agent/cache: blank cache key means to always fetch

agent/cache/cache.go

@@ -20,29 +20,10 @@ import (
 
 //go:generate mockery -all -inpkg
 
-// Pre-written options for type registration. These should not be modified.
+// TODO: DC-aware, ACL-aware
-var (
-	// RegisterOptsPeriodic performs a periodic refresh of data fetched
-	// by the registered type.
-	RegisterOptsPeriodic = &RegisterOptions{
-		Refresh:        true,
-		RefreshTimer:   30 * time.Second,
-		RefreshTimeout: 5 * time.Minute,
-	}
-)
-
-// TODO: DC-aware
-
-// RPC is an interface that an RPC client must implement.
-type RPC interface {
-	RPC(method string, args interface{}, reply interface{}) error
-}
 
 // Cache is a agent-local cache of Consul data.
 type Cache struct {
-	// rpcClient is the RPC-client.
-	rpcClient RPC
-
 	entriesLock sync.RWMutex
 	entries     map[string]cacheEntry
 
@@ -50,6 +31,7 @@ type Cache struct {
 	types     map[string]typeEntry
 }
 
+// cacheEntry stores a single cache entry.
 type cacheEntry struct {
 	// Fields pertaining to the actual value
 	Value interface{}
@@ -68,13 +50,17 @@ type typeEntry struct {
 	Opts *RegisterOptions
 }
 
+// Options are options for the Cache.
+type Options struct {
+	// Nothing currently, reserved.
+}
+
 // New creates a new cache with the given RPC client and reasonable defaults.
 // Further settings can be tweaked on the returned value.
-func New(rpc RPC) *Cache {
+func New(*Options) *Cache {
 	return &Cache{
-		rpcClient: rpc,
+		entries: make(map[string]cacheEntry),
-		entries:   make(map[string]cacheEntry),
+		types:   make(map[string]typeEntry),
-		types:     make(map[string]typeEntry),
 	}
 }
 
@@ -124,7 +110,11 @@ func (c *Cache) RegisterType(n string, typ Type, opts *RegisterOptions) {
 // block on a single network request.
 func (c *Cache) Get(t string, r Request) (interface{}, error) {
 	key := r.CacheKey()
-	idx := r.CacheMinIndex()
+	if key == "" {
+		// If no key is specified, then we do not cache this request.
+		// Pass directly through to the backend.
+		return c.fetchDirect(t, r)
+	}
 
 RETRY_GET:
 	// Get the current value
@@ -136,8 +126,11 @@ RETRY_GET:
 	// currently stored index then we return that right away. If the
 	// index is zero and we have something in the cache we accept whatever
 	// we have.
-	if ok && entry.Valid && (idx == 0 || idx < entry.Index) {
+	if ok && entry.Valid {
-		return entry.Value, nil
+		idx := r.CacheMinIndex()
+		if idx == 0 || idx < entry.Index {
+			return entry.Value, nil
+		}
 	}
 
 	// At this point, we know we either don't have a value at all or the
@@ -192,7 +185,6 @@ func (c *Cache) fetch(t string, r Request) (<-chan struct{}, error) {
 		// Start building the new entry by blocking on the fetch.
 		var newEntry cacheEntry
 		result, err := tEntry.Type.Fetch(FetchOptions{
-			RPC:      c.rpcClient,
 			MinIndex: entry.Index,
 		}, r)
 		newEntry.Value = result.Value
@@ -223,6 +215,28 @@ func (c *Cache) fetch(t string, r Request) (<-chan struct{}, error) {
 	return entry.Waiter, nil
 }
 
+// fetchDirect fetches the given request with no caching.
+func (c *Cache) fetchDirect(t string, r Request) (interface{}, error) {
+	// Get the type that we're fetching
+	c.typesLock.RLock()
+	tEntry, ok := c.types[t]
+	c.typesLock.RUnlock()
+	if !ok {
+		return nil, fmt.Errorf("unknown type in cache: %s", t)
+	}
+
+	// Fetch it with the min index specified directly by the request.
+	result, err := tEntry.Type.Fetch(FetchOptions{
+		MinIndex: r.CacheMinIndex(),
+	}, r)
+	if err != nil {
+		return nil, err
+	}
+
+	// Return the result and ignore the rest
+	return result.Value, nil
+}
+
 func (c *Cache) refresh(opts *RegisterOptions, t string, r Request) {
 	// Sanity-check, we should not schedule anything that has refresh disabled
 	if !opts.Refresh {

agent/cache/cache_test.go

@@ -41,6 +41,38 @@ func TestCacheGet_noIndex(t *testing.T) {
 	typ.AssertExpectations(t)
 }
 
+// Test a Get with a request that returns a blank cache key. This should
+// force a backend request and skip the cache entirely.
+func TestCacheGet_blankCacheKey(t *testing.T) {
+	t.Parallel()
+
+	require := require.New(t)
+
+	typ := TestType(t)
+	defer typ.AssertExpectations(t)
+	c := TestCache(t)
+	c.RegisterType("t", typ, nil)
+
+	// Configure the type
+	typ.Static(FetchResult{Value: 42}, nil).Times(2)
+
+	// Get, should fetch
+	req := TestRequest(t, "", 0)
+	result, err := c.Get("t", req)
+	require.Nil(err)
+	require.Equal(42, result)
+
+	// Get, should not fetch since we already have a satisfying value
+	result, err = c.Get("t", req)
+	require.Nil(err)
+	require.Equal(42, result)
+
+	// Sleep a tiny bit just to let maybe some background calls happen
+	// then verify that we still only got the one call
+	time.Sleep(20 * time.Millisecond)
+	typ.AssertExpectations(t)
+}
+
 // Test that Get blocks on the initial value
 func TestCacheGet_blockingInitSameKey(t *testing.T) {
 	t.Parallel()

agent/cache/rpc.go

@@ -0,0 +1,8 @@
+package cache
+
+// RPC is an interface that an RPC client must implement. This is a helper
+// interface that is implemented by the agent delegate so that Type
+// implementations can request RPC access.
+type RPC interface {
+	RPC(method string, args interface{}, reply interface{}) error
+}

agent/cache/testing.go

@@ -11,7 +11,7 @@ import (
 // TestCache returns a Cache instance configuring for testing.
 func TestCache(t testing.T) *Cache {
 	// Simple but lets us do some fine-tuning later if we want to.
-	return New(TestRPC(t))
+	return New(nil)
 }
 
 // TestCacheGetCh returns a channel that returns the result of the Get call.

agent/cache/type.go

@@ -20,9 +20,6 @@ type Type interface {
 
 // FetchOptions are various settable options when a Fetch is called.
 type FetchOptions struct {
-	// RPC is the RPC client to communicate to a Consul server.
-	RPC RPC
-
 	// MinIndex is the minimum index to be used for blocking queries.
 	// If blocking queries aren't supported for data being returned,
 	// this value can be ignored.
@@ -42,27 +39,3 @@ type FetchResult struct {
 	// Index is the corresponding index value for this data.
 	Index uint64
 }
-
-/*
-type TypeCARoot struct{}
-
-func (c *TypeCARoot) Fetch(delegate RPC, idx uint64, req Request) (interface{}, uint64, error) {
-	// The request should be a DCSpecificRequest.
-	reqReal, ok := req.(*structs.DCSpecificRequest)
-	if !ok {
-		return nil, 0, fmt.Errorf(
-			"Internal cache failure: request wrong type: %T", req)
-	}
-
-	// Set the minimum query index to our current index so we block
-	reqReal.QueryOptions.MinQueryIndex = idx
-
-	// Fetch
-	var reply structs.IndexedCARoots
-	if err := delegate.RPC("ConnectCA.Roots", reqReal, &reply); err != nil {
-		return nil, 0, err
-	}
-
-	return &reply, reply.QueryMeta.Index, nil
-}
-*/

agent/cache/type_connect_ca.go

@@ -0,0 +1,39 @@
+package cache
+
+/*
+import (
+	"fmt"
+
+	"github.com/hashicorp/consul/agent/structs"
+)
+
+// TypeCARoot supports fetching the Connect CA roots.
+type TypeCARoot struct {
+	RPC RPC
+}
+
+func (c *TypeCARoot) Fetch(opts FetchOptions, req Request) (FetchResult, error) {
+	var result FetchResult
+
+	// The request should be a DCSpecificRequest.
+	reqReal, ok := req.(*structs.DCSpecificRequest)
+	if !ok {
+		return result, fmt.Errorf(
+			"Internal cache failure: request wrong type: %T", req)
+	}
+
+	// Set the minimum query index to our current index so we block
+	reqReal.QueryOptions.MinQueryIndex = opts.MinIndex
+	reqReal.QueryOptions.MaxQueryTime = opts.Timeout
+
+	// Fetch
+	var reply structs.IndexedCARoots
+	if err := c.RPC.RPC("ConnectCA.Roots", reqReal, &reply); err != nil {
+		return result, err
+	}
+
+	result.Value = &reply
+	result.Index = reply.QueryMeta.Index
+	return result, nil
+}
+*/