about summary refs log tree commit diff
path: root/tvix/castore/src/blobservice/combinator.rs
blob: 6a964c8a844003573b7f846e4308004b9a94a252 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
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 "local" and "remote" blobservice.
/// Requests are tried in (and returned from) the local store first, only if
/// things are not present there, the remote BlobService is queried.
/// In case the local blobservice doesn't have the blob, we ask the remote
/// blobservice for chunks, and try to read each of these chunks from the local
/// blobservice again, before falling back to the remote one.
/// The remote BlobService is never written to.
pub struct CombinedBlobService<BL, BR> {
    local: BL,
    remote: BR,
}

impl<BL, BR> Clone for CombinedBlobService<BL, BR>
where
    BL: Clone,
    BR: Clone,
{
    fn clone(&self) -> Self {
        Self {
            local: self.local.clone(),
            remote: self.remote.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))]
    async fn has(&self, digest: &B3Digest) -> std::io::Result<bool> {
        Ok(self.local.as_ref().has(digest).await? || self.remote.as_ref().has(digest).await?)
    }

    #[instrument(skip(self, digest), fields(blob.digest=%digest), err)]
    async fn open_read(&self, digest: &B3Digest) -> std::io::Result<Option<Box<dyn BlobReader>>> {
        if self.local.as_ref().has(digest).await? {
            // local store has the blob, so we can assume it also has all chunks.
            self.local.as_ref().open_read(digest).await
        } else {
            // Local 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
            // locally, meaning we don't need to fetch them all from the remote
            // BlobService.
            match self.remote.as_ref().chunks(digest).await? {
                // blob doesn't exist on the remote side either, nothing we can do.
                None => Ok(None),
                Some(remote_chunks) => {
                    // if there's no more granular chunks, or the remote
                    // blobservice doesn't support chunks, read the blob from
                    // the remote blobservice directly.
                    if remote_chunks.is_empty() {
                        return self.remote.as_ref().open_read(digest).await;
                    }
                    // otherwise, a chunked reader, which will always try the
                    // local 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)]
    async fn open_write(&self) -> Box<dyn BlobWriter> {
        // direct writes to the local one.
        self.local.as_ref().open_write().await
    }
}

#[derive(serde::Deserialize, Debug, Clone)]
#[serde(deny_unknown_fields)]
pub struct CombinedBlobServiceConfig {
    local: String,
    remote: 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.local.clone()),
            context.resolve(self.remote.clone())
        );
        Ok(Arc::new(CombinedBlobService {
            local: local?,
            remote: remote?,
        }))
    }
}