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use std::sync::Arc;
use tonic::async_trait;
use tracing::instrument;
use crate::composition::{CompositionContext, ServiceBuilder};
use crate::{B3Digest, Error};
use super::{BlobReader, BlobService, BlobWriter, ChunkedReader};
/// Combinator for a BlobService, using a "near" and "far" blobservice.
/// Requests are tried in (and returned from) the near store first, only if
/// things are not present there, the far BlobService is queried.
/// In case the near blobservice doesn't have the blob, we ask the remote
/// blobservice for chunks, and try to read each of these chunks from the near
/// blobservice again, before falling back to the far one.
/// The far BlobService is never written to.
pub struct CombinedBlobService<BL, BR> {
instance_name: String,
near: BL,
far: BR,
}
impl<BL, BR> Clone for CombinedBlobService<BL, BR>
where
BL: Clone,
BR: Clone,
{
fn clone(&self) -> Self {
Self {
instance_name: self.instance_name.clone(),
near: self.near.clone(),
far: self.far.clone(),
}
}
}
#[async_trait]
impl<BL, BR> BlobService for CombinedBlobService<BL, BR>
where
BL: AsRef<dyn BlobService> + Clone + Send + Sync + 'static,
BR: AsRef<dyn BlobService> + Clone + Send + Sync + 'static,
{
#[instrument(skip(self, digest), fields(blob.digest=%digest, instance_name=%self.instance_name))]
async fn has(&self, digest: &B3Digest) -> std::io::Result<bool> {
Ok(self.near.as_ref().has(digest).await? || self.far.as_ref().has(digest).await?)
}
#[instrument(skip(self, digest), fields(blob.digest=%digest, instance_name=%self.instance_name), err)]
async fn open_read(&self, digest: &B3Digest) -> std::io::Result<Option<Box<dyn BlobReader>>> {
if self.near.as_ref().has(digest).await? {
// near store has the blob, so we can assume it also has all chunks.
self.near.as_ref().open_read(digest).await
} else {
// near store doesn't have the blob.
// Ask the remote one for the list of chunks,
// and create a chunked reader that uses self.open_read() for
// individual chunks. There's a chance we already have some chunks
// in near, meaning we don't need to fetch them all from the far
// BlobService.
match self.far.as_ref().chunks(digest).await? {
// blob doesn't exist on the near side either, nothing we can do.
None => Ok(None),
Some(remote_chunks) => {
// if there's no more granular chunks, or the far
// blobservice doesn't support chunks, read the blob from
// the far blobservice directly.
if remote_chunks.is_empty() {
return self.far.as_ref().open_read(digest).await;
}
// otherwise, a chunked reader, which will always try the
// near backend first.
let chunked_reader = ChunkedReader::from_chunks(
remote_chunks.into_iter().map(|chunk| {
(
chunk.digest.try_into().expect("invalid b3 digest"),
chunk.size,
)
}),
Arc::new(self.clone()) as Arc<dyn BlobService>,
);
Ok(Some(Box::new(chunked_reader)))
}
}
}
}
#[instrument(skip_all, fields(instance_name=%self.instance_name))]
async fn open_write(&self) -> Box<dyn BlobWriter> {
// direct writes to the near one.
self.near.as_ref().open_write().await
}
}
#[derive(serde::Deserialize, Debug, Clone)]
#[serde(deny_unknown_fields)]
pub struct CombinedBlobServiceConfig {
near: String,
far: String,
}
impl TryFrom<url::Url> for CombinedBlobServiceConfig {
type Error = Box<dyn std::error::Error + Send + Sync>;
fn try_from(_url: url::Url) -> Result<Self, Self::Error> {
Err(Error::StorageError(
"Instantiating a CombinedBlobService from a url is not supported".into(),
)
.into())
}
}
#[async_trait]
impl ServiceBuilder for CombinedBlobServiceConfig {
type Output = dyn BlobService;
async fn build<'a>(
&'a self,
instance_name: &str,
context: &CompositionContext,
) -> Result<Arc<dyn BlobService>, Box<dyn std::error::Error + Send + Sync>> {
let (local, remote) = futures::join!(
context.resolve(self.near.clone()),
context.resolve(self.far.clone())
);
Ok(Arc::new(CombinedBlobService {
instance_name: instance_name.to_string(),
near: local?,
far: remote?,
}))
}
}
|
