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feat: implement LRU TTL refresh for S3 cache on Open #173

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Merged
worstell merged 2 commits into from
Mar 12, 2026
Merged

feat: implement LRU TTL refresh for S3 cache on Open #173

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b34c64b
feat: implement LRU TTL refresh for S3 cache on Open
worstell Mar 11, 2026
cd95556
Run S3 expiration refresh in background goroutine
worstell Mar 12, 2026
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46 changes: 46 additions & 0 deletions internal/cache/s3.go
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Original file line number Diff line number Diff line change
Expand Up @@ -244,6 +244,21 @@ func (s *S3) Open(ctx context.Context, key Key) (io.ReadCloser, http.Header, err
headers.Set("Last-Modified", objInfo.LastModified.UTC().Format(http.TimeFormat))
}

// Reset expiration time to implement LRU (same as disk cache).
// Only refresh when remaining TTL is below 50% of max to avoid a
// server-side copy on every read.
now := time.Now()
if expiresAtStr != "" {
var expiresAt time.Time
if err := expiresAt.UnmarshalText([]byte(expiresAtStr)); err == nil {
remaining := expiresAt.Sub(now)
if remaining < s.config.MaxTTL/2 {
newExpiresAt := now.Add(s.config.MaxTTL)
go s.refreshExpiration(context.WithoutCancel(ctx), objectName, objInfo, newExpiresAt)
}
}
}

// Get object
obj, err := s.client.GetObject(ctx, s.config.Bucket, objectName, minio.GetObjectOptions{})
if err != nil {
Expand All @@ -253,6 +268,37 @@ func (s *S3) Open(ctx context.Context, key Key) (io.ReadCloser, http.Header, err
return &s3Reader{obj: obj}, headers, nil
}

// refreshExpiration updates the Expires-At metadata on an S3 object using
// server-side copy-to-self with metadata replacement. This avoids re-uploading
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@alecthomas alecthomas Mar 12, 2026

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Is this fast?

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@worstell worstell Mar 12, 2026

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going to spin it off into an async routine so it doesnt block. it will also only trigger when we're 50% of the way or more towards the TTL

// the object data. Errors are logged but not returned since this is best-effort.
func (s *S3) refreshExpiration(ctx context.Context, objectName string, objInfo minio.ObjectInfo, newExpiresAt time.Time) {
newExpiresAtBytes, err := newExpiresAt.MarshalText()
if err != nil {
return
}

// Rebuild user metadata with updated expiration
newMetadata := make(map[string]string)
maps.Copy(newMetadata, objInfo.UserMetadata)
newMetadata["Expires-At"] = string(newExpiresAtBytes)

src := minio.CopySrcOptions{
Bucket: s.config.Bucket,
Object: objectName,
}
dst := minio.CopyDestOptions{
Bucket: s.config.Bucket,
Object: objectName,
UserMetadata: newMetadata,
ReplaceMetadata: true,
}
if _, err := s.client.CopyObject(ctx, dst, src); err != nil {
s.logger.WarnContext(ctx, "Failed to refresh S3 expiration",
"object", objectName,
"error", err.Error())
}
}

const s3ErrNoSuchKey = "NoSuchKey"

// s3Reader wraps minio.Object to convert S3 errors to standard errors.
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