Simplify Go Endpoints + Add Tests (#120)

This MR represents a major refactor of the Go codebase, as well as introducing tests for the handlers. The MR also introduces an endpoint to shutdown or restart the Go server, which may be useful for clients who want to refresh the state of the plugin after checking out branches. Finally, this MR adds a contributing document for users who want to make feature changes.

cmd/approve.go

@@ -2,36 +2,38 @@ package main
 
 import (
 	"encoding/json"
-	"errors"
 	"net/http"
 )
 
-func ApproveHandler(w http.ResponseWriter, r *http.Request) {
+/* approveHandler approves a merge request. */
+func (a *api) approveHandler(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "application/json")
-	c := r.Context().Value("client").(Client)
-
 	if r.Method != http.MethodPost {
-		w.Header().Set("Allow", http.MethodPost)
-		c.handleError(w, errors.New("Invalid request type"), "That request type is not allowed", http.StatusMethodNotAllowed)
+		w.Header().Set("Access-Control-Allow-Methods", http.MethodPost)
+		handleError(w, InvalidRequestError{}, "Expected POST", http.StatusMethodNotAllowed)
 		return
 	}
 
-	_, res, err := c.git.MergeRequestApprovals.ApproveMergeRequest(c.projectId, c.mergeId, nil, nil)
+	_, res, err := a.client.ApproveMergeRequest(a.projectInfo.ProjectId, a.projectInfo.MergeId, nil, nil)
 
 	if err != nil {
-		c.handleError(w, err, "Could not approve MR", http.StatusBadRequest)
+		handleError(w, err, "Could not approve merge request", http.StatusInternalServerError)
 		return
 	}
 
-	/* TODO: Check for non-200 status codes */
-	w.WriteHeader(res.StatusCode)
+	if res.StatusCode >= 300 {
+		handleError(w, GenericError{endpoint: "/approve"}, "Could not approve merge request", res.StatusCode)
+		return
+	}
+
+	w.WriteHeader(http.StatusOK)
 	response := SuccessResponse{
-		Message: "Success! Approved MR.",
+		Message: "Approved MR",
 		Status:  http.StatusOK,
 	}
 
 	err = json.NewEncoder(w).Encode(response)
 	if err != nil {
-		c.handleError(w, err, "Could not encode response", http.StatusInternalServerError)
+		handleError(w, err, "Could not encode response", http.StatusInternalServerError)
 	}
 }