errcode: introduce error code management

Introduces a pkg to manage error codes. Documentation
and tooling to inspect errors will be built around
the error code and description mapping provided by
this pkg.

Part of openservicemesh#2866

Signed-off-by: Shashank Ram <shashr2204@gmail.com>

cmd/osm-controller/osm-controller.go

@@ -34,6 +34,7 @@ import (
 	"github.com/openservicemesh/osm/pkg/endpoint"
 	"github.com/openservicemesh/osm/pkg/envoy/ads"
 	"github.com/openservicemesh/osm/pkg/envoy/registry"
+	"github.com/openservicemesh/osm/pkg/errcode"
 	"github.com/openservicemesh/osm/pkg/gen/client/config/clientset/versioned"
 	"github.com/openservicemesh/osm/pkg/health"
 	"github.com/openservicemesh/osm/pkg/httpserver"
@@ -109,7 +110,7 @@ func init() {
 func main() {
 	log.Info().Msgf("Starting osm-controller %s; %s; %s", version.Version, version.GitCommit, version.BuildDate)
 	if err := parseFlags(); err != nil {
-		log.Fatal().Err(err).Msg("Error parsing cmd line arguments")
+		log.Fatal().Err(err).Str(errcode.Kind, errcode.ErrInvalidCLIArgument.String()).Msg("Error parsing cmd line arguments")
 	}
 
 	if err := logger.SetLogLevel(verbosity); err != nil {

pkg/errcode/errcode.go

@@ -0,0 +1,32 @@
+// Package errcode defines the error codes for error messages and an explanation
+// of what the error signifies.
+package errcode
+
+import (
+	"fmt"
+)
+
+type errCode int
+
+const (
+	// Kind defines the kind for the error code constants
+	Kind = "error_code"
+)
+
+// Range 1000-1050 is reserved for errors related to
+const (
+	// ErrInvalidCLIArgument refers to an invalid CLI argument being specified
+	ErrInvalidCLIArgument errCode = iota + 1000
+)
+
+// String returns the error code as a string, ex. E1000
+func (e errCode) String() string {
+	return fmt.Sprintf("E%d", e)
+}
+
+//nolint: deadcode,varcheck,unused
+var errCodeMap = map[errCode]string{
+	ErrInvalidCLIArgument: `
+An invalid comment line argument was passed to the application.
+`,
+}