Add simple status check for node to backend (#608)

* wip

* wip

routes/server.go

@@ -317,7 +317,8 @@ const (
 	RoutePathStateChecksum         = "/api/v0/state-checksum"
 
 	// validators.go
-	RoutePathValidators = "/api/v0/validators"
+	RoutePathValidators      = "/api/v0/validators"
+	RoutePathCheckNodeStatus = "/api/v0/check-node-status"
 
 	// stake.go
 	RoutePathStake       = "/api/v0/stake"
@@ -1353,6 +1354,13 @@ func (fes *APIServer) NewRouter() *muxtrace.Router {
 			fes.GetValidatorByPublicKeyBase58Check,
 			PublicAccess,
 		},
+		{
+			"CheckNodeStatus",
+			[]string{"POST", "OPTIONS"},
+			RoutePathCheckNodeStatus,
+			fes.CheckNodeStatus,
+			PublicAccess,
+		},
 		{
 			"CreateStakeTxn",
 			[]string{"POST", "OPTIONS"},

routes/validators.go

@@ -9,7 +9,9 @@ import (
 	"github.com/gorilla/mux"
 	"github.com/holiman/uint256"
 	"io"
+	"net"
 	"net/http"
+	"time"
 )
 
 type RegisterAsValidatorRequest struct {
@@ -352,6 +354,44 @@ func (fes *APIServer) GetValidatorByPublicKeyBase58Check(ww http.ResponseWriter,
 	}
 }
 
+type CheckNodeStatusRequest struct {
+	NodeHostPort string `safeForLogging:"true"`
+}
+
+type CheckNodeStatusResponse struct {
+	Success bool `safeForLogging:"true"`
+}
+
+func (fes *APIServer) CheckNodeStatus(ww http.ResponseWriter, req *http.Request) {
+	// Decode request body.
+	decoder := json.NewDecoder(io.LimitReader(req.Body, MaxRequestBodySizeBytes))
+	requestData := CheckNodeStatusRequest{}
+	if err := decoder.Decode(&requestData); err != nil {
+		_AddBadRequestError(ww, "UnjailValidator: problem parsing request body")
+		return
+	}
+
+	// We do an *extremely* simple check for now, which is that we just check to see if the node
+	// is reachable at all.
+	// TODO: We should beef this up to test an actual version handshake or something more robust.
+	conn, err := net.DialTimeout("tcp", requestData.NodeHostPort, 5*time.Second)
+	if err != nil {
+		_AddBadRequestError(ww, fmt.Sprintf(
+			"Problem connecting to %v: %v", requestData.NodeHostPort, err))
+		return
+	}
+	// If we get here it means we succeeded. Close the connection to clean up.
+	conn.Close()
+
+	res := CheckNodeStatusResponse{
+		Success: true,
+	}
+	if err := json.NewEncoder(ww).Encode(res); err != nil {
+		_AddInternalServerError(ww, "UnjailValidator: problem encoding response as JSON")
+		return
+	}
+}
+
 func _convertValidatorEntryToResponse(
 	utxoView *lib.UtxoView, validatorEntry *lib.ValidatorEntry, params *lib.DeSoParams,
 ) *ValidatorResponse {