Webhook notification support in registry webapp

Endpoints are now created at applications startup time, using notification
configuration. The instances are then added to a Broadcaster instance, which
becomes the main event sink for the application. At request time, an event
bridge is configured to listen to repository method calls. The actor and source
of the eventBridge are created from the requeest context and application,
respectively. The result is notifications are dispatched with calls to the
context's Repository instance and are queued to each endpoint via the
broadcaster.

This commit also adds the concept of a RequestID and App.InstanceID. The
request id uniquely identifies each request and the InstanceID uniquely
identifies a run of the registry. These identifiers can be used in the future
to correlate log messages with generated events to support rich debugging.

The fields of the app were slightly reorganized for clarity and a few horrid
util functions have been removed.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

configuration/configuration_test.go

@@ -2,6 +2,7 @@ package configuration
 
 import (
 	"bytes"
+	"net/http"
 	"os"
 	"testing"
 
@@ -40,6 +41,17 @@ var configStruct = Configuration{
 			APIKey: "BugsnagApiKey",
 		},
 	},
+	Notifications: Notifications{
+		Endpoints: []Endpoint{
+			{
+				Name: "endpoint-1",
+				URL:  "http://example.com",
+				Headers: http.Header{
+					"Authorization": []string{"Bearer <example>"},
+				},
+			},
+		},
+	},
 }
 
 // configYamlV0_1 is a Version 0.1 yaml document representing configStruct
@@ -61,6 +73,12 @@ auth:
   silly:
     realm: silly
     service: silly
+notifications:
+  endpoints:
+    - name: endpoint-1
+      url:  http://example.com
+      headers:
+        Authorization: [Bearer <example>]
 reporting:
   bugsnag:
     apikey: BugsnagApiKey
@@ -76,6 +94,12 @@ auth:
   silly:
     realm: silly
     service: silly
+notifications:
+  endpoints:
+    - name: endpoint-1
+      url:  http://example.com
+      headers:
+        Authorization: [Bearer <example>]
 `
 
 type ConfigSuite struct {
@@ -129,6 +153,7 @@ func (suite *ConfigSuite) TestParseIncomplete(c *C) {
 	suite.expectedConfig.Storage = Storage{"filesystem": Parameters{"rootdirectory": "/tmp/testroot"}}
 	suite.expectedConfig.Auth = Auth{"silly": Parameters{"realm": "silly"}}
 	suite.expectedConfig.Reporting = Reporting{}
+	suite.expectedConfig.Notifications = Notifications{}
 
 	os.Setenv("REGISTRY_STORAGE", "filesystem")
 	os.Setenv("REGISTRY_STORAGE_FILESYSTEM_ROOTDIRECTORY", "/tmp/testroot")
@@ -292,5 +317,10 @@ func copyConfig(config Configuration) *Configuration {
 		configCopy.Auth.setParameter(k, v)
 	}
 
+	configCopy.Notifications = Notifications{Endpoints: []Endpoint{}}
+	for _, v := range config.Notifications.Endpoints {
+		configCopy.Notifications.Endpoints = append(configCopy.Notifications.Endpoints, v)
+	}
+
 	return configCopy
 }