Add server/cache support to gaeconfig.

appengine/gaeconfig/default.go

Index: appengine/gaeconfig/default.go
diff --git a/appengine/gaeconfig/default.go b/appengine/gaeconfig/default.go
index 18cd7db2fd97559735b62e9b06c743cae9f10e8a..869b558c5c23b682103e7bf8797f1b67dbfe69f3 100644
--- a/appengine/gaeconfig/default.go
+++ b/appengine/gaeconfig/default.go
@@ -7,23 +7,23 @@ package gaeconfig
 import (
 	"errors"
 	"fmt"
-	"net/http"
 	"os"
 	"path/filepath"
-	"sync"
 	"time"
 
-	"golang.org/x/net/context"
+	"github.com/luci/luci-go/common/config/impl/filesystem"
+	"github.com/luci/luci-go/server/config"
+	"github.com/luci/luci-go/server/config/caching"
+	"github.com/luci/luci-go/server/config/erroring"
+	"github.com/luci/luci-go/server/config/testconfig"
+	"github.com/luci/luci-go/server/config/textproto"
 
 	"github.com/luci/gae/service/info"
-	"github.com/luci/luci-go/common/config"
-	"github.com/luci/luci-go/common/config/impl/erroring"
-	"github.com/luci/luci-go/common/config/impl/filesystem"
-	"github.com/luci/luci-go/common/config/impl/remote"
-	"github.com/luci/luci-go/server/auth"
+
+	"golang.org/x/net/context"
 )
 
-// ErrNotConfigured is returned by methods of config.Interface object returned
+// ErrNotConfigured is returned by methods of config.Backend object returned
 // by New if config service URL is not set. Usually happens for new apps.
 var ErrNotConfigured = errors.New("config service URL is not set in settings")
 
@@ -31,21 +31,7 @@ var ErrNotConfigured = errors.New("config service URL is not set in settings")
 // local dev appserver model. See New for details.
 const devCfgDir = "devcfg"
 
-// implCache is used to avoid reallocating config.Interface implementation
-// during each request.
-//
-// config.Interface instances don't actually depend on the context and thus we
-// can share them between requests.
-//
-// Cache key is the current value of Settings struct. We don't bother to clean
-// up old entries, since in most cases there'll be none (the settings are mostly
-// static).
-var implCache struct {
-	lock  sync.RWMutex
-	cache map[Settings]config.Interface
-}
-
-// New constructs default luci-config client.
+// Use installs the default luci-config client.
 //
 // The client is configured to use luci-config URL specified in the settings,
 // using GAE app service account for authentication.
@@ -64,58 +50,61 @@ var implCache struct {
 //
 // Panics if it can't load the settings (should not happen since they are in
 // the local memory cache usually).
-func New(c context.Context) config.Interface {
-	settings, err := FetchCachedSettings(c)
-	if err != nil {
-		panic(err)
-	}
+func Use(c context.Context) context.Context { return useImpl(c, nil) }

[iannucci, 2017/01/07 21:05:26]

if you do the package renaming, this should move out (maybe
`luci-config/setup/gaeluciconfig` with just the relevant usage bits, the intent
being that the setup/* packages would be full instantiations for various
environments or something.)

[dnj, 2017/01/10 03:30:07]

I'll move to luci_config/appengine/gaeconfig.

 
-	if settings.ConfigServiceURL == "" {
-		if info.IsDevAppServer(c) {
-			return devServerConfig()
-		}
-		return erroring.New(ErrNotConfigured)
-	}
-
-	return configImplForSettings(settings)
+func useImpl(c context.Context, backend config.Backend) context.Context {
+	return installConfigBackend(c, mustFetchCachedSettings(c), backend)
 }
 
-// configImplForSettings returns config.Interface based on given settings.
-//
-// Split out from New to enforce that returned config.Interface doesn't depend
-// on the context (since this function doesn't accept a context).
-func configImplForSettings(settings Settings) config.Interface {
-	implCache.lock.RLock()
-	impl, ok := implCache.cache[settings]
-	implCache.lock.RUnlock()
-	if ok {
-		return impl
+func installConfigBackend(c context.Context, s *Settings, backend config.Backend) context.Context {
+	if backend == nil {
+		// Non-testing, build a Backend.
+		backend = getPrimaryBackend(c, s)
 	}
 
-	implCache.lock.Lock()
-	defer implCache.lock.Unlock()
+	// Install a FormatRegistry. Register common config service protobufs with it.
+	c = withFormatRegistry(c, defaultFormatterRegistry())
 
-	if impl, ok := implCache.cache[settings]; ok {
-		return impl
+	backend = &config.FormatBackend{
+		Backend:     backend,
+		GetRegistry: GetFormatterRegistry,
 	}
 
-	impl = remote.New(settings.ConfigServiceURL+"/_ah/api/config/v1/", authenticatedClient)
-	if settings.CacheExpirationSec != 0 {
-		impl = WrapWithCache(impl, time.Duration(settings.CacheExpirationSec)*time.Second)
+	// Apply caching configuration.
+	exp := time.Duration(s.CacheExpirationSec) * time.Second
+	if exp > 0 {
+		// Add a ProcCache, backed by memcache.
+		backend = caching.ProcCache(backend, exp)
+		backend = memcacheBackend(backend, exp)
 	}
 
-	if implCache.cache == nil {
-		implCache.cache = make(map[Settings]config.Interface, 1)
+	c = config.WithBackend(c, backend)
+	return c
+}
+
+func getPrimaryBackend(c context.Context, settings *Settings) (backend config.Backend) {
+	// Identify our config service Backend (in testing, it will be supplied).
+	if settings.ConfigServiceURL == "" {
+		if info.IsDevAppServer(c) {
+			return devServerBackend()
+		}
+		return erroring.New(ErrNotConfigured)
 	}
-	implCache.cache[settings] = impl
+	return &config.ClientBackend{&config.RemoteClientProvider{
+		BaseURL: settings.ConfigServiceURL,
+	}}
+}
 
-	return impl
+func defaultFormatterRegistry() *config.FormatterRegistry {
+	var fr config.FormatterRegistry
+	textproto.RegisterFormatter(&fr)
+	return &fr
 }
 
 // devServerConfig returns config.Interface to use on a devserver.
 //
 // See New for details.
-func devServerConfig() config.Interface {
+func devServerBackend() config.Backend {
 	pwd := os.Getenv("PWD") // os.Getwd works funny with symlinks, use PWD
 	candidates := []string{
 		filepath.Join(pwd, devCfgDir),
@@ -127,20 +116,22 @@ func devServerConfig() config.Interface {
 			if err != nil {
 				return erroring.New(err)
 			}
-			return fs
+			return &config.ClientBackend{&testconfig.LocalClientProvider{
+				Base: fs,
+			}}
 		}
 	}
 	return erroring.New(fmt.Errorf("luci-config: could not find local configs in any of %s", candidates))
 }
 
-// authenticatedClient returns http.Client to use for making authenticated
-// request to the config service.
-//
-// The returned client uses GAE app's service account for authentication.
-func authenticatedClient(ctx context.Context) (*http.Client, error) {
-	t, err := auth.GetRPCTransport(ctx, auth.AsSelf)
-	if err != nil {
-		return nil, err
-	}
-	return &http.Client{Transport: t}, nil
+var formatRegistryKey = "github.com/luci/luci-go/appengine/gaeconfig:formatRegistry"
+
+func withFormatRegistry(c context.Context, fr *config.FormatterRegistry) context.Context {
+	return context.WithValue(c, &formatRegistryKey, fr)
+}
+
+// GetFormatterRegistry is used to retrieve the config service format registry
+// from the supplied Context.
+func GetFormatterRegistry(c context.Context) *config.FormatterRegistry {
+	return c.Value(&formatRegistryKey).(*config.FormatterRegistry)
 }