Add etcd sequence implementation

internal/sequence/sequence.go

@@ -0,0 +1,128 @@
+// Copyright 2019 Sorint.lab
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sequence
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/pkg/errors"
+	"github.com/sorintlab/agola/internal/etcd"
+)
+
+type Sequence struct {
+	Epoch uint64
+	C     uint64
+}
+
+func (s *Sequence) String() string {
+	// 1<<64 -1 in base 32 is "3w5e11264sgsf" and uses 13 chars
+	return fmt.Sprintf("%013s-%013s", strconv.FormatUint(s.Epoch, 32), strconv.FormatUint(s.C, 32))
+}
+
+func (s *Sequence) Reverse() *Sequence {
+	return &Sequence{
+		Epoch: math.MaxUint64 - s.Epoch,
+		C:     math.MaxUint64 - s.C,
+	}
+}
+
+func Parse(s string) (*Sequence, error) {
+	parts := strings.Split(s, "-")
+	if len(parts) != 2 {
+		return nil, errors.Errorf("bad sequence %q", s)
+	}
+	epoch, err := strconv.ParseUint(parts[0], 32, 64)
+	if err != nil {
+		return nil, errors.Wrapf(err, "cannot parse sequence epoch %q", epoch)
+	}
+	c, err := strconv.ParseUint(parts[1], 32, 64)
+	if err != nil {
+		return nil, errors.Wrapf(err, "cannot parse sequence count %q", c)
+	}
+	return &Sequence{
+		Epoch: epoch,
+		C:     c,
+	}, nil
+}
+
+func (s *Sequence) EqualEpoch(s2 *Sequence) bool {
+	return s.Epoch == s2.Epoch
+}
+
+func CurSequence(ctx context.Context, e *etcd.Store, key string) (*Sequence, bool, error) {
+	resp, err := e.Get(ctx, key)
+	if err != nil && err != etcd.ErrKeyNotFound {
+		return nil, false, err
+	}
+	if err == etcd.ErrKeyNotFound {
+		return nil, false, nil
+	}
+
+	seq := &Sequence{}
+	if err != etcd.ErrKeyNotFound {
+		kv := resp.Kvs[0]
+		if err := json.Unmarshal(kv.Value, &seq); err != nil {
+			return nil, false, err
+		}
+	}
+	return seq, true, nil
+}
+
+func IncSequence(ctx context.Context, e *etcd.Store, key string) (*Sequence, error) {
+	resp, err := e.Get(ctx, key)
+	if err != nil && err != etcd.ErrKeyNotFound {
+		return nil, err
+	}
+
+	var revision int64
+	seq := &Sequence{}
+	if err != etcd.ErrKeyNotFound {
+		kv := resp.Kvs[0]
+		if err := json.Unmarshal(kv.Value, &seq); err != nil {
+			return nil, err
+		}
+		revision = kv.ModRevision
+	}
+
+	// if the epoch is zero then this is a new etcd cluster. This will happen on
+	// first creation or if the etcd cluster is recreated. The epoch is used to
+	// keep the seq incremental and we assume the new epoch will always be greater
+	// than the previous ones (it not then there was a big backward time drift)
+	//
+	// TODO(sgotti) check that the new epoch is greater then previous ones???
+	if seq.Epoch == 0 {
+		seq.Epoch = uint64(time.Now().Unix())
+	}
+
+	seq.C++
+
+	seqj, err := json.Marshal(seq)
+	if err != nil {
+		return nil, err
+	}
+
+	_, err = e.AtomicPut(ctx, key, seqj, revision, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	return seq, nil
+}