Add transactions cache, write tests.

Add a transactions module in dendrite/common. This is needed for idempotent APIs.

Signed-off-by: Anant Prakash <anantprakashjsr@gmail.com>

src/github.com/matrix-org/dendrite/common/transactions/transactions.go

@@ -0,0 +1,87 @@
+// 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 transactions
+
+import (
+	"errors"
+	"sync"
+	"time"
+
+	"github.com/matrix-org/util"
+)
+
+// CleanupPeriod represents time in nanoseconds after which cacheCleanService runs.
+const CleanupPeriod time.Duration = 30 * time.Minute
+
+type entry struct {
+	value     *util.JSONResponse
+	entryTime time.Time
+}
+
+// Cache represents a temporary store for entries.
+// Entries are evicted after a certain period, defined by CleanupPeriod.
+type Cache struct {
+	sync.RWMutex
+	txns map[string]entry
+}
+
+// New creates a new Cache object, starts cacheCleanService.
+// Returns a referance to newly created Cache.
+func New() *Cache {
+	t := Cache{txns: make(map[string]entry)}
+
+	// Start cleanup service as the Cache is created
+	go cacheCleanService(&t)
+	return &t
+}
+
+// FetchTransaction looks up an entry for txnID in Cache.
+// Returns a JSON response if txnID is found, else returns error.
+func (t *Cache) FetchTransaction(txnID string) (*util.JSONResponse, error) {
+	t.RLock()
+	res, ok := t.txns[txnID]
+	t.RUnlock()
+
+	if ok {
+		return res.value, nil
+	}
+	return nil, errors.New("TxnID not present")
+}
+
+// AddTransaction adds a entry for txnID in Cache for later access.
+func (t *Cache) AddTransaction(txnID string, res *util.JSONResponse) {
+	t.Lock()
+	defer t.Unlock()
+
+	t.txns[txnID] = entry{value: res, entryTime: time.Now()}
+}
+
+// cacheCleanService is responsible for cleaning up transactions older than CleanupPeriod.
+// It guarantees that a transaction will be present in cache for at least CleanupPeriod & at most 2 * CleanupPeriod.
+func cacheCleanService(t *Cache) {
+	for {
+		time.Sleep(CleanupPeriod)
+		go clean(t)
+	}
+}
+
+func clean(t *Cache) {
+	expire := time.Now().Add(-CleanupPeriod)
+	for key := range t.txns {
+		t.Lock()
+		if t.txns[key].entryTime.Before(expire) {
+			delete(t.txns, key)
+		}
+		t.Unlock()
+	}
+}

src/github.com/matrix-org/dendrite/common/transactions/transactions_test.go

@@ -0,0 +1,75 @@
+// 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 transactions
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/matrix-org/util"
+)
+
+type fakeType struct {
+	ID string `json:"ID"`
+}
+
+var (
+	fakeTxnID    = "aRandomTxnID"
+	fakeResponse = &util.JSONResponse{Code: http.StatusOK, JSON: fakeType{ID: "0"}}
+)
+
+// TestCache creates a New Cache and tests AddTransaction & FetchTransaction
+func TestCache(t *testing.T) {
+
+	fakeTxnCache := New()
+	fakeTxnCache.AddTransaction(fakeTxnID, fakeResponse)
+
+	// Add entries for noise.
+	for i := 1; i <= 100; i++ {
+		fakeTxnCache.AddTransaction(
+			fakeTxnID+string(i),
+			&util.JSONResponse{Code: http.StatusOK, JSON: fakeType{ID: string(i)}},
+		)
+	}
+
+	testResponse, err := fakeTxnCache.FetchTransaction(fakeTxnID)
+	if err != nil {
+		t.Error("Failed to retrieve entry for txnID: ", fakeTxnID)
+	} else if testResponse.JSON != fakeResponse.JSON {
+		t.Error("Incorrect fetched response. Expected: ", fakeResponse.JSON, " got: ", testResponse.JSON)
+	}
+}
+
+// TestConcurentAccess provides some guarantee against corruption.
+func TestConcurentAccess(t *testing.T) {
+	fakeTxnCache := New()
+	// Signal that this test should run in parallel
+	t.Parallel()
+	// Add entries concurrently to test concurrent access.
+	for i := 1; i <= 1000; i++ {
+		go check(t, fakeTxnCache, i)
+	}
+}
+
+// Adds an entry and checks it is retrieved.
+func check(t *testing.T, fakeTxnCache *Cache, i int) {
+	fakeTxnCache.AddTransaction(
+		fakeTxnID+string(i),
+		&util.JSONResponse{Code: http.StatusOK, JSON: fakeType{ID: string(i)}},
+	)
+	_, err := fakeTxnCache.FetchTransaction(fakeTxnID + string(i))
+
+	if err != nil {
+		t.Error("Failed to retrieve entry for txnID: ", fakeTxnID+string(i))
+	}
+}