Final changes to config sub-system (#8600)

- Introduces changes such as certain types of
  errors that can be ignored or which need to 
  go into safe mode.
- Update help text as per the review

cmd/config/errors-utils.go

@@ -0,0 +1,132 @@
+/*
+ * MinIO Cloud Storage, (C) 2018-2019 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 config
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"syscall"
+
+	"github.com/minio/minio/pkg/color"
+)
+
+// Err is a structure which contains all information
+// to print a fatal error message in json or pretty mode
+// Err implements error so we can use it anywhere
+type Err struct {
+	msg    string
+	detail string
+	action string
+	hint   string
+}
+
+// Return the error message
+func (u Err) Error() string {
+	if u.detail == "" {
+		return u.msg
+	}
+	return u.detail
+}
+
+// Msg - Replace the current error's message
+func (u Err) Msg(m string, args ...interface{}) Err {
+	return Err{
+		msg:    fmt.Sprintf(m, args...),
+		detail: u.detail,
+		action: u.action,
+		hint:   u.hint,
+	}
+}
+
+// ErrFn function wrapper
+type ErrFn func(err error) Err
+
+// Create a UI error generator, this is needed to simplify
+// the update of the detailed error message in several places
+// in MinIO code
+func newErrFn(msg, action, hint string) ErrFn {
+	return func(err error) Err {
+		u := Err{
+			msg:    msg,
+			action: action,
+			hint:   hint,
+		}
+		if err != nil {
+			u.detail = err.Error()
+		}
+		return u
+	}
+}
+
+// ErrorToErr inspects the passed error and transforms it
+// to the appropriate UI error.
+func ErrorToErr(err error) Err {
+	// If this is already a Err, do nothing
+	if e, ok := err.(Err); ok {
+		return e
+	}
+
+	// Show a generic message for known golang errors
+	if errors.Is(err, syscall.EADDRINUSE) {
+		return ErrPortAlreadyInUse(err).Msg("Specified port is already in use")
+	} else if errors.Is(err, syscall.EACCES) {
+		return ErrPortAccess(err).Msg("Insufficient permissions to use specified port")
+	} else if os.IsPermission(err) {
+		return ErrNoPermissionsToAccessDirFiles(err).Msg("Insufficient permissions to access path")
+	} else if errors.Is(err, io.ErrUnexpectedEOF) {
+		return ErrUnexpectedDataContent(err)
+	} else {
+		// Failed to identify what type of error this, return a simple UI error
+		return Err{msg: err.Error()}
+	}
+
+}
+
+// FmtError converts a fatal error message to a more clear error
+// using some colors
+func FmtError(introMsg string, err error, jsonFlag bool) string {
+	renderedTxt := ""
+	uiErr := ErrorToErr(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 += color.Bold(uiErr.msg)
+	} else {
+		introMsg += color.Bold(err.Error())
+	}
+	renderedTxt += color.Red(introMsg) + "\n"
+	// Add action message
+	if uiErr.action != "" {
+		renderedTxt += "> " + color.BgYellow(color.Black(uiErr.action)) + "\n"
+	}
+	// Add hint
+	if uiErr.hint != "" {
+		renderedTxt += color.Bold("HINT:") + "\n"
+		renderedTxt += "  " + uiErr.hint
+	}
+	return renderedTxt
+}