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|
package post
import (
"bytes"
"database/sql"
"errors"
"fmt"
"io"
"sync"
)
var (
// ErrAssetNotFound is used to indicate an Asset could not be found in the
// AssetStore.
ErrAssetNotFound = errors.New("asset not found")
)
// AssetStore implements the storage and retrieval of binary assets, which are
// intended to be used by posts (e.g. images).
type AssetStore interface {
// Set sets the id to the contents of the given io.Reader.
Set(id string, from io.Reader) error
// Get writes the id's body to the given io.Writer, or returns
// ErrAssetNotFound.
Get(id string, into io.Writer) error
// Delete's the body stored for the id, if any.
Delete(id string) error
}
type assetStore struct {
db *sql.DB
}
// NewAssetStore initializes a new AssetStore using an existing SQLDB.
func NewAssetStore(db *SQLDB) AssetStore {
return &assetStore{
db: db.db,
}
}
func (s *assetStore) Set(id string, from io.Reader) error {
body, err := io.ReadAll(from)
if err != nil {
return fmt.Errorf("reading body fully into memory: %w", err)
}
_, err = s.db.Exec(
`INSERT INTO assets (id, body)
VALUES (?, ?)
ON CONFLICT (id) DO UPDATE SET body=excluded.body`,
id, body,
)
if err != nil {
return fmt.Errorf("inserting into assets: %w", err)
}
return nil
}
func (s *assetStore) Get(id string, into io.Writer) error {
var body []byte
err := s.db.QueryRow(`SELECT body FROM assets WHERE id = ?`, id).Scan(&body)
if errors.Is(err, sql.ErrNoRows) {
return ErrAssetNotFound
} else if err != nil {
return fmt.Errorf("selecting from assets: %w", err)
}
if _, err := io.Copy(into, bytes.NewReader(body)); err != nil {
return fmt.Errorf("writing body to io.Writer: %w", err)
}
return nil
}
func (s *assetStore) Delete(id string) error {
_, err := s.db.Exec(`DELETE FROM assets WHERE id = ?`, id)
return err
}
////////////////////////////////////////////////////////////////////////////////
type cachedAssetStore struct {
inner AssetStore
m sync.Map
}
// NewCachedAssetStore wraps an AssetStore in an in-memory cache.
func NewCachedAssetStore(assetStore AssetStore) AssetStore {
return &cachedAssetStore{
inner: assetStore,
}
}
func (s *cachedAssetStore) Set(id string, from io.Reader) error {
buf := new(bytes.Buffer)
from = io.TeeReader(from, buf)
if err := s.inner.Set(id, from); err != nil {
return err
}
s.m.Store(id, buf.Bytes())
return nil
}
func (s *cachedAssetStore) Get(id string, into io.Writer) error {
if bodyI, ok := s.m.Load(id); ok {
if err, ok := bodyI.(error); ok {
return err
}
if _, err := io.Copy(into, bytes.NewReader(bodyI.([]byte))); err != nil {
return fmt.Errorf("writing body to io.Writer: %w", err)
}
return nil
}
buf := new(bytes.Buffer)
into = io.MultiWriter(into, buf)
if err := s.inner.Get(id, into); errors.Is(err, ErrAssetNotFound) {
s.m.Store(id, err)
return err
} else if err != nil {
return err
}
s.m.Store(id, buf.Bytes())
return nil
}
func (s *cachedAssetStore) Delete(id string) error {
if err := s.inner.Delete(id); err != nil {
return err
}
s.m.Delete(id)
return nil
}
|
