API extension points (#473)

* API endpoint extensions working.

extensions example.

* Added server.NewEnv and some docs for the API extensions example.

extensions example.
example main.go.

* Uncommented special handler stuff.

* Added section in docs for extending API linking to example main.go.

* Commented out special_handler test

* Changed to NewFromEnv

api/server/extension_points.go

@@ -0,0 +1,81 @@
+// TODO: it would be nice to move these into the top level folder so people can use these with the "functions" package, eg: functions.ApiHandler
+package server
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/iron-io/functions/api"
+	"github.com/iron-io/functions/api/models"
+)
+
+type ApiHandlerFunc func(w http.ResponseWriter, r *http.Request)
+
+// ServeHTTP calls f(w, r).
+func (f ApiHandlerFunc) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	f(w, r)
+}
+
+type ApiHandler interface {
+	// Handle(ctx context.Context)
+	ServeHTTP(w http.ResponseWriter, r *http.Request)
+}
+
+type ApiAppHandler interface {
+	// Handle(ctx context.Context)
+	ServeHTTP(w http.ResponseWriter, r *http.Request, app *models.App)
+}
+
+type ApiAppHandlerFunc func(w http.ResponseWriter, r *http.Request, app *models.App)
+
+// ServeHTTP calls f(w, r).
+func (f ApiAppHandlerFunc) ServeHTTP(w http.ResponseWriter, r *http.Request, app *models.App) {
+	f(w, r, app)
+}
+
+func (s *Server) apiHandlerWrapperFunc(apiHandler ApiHandler) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		apiHandler.ServeHTTP(c.Writer, c.Request)
+	}
+}
+
+func (s *Server) apiAppHandlerWrapperFunc(apiHandler ApiAppHandler) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		// get the app
+		appName := c.Param(api.CApp)
+		app, err := s.Datastore.GetApp(c.Request.Context(), appName)
+		if err != nil {
+			c.AbortWithError(http.StatusInternalServerError, err)
+			return
+		}
+		if app == nil {
+			c.AbortWithStatus(http.StatusNotFound)
+			return
+		}
+
+		apiHandler.ServeHTTP(c.Writer, c.Request, app)
+	}
+}
+
+// AddEndpoint adds an endpoint to /v1/x
+func (s *Server) AddEndpoint(method, path string, handler ApiHandler) {
+	v1 := s.Router.Group("/v1")
+	// v1.GET("/apps/:app/log", logHandler(cfg))
+	v1.Handle(method, path, s.apiHandlerWrapperFunc(handler))
+}
+
+// AddEndpoint adds an endpoint to /v1/x
+func (s *Server) AddEndpointFunc(method, path string, handler func(w http.ResponseWriter, r *http.Request)) {
+	s.AddEndpoint(method, path, ApiHandlerFunc(handler))
+}
+
+// AddAppEndpoint adds an endpoints to /v1/apps/:app/x
+func (s *Server) AddAppEndpoint(method, path string, handler ApiAppHandler) {
+	v1 := s.Router.Group("/v1")
+	v1.Handle(method, "/apps/:app"+path, s.apiAppHandlerWrapperFunc(handler))
+}
+
+// AddAppEndpoint adds an endpoints to /v1/apps/:app/x
+func (s *Server) AddAppEndpointFunc(method, path string, handler func(w http.ResponseWriter, r *http.Request, app *models.App)) {
+	s.AddAppEndpoint(method, path, ApiAppHandlerFunc(handler))
+}