Enhance fatal errors printing of common issues seen by users (#5878)

cmd/ui-errors-utils.go

@@ -0,0 +1,135 @@
+/*
+ * Minio Cloud Storage, (C) 2018 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cmd
+
+import (
+	"fmt"
+	"io"
+	"net"
+	"os"
+)
+
+// uiErr is a structure which contains all information
+// to print a fatal error message in json or pretty mode
+// uiErr implements error so we can use it anywhere
+type uiErr struct {
+	msg    string
+	detail string
+	action string
+	help   string
+}
+
+// Return the error message
+func (u uiErr) Error() string {
+	if u.detail == "" {
+		return u.msg
+	}
+	return u.detail
+}
+
+// Replace the current error's message
+func (u uiErr) Msg(m string, args ...interface{}) uiErr {
+	return uiErr{
+		msg:    fmt.Sprintf(m, args...),
+		detail: u.detail,
+		action: u.action,
+		help:   u.help,
+	}
+}
+
+type uiErrFn func(err error) uiErr
+
+// Create a UI error generator, this is needed to simplify
+// the update of the detailed error message in several places
+// in Minio code
+func newUIErrFn(msg, action, help string) uiErrFn {
+	return func(err error) uiErr {
+		u := uiErr{
+			msg:    msg,
+			action: action,
+			help:   help,
+		}
+		if err != nil {
+			u.detail = err.Error()
+		}
+		return u
+	}
+}
+
+// errorToUIError inspects the passed error and transforms it
+// to the appropriate UI error.
+func errorToUIErr(err error) uiErr {
+	// If this is already a uiErr, do nothing
+	if e, ok := err.(uiErr); ok {
+		return e
+	}
+
+	// Show a generic message for known golang errors
+	switch e := err.(type) {
+	case *net.OpError:
+		if e.Op == "listen" {
+			return uiErrPortAlreadyInUse(e).Msg("Port " + e.Addr.String() + " is already in use")
+
+		}
+	case *os.PathError:
+		if os.IsPermission(e) {
+			return uiErrNoPermissionsToAccessDirFiles(e).Msg("Unsufficent permissions to access `" + e.Path + "` path")
+		}
+	}
+
+	switch err {
+	case io.ErrUnexpectedEOF:
+		return uiErrUnexpectedDataContent(err)
+	default:
+		// Failed to identify what type of error this, return a simple UI error
+		return uiErr{msg: err.Error()}
+	}
+
+}
+
+// fmtError() converts a fatal error message to a more understood error
+// using some colors
+func fmtError(introMsg string, err error, jsonFlag bool) string {
+	renderedTxt := ""
+	uiErr := errorToUIErr(err)
+	// JSON print
+	if jsonFlag {
+		// Message text in json should be simple
+		if uiErr.detail != "" {
+			return uiErr.msg + ": " + uiErr.detail
+		}
+		return uiErr.msg
+	}
+	// Pretty print error message
+	introMsg += ": "
+	if uiErr.msg != "" {
+		introMsg += colorBold(uiErr.msg + ".")
+	} else {
+		introMsg += colorBold(err.Error() + ".")
+	}
+	renderedTxt += colorRed(introMsg) + "\n"
+	// Add action message
+	if uiErr.action != "" {
+		renderedTxt += "> " + colorBgYellow(colorBlack(uiErr.action+".")) + "\n"
+	}
+	// Add help
+	if uiErr.help != "" {
+		renderedTxt += colorBold("HELP:") + "\n"
+		renderedTxt += "  " + uiErr.help
+	}
+	return renderedTxt
+}