Rapl node capping daemon (#21)

* Initial work on rapl-daemon. Initial server set up. API to read max power per zone and API to write new power cap have both been written.

* Removing python script since this has been ported to go code now.

* Adding test for happy path retrieving max power.

* Change some data types around to avoid too much conversion.

* Add happy path test for cap zone

* Removing uncessary print statement.

* Change cap node to use a temporary setup.

* Renaming arguments to be more descriptive.

* Changing todo message.

* Changing test structure to only set up mock subsystem once and allowing functions to test on it later.

* Adding some more coverage for unhappy paths and fixing some values to reflect they are no longer floats.

* Keeping the old script around as it should be removed in a different PR.

* Delegating percentage check to capNode function.

* Fixing typo.

* Fixing typos.

* Changing shortWindow to longWindow as constraint_0 actually points to the long window.

* Renaming variable in test.

* capping funciton now returns which zones were sucessfully capped and which zones could not be capped. This information is now returned to the caller of the HTTP api.

rapl-daemon/main.go

@@ -0,0 +1,60 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"html"
+	"log"
+	"net/http"
+)
+
+const powercapDir = "/sys/class/powercap/"
+
+// Cap is a payload that is expected from Elektron to cap a node.
+type Cap struct {
+	Percentage int
+}
+
+// CapResponse is the payload sent with information about the capping call
+type CapResponse struct {
+	CappedZones []string `json:"cappedZones"`
+	FailedZones []string `json:"failedZones"`
+	Error       *string  `json:"error"`
+}
+
+func main() {
+	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintf(w, "Unsupported endpoint %s", html.EscapeString(r.URL.Path))
+	})
+
+	http.HandleFunc("/powercap", powercapEndpoint)
+	log.Fatal(http.ListenAndServe(":9090", nil))
+}
+
+// Handler for the powercapping HTTP API endpoint.
+func powercapEndpoint(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+
+	var payload Cap
+	var response CapResponse
+
+	decoder := json.NewDecoder(r.Body)
+	err := decoder.Decode(&payload)
+	if err != nil {
+		errorMsg := "error parsing payload: " + err.Error()
+		response.Error = &errorMsg
+		json.NewEncoder(w).Encode(response)
+		return
+	}
+
+	cappedZones, failedZones, err := capNode(powercapDir, payload.Percentage)
+	if err != nil {
+		errorMsg := err.Error()
+		response.Error = &errorMsg
+	}
+
+	response.CappedZones = cappedZones
+	response.FailedZones = failedZones
+
+	json.NewEncoder(w).Encode(response)
+}