Support unknown gateway errors and convert at handler layer (#7219)

Different gateway implementations due to different backend
API errors, might return different unsupported errors at
our handler layer. Current code posed a problem for us because
this information was lost and we would convert it to InternalError
in this situation all S3 clients end up retrying the request.

To avoid this unexpected situation implement a way to support
this cleanly such that the underlying information is not lost
which is returned by gateway.

cmd/admin-heal-ops.go

@@ -63,8 +63,7 @@ var (
 	errHealStopSignalled    = fmt.Errorf("heal stop signaled")
 
 	errFnHealFromAPIErr = func(ctx context.Context, err error) error {
-		errCode := toAPIErrorCode(ctx, err)
-		apiErr := getAPIError(errCode)
+		apiErr := toAPIError(ctx, err)
 		return fmt.Errorf("Heal internal error: %s: %s",
 			apiErr.Code, apiErr.Description)
 	}
@@ -150,7 +149,7 @@ func (ahs *allHealState) getHealSequence(path string) (h *healSequence, exists b
 	return h, exists
 }
 
-func (ahs *allHealState) stopHealSequence(path string) ([]byte, APIErrorCode) {
+func (ahs *allHealState) stopHealSequence(path string) ([]byte, APIError) {
 	var hsp madmin.HealStopSuccess
 	he, exists := ahs.getHealSequence(path)
 	if !exists {
@@ -176,7 +175,7 @@ func (ahs *allHealState) stopHealSequence(path string) ([]byte, APIErrorCode) {
 	}
 
 	b, err := json.Marshal(&hsp)
-	return b, toAdminAPIErrCode(context.Background(), err)
+	return b, toAdminAPIErr(context.Background(), err)
 }
 
 // LaunchNewHealSequence - launches a background routine that performs
@@ -190,7 +189,7 @@ func (ahs *allHealState) stopHealSequence(path string) ([]byte, APIErrorCode) {
 // background routine to clean up heal results after the
 // aforementioned duration.
 func (ahs *allHealState) LaunchNewHealSequence(h *healSequence) (
-	respBytes []byte, errCode APIErrorCode, errMsg string) {
+	respBytes []byte, apiErr APIError, errMsg string) {
 
 	existsAndLive := false
 	he, exists := ahs.getHealSequence(h.path)
@@ -213,8 +212,7 @@ func (ahs *allHealState) LaunchNewHealSequence(h *healSequence) (
 				"(use force-start option to stop and start afresh). " +
 				fmt.Sprintf("The heal was started by IP %s at %s, token is %s",
 					h.clientAddress, h.startTime.Format(http.TimeFormat), h.clientToken)
-
-			return nil, ErrHealAlreadyRunning, errMsg
+			return nil, errorCodes.ToAPIErr(ErrHealAlreadyRunning), errMsg
 		}
 	}
 
@@ -229,7 +227,7 @@ func (ahs *allHealState) LaunchNewHealSequence(h *healSequence) (
 
 			errMsg = "The provided heal sequence path overlaps with an existing " +
 				fmt.Sprintf("heal path: %s", k)
-			return nil, ErrHealOverlappingPaths, errMsg
+			return nil, errorCodes.ToAPIErr(ErrHealOverlappingPaths), errMsg
 		}
 	}
 
@@ -246,9 +244,9 @@ func (ahs *allHealState) LaunchNewHealSequence(h *healSequence) (
 	})
 	if err != nil {
 		logger.LogIf(h.ctx, err)
-		return nil, ErrInternalError, ""
+		return nil, toAPIError(h.ctx, err), ""
 	}
-	return b, ErrNone, ""
+	return b, noError, ""
 }
 
 // PopHealStatusJSON - Called by heal-status API. It fetches the heal