Cherry-pick #22605 to 7.x: Add support for customized monitoring API (#…

…23279)

Co-authored-by: Peter Deng <[email protected]>

CHANGELOG-developer.next.asciidoc

@@ -96,3 +96,5 @@ The list below covers the major changes between 7.0.0-rc2 and master only.
 - Update Go version to 1.14.7. {pull}20508[20508]
 - Add packaging for docker image based on UBI minimal 8. {pull}20576[20576]
 - Make the mage binary used by the build process in the docker container to be statically compiled. {pull}20827[20827]
+- Add support for customized monitoring API. {pull}22605[22605]
+

libbeat/api/routes.go

@@ -30,6 +30,8 @@ import (
 type handlerFunc func(http.ResponseWriter, *http.Request)
 type lookupFunc func(string) *monitoring.Namespace
 
+var handlerFuncMap = make(map[string]handlerFunc)
+
 // NewWithDefaultRoutes creates a new server with default API routes.
 func NewWithDefaultRoutes(log *logp.Logger, config *common.Config, ns lookupFunc) (*Server, error) {
 	mux := http.NewServeMux()
@@ -38,6 +40,10 @@ func NewWithDefaultRoutes(log *logp.Logger, config *common.Config, ns lookupFunc
 	mux.HandleFunc("/state", makeAPIHandler(ns("state")))
 	mux.HandleFunc("/stats", makeAPIHandler(ns("stats")))
 	mux.HandleFunc("/dataset", makeAPIHandler(ns("dataset")))
+
+	for api, h := range handlerFuncMap {
+		mux.HandleFunc(api, h)
+	}
 	return New(log, mux, config)
 }
 
@@ -73,3 +79,12 @@ func prettyPrint(w http.ResponseWriter, data common.MapStr, u *url.URL) {
 		fmt.Fprintf(w, data.String())
 	}
 }
+
+// AddHandlerFunc provides interface to add customized handlerFunc
+func AddHandlerFunc(api string, h handlerFunc) error {
+	if _, exist := handlerFuncMap[api]; exist {
+		return fmt.Errorf("%s already exist", api)
+	}
+	handlerFuncMap[api] = h
+	return nil
+}