }
+}
+
+/// Lookup a directory, optionally recurse, and send the result to the passed sender.
+/// We pass in a txn, that has been opened on the outside.
+/// It's up to the user to wrap this in a TransactionError appropriately.
+/// This will open a sled txn to ensure a consistent view.
+fn send_directories(
+    txn: &sled::transaction::TransactionalTree,
+    tx: &Sender<Result<Directory>>,
+    req: GetDirectoryRequest,
+) -> Result<(), Status> {
+    // keep the list of directories to traverse
+    let mut deq: VecDeque<Vec<u8>> = VecDeque::new();
+
+    // look at the digest in the request and put it in the top of the queue.
+    match &req.by_what {
+        None => return Err(Status::invalid_argument("by_what needs to be specified")),
+        Some(ByWhat::Digest(digest)) => {
+            if digest.len() != 32 {
+                return Err(Status::invalid_argument("invalid digest length"));
+            }
+            deq.push_back(digest.clone());
+        }
+    }
+
+    // look up the directory at the top of the queue
+    while let Some(ref digest) = deq.pop_front() {
+        let digest_b64: String = BASE64.encode(digest);
+
+        match txn.get(digest) {
+            // The directory was not found, abort
+            Ok(None) => {
+                return Err(Status::not_found(format!(
+                    "directory {} not found",
+                    digest_b64
+                )))
+            }
+            // The directory was found, try to parse the data as Directory message
+            Ok(Some(data)) => match Directory::decode(&*data) {
+                Err(e) => {
+                    warn!("unable to parse directory {}: {}", digest_b64, e);
+                    return Err(Status::internal(format!(
+                        "unable to parse directory {}",
+                        digest_b64
+                    )));
+                }
+                Ok(directory) => {
+                    // Validate the retrieved Directory indeed has the
+                    // digest we expect it to have, to detect corruptions.
+                    let actual_digest = directory.digest();
+                    if actual_digest != digest.clone() {
+                        return Err(Status::data_loss(format!(
+                            "requested directory with digest {}, but got {}",
+                            digest_b64,
+                            BASE64.encode(&actual_digest)
+                        )));
+                    }
+
+                    // if recursion was requested, all its children need to be added to the queue.
+                    if req.recursive {
+                        for child_directory_node in &directory.directories {
+                            deq.push_back(child_directory_node.digest.clone());
+                        }
+                    }
+
+                    // send the directory message to the client
+                    if let Err(e) = tx.blocking_send(Ok(directory)) {
+                        debug!("error sending: {}", e);
+                        return Err(Status::internal("error sending"));
+                    }
+                }
+            },
+            // some storage error?
+            Err(e) => {
+                // TODO: check what this error really means
+                warn!("storage error: {}", e);
+                return Err(Status::internal("storage error"));
+            }
+        };
+    }
+
+    // nothing left, we're done
+    Ok(())
+}
+
+/// Consume directories, and insert them into the database.
+/// Reject directory messages that refer to Directories not sent in the same stream.
+fn insert_directories(
+    txn: &sled::transaction::TransactionalTree,
+    directories: &Vec<Directory>,
+) -> Result<Vec<u8>, Status> {
+    // This keeps track of the seen directory keys.
+    // We don't need to keep the contents around, they're stored in the DB.
+    let mut seen_directory_dgsts: HashSet<Vec<u8>> = HashSet::new();
+    let mut last_directory_dgst: Option<Vec<u8>> = None;
+
+    for directory in directories {
+        // for each child directory this directory refers to, we need
+        // to ensure it has been seen already in this stream.
+        for child_directory in &directory.directories {
+            if !seen_directory_dgsts.contains(&child_directory.digest) {
+                return Err(Status::invalid_argument(format!(
+                    "referred child directory {} not seen yet",
+                    BASE64.encode(&child_directory.digest)
+                )));
+            }
+        }
+
+        // TODO: do we want to verify this somehow is connected to the current graph?
+        // theoretically, this currently allows uploading multiple
+        // disconnected graphs at the same time…
+
+        let dgst = directory.digest();
+        seen_directory_dgsts.insert(dgst.clone());
+        last_directory_dgst = Some(dgst.clone());
+
+        // insert the directory into the database
+        if let Err(e) = txn.insert(dgst, directory.encode_to_vec()) {
+            match e {
+                // TODO: conflict is a problem, as the whole transaction closure is retried?
+                sled::transaction::UnabortableTransactionError::Conflict => todo!(),
+                sled::transaction::UnabortableTransactionError::Storage(e) => {
+                    warn!("storage error: {}", e);
+                    return Err(Status::internal("storage error"));
+                }
+            }
+        }
+    }
+
+    // no more directories to be send. Return the digest of the
+    // last (root) node, or an error if we don't receive a single one.
+    match last_directory_dgst {
+        Some(last_directory_dgst) => Ok(last_directory_dgst),
+        None => Err(Status::invalid_argument("no directories received")),
+    }
+}
+
+#[tonic::async_trait]
+impl DirectoryService for SledDirectoryService {
+    type GetStream = ReceiverStream<Result<Directory>>;
+
+    #[instrument(skip(self))]
+    async fn get(
+        &self,
+        request: Request<GetDirectoryRequest>,
+    ) -> Result<Response<Self::GetStream>, Status> {
+        let (tx, rx) = channel(5);
+
+        let req_inner = request.into_inner();
+
+        // clone self.db (cheap), so we don't refer to self in the thread.
+        let db = self.db.clone();
+
+        // kick off a thread
+        task::spawn_blocking(move || {
+            // open a DB transaction.
+            let txn_res = db.transaction(|txn| {
+                send_directories(txn, &tx, req_inner.clone())
+                    .map_err(sled::transaction::ConflictableTransactionError::Abort)
+            });
+
+            // handle transaction errors
+            match txn_res {
+                Ok(()) => Ok(()),
+                Err(sled::transaction::TransactionError::Abort(status)) => {
+                    // if the transaction was aborted, there was an error. Send it to the client
+                    tx.blocking_send(Err(status))
+                }
+                Err(sled::transaction::TransactionError::Storage(e)) => {
+                    warn!("storage error: {}", e);
+                    tx.blocking_send(Err(Status::internal("storage error")))
+                }
+            }
+        });
+
+        // NOTE: this always returns an Ok response, with the first item in the
+        // stream being a potential error, instead of directly returning the
+        // first error.
+        // Peeking on the first element seems to be extraordinarily hard,
+        // and client code considers these two equivalent anyways.
+        let receiver_stream = ReceiverStream::new(rx);
+        Ok(Response::new(receiver_stream))
+    }
+
+    #[instrument(skip(self, request))]
+    async fn put(
+        &self,
+        request: Request<Streaming<Directory>>,
+    ) -> Result<Response<PutDirectoryResponse>> {
+        let mut req_inner = request.into_inner();
+
+        // TODO: for now, we collect all Directory messages into a Vec, and
+        // pass it to the helper function.
+        // Ideally, we would validate things as we receive it, and have a way
+        // to reject early - but the semantics of transactions (and its
+        // retries) don't allow us to discard things that early anyways.
+        let mut directories: Vec<Directory> = Vec::new();
+
+        while let Some(directory) = req_inner.message().await? {
+            directories.push(directory)
+        }
+
+        let txn_res = self.db.transaction(|txn| {
+            insert_directories(txn, &directories)
+                .map_err(sled::transaction::ConflictableTransactionError::Abort)
+        });
+
+        match txn_res {
+            Ok(last_directory_dgst) => Ok(Response::new(PutDirectoryResponse {
+                root_digest: last_directory_dgst,
+            })),
+            Err(sled::transaction::TransactionError::Storage(e)) => {
+                warn!("storage error: {}", e);
+                Err(Status::internal("storage error"))
+            }
+            Err(sled::transaction::TransactionError::Abort(e)) => Err(e),
+        }
+    }
+}