Move notifications package to distribution

Since the notifications package is now decoupled from storage, we are moving it
to the root package.

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

notifications/endpoint.go

@@ -0,0 +1,86 @@
+package notifications
+
+import (
+	"net/http"
+	"time"
+)
+
+// EndpointConfig covers the optional configuration parameters for an active
+// endpoint.
+type EndpointConfig struct {
+	Headers   http.Header
+	Timeout   time.Duration
+	Threshold int
+	Backoff   time.Duration
+}
+
+// defaults set any zero-valued fields to a reasonable default.
+func (ec *EndpointConfig) defaults() {
+	if ec.Timeout <= 0 {
+		ec.Timeout = time.Second
+	}
+
+	if ec.Threshold <= 0 {
+		ec.Threshold = 10
+	}
+
+	if ec.Backoff <= 0 {
+		ec.Backoff = time.Second
+	}
+}
+
+// Endpoint is a reliable, queued, thread-safe sink that notify external http
+// services when events are written. Writes are non-blocking and always
+// succeed for callers but events may be queued internally.
+type Endpoint struct {
+	Sink
+	url  string
+	name string
+
+	EndpointConfig
+
+	metrics *safeMetrics
+}
+
+// NewEndpoint returns a running endpoint, ready to receive events.
+func NewEndpoint(name, url string, config EndpointConfig) *Endpoint {
+	var endpoint Endpoint
+	endpoint.name = name
+	endpoint.url = url
+	endpoint.EndpointConfig = config
+	endpoint.defaults()
+	endpoint.metrics = newSafeMetrics()
+
+	// Configures the inmemory queue, retry, http pipeline.
+	endpoint.Sink = newHTTPSink(
+		endpoint.url, endpoint.Timeout, endpoint.Headers,
+		endpoint.metrics.httpStatusListener())
+	endpoint.Sink = newRetryingSink(endpoint.Sink, endpoint.Threshold, endpoint.Backoff)
+	endpoint.Sink = newEventQueue(endpoint.Sink, endpoint.metrics.eventQueueListener())
+
+	register(&endpoint)
+	return &endpoint
+}
+
+// Name returns the name of the endpoint, generally used for debugging.
+func (e *Endpoint) Name() string {
+	return e.name
+}
+
+// URL returns the url of the endpoint.
+func (e *Endpoint) URL() string {
+	return e.url
+}
+
+// ReadMetrics populates em with metrics from the endpoint.
+func (e *Endpoint) ReadMetrics(em *EndpointMetrics) {
+	e.metrics.Lock()
+	defer e.metrics.Unlock()
+
+	*em = e.metrics.EndpointMetrics
+	// Map still need to copied in a threadsafe manner.
+	em.Statuses = make(map[string]int)
+	for k, v := range e.metrics.Statuses {
+		em.Statuses[k] = v
+	}
+}