rename FindHandlerByTypeIfLoaded to be shorter. document better.

Change-Id: I20b1a191d2d67972ba1f7a7fd3678d4ab4adae55

pkg/blobserver/registry.go

@@ -17,6 +17,7 @@ limitations under the License.
 package blobserver
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
 	"sync"
@@ -24,14 +25,22 @@ import (
 	"camlistore.org/pkg/jsonconfig"
 )
 
+var ErrHandlerTypeNotFound = errors.New("requested handler type not loaded")
+
 type Loader interface {
 	GetStorage(prefix string) (Storage, error)
-	GetHandlerType(prefix string) string // or ""
+	GetHandlerType(prefix string) string // returns "" if unknown
 
 	// Returns either a Storage or an http.Handler
 	GetHandler(prefix string) (interface{}, error)
 
-	FindHandlerByTypeIfLoaded(htype string) (prefix string, handler interface{}, err error)
+	// FindHandlerByType finds a handler by its handlerType and
+	// returns its prefix and handler if it's loaded.  If it's not
+	// loaded, the error will be ErrHandlerTypeNotFound.
+	//
+	// This is used by handler constructors to find siblings (such as the "ui" type handler)
+	// which might have more knowledge about the configuration for discovery, etc.
+	FindHandlerByType(handlerType string) (prefix string, handler interface{}, err error)
 
 	// If we're loading configuration in response to a web request
 	// (as we do with App Engine), then this returns a request and

pkg/server/publish.go

@@ -160,7 +160,7 @@ func (ph *PublishHandler) serveDiscovery(rw http.ResponseWriter, req *http.Reque
 		})
 		return
 	}
-	_, handler, err := ph.bsLoader.FindHandlerByTypeIfLoaded("ui")
+	_, handler, err := ph.bsLoader.FindHandlerByType("ui")
 	if err != nil {
 		discoveryHelper(rw, req, map[string]interface{}{
 			"error": "no admin handler running",

pkg/serverconfig/serverconfig.go

@@ -159,13 +159,13 @@ func (hl *handlerLoader) GetRequestContext() (req *http.Request, ok bool) {
 	return hl.context, hl.context != nil
 }
 
-func (hl *handlerLoader) FindHandlerByTypeIfLoaded(htype string) (prefix string, handler interface{}, err error) {
+func (hl *handlerLoader) FindHandlerByType(htype string) (prefix string, handler interface{}, err error) {
 	for prefix, config := range hl.config {
 		if config.htype == htype {
 			return prefix, hl.handler[prefix], nil
 		}
 	}
-	return "", nil, os.ErrNotExist
+	return "", nil, blobserver.ErrHandlerTypeNotFound
 }
 
 func (hl *handlerLoader) setupAll() {