Set shortcodes in trigger response entities based on config or request URL (#1099)

* adding trigger short code injection

* more annotation provider stuff

* fixed up tests

* Fix validator

api/server/trigger_annotator.go

@@ -0,0 +1,63 @@
+package server
+
+import (
+	"fmt"
+	"github.com/fnproject/fn/api/models"
+	"github.com/gin-gonic/gin"
+	"strings"
+)
+
+//TriggerAnnotator Is used to inject trigger context (such as request URLs) into outbound trigger resources
+type TriggerAnnotator interface {
+	// Annotates a trigger on read
+	AnnotateTrigger(ctx *gin.Context, a *models.App, t *models.Trigger) (*models.Trigger, error)
+}
+
+type requestBasedTriggerAnnotator struct{}
+
+func annotateTriggerWithBaseUrl(baseURL string, app *models.App, t *models.Trigger) (*models.Trigger, error) {
+	if t.Type != models.TriggerTypeHTTP {
+		return t, nil
+	}
+
+	baseURL = strings.TrimSuffix(baseURL, "/")
+	src := strings.TrimPrefix(t.Source, "/")
+	triggerPath := fmt.Sprintf("%s/t/%s/%s", baseURL, app.Name, src)
+
+	newT := t.Clone()
+	newAnnotations, err := newT.Annotations.With(models.TriggerHTTPEndpointAnnotation, triggerPath)
+	if err != nil {
+		return nil, err
+	}
+	newT.Annotations = newAnnotations
+	return newT, nil
+}
+
+func (tp *requestBasedTriggerAnnotator) AnnotateTrigger(ctx *gin.Context, app *models.App, t *models.Trigger) (*models.Trigger, error) {
+
+	//No, I don't feel good about myself either
+	scheme := "http"
+	if ctx.Request.TLS != nil {
+		scheme = "https"
+	}
+
+	return annotateTriggerWithBaseUrl(fmt.Sprintf("%s://%s", scheme, ctx.Request.Host), app, t)
+}
+
+func NewRequestBasedTriggerAnnotator() TriggerAnnotator {
+	return &requestBasedTriggerAnnotator{}
+}
+
+type staticUrlTriggerAnnotator struct {
+	urlBase string
+}
+
+func NewStaticURLTriggerAnnotator(baseUrl string) TriggerAnnotator {
+
+	return &staticUrlTriggerAnnotator{urlBase: baseUrl}
+}
+
+func (s *staticUrlTriggerAnnotator) AnnotateTrigger(ctx *gin.Context, app *models.App, trigger *models.Trigger) (*models.Trigger, error) {
+	return annotateTriggerWithBaseUrl(s.urlBase, app, trigger)
+
+}