Rename storage certificate cache

This cache is used only for ACME certificates.

Being explicit is always better.

storage/certificate_cache.go

@@ -0,0 +1,63 @@
+// Copyright 2020 Dave Marquard. All rights reserved.
+// Use of this source code is governed by the Apache 2.0
+// license that can be found in the LICENSE file.
+
+package storage // import "miniflux.app/storage"
+
+import (
+	"context"
+	"database/sql"
+
+	"golang.org/x/crypto/acme/autocert"
+)
+
+// Making sure that we're adhering to the autocert.Cache interface.
+var _ autocert.Cache = (*CertificateCache)(nil)
+
+// CertificateCache provides a SQL backend to the autocert cache.
+type CertificateCache struct {
+	storage *Storage
+}
+
+// NewCertificateCache creates an cache instance that can be used with autocert.Cache.
+// It returns any errors that could happen while connecting to SQL.
+func NewCertificateCache(storage *Storage) *CertificateCache {
+	return &CertificateCache{
+		storage: storage,
+	}
+}
+
+// Get returns a certificate data for the specified key.
+// If there's no such key, Get returns ErrCacheMiss.
+func (c *CertificateCache) Get(ctx context.Context, key string) ([]byte, error) {
+	query := `SELECT data::bytea FROM acme_cache WHERE key = $1`
+	var data []byte
+	err := c.storage.db.QueryRowContext(ctx, query, key).Scan(&data)
+	if err == sql.ErrNoRows {
+		return nil, autocert.ErrCacheMiss
+	}
+
+	return data, err
+}
+
+// Put stores the data in the cache under the specified key.
+func (c *CertificateCache) Put(ctx context.Context, key string, data []byte) error {
+	query := `INSERT INTO acme_cache (key, data, updated_at) VALUES($1, $2::bytea, now())
+	          ON CONFLICT (key) DO UPDATE SET data = $2::bytea, updated_at = now()`
+	_, err := c.storage.db.ExecContext(ctx, query, key, data)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// Delete removes a certificate data from the cache under the specified key.
+// If there's no such key in the cache, Delete returns nil.
+func (c *CertificateCache) Delete(ctx context.Context, key string) error {
+	query := `DELETE FROM acme_cache WHERE key = $1`
+	_, err := c.storage.db.ExecContext(ctx, query, key)
+	if err != nil {
+		return err
+	}
+	return nil
+}