Implement runners execute route

Co-authored-by: Tobias Kantusch <tobias.kantusch@student.hpi.uni-potsdam.de>

api/helpers.go

@@ -0,0 +1,43 @@
+package api
+
+import (
+	"encoding/json"
+	"gitlab.hpi.de/codeocean/codemoon/poseidon/api/dto"
+	"log"
+	"net/http"
+)
+
+func writeInternalServerError(writer http.ResponseWriter, err error, errorCode dto.ErrorCode) {
+	sendJson(writer, &dto.InternalServerError{Message: err.Error(), ErrorCode: errorCode}, http.StatusInternalServerError)
+}
+
+func writeBadRequest(writer http.ResponseWriter, err error) {
+	sendJson(writer, &dto.ClientError{Message: err.Error()}, http.StatusBadRequest)
+}
+
+func writeNotFound(writer http.ResponseWriter, err error) {
+	sendJson(writer, &dto.ClientError{Message: err.Error()}, http.StatusNotFound)
+}
+
+func sendJson(writer http.ResponseWriter, content interface{}, httpStatusCode int) {
+	writer.Header().Set("Content-Type", "application/json")
+	writer.WriteHeader(httpStatusCode)
+	response, err := json.Marshal(content)
+	if err != nil {
+		// cannot produce infinite recursive loop, since json.Marshal of dto.InternalServerError won't return an error
+		writeInternalServerError(writer, err, dto.ErrorUnknown)
+		return
+	}
+	if _, err = writer.Write(response); err != nil {
+		log.Printf("Error writing JSON to response: %v\n", err)
+		http.Error(writer, err.Error(), http.StatusInternalServerError)
+	}
+}
+
+func parseRequestBodyJSON(writer http.ResponseWriter, request *http.Request, structure interface{}) error {
+	if err := json.NewDecoder(request.Body).Decode(structure); err != nil {
+		writeBadRequest(writer, err)
+		return err
+	}
+	return nil
+}