Ilia Denisov
69 lines
1.8 KiB
Go
69 lines
1.8 KiB
Go
package session
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import (
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"context"
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"errors"
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"fmt"
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)
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// ReadThroughCache resolves authenticated sessions from a process-local
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// SnapshotStore first and falls back to another Cache only on a local miss.
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type ReadThroughCache struct {
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local SnapshotStore
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fallback Cache
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}
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// NewReadThroughCache constructs a hot-path cache that seeds local snapshots
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// from fallback on demand.
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func NewReadThroughCache(local SnapshotStore, fallback Cache) (*ReadThroughCache, error) {
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if local == nil {
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return nil, errors.New("new read-through session cache: nil local cache")
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}
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if fallback == nil {
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return nil, errors.New("new read-through session cache: nil fallback cache")
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}
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return &ReadThroughCache{
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local: local,
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fallback: fallback,
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}, nil
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}
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// Lookup resolves deviceSessionID from local first, then performs one fallback
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// lookup on a local miss and seeds the local cache with the returned snapshot.
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func (c *ReadThroughCache) Lookup(ctx context.Context, deviceSessionID string) (Record, error) {
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if c == nil {
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return Record{}, errors.New("lookup session from read-through cache: nil cache")
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}
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record, err := c.local.Lookup(ctx, deviceSessionID)
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switch {
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case err == nil:
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return record, nil
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case !errors.Is(err, ErrNotFound):
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return Record{}, fmt.Errorf("lookup session from read-through cache: %w", err)
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}
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record, err = c.fallback.Lookup(ctx, deviceSessionID)
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if err != nil {
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return Record{}, err
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}
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if err := c.local.Upsert(record); err != nil {
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return Record{}, fmt.Errorf("lookup session from read-through cache: seed local cache: %w", err)
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}
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return cloneRecord(record), nil
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}
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// Local returns the mutable process-local snapshot store used by c.
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func (c *ReadThroughCache) Local() SnapshotStore {
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if c == nil {
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return nil
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}
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return c.local
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}
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var _ Cache = (*ReadThroughCache)(nil)
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