feat: Add etcd database support

improve concurrent access and high availability of aptly with the help of the characteristics of etcd

database/etcddb/transaction.go

@@ -0,0 +1,55 @@
+package etcddb
+
+import (
+	"github.com/aptly-dev/aptly/database"
+	clientv3 "go.etcd.io/etcd/client/v3"
+	"go.etcd.io/etcd/client/v3/clientv3util"
+)
+
+type transaction struct {
+	t clientv3.KV
+}
+
+// Get implements database.Reader interface.
+func (t *transaction) Get(key []byte) ([]byte, error) {
+	getResp, err := t.t.Get(Ctx, string(key))
+	if err != nil {
+		return nil, err
+	}
+
+	var value []byte
+	for _, kv := range getResp.Kvs {
+		valc := make([]byte, len(kv.Value))
+		copy(valc, kv.Value)
+		value = valc
+	}
+
+	return value, nil
+}
+
+// Put implements database.Writer interface.
+func (t *transaction) Put(key, value []byte) (err error) {
+	_, err = t.t.Txn(Ctx).
+		If().Then(clientv3.OpPut(string(key), string(value))).Commit()
+	return
+}
+
+// Delete implements database.Writer interface.
+func (t *transaction) Delete(key []byte) (err error) {
+	_, err = t.t.Txn(Ctx).
+		If(clientv3util.KeyExists(string(key))).
+		Then(clientv3.OpDelete(string(key))).Commit()
+	return
+}
+
+func (t *transaction) Commit() (err error) {
+	return
+}
+
+// Discard is safe to call after Commit(), it would be no-op
+func (t *transaction) Discard() {
+	return
+}
+
+// transaction should implement database.Transaction
+var _ database.Transaction = &transaction{}